the origin and distribution of trace metals in the rio santa

100
The origin and distribution of trace metals in the Rio Santa Watershed, Peru Elizabeth A. Walsh Department of Earth and Planetary Sciences McGill University, Montreal, Quebec, Canada April, 2013 A thesis submitted to McGill University in partial fulfillment of the requirements of the degree of Master of Science © Elizabeth Walsh 2013

Upload: phungkhuong

Post on 30-Jan-2017

212 views

Category:

Documents


0 download

TRANSCRIPT

Page 1: The origin and distribution of trace metals in the Rio Santa

The origin and distribution of trace metals in the Rio Santa Watershed, Peru

Elizabeth A. Walsh

Department of Earth and Planetary Sciences

McGill University,

Montreal, Quebec, Canada

April, 2013

A thesis submitted to McGill University in partial fulfillment of the requirements of the degree

of Master of Science

© Elizabeth Walsh 2013

Page 2: The origin and distribution of trace metals in the Rio Santa

ii

Abstract

The world’s highest density of tropical glaciers is found in the Cordillera Blanca of the Peruvian

Andes. During the dry season, glacial meltwater is a vital fresh water resource in the region as it

supplies up to 40% of river discharge. Climate change is driving rapid glacial retreat, causing

serious concerns about future availability and quality of fresh water supplies. The purpose of

this thesis is to survey water quality in the Rio Santa Watershed (which drains the western side

of the Cordillera Blanca), with a particular focus on potentially toxic trace metals released by

acid mine drainage and acid rock drainage. In July 2011, major ion samples were collected from

23 sites in the Rio Santa and nine of its tributaries. Samples for trace metal analysis were

collected from 11 Rio Santa sites and eight tributaries. pH, temperature, and dissolved oxygen

were measured in situ at all sites. Rio Santa discharge was measured directly at 15 locations and

calculated by mass balance analysis for another 12 locations. Water in the Rio Santa Watershed

is characterized by high concentrations of SO4, Ca, and HCO3. These species are derived from

sulfide oxidation (both naturally occurring and enhanced by mining) and carbonate dissolution.

The pH is circumneutral at all sites except for two tributaries, Rio Olleros and Rio Quilcay,

which both had a pH below 5. Fe-oxyhydroxide coatings cover the streambeds of acid tributaries

and some sites along the Rio Santa.

As, Cd, Pb, Cu, Mo, Ni, and U concentrations tend to fluctuate above the detection level but

below 10 ug/L at most sites in the watershed. Locally elevated concentrations occurred in the

acidified Rio Olleros (70 ug/L of Ni) and Rio Quilcay (82 ug/L, 27 ug/L, 34 ug/L and 14 ug/L of

Pb, Cd, Ni, and U, respectively.) Elevated concentrations also occurred in circumneutral

tributaries Rio Tabla (43 ug/L of Ni) and Rio Llullan (720 ug/L of Mo and 180 ug/L of U.) In

the Rio Santa, elevated trace metal concentrations occurred downstream of Ticapampa mine

tailings pile (30 ug/L of As) and the city of Huaraz (73 ug/L, 58 ug/L, 53 ug/L, 40 ug/L, and 23

ug/L of Pb, Cd, U, Mo, and Ni, respectively.) Bulk loads of these indicator trace metals were

near zero at the headwaters of the Rio Santa, and tended to increase steadily along the river’s

length in proportion to increasing discharge, with large spikes in loads at Ticapampa and Huaraz.

The dramatic decline in loads immediately after these sites is indicative of the non-conservative

behavior of dissolved trace elements in the Eh-pH conditions of the Rio Santa. As dry season

discharge continues to decline due to glacier recession, current contamination problems may be

exacerbated and lower flows will inhibit the capacity of the watershed to buffer against acidic

tributary and mining effluent inputs.

Page 3: The origin and distribution of trace metals in the Rio Santa

iii

Resume

La plus grande densité de glaciers tropicaux se trouve dans la Cordillera Blanca des Andes

péruviennes. Durant la saison sèche, l’eau issue de la fonte glaciaire est une ressource vitale, car

celle-ci alimente jusqu’à 40% du débit des rivières. Les changements climatiques entraînant un

retrait rapide des glaciers, l’approvisionnement de la population en eau potable de qualité devient

une préoccupation sérieuse. L’objectif de ce mémoire est de faire le relevé de la qualité de l’eau

dans le bassin hydrologique du Rio Santa, qui draine la portion occidentale de la Cordillera

Blanca, en mettant l’emphase sur les éléments-traces métalliques potentiellement toxiques

libérés par le drainage minier acide et par le drainage géologique naturel. En juillet 2011, des

échantillons d’ions majeurs ont été récoltés dans 23 sites du Rio Santa et de neuf de ses affluents.

Des échantillons d’éléments-traces métalliques ont quant à eux été récoltés dans 11 sites du Rio

Santa et de 8 de ses affluents. Le pH, la température et l’oxygène dissout ont été mesurés sur

place à tous les sites. Le débit du Rio Santa a été mesuré directement à 15 endroits et calculé par

bilan massique pour 12 autres endroits. L’eau du bassin hydrologique du Rio Santa est

caractérisée par une forte teneur en SO4, Ca et HCO3, dû à l’oxydation, naturelle et accélérée par

les mines, des minéraux sulfureux et de la dissolution du carbonate. Le pH est

approximativement neutre pour tous les sites sauf pour les affluents Rio Olleros et Rio Quilcay,

qui ont tous deux un pH inférieur à 5. Un revêtement de Fe-oxyhydroxide recouvre le lit de ces

affluents acides et quelques autres sites le long du Rio Santa.

Les concentrations de As, Cd, Pb, Cu, Mo, Ni et U tendent à fluctuer au-dessus des niveaux de

détection mais restent sous 10 ug/L pour la majorité des sites dans les bassins hydrologique. Des

concentrations locales élevées apparaissent dans les affluents acides du Rio Olleros (70 ug/L de

Ni) et du Rio Quilcay (82 ug/L, 27 ug/L, 34 ug/L and 14 ug/L de Pb, Cd, Ni et U,

respectivement.) Des concentrations élevées ont aussi été trouvées dans les affluents dont le pH

est approximativement neutre, soit le Rio Tabla (43 ug/L de Ni) et le Rio Llullan (720 ug/L de

Mo et 180 ug/L de U.) Dans le Rio Santa, des concentrations élevées d’éléments-traces

métalliques ont été détectées en aval des résidus de la mine Ticapampa (30 ug/L de As) et de la

ville de Huaraz (73 ug/L, 58 ug/L, 53 ug/L, 40 ug/L et 23 ug/L de Pb, Cd, U, Mo et Ni,

respectivement.) Le débit massique de ces éléments-traces métalliques de référence était près de

zéro à la source du Rio Santa et tendait à augmenter graduellement au long de la rivière

proportionnellement à l’augmentation du débit d’eau avec des grands pics de débits massiques

d’éléments-traces métalliques à Ticapampa et Huaraz. La diminution dramatique de ses débits

massiques après ces sites indique le comportement non-conservatif d’éléments-traces dissous

dans les conditions de pH du Rio Santa. Alors que le débit d’eau de la saison sèche continue de

décliner à cause du recul des glaciers, les problèmes de contamination actuels seront

potentiellement exacerbés et des flux réduit empêcheront le Rio Santa et ses affluents d’agir

comme tampon des affluents acides et des admissions d’eau résiduaires issue des mines.

Page 4: The origin and distribution of trace metals in the Rio Santa

iv

Acknowledgements

Thank you to Dr. Jeffrey McKenzie for his dedication as a research supervisor. I have

greatly appreciated his insight, availability, helpfulness, and good humor throughout the thesis

process. Under his supervision I have learned so much and had a very positive grad school

experience. Thank you to my former office mate, Dr. Michel Baraer, for assistance in planning

and conducting field work, and for hours spent discussing my research and teaching me about

hydrology.

Dr. Sarah Fortner of Wittenberg University provided valuable assistance while I was

getting started with trace metal research and continued to share her knowledge and datasets ever

since, for which I am very grateful. Thank you to Bryan Mark of the Ohio State University for

his role in project planning, field work, and data analysis. Thank you to Keith Hodson and Alex

Eddie for much-needed ArcGIS assistance and sharing resources from their own research groups.

Thank you also to Ollie Wigmore, Jeff Lafreniere, and Adam French for their help with field

sampling.

The other students in my research group have made it an excellent work environment and

helped in many small ways over the years. Thanks to Danny Chavez, Rob Carver, and Laura

Maharaj. Thank you to Anne Kosowski, Kristy Thornton, and Angela Di Ninno for keeping me

on track all this time, answering my never-ending stream of questions, and making EPS such a

great department. Similar thanks go to Brigitte Dionne for huge amounts of technical assistance.

Page 5: The origin and distribution of trace metals in the Rio Santa

v

Preface

The following thesis presents original research by the author at the Department of Earth

and Planetary Sciences, McGill University during the 2011-2013 academic years. It is submitted

in a traditional thesis format, and is ultimately intended to form a manuscript to be submitted to a

peer-reviewed journal.

This research was supervised by Dr. Jeffrey McKenzie from McGill University. Field

work took place in the Rio Santa Watershed, Peru, in July 2011. Sample collection was done by

a team of researchers, including the author, that were led by Dr. McKenzie and Dr. Bryan Mark

from Ohio State University. Samples were analyzed at Ohio State University. Data was

incorporated with pre-existing data sets collected principally by Dr. McKenzie and Dr. Mark

since 1998, with additional data supplied by Dr. Sarah Fortner of the Wittenberg University.

Analysis and interpretation of the data were done by the author at McGill University.

Page 6: The origin and distribution of trace metals in the Rio Santa

vi

Table of Contents

Abstract ............................................................................................................................. ii

Resume ............................................................................................................................. iii

Acknowledgements .......................................................................................................... iv

Preface............................................................................................................................... v

Table of Contents ............................................................................................................. vi

Table of Figures ............................................................................................................. viii

Table of Tables ................................................................................................................. x

1. Introduction ................................................................................................................... 1

2. Study Area .................................................................................................................... 6

3. Methods....................................................................................................................... 11

. 3.1. Preparation of trace metal sample materials………………………………11

3.2. Field sampling .............................................................................................. 12

3.3. Laboratory work........................................................................................... 14

3.4. Other sources of data ................................................................................... 15

3.5. Discharge calculations ................................................................................. 15

3.6. Denudation calculations ............................................................................... 17

4. Results ......................................................................................................................... 18

4.1. Discharge ..................................................................................................... 21

4.2. Major ion geochemistry ............................................................................... 23

4.3. Trace metal geochemistry ............................................................................ 31

4.4. GIS Analysis ................................................................................................ 35

5. Discussion .................................................................................................................. 35

5.1. Discharge relationships ................................................................................ 35

5.2. Major ion chemistry ..................................................................................... 38

5.2.1. Sulfate ........................................................................................... 38

5.2.2. Alkalinity ...................................................................................... 42

Page 7: The origin and distribution of trace metals in the Rio Santa

vii

5.2.3. Comparison with other rivers........................................................ 44

5.3. Trace element chemistry .............................................................................. 45

5.3.1. Dissolved metals in the Rio Santa Watershed .............................. 45

5.3.2. Aqueous trace metal relationships ................................................ 48

5.3.3. Temporal variations in trace metals .............................................. 53

5.3.4. Implications for water quality ....................................................... 57

5.5. Temporal variations in water chemistry ...................................................... 56

5.5.1. Temporal variations ...................................................................... 56

5.5.2. Case study: Chemical weathering in the Querococha Basin ........ 66

5.5.3. Chemical weathering rates in the Cordillera Blanca..................... 70

5.5.4. Implications of changing hydrology on water chemistry ............. 71

6. Conclusions ................................................................................................................. 74

7. References ................................................................................................................... 77

Appendix ......................................................................................................................... 85

Page 8: The origin and distribution of trace metals in the Rio Santa

viii

Table of Figures

Figure 2.1. The Rio Santa Watershed, Peru ..................................................................... 7

Figure 2.2. The glacier-rich Cordillera Blanca ................................................................ 8

Figure 2.3. The extremely arid Cordillera Negra ............................................................. 8

Figure 2.4. Surficial geology map of the Rio Santa Watershed..................................... 10

Figure 3.1. Collection of a trace metal sample .............................................................. 15

Figure 4.1. July 2011 sampling locations in the Rio Santa Watershed.......................... 20

Figure 4.2. Discharge profile along Rio Santa ............................................................... 23

Figure 4.3. Rio Santa: major dissolved cations and SiO2 .............................................. 25

Figure 4.4. Rio Santa: major dissolved anions .............................................................. 26

Figure 4.5. Rio Santa: nutrients ..................................................................................... 27

Figure 4.6. Tributaries: major ions ................................................................................ 27

Figure 4.7. Rio Santa: trace metals ................................................................................ 28

Figure 4.8. Rio Santa: bulk loads ................................................................................... 30

Figure 4.9. Tributaries: trace metals .............................................................................. 32

Figure 5.1. Tributaries: discharge versus area ............................................................... 37

Figure 5.2. Tributaries: specific discharge versus glaciation ......................................... 37

Figure 5.3. Rio Santa: SO4 versus total cations ............................................................. 40

Figure 5.4. Tributaries: SO4 versus total cations ........................................................... 40

Figure 5.5. Dissolved oxygen versus SO4 ...................................................................... 42

Figure 5.6. Urban garbage in the Rio Santa near Huaraz .............................................. 47

Figure 5.7. Oxidation control of Fe and Mn .................................................................. 49

Figure 5.8. Relationship between trace metals and Mn ................................................. 50

Figure 5.9. Relationship between As and Mn ................................................................ 50

Figure 5.10. Quilcay Out: dissolved metals ................................................................... 52

Figure 5.11. Dissolved metal concentrations in July 2008 and July 2011 ..................... 55

Figure 5.12. Conductivity versus SO4............................................................................ 57

Page 9: The origin and distribution of trace metals in the Rio Santa

ix

Figure 5.13. pH values at synoptically sampled sites .................................................... 57

Figure 5.14. SO4 at synoptically sampled sites .............................................................. 57

Figure 5.15. Ca at synoptically sampled sites ................................................................ 58

Figure 5.16. Map of the Callejon de Huaylas ................................................................ 58

Figure 5.17. Querococha: annual chemical weathering rates ........................................ 62

Figure 5.18. Querococha: monthly chemical weathering rates ...................................... 62

Figure 5.19. Querococha: specific discharge and precipitation ..................................... 63

Figure 5.20. Subglacial chemical weathering reactions ................................................. 65

Figure 5.21. Proglacial chemical weathering reactions ................................................. 65

Figure 5.22. Deglaciated chemical weathering reactions .............................................. 66

Figure 5.23. Distal chemical weathering reactions ........................................................ 66

Figure 5.24. Querococha denudation rates versus other watersheds ............................. 68

Figure 5.25. Callejon de Huaylas: dry and wet season CDR ......................................... 70

Figure 5.26. Rio Santa Low: dry and wet season concentrations .................................. 70

Page 10: The origin and distribution of trace metals in the Rio Santa

x

Table of Tables

Table 4.1. July 2011 sampling locations in the Rio Santa Watershed ........................... 18

Table 4.2. Discharge in the Rio Santa Watershed ......................................................... 22

Table 4.3. Hydrochemistry of the Rio Santa .................................................................. 27

Table 4.4. Hydrochemistry of tributaries ....................................................................... 28

Table 4.5. Dissolved trace metal concentration in the Rio Santa Watershed ................ 32

Table 4.6. Physical characteristics of tributaries to the Rio Santa ................................. 34

Table 5.1. Comparison of Rio Santa to other major rivers ............................................ 45

Table 5.2. Filtered and unfiltered concentrations of As ................................................. 53

Table 5.3. pH in Rio Santa Watershed in 2008 and 2011 .............................................. 52

Table 5.4. Trace metal concentrations in Rio Santa and drinking water guidelines ...... 55

Table 5.5. Legend of site numbers for Figures 5.13-5.15 .............................................. 59

Page 11: The origin and distribution of trace metals in the Rio Santa

1

1. Introduction

The world’s highest density of tropical glaciers is found in the Cordillera Blanca

mountain range of the Peruvian Andes (Bury et al., 2010). The 700 glaciers in the Cordillera

Blanca (Ames et al., 1989) are undergoing rapid retreat driven by climate change-related

temperature increases. In semi-arid tropic and subtropic settings, such as this region, over 80%

of freshwater available for downstream populations originates in mountains. Glacial meltwater

is vital to the fresh water supply as it provides up to 30% of river discharge during the dry season

(Mark and McKenzie, 2007).

Since 1970, there has been a >22% decrease in glaciated area, with glacier termini rising

by average elevations of 113 m (Racoviteau et al., 2005). With ongoing glacial retreat, there is

initially an increase in runoff as their masses decrease (Mark and McKenzie, 2007). At some

point in time, the glacial ice volume decreases past a critical point, known as peak discharge,

after which the annual runoff decreases (Mark et al., 2005). In the Cordillera Blanca, many

glaciers have passed peak discharge and their annual and dry season discharges are in decline.

These declines are predicted to continue irreversibly for many decades until glacial contribution

to the hydrologic system becomes negligible. Dry season discharge is predicted to decline by

30% with the complete loss of glaciers (Baraer et al., 2012).

In addition to declining water quantity in the Rio Santa Watershed, there are ongoing

concerns about water quality due to glacial loss, mining activities, and increasing anthropogenic

inputs. There is evidence that high levels of potentially toxic trace metals are present in the

surface waters. Preliminary sampling along the length of the Quilcayhaunca tributary, which

drains into the Rio Santa, revealed that the river contained elevated levels of Al, Fe, Mn, Co, Ni,

Page 12: The origin and distribution of trace metals in the Rio Santa

2

and Pb; these elevated levels were attributed to naturally-occurring acid rock drainage (ARD)

(Burns et al., 2011; Fortner et al., 2011). Along the Rio Santa itself, three out of eight water

samples analyzed for dissolved As concentration had values >10 ug/L (Fortner, unpublished),

which exceeds World Health Organization drinking water standards (WHO, 2008).

Beyond the research by Burns et al. (2011) and Fortner et al. (2011), there have not been

other published trace metal studies from the Rio Santa. Hydrologic research in the region has

primarily focused on using stable isotopes and major ion compositions of water to study physical

hydrology in the upper portion of the watershed, which known as the Callejon de Huaylas. Mark

and Seltzer (2003) collected major ion samples in the Querococha Watershed, at the southern

end of the Cordillera Blanca, on a monthly basis in1998-1999. Subsequently, Mark et al. (2005)

used hydrochemical end-member mixing models to estimate that 66% of water leaving the

Callejon de Huaylas was derived from glacierized tributaries of the Cordillera Blanca. Mark and

McKenzie (2007) used synoptically sampled stable isotopes of water to show that specific

discharge from glacierized tributaries in the Cordillera Blanca has been increasing in recent years

due to increasing annual meltwater contribution from glaciers. Baraer et al. (2009) used a

hydrochemical and isotopic mass balance mixing model to determine that during the dry season,

ground water is the largest contributor to outflow from the Querococha Watershed.

Rich deposits of precious metals in the Rio Santa Watershed have given rise to a large

mining industry. There is a long history of small-scale artisanal mining, although today the

industry is dominated by large multinational corporations. In 2008, mining profits comprised

7.3% of Peru’s gross domestic product (USGS, 2008) and activities are accelerating at a rapid

rate (Bebbington and Williams, 2008). The main commodities are Au, Cu, Pb, Sb, and Zn

(Banco Central de Reserva del Peru, 2009).

Page 13: The origin and distribution of trace metals in the Rio Santa

3

Acid mine drainage (AMD) is one of the most serious environmental problems associated

with metal ore mining. It occurs when large amounts of sulfide-bearing rocks are fractured and

exposed to air and water, which causes the acceleration of naturally occurring sulfide oxidation

processes (Akcil and Koldas, 2006). Any geologic deposit containing sulfide is a potential AMD

source; however, the mining of metals such as Ag, Fe, Cu, Pb, and Zn are noted as being

particularly prone to causing AMD (Salomons, 1995). AMD is particularly associated with older

mines, unregulated artisanal mining, and tailings that have been stored in poorly constructed

piles or released directly into rivers (McMahon et al., 1999). Leachate from tailings piles and

water that is pumped or naturally discharged from underground mine workings are commonly

contaminated by AMD, particularly when prevention techniques have never been employed

(Johnson, 2003). Naturally occurring, rapid weathering of exposed sulfide mineral lithologies

can also induce this process, in which case it is described as ARD (Gray, 1997).

Chemical parameters affecting the rate of acid generation include pH, temperature,

oxygen concentration, and chemical activity of ferric iron (Salomons, 1995). The concentration

of oxygen in groundwater is small compared to the relatively large amount required for sulfide

oxidation. For typical AMD systems, water must be continually reoxidized through contact with

air. Physical aspects of the waste materials also affect rates of AMD generation. Sediment size

plays an important role: coarse-grained sediments promote oxygenation of water but have a

lower surface area for dissolution, while finer grained sediments have a higher surface area for

dissolution yet lower oxygen diffusion rates. The volume of neutralizing minerals in the vicinity

also affects the rate of AMD formation (Salomons, 1995).

AMD waters are commonly associated with high dissolved metal and metalloid

concentrations. Trace elements found in these waters may include As, Ba, Cd, Cu, Mn, Mo, Ni,

Page 14: The origin and distribution of trace metals in the Rio Santa

4

Pb, Se, and Zn (Sullivan and Yelton, 1988). The high concentrations occur for three main

reasons: (1) many heavy metals and metalloids are often found in sulfide minerals, (2) the acidic

and ferric iron-rich solution derived from pyrite dissolution readily degrades aluminosilicates

and other minerals, thereby releasing their metals into solution, and (3) many metals are highly

soluble in acidic waters (Johnson, 2003).

The overall impact of AMD in streams is largely controlled by the buffering capacity of

stream water and the quantity of water available for dilution (Olias et al., 2004). The solubilities

of trace metals decrease with increasing pH. At a pH above 4, Fe-oxyhydroxides (“ochre”)

precipitate from solution, forming the rust-covered streambed coatings that are characteristic of

AMD/ARD environments. Other dissolved metals may co-precipitate with the ochre or be

adsorbed to surfaces of clay minerals, carbonates, quartz, feldspars, and/or particulate organic

carbon. These surfaces may already have an ochreous coating, in which case the metals will

adsorb to the coating. The adsorption of metals increases from near zero to near 100% over a pH

range of 1-2 units; thus, a relatively small pH shift may have a significant effect on dissolved

metal content (Salomons, 1995).

Research has demonstrated that chemical erosion rates are linked to physical erosion

rates (e.g. Anderson, 2005, Lyons et al., 2005.) In areas where physical, and therefore chemical,

weathering of sulfide minerals is accelerated by glacial abrasion or mining, there is potential for

initiation of AMD/ARD processes. Fortner et al. (2011) linked high trace metal concentrations

in the Rio Quilcay to rapid chemical weathering of the sulfide-rich Jurassic Chicama Formation.

In addition to the abundant Chicama Formation, there are extensive secondary sulfide deposits

throughout the Cordillera Blanca. Thus, there is high potential for AMD and ARD initiation

throughout the watershed.

Page 15: The origin and distribution of trace metals in the Rio Santa

5

Seasonal trends in trace metals have been noted in other AMD-affected watersheds with

pronounced wet and dry seasons, including the Odiel River in Spain (Olias et al., 2004) and the

Montalbian mine drainage basin in Australia (Harris et al., 2003). In general, dissolved trace

metal levels gradually increase during the dry season due to evaporative concentration. At the

start of the wet season, flushing of concentrated waters and dissolution of ochreous precipitates

and other soluble salts causes sudden, large increases in concentrations. As wet season river

discharge increases, dissolved metals concentrations are gradually diluted to their lowest annual

levels. Nordstrum (2009) described an amplification of discharge-related trends in trace metal

concentrations in alpine watersheds. In the Cordillera Blanca, glacial loss is increasing the

contrast between wet and dry season river flows, which may similarly amplify current seasonal

trends in weathering of sulfide minerals.

To date, the limited water quality research on the Rio Santa Watershed has focused on the

Callejon de Huaylas. The objective of this study is to characterize dry season water quality and

quantity across the entire Rio Santa Watershed. Trace metal samples will be collected

throughout the watershed to establish preliminary baseline concentrations and to identify

potential sources of contamination, if any. This is an important first step for ongoing hydrologic

monitoring efforts, which are vital in this region given the abundance of mining activities and

potential for AMD and ARD. Trace metal concentrations will be assessed in the contexts of

basic hydrochemical parameters and spatial relations to potential sources. Current dynamics will

be examined in relation to potential changes derived from climate change, glacial recession, and

chemical weathering rates.

Page 16: The origin and distribution of trace metals in the Rio Santa

6

2. Study Area

The Cordillera Blanca extends 120 km along the South American Continental Divide in

Peru. The river originates at an elevation of 4000 m.a.s.l. at Lake Conococha and flows north

between the Cordillera Blanca to the east and the Cordillera Negra to the west for over 300 km

before turning west and flowing to the Pacific Ocean (Figure 2.1). The total watershed area

drained by the Rio Santa is over 12 000 km2 (Mark and McKenzie, 2007). Glacierized

watersheds on the western side of the Cordillera Blanca drain into the 4900 km2 upper Rio Santa

Watershed. The upper watershed is referred to as the Callejon de Huaylas and delimited to the

north by the La Balsa hydroelectric dam (1320 m.a.s.l.) (Figure 2.2) (Mark and McKenzie,

2007). Below the Callejon de Huaylas, the river flows in a westward direction through the

narrow gorge of the Canon del Pato and emerges onto a flat coastal ridge before flowing into the

ocean.

Temperatures in the Cordillera Blanca are characterized by large diurnal variations but

small average daily annual variations of approximately 0.8° C. Annual oscillations of the

intertropical convergence zone cause distinct wet/dry seasonality. Seventy to eighty percent of

annual precipitation falls between October and April, the austral summer in Peru (Kaser et al.,

2003). During this period, maximum glacial accumulation occurs above the glacier’s

equilibrium line altitude (ELA), and the relatively warmer temperatures and higher humidity

cause maximum ablation below the ELA (Kaser and Ostmaston, 2002). Ablation continues year

round, thus buffering stream melt throughout the year. The rain shadow effect of the Cordillera

Blanca causes the Cordillera Negra to remain extremely arid throughout the year (Figure 2.3)

(Kaser et al., 2003).

Page 17: The origin and distribution of trace metals in the Rio Santa

7

Figure 2.1. The Rio Santa Watershed, Peru. Modified from USGS (2006).

Page 18: The origin and distribution of trace metals in the Rio Santa

8

Figure 2.2. The glacier-rich Cordillera Blanca.

Figure 2.3. The extremely arid Cordillera Negra.

Page 19: The origin and distribution of trace metals in the Rio Santa

9

The geology of high altitude peaks of the Cordillera Blanca is dominated by the Jurassic

Chicama Formation, which is composed of pyrite-rich shales interbedded with quartzite and

argillite (Figure 2.4). The predominant exposures at mid-altitudes are the granodiorites and

tonalities of the Cordillera Blanca Batholith and coeval ignimbrite deposits (Petford and

Atherton, 1996). There are minor deposits of Cretaceous marine sediments exposed in the

northernmost portion of the watershed. The Cordillera Negra is dominated by the Tertiary

Calipuy formation to the south, which is composed of calc-alkalic lava flows, tuffs, and

pyroclastic breccias (Cobbing et al., 1981); to the north there is increasing exposure of the

Cretaceous Goyllarisquizga Formation, which is composed of limestone, sandstone, and siltstone

(Araneda, 2003). At low altitudes between the two mountain ranges, the valley has been infilled

by Quaternary glaciofluvial, glacial, and fluvial sediments. To the northwest, where the Rio

Santa bends in a westerly direction towards the Pacific Ocean, there is exposure of Paleogene-

Cretaceous granodiorites and tonalities. There has been extensive metamorphism and secondary

metal ore deposition throughout the Cordilleras Blanca and Negra. The rich metal deposits occur

along north-west trending fault lines and are known collectively as the Miocene Metallogenic

Belt (e.g. Cobbing et al., 1981; Taylor et al., 2007).

The Callejon de Huaylas is the most densely populated portion of the watershed, with

approximately 267 000 people scattered across small rural settlements and larger urban centers.

Most towns are located along the Rio Santa, including the provincial capital of Huaraz, which

has a population of 120 000 people (INEI, 2007). Nearly half the population of the region

survives on subsistence agriculture, although large-scale, irrigation-intensive activities are

increasing within the Callejon de Huaylas and along the coastal shelf (INEI, 2007; Painter,

2007). Along the final 75 km of the Rio Santa are a series of water diversions that remove

Page 20: The origin and distribution of trace metals in the Rio Santa

10

significant quantities for coastal irrigation projects. The La Balsa hydroelectric dam at the

entrance to the Canon del Pato provides 10% of Peru’s hydroelectric capacity (MEM, 2008).

Figure 2.4. Surficial geology map of the Rio Santa Watershed. Modified from Cobbing and

Sanchez (1996) and USGS (1996).

Page 21: The origin and distribution of trace metals in the Rio Santa

11

3. Methods

3.1. Preparation of trace metal sample materials

Trace metal sampling materials underwent rigorous laboratory preparation prior to the

field expedition. New 30 mL high density polyethylene (HDPE) sampling bottles, HDPE

rubber-free syringes, and lengths of HDPE tubing were prepared in accordance with United

States Environmental Protection Agency (U.S. E.P.A) standard operating procedures (U.S. EPA,

2000). New elbow-length polyethylene gloves were worn at all times throughout the preparation

of sampling materials. The materials were immersed in a series of week-long acid baths in large

HDPE basins. The first week was in 10% trace metal grade HCl, the second week in 10% trace

metal grade HNO3, and the third week in 1% ultrapure trace metal grade HNO3. 18-MΩ

distilled-deionized ultrapure (DI) water was used to dilute the concentrated acids and to rinse

basins and materials between baths. After the series of baths were completed, the sample bottles

were completely filled with 2% ultrapure trace metal grade HNO3 and sealed.

HDPE syringe filters were cleaned using methods modified from Shiller (2003). Forty

millimeters of DI water were pressed through the filters, followed by 40 mL of 2% ultrapure

trace metal grade HNO3, followed by an additional 40 mL of DI water. The cleaned filters were

attached to the acid-cleaned tubing and dried with a vacuum pump.

Individual sampling kits were prepared for each site. A syringe and syringe filter were

placed in a polyethylene glove. A sample bottle was placed in a second glove. Both gloves were

tied off and double bagged inside new HDPE ziplock bags.

Page 22: The origin and distribution of trace metals in the Rio Santa

12

3.2. Field sampling

In the field, trace metal samples were collected upriver from other sampling activities,

bridges, and other obvious potential airborne contamination sources. Samples were collected

according to the “clean hands, dirty hands” standard operating procedure set out by the U.S.

E.P.A. (2004). In this two-person method, one member is designated as “dirty hands” and the

other as “clean hands”. “Dirty hands” (DH) wears elbow-length polyethylene gloves and is

responsible for opening and closing the outer bag of the sampling kit. “Clean hands” (CH)

wears shoulder-length polyethylene gloves and is responsible for opening and closing the inner

bag of the sampling kit and collecting the trace metal sample.

To collect a sample, DH opens the outer bag. CH opens the inner bag, removes the

syringe, filter, and sample bottle, and then closes the inner bag. DH closes the outer bag. CH

rinses the syringe with river water three times, then fills it and attaches the syringe filter. Five

mL of water is pressed through the filter and discarded, 15 mL of water is used to rinse the

sample bottle, and 30 mL is used to fill the sample bottle completely. CH caps the bottle. DH

opens the outer bag, CH opens the inner bag and places the sample inside; the inner and outer

bags are sealed and the package is stored in a cooler or refrigerator.

New HDPE containers were used to collect filtered samples for analysis of major ions,

alkalinity, nutrients, and stable isotopes of water. Discharge, temperature, pH, conductivity, and

dissolved oxygen were measured in situ with an YSI 556 multiprobe meter.

Page 23: The origin and distribution of trace metals in the Rio Santa

13

Figure 3.1. Collection of a trace metal sample.

An Acoustic Doppler Current Profiler (ADCP) apparatus attached to a small boat

measured discharge. The ADCP contains sonar, which creates a vertical profile of current

velocities. When pulled slowly across a river, it creates a cross sectional profile of area and

current velocity, allowing for a very accurate discharge measurement. A minimum of three

discharge measurements were made at each river site and the average discharge value was

calculated.

Nine major tributaries were sampled near their outlet points to the Rio Santa. Twenty

three water samples were collected in the Rio Santa, often within a few kilometers upstream and

downstream of sampled tributaries. Water samples were also collected at the outlet of Lake

Page 24: The origin and distribution of trace metals in the Rio Santa

14

Conococha. Fewer samples were collected along the final 100 km of river due to the difficulty

of accessing the river in the Canon del Pato. Trace metal samples were obtained at 11 sites along

the Rio Santa, at the outlets of eight tributaries, and near the mid-length point of the Rio Quilcay.

Field blanks, samples in which DI water is collected using the same method as for trace metal

sampling, were obtained to ensure cleanliness of sampling materials and methods.

3.3. Laboratory work

All chemical analyses were done at The Ohio State University. Major cations were

measured using an Optima 3000 DV Inductively Coupled Plasma-Optical Emission

Spectrometer (ICP-OES), using five calibration standards that bracketed the range of

concentrations within the samples. Major anions were measured using a Dionex DX-120 Ion

Chromatographer. Concentrations of PO4, NO3, NH3, and Si (reported as SiO2) were measured

with a Skalar San++ Automated Wet Chemistry Analyzer. Precision and accuracy were within

5% for all analyses.

Trace elements were measured at the Trace Element Research Laboratory using a

ThermoFinnigan Element2 Inductively Coupled Plasma Sector Field Mass Spectrometer (ICP-

MS). The samples were acidified in the lab with 2% v/v double distilled NO3. The detection

limit for each element was determined using a blank and a 1 ppb calibration standard. Accuracy

was within 10% for all analyses.

Values of δ18O and δ2H were measured were measured at Byrd Polar Research Center

using a Finnigan MAT Delta Plus Mass Spectrometer coupled to a HDO water equilibrator.

Page 25: The origin and distribution of trace metals in the Rio Santa

15

Stable isotopes were reported using the δ-notation relative to the Vienna-Standard Mean Ocean

Water standard, with an accuracy of ±0.1 ‰ for δ18O and ±1 ‰ for δ2H.

3.4. Other sources of data

Water analyses in this study are compared with data from previous studies from the

Cordillera Blanca. Cations and anion concentrations of samples collected between 2005 and

2010 were measured at The Ohio State University with ion chromatography or at McGill

University with atomic adsorption (e.g. Baraer et al., 2012). Analysis and methods of monthly

discharge and water chemistry from the Querococha Watershed from 1998-1999 are presented in

Mark and Seltzer (2003) and analysis of samples from 2004 in Mark and McKenzie (2005). For

these samples, cations were analyzed at Syracuse University with a direct current plasma

spectrometer and anions were measured using a Dionex ion chromatography system. Major ions

and trace metal samples from Quilcayhaunca and the Rio Santa, 2008, are part of a data set that

was partially published in Fortner et al. (2011). Water analyses were performed at The Ohio

State University. Anion concentrations were measured with an ion chromatography system,

major cation concentrations were measured with ICP-OES, and trace metal concentrations were

measured with ICP-MS.

3.5. Discharge calculations

Mass balance equations were used to determine discharge (Qcalc) for some locations

where direct measurement was not possible. At a site where a tributary enters the Rio Santa (a

Page 26: The origin and distribution of trace metals in the Rio Santa

16

“triple point”), conservative tracer concentrations at sites upstream of, downstream of, and

within the tributary were required, along with a discharge measurement from one of these three

points (Qmeas). On the subbasin scale, it is assumed that the mass flux of conservative tracers at

the downriver site is the sum of the fluxes from upriver and the tributary (Equation 1):

Massu + Masst = Massd (1)

The subscripts u, t, and d denote upstream, tributary, and downstream, respectively.

To evaluate if a tracer is conservative, we used the following rules based on Baraer et al.

(2009): (1) the tracer concentration at the downstream site must be intermediate between the

upstream and tributary concentrations, (2) the tracer concentration at the downstream sample and

in one other sample must be above the limits of analysis detection, and (3) there must be > 20%

difference between minimum and maximum concentrations.

The mass balance models are derived from Equation (1):

QuCu + QtCt = QdCd (2)

Where Qu, Qt, and Qd are the upstream, tributary, and downstream discharges respectively, and

Cu, Ct, and Cd are the concentrations of a given tracer for the upstream, tributary and downstream

locations respectively. Because Qd = Qu + Qt, Equation (2) can be further simplified:

QuCu + QtCt = QuCd + QtCd (3)

Equation (3) can be solved for Qu (Equation 4) or Qt (Equation 5). A similar manipulation of

Equation (2) yields the solution for Qd (Equation 6):

Qu = Qt(Cd – Ct)/(Cu – Cd) (4)

Page 27: The origin and distribution of trace metals in the Rio Santa

17

Qt = Qu(Cd – Cd)/(Cd – Ct) (5)

Qd = Qt(Ct – Cu)/(Cd-Cu) (6)

Major ions, nutrients, and the stable isotopes of water were examined for conservative

behavior at each triple point. Tracers deemed conservative were Li, Mg, Ca, SO4, F, and δ18O.

Seven triple point locations had two or more conservative tracer species which enabled the

calculation of discharge. The Qcalc values were averaged for each triple point to determine a final

calculated discharge.

3.6. Denudation calculations

The rate of chemical weathering reactions, normalized to watershed area, can be

determined with the cation denudation rate (CDR), which describes how rapidly cations are

weathered from a given surface area per unit time (Anderson, 2007). ArcGIS is used to obtain

the area of a given watershed. The CDR is then calculated in three steps:

1. Concentration of ion x discharge = bulk load of ion

2. ∑ bulk loads of major cations = cation flux

3. Cation flux / area of watershed = CDR

The silicate denudation rate is also a useful indicator in weathering reactions. The

silicate denudation rate is calculated in a similar manner to the CDR, but for just silicate (i.e. the

second step is omitted.)

Page 28: The origin and distribution of trace metals in the Rio Santa

18

4. Results

Twenty-eight samples were collected throughout the Rio Santa Watershed (Figure 4.1;

Table 4.1). The tributaries drain basins with a range of lithologies, glaciation, discharge, and

variable proximity to mining activity and hot springs. The hydrochemical characteristics of

surface waters vary widely throughout the watershed. The Rio Santa evolves along its length

from a Ca-HCO3-rich stream trickling from Lake Conococha to a Ca-SO4-rich river flowing into

the Pacific Ocean. There is significant variability in discharge and major ion composition of

tributaries that drain into the Rio Santa.

Table 4.1. Dry season (July 2011) sampling locations in the Rio Santa Watershed.

Sample Latitude Longitude Location notes Known mining

activity

Notes

S1 -8.96759 -78.6223 North of Chimbote

S2 -8.66136 -78.2886 Chavimochic

Bocatoma

S3 RSD -8.65722 -78.2456 Beside main road

S3 Tabla -8.64801 -78.2332 Rio Tabla Yes Hot springs

S3 RSU -8.65788 -78.2336 Puente over Rio

Santa

S4 -8.6641 -78.0462 Puente over Rio

Santa

S7 RSD -8.80976 -77.8792 Huallanca, above

power plant

S7 Quitarscara -8.80189 -77.8517 Rio Quitarscara

S7 RSD -8.80976 -77.8792 La Balsa Bocatoma

S9 RSD -8.9919 -77.82168 Puente

Choquechaca

S9 RSU -9.0556 -77.8126 Cuidad Caraz

S9 Llullan -9.04478 -77.8164 Rio Llullan Barrick

Au-Ag-Zn-Cu-Pb

Drains Lake Paron

S10 Mancos -9.19085 -77.7102 Rio Mancos California mine;

tailings

Hot springs

Continued on page 19.

Page 29: The origin and distribution of trace metals in the Rio Santa

19

Table 4.1 (Continued.) Dry season (July 2011) sampling locations in the Rio Santa Watershed.

S11 Marcara -9.32475 -77.604 Rio Marcara Tailings in upper

watershed

Hot springs

S11 RSU -9.33162 -77.6031 Cuidad Marcara

S12 RSD -9.50507 -77.5365 Cuidad Huaraz at

Miraflores

S12 Quilcay -9.52371 -77.5256 Rio Quilcay

S12 RSU -9.55964 -77.5401 Cuidad Huaraz Significant mining

and tailings

S12.5 RSD -9.66885 -77.4807 Cuidad Olleros Significant ochreous

precipitates

S12.5 Olleros -9.67205 -77.4789 Rio Negro Silvania Ag-Pb mine;

tailings

Hot springs;

Ochreous precipitates

S12.5 RSU -9.67205 -77.4806 Cuidad Olleros

S13 RSD -9.73509 -77.4484 Cuidad Ticapampa Ochreous precipitates

S13 Yanayacu -9.77532 -77.4177 Rio Yanayacu Tailings Querococha Lake;

Ochreous precipitates

S13 RSU -9.77688 -77.4395 Cuidad Catac

S14 RSD -9.8219 -77.4209 Cuidad Pachacoto Ochreous precipitates

S14 Pachacoto -9.85253 -77.4024 Beside road to

Pastoruri

Tailings in upper

watershed

Ochreous precipitates

S14 RSU -9.84826 -77.4088 Cuidad Pachacoto

S15 RSD -10.0311 -77.3257 Puente over Rio

Santa

S15 Shiki -10.0325 -77.3241 Rio Shiki

S15 RSU -10.034 -77.3249 Beside main road

S16 RSD -10.114 -77.2845 Lake Conococha

S16 Tucco -10.1162 -77.2818 Rio Tucco Yes

S16 Conococha -10.1192 -77.2835 Lake Conococha

Page 30: The origin and distribution of trace metals in the Rio Santa

20

Figure 4.1. Sampling locations in the Rio Santa Watershed, July 2011.

Page 31: The origin and distribution of trace metals in the Rio Santa

21

4.1. Discharge

Figure 4.2. Discharge profile along the length of the Rio Santa. The dashed vertical line

represents the location of the Chavimochic water diversion project.

Along the Rio Santa, the minimum discharge was 0.1 m3/s at the river’s headwaters at

Lake Conococha (Table 4.2; Figure 4.2). Discharge increased steadily along the length of the

river to maximum values of 45 m3/s and 38 m

3/s at sites S3 RSD and S2, respectively, located 60

km and 65 km downstream of La Balsa. At site S1, where the Rio Santa flows into the Pacific

Ocean, discharge decreased to 5 m3/s. The estimated error for ADCP measurements is 5-10%

(Personal Communication, O. Wigmore, The Ohio State University, USA, March 26, 2013) and

15-20% for calculated discharge.

0

10

20

30

40

50

60

0 50 100 150 200 250 300 350

Dis

char

ge (

m3 /s

)

Distance from Lake Conococha (km)

Rio Santa: discharge

Calculated

Measured

Page 32: The origin and distribution of trace metals in the Rio Santa

22

Table 4.2. Measured and calculated discharge at select sampling sites along the Rio Santa and its

tributaries.

Rio Santa Discharge (m3/s)

Tributaries Discharge (m3/s)

S1 5.0

S3 Tabla 12.0*

S2 37.8

S7 Quitarscara 1.9

S3 RSD 45.3*

S9 Llullan 3.8*

S3 RSU 33.4

S10 Mancos 0.7*

S4 30.2

S11 Marcara n/a

S7 RSD n/a

S12 Quilcay 1.3

S7 RSU n/a

S12.5 Olleros 0.8*

S9 RSD 19.4

S13 Yanayacu 0.8*

S9 RSU 10.7*

S14 Pachacoto 0.4*

S10 RSU 13.1

S15 Shiki 0.3*

S10 RSD 13.8

S16 Tucco n/a

S11 RSU 9.4

S12 RSD 10.6*

S12 RSU 9.3

S12.5 RSD 6.7

S12.5 RSU 5.9*

S13 RSD 4.2

S13 RSU 3.0*

S14 RSD 2.5

S14 RSU 2.0

S15 RSD 1.9

S15 RSU 1.1*

S16 RSD n/a

S16 Conococha 0.1

*Calculated values using Equations (4) to (6).

Page 33: The origin and distribution of trace metals in the Rio Santa

23

4.2. Major ion geochemistry

Major ion samples were analyzed in samples collected at 23 sites along the Rio Santa and

at the outlets of nine major tributaries. Trace elements were analyzed in samples from 11 Rio

Santa sites samples and eight tributary sites. An additional trace element sample was collected

along the Rio Quilcay, approximately 12 km from the headwaters of the tributary, in order to

compare its trace metal concentrations with a previous sample collected in 2008 by Fortner et al.

(2011).

Figure 4.3. Profiles of major dissolved cations and SiO2 (mg/L) with distance along the length of

the Rio Santa, measured in kilometers from its origin at Lake Conococha.

Calcium is the main dissolved cation in the Rio Santa. Its lowest concentration, 12 mg/L,

is at Lake Conococha. It generally increases along the length of the river to a maximum of 64

mg/L at the outlet to the Pacific Ocean (Figure 4.3; Table. 4.2). The next highest species are Na,

SiO2, Mg, K, and Li, in descending order. They all increase in concentration for the first 100 km

0.01

0.1

1

10

100

0 50 100 150 200 250 300 350

Co

nce

ntr

atio

n (

mg/

L)

Distance from Lake Conococha (km)

Rio Santa: dissolved major cations and SiO2

Li

Na

K

Mg

Ca

SiO2

Page 34: The origin and distribution of trace metals in the Rio Santa

24

of the river, and then remain at a relatively constant concentration along the length of the Rio

Santa.

Figure 4.4. Profiles of major dissolved anions (mg/L) along the length of the Rio Santa,

measured in kilometers from its origin at Lake Conococha.

SO4 and HCO3 are the main anions in the Rio Santa; they have an inverse relationship

with each other (Figure 4.4; Table 4.3). SO4 increases northwards from below detection at Lake

Conococha to a maximum value of 200 mg/L at the mouth of the Rio Santa. There is more

fluctuation in HCO3 concentrations, which vary between 20 - 100 mg/L, but generally decreases

along the length of the river. Concentrations of F and Cl are low in the Rio Santa, varying

between near 0 – 0.5 mg/L and 5 - 10 mg/L respectively. Water along the Rio Santa is slightly

basic at all sites, with pH ranging from 7.5 – 8.3 (Table 4.3).

0.1

1

10

100

1000

0 50 100 150 200 250 300 350

Co

nce

ntr

atio

n (

mg/

L)

Distance from Lake Concococha (km)

Rio Santa: dissolved major anions

F

SO4

Cl

HCO3

Page 35: The origin and distribution of trace metals in the Rio Santa

25

Figure 4.5. Dissolved nutrient concentrations (ug/L) along the Rio Santa, measured in

kilometers from its origin at Lake Conococha. The black vertical line denotes the location of the

Marcara tributary (at 100 km) and the red vertical line denotes the location of Huallanca (at 195

km.)

Nutrient concentrations fluctuate widely along the length of the Rio Santa (Figure 4.5;

Table 4.3). There is a significant increase in NO3, to its maximum concentration of 1100 ug/L,

at site S11 RSU just downstream of Huaraz and close to the town of Marcara. Concentrations

remain greater than 500 ug/L along the remaining length of the Rio Santa. NH3 concentrations

remain between 10 ug/L and 25 ug/L along most of the Rio Santa, except for elevated

concentrations at Lake Conococha (90 ug/L) and near Huallanca at site S7 RSD (40 ug/L). PO4

concentrations fluctuate slightly, yet consistently remain below 10 ug/L.

0

200

400

600

800

1000

1200

1400

0

20

40

60

80

100

120

-50 0 50 100 150 200 250 300 350

NO

3 (u

g/L)

NH

3 an

d P

O4

(ug/

L)

Distance from Lake Conococha (km)

Rio Santa: nutrient concentrations

NH3

PO4

NO3

Page 36: The origin and distribution of trace metals in the Rio Santa

26

Table 4.3. Dissolved oxygen, pH, major dissolved ion, and nutrient concentrations in the Rio

Santa.

Sample dO2 (%) pH Li Na K Mg Ca F Cl SO4 HCO3 SiO2 NH3 NO3 PO4

S1 n/a 8 0.12 23.22 3.13 10.14 64.23 0.47 8.74 203.02 42.6 12.45 0.00 0.54 0.02

S2 98.5 8 0.15 20.21 2.97 11.61 52.30 0.48 7.46 190.00 22.8 12.34 0.00 0.67 0.02

S3 RSD 99.8 8 0.16 21.06 2.98 12.37 52.69 0.47 7.74 190.18 29.6 12.16 0.00 0.66 0.02

S3 RSU 99.5 8 0.14 19.95 2.94 8.73 46.98 0.47 7.60 156.74 51 12.69 0.00 0.77 0.02

S4 97.0 7.9 0.14 19.47 2.86 9.21 44.93 0.48 7.16 151.29 47 11.84 0.00 0.62 0.02

S7 RSD 95.5 7.8 0.15 18.15 3.02 4.79 40.93 0.38 6.77 84.27 60 12.33 0.00 0.29 0.07

S7 RSU 88.9 8.2 0.18 20.96 3.51 5.26 43.14 0.34 8.54 83.52 69 13.86 0.00 0.29 0.19

S9 RSU 79.9 8 0.20 22.13 3.91 6.08 48.30 0.26 10.24 92.46 63 13.71 0.01 0.79 0.05

S9 RSD n/a n/a 0.20 21.21 3.81 5.88 47.68 0.31 9.74 90.83 69 13.87 0.01 0.69 0.03

S10 RSD n/a n/a 0.23 22.43 3.87 5.61 40.87 0.24 10.9 76.21 111.2 12.04 0.00 0.38 0.02

S10 RSU 72.3 7.7 0.16 17.35 3.27 4.85 42.72 0.25 8.20 80.13 61 12.53 0.00 0.41 0.12

S11 RSU n/a n/a 0.19 19.50 3.72 4.22 34.04 0.21 10.09 68.38 60 12.05 0.00 1.06 0.02

S12 RSD 68.2 8.3 0.14 15.77 2.98 3.07 21.51 0.18 7.31 55.96 47.6 10.35 0.01 0.28 0.02

S12 RSU 66.6 7.9 0.18 16.42 2.91 2.98 22.60 0.14 8.72 53.00 54.6 9.29 0.00 0.16 0.01

S12.5 RSD n/a n/a 0.21 18.10 2.87 3.44 23.64 0.16 9.25 60.85 53.7 11.34 0.00 0.15 0.02

S12.5 RSU 70.1 7.6 0.20 17.49 2.75 2.82 24.96 0.11 9.03 37.91 50 11.24 0.10 0.10 0.05

S13 RSD n/a n/a 0.12 10.85 2.00 2.50 21.30 0.11 5.18 26.64 27 10.23 0.01 0.05 0.01

S13 RSU 70.9 7.5 0.10 8.95 1.89 2.80 27.13 0.11 3.67 31.95 83.2 9.08 0.00 0.00 0.01

S14 RSD 66 7.8 0.07 7.77 1.64 2.71 26.57 0.12 3.19 30.27 80.0 8.66 0.00 0.00 0.01

S14 RSU n/a n/a 0.06 8.12 1.52 2.35 28.10 0.1 2.97 22.11 95.4 9.86 0.00 0.05 0.01

S15 RSD 66.6 7.9 0.05 6.43 1.30 1.84 28.90 0.1 2.40 20.93 92.6 8.30 0.00 0.00 0.01

S15 RSU 68.6 7.5 0.05 6.58 1.30 2.31 29.97 0.12 3.82 31.49 53 8.12 0.00 0.00 0.02

S16 RSD 66.7 8.1 0.01 2.06 0.62 2.10 26.81 0.1 1.16 21.91 54 4.82 0.00 0.00 0.01

Conococha 66.2 7 0.02 11.39 1.58 1.97 12.56 0.3 2.58 3.47 45 0.36 0.00 0.00 0.09

Concentrations in mg/L. dO2 and pH were measured in situ. n/a denotes sites where dO2 and pH

were not measured due to instrument failure.

Page 37: The origin and distribution of trace metals in the Rio Santa

27

Figure 4.6. Concentrations of select major constituents (mg/L) in tributaries to the Rio Santa; pH

is in parenthesis after site names.

SO4 is the main anion in seven of the tributaries and HCO3 is the principal species in four

(Figure 4.6; Table 4.4). SO4 concentrations range from 3 - 305 mg/L. HCO3 concentrations

range from near 0 - 130 mg/L. In general, HCO3 dominates tributaries in the southern portion of

the Rio Santa Watershed, while SO4 is more dominant in northern tributaries. Calcium is the

main cation in all tributaries, with concentrations between 2 mg/L and 90 mg/L. K, Mg, and

SiO2 generally remain below 25 mg/L.

There is a significant range of pH in the sampled tributaries (Figure 4.6, Table 4.4). The

most acidic are S12.5 Olleros (pH=3.0) and S12 Quilcay (pH=4.7); the most basic are S16 Tucco

(pH=9.2) and S10 Mancos (pH=8.2). The pH in other tributaries is between 7 and 8.

0

50

100

150

200

250

300

350

Co

nce

ntr

atio

n (

mg/

L)

Tributary

Tributaries: major dissolved species

K

Mg

Ca

SO4

Page 38: The origin and distribution of trace metals in the Rio Santa

28

Table 4.4. Dissolved oxygen, pH, major dissolved ion, and nutrient concentration in tributaries

to the Rio Santa.

Sample dO (%) pH Li Na K Mg Ca F Cl SO4 HCO3 SiO2 NH3 NO3 PO4

S3 Tabla 98.4 8 0.19 22.03 2.73 21.65 68.17 0.48 7.31 309.11 55.0 10.99 0.00 0.31 0.01

S7 Quitarscara 89.9 7.4 0.02 4.09 0.75 2.69 31.93 0.35 1.30 91.50 12.0 9.12 0.00 0.05 0.10

S9 Llullan 76.9 7.3 0.02 4.94 0.84 1.65 10.64 0.63 1.43 14.66 31.0 9.68 0.00 0.00 0.01

S10 Mancos 75 8.2 0.02 13.02 2.66 13.38 86.61 0.30 2.33 188.11 127.0 23.08 0.05 2.25 0.03

S11 Marcara 72.9 7.4 0.14 10.50 2.36 2.69 16.41 0.42 4.90 46.54 21.0 11.06 0.00 0.09 0.02

S12 Quilcay 71.8 4.7 0.02 2.89 1.07 3.04 14.14 0.34 1.23 71.64 2.0 11.13 0.00 0.23 0.06

S12.5 Olleros 70.2 3 0.21 15.99 2.89 8.22 18.92 0.35 8.79 196.44 0.0 13.03 0.00 0.12 0.09

S13 Yanayacu 67.4 7 0.01 2.73 0.80 1.56 6.40 0.07 1.11 5.99 28.3 8.30 0.00 0.00 0.01

S14 Pachacoto 66.4 7.7 0.13 6.28 1.87 4.59 23.16 0.15 3.88 63.10 30.0 4.47 0.00 0.08 0.01

S15 Shiki 71.1 7.6 0.03 5.57 1.10 1.68 21.84 0.10 1.61 17.33 64.0 11.40 0.00 0.00 0.01

S16 Tucco 45.2 9.2 0.01 1.14 0.52 2.09 28.53 0.09 1.03 23.53 75.0 5.20 0.00 0.00 0.01

Concentration data is given in mg/L. HCO3 was calculated by charge balance using the same

method as Mark and Seltzer (2003).

4.3. Trace metal geochemistry

Figure 4.7. Profiles of select dissolved trace metals (ug/L) along the length of the Rio Santa,

measured in kilometers from its origin at Lake Conococha. Concentrations are accurate within

10%.

Between the headwaters of the Rio Santa and Huaraz, the concentrations of dissolved

indicator trace metals are vary significantly; between Huaraz and the outlet to the Pacific Ocean

concentrations are consistently low (Figure 4.7; Table 4.5). At Lake Conococha, As and Fe are

Ticapampa

Huaraz

Page 39: The origin and distribution of trace metals in the Rio Santa

29

elevated to 12 ug/L and 202 ug/L, respectively, which is the latter’s highest concentration in the

river. All metals have relatively low concentrations at site S14 RSD, 53 km from the lake. 1.2

km downstream of Ticapampa, at site S13 RSD, As is present at its maximum concentration of

30 ug/L, and Fe is elevated to 94 ug/L. Maximum concentrations of Pb, Cd, U, Mo, and Ni

occur at site S12 RSU in Huaraz, with concentrations of 73 ug/L, 58 ug/L, 53 ug/L, 40 ug/L, and

23 ug/L, respectively. Beyond Huaraz, concentrations of all trace elements fluctuate between

detection and 12 ug/L.

The bulk loads of individual trace elements fluctuate along the length of the Rio Santa

(Figure 4.8). At Lake Conococha, As, Cd, Cu, Mo, Ni, Pb, and U loads are near zero and Fe is 2

kg/day. At Ticapampa (site S13 RSD), 56 km downriver, there are significant increases in As, to

10 kg/day, and Fe, to 33 kg/day. At Huaraz, the load of dissolved As is near zero, and loads of

Pb, Fe, Cd, U, and Ni peak at 60 kg/day, 55 kg/day, 43 kg/day, 42 kg/day, and 19 kg/day,

respectively. Near the northern outskirts of Huaraz, the loads of Pb, Cd, and U decrease to near

zero, Ni decreases to 10 kg/day, Fe decreases to 5 kg/day, and As increases to 5 kg/day. Along

the next 170 km of the river, Ni, Cu, Mo, U, and Cd proportionally increase to maximum

amounts of 30 kg/day, 20 kg/day, 12 kg/day, 10 kg/day, and 2 kg/day, respectively. The As load

remains low, between 2 kg/day and 7 kg/day, Fe loads remain below 2 kg/day, and Pb loads

remain below detection limits.

Between S2 and S1, the bulk loads of all species decrease sharply. This coincides with

the drop in discharge in the vicinity of the Chavimochic irrigation dam. This causes the Rio

Santa to discharge only 0-5 kg/day of each trace metal into the Pacific Ocean.

Page 40: The origin and distribution of trace metals in the Rio Santa

30

Figure 4.8. Bulk loads of select dissolved trace metals (kg/day) at sampled sites along the Rio

Santa, measured in km from its origin at Lake Conococha.

Huaraz

Chavimochic

Ticapampa

Page 41: The origin and distribution of trace metals in the Rio Santa

31

The dissolved trace metal concentration profiles vary widely between tributaries (Figure

4.9; Table 4.5). There is high inter-tributary variation in terms of which species have low

concentrations (from 1 – 10 ug/L.) Concentrations greater than 10 ug/L include: Ni in S12.5

Olleros (70 ug/L) and S3 Tabla (43 ug/L), Mo and U in S9 Llullan (720 ug/L and 180 ug/L,

respectively), and Mo in S13 Yanayacu (53 ug/L.) Quilcay Out, located 12 km from the

tributaries outlet to the Rio Santa, has elevated concentrations of Cd (27 ug/L), Ni (34 ug/L), Pb

(82 ug/L), and U (14 ug/L.)

Figure 4.9. Concentrations of select dissolved metals (ug/L) in tributaries to the Rio Santa.

Concentrations are accurate within 10%. All tributaries were sampled near their outlet to the Rio

Santa, with the exception of Quilcay Out (sampled 12 km from outlet.)

Page 42: The origin and distribution of trace metals in the Rio Santa

32

Table 4.5. Dissolved trace metal concentration in the Rio Santa and its tributaries.

All tributary samples were collected near stream outlet, with the exception of Quilcay Out. All

values are in ug /L. Non detection of results is indicated by a less than sign (<) followed by the

detection limit.

4.4. GIS analysis

The tributary watersheds range in area from 51.0 – 3195.4 km2, with an average area of

464.3 km2

and a median area of 206.1 km2

(Table 4.6). Glaciation within the tributary

watersheds is variable. The Marcara watershed is the most glaciated, with 72.3 km2

of glacial

coverage, equivalent to 26.4% of watershed area, while the Tabla watershed is the least glaciated

with 1.3 km2 of glacial coverage, equivalent to less than 0.05% of the watershed area. The

average glaciated area within the tributaries was 24.3 km2 or 13% of the respective watershed

area. Spatial data was derived from Shuttle Radar Topography Mission digital elevation maps

(USGS, 2006), and digitized glacial coverage data was provided by the Autoridad Nacional del

Agua (ANA, 2010).

Page 43: The origin and distribution of trace metals in the Rio Santa

33

The lithologies of the subwatersheds are varied (Table 4.6). The main surficial

lithologies are the Chicama Formation, which comprises 0.0 - 724.9 km2

(0-40%) of the

watersheds, Quaternary surficial sediments, which comprise 0.0 - 156.4 km2

(0-63.1%), and the

Cordillera Blanca batholith, which comprises 0.0 – 354.2 km2 (0.0 – 48.7%.) Various other

volcanic and metasedimentary sequences make up the rest of the surficial geology.

Page 44: The origin and distribution of trace metals in the Rio Santa

34

Table 4.6. Physical characteristics of tributaries to the Rio Santa.

Blank spaces indicate zero.

S3 Tabla

S7 Quitarasca

S10 Mancos

S11 Marcara

S9 Llullan

S14 Pachacoto

S15 Shiki

S16 Rio Tucco

S12 Quilcay

S12.5 Olleros

S13 Yanayacu

km

2

%

km

2

%

km

2

%

km

2

%

km

2

%

km

2

%

km

2

%

km

2

%

km

2

%

km

2

%

km

2

%

Are

a

31

95

.4

3

83.6

67

.1

2

73.6

14

3.7

20

6.1

51

.0

9

2.4

24

5.3

17

8.6

27

0.1

Gla

cia

l A

rea

1

.3

0.0

3

1.0

8

.1

14

.6

21

.8

72

.3

26

.4

33

.1

23

.0

21

.8

10

.6

6.5

1

2.7

4

.7

5.1

4

7.3

1

9.3

1

8.8

1

0.5

1

5.9

5

.9

Geo

log

y

G

laci

ofl

uvi

al

sed

imen

ts

37

.0

9.6

3

6.7

5

4.7

1

24.1

4

5.4

5

7.8

4

0.2

7

3.1

3

5.5

3

2.2

6

3.1

4

4.7

4

8.4

1

19.4

4

8.7

8

6.0

4

8.1

1

56.4

5

7.9

Co

rdil

lera

Bla

nca

Ba

tho

lith

3

54.2

1

1.1

1

36.0

3

5.5

9

.0

13

.4

86

.4

31

.6

55

.5

38

.7

11

0.5

4

5.0

3

1.2

1

7.5

8

8.7

3

2.9

Ass

oci

ate

d i

gn

imb

rite

s

11

.7

17

.5

4.7

1

.7

27

.5

19

.2

Ca

lip

uy

Fo

rma

tio

n

12

10

.8

37

.9

66

.2

32

.1

18

.8

36

.9

31

.5

34

.1

0.0

5

.2

2.9

Gra

no

dio

rite

/to

na

lite

2

3.1

0

.7

Ma

rin

e se

dim

ents

2

05.9

6

.4

0.0

1.8

1

.9

Go

ylla

risq

uiz

ga

Fo

rma

tio

n

67

6.6

2

1.2

5

7.1

1

4.9

9

.7

14

.4

31

.5

11

.5

2.8

2

.0

17

.3

8.4

14

.4

15

.5

Ch

ica

ma

Fo

rma

tio

n

72

4.9

2

2.7

1

53.5

4

0.0

26

.8

9.8

49

.6

24

.1

15

.3

6.2

5

6.2

3

1.5

2

4.9

9

.2

Page 45: The origin and distribution of trace metals in the Rio Santa

35

5. Discussion

5.1. Discharge relationships

In the Rio Santa Watershed, precipitation is minimal during the dry season from May to

September (Kaser et al., 2003). During this time, surface runoff is supplied by groundwater and

glacial meltwater (Baraer et al., 2009). Mark et al. (2005a) used tracers to estimate that glacial

meltwater provides 40% of total dry season discharge in the Rio Santa. In this study, flow within

the tributaries ranges from 0.3 m3/s to 12 m

3/s (Table 4.2). The 11 surveyed tributaries

contribute a net volume of 22 m3/s to the Rio Santa.

Mark and McKenzie (2007) used isotopic methods to calculate that glacier-fed tributaries

supply 66% of the total discharge in the Rio Santa at the outlet of the Callejon de Huaylas (near

site S9 RSD.) In this study, discharge in the Rio Santa at site S9 RSD was 19.4 m3/s. The net

discharge of sampled tributaries upriver of this point was 8.1 m3/s, or 42% of the total discharge.

This indicates that tributary sampling captured almost half of the inflow to the Rio Santa.

Considering that numerous smaller and inaccessible tributaries were tributaries were unable to be

sampled, this suite of tributary samples still provides a good characterization of the

hydrochemical system.

A primary control on total discharge of tributaries was their watershed area (Figure 5.1).

The Tabla watershed has significantly greater surface area and discharge than other tributaries;

the Shiki is the smallest watershed and has the lowest discharge. Net discharge is not related to

specific discharge in the sample watersheds (where specific discharge is the discharge divided by

the watershed area.) The Tabla watershed has the lowest specific discharge, the Llullan

watershed has the highest, and the Shiki watershed is intermediate between the two. High levels

Page 46: The origin and distribution of trace metals in the Rio Santa

36

of specific discharge are loosely correlated with higher proportions of glacierized area (Figure

5.2). Variations in aquifer permeability and storage capacity, and glacial melt rates likely affect

the total and specific discharge rates from individual watersheds.

Baraer et al. (2012) modelled potential future discharge declines in a number of

tributaries also examined in this study, and determined that the watersheds with the highest % of

glacial cover will experience greater discharge declines. Specifically, discharge from the Llullan

watershed might decline by up to 60%, while there will only be small discharge declines in less

glaciated watersheds such as the Shiki and Querococha (a subwatershed that feeds Rio

Yanayacu.) All of the tributaries in this study have some degree of glaciation and are vulnerable

to declining discharge with ongoing glacial recession. The greatest discharge declines may occur

in Rios Marcara, Llullan, and Mancos, which have the highest proportions of glacierized area.

Rivers such as the Tabla, with effectively no significant glacier coverage, are at this point

immune to the effects of ongoing glacier recession.

Within the greater Rio Santa Watershed, the highest density of glaciers is in the Callejon

de Huaylas, which is where the majority of the region’s population resides. Declining glacial

meltwater contributions will affect this portion of the watershed most, intensifying the water-

resource related difficulties currently experienced by inhabitants.

There was a large decrease in discharge along the Rio Santa, from 35 m3/s – 40 m

3/s to

5.0 m3/s, between sites S1 and S2 (Figure 4.2). The primary causes of this are the Chavimochic

and Chanacis Projects, which divert significant quantities of water from the lower Rio Santa for

irrigation along Peru’s arid Pacific Coastline. Water can also be lost to other minor irrigation

activities and evaporation. The primarily groundwater-fed Rio Tabla contributed 12 m3/s of

Page 47: The origin and distribution of trace metals in the Rio Santa

37

discharge to the Rio Santa upstream of site S2. As glacial meltwater inputs to the Rio Santa

decline, the inputs from the Tabla subwatershed will become increasingly important for the

maintenance of coastal irrigation activities.

Figure 5.1. Plot of subwatershed area (km2) versus discharge (m

3/s) in tributaries to the Rio

Santa. Labels are shortened by excluding formal name of tributaries.

Figure 5.2. Plot of glaciation (% of total area) versus specific discharge (m/yr) for tributary

watersheds. Values in Table 4.2 were extrapolated to calculate specific discharge; these values

are underestimations as the increases in wet season discharge are not included. Labels are

shortened by excluding formal name of tributaries.

S10 S12 S12.5 S13 S14 S15

S3 Tabla

S7 Quitarscara

S9 Llullan

0

2

4

6

8

10

12

14

16

10 100 1000 10000

Dis

char

ge (

m3/s

)

Watershed Area (km2)

Tributaries: discharge vs. area

S10 Mancos S12 S12.5

S13

S14 S15 Shiki

S3 Tabla S7

S9 Llullan

0

0.2

0.4

0.6

0.8

1

1.2

0 5 10 15 20 25 30

Spe

cifi

c D

isch

arge

(m

/yr)

% Glaciation

Specific discharge vs. glaciation

Page 48: The origin and distribution of trace metals in the Rio Santa

38

5.2. Major ion chemistry

The major ion chemistry of surface waters in the Rio Santa is primarily a result of

chemical weathering reactions. The extent of weathering may be affected by the type of

mineralization, exposure time, quality of water-rock interactions, and rock textures. Weathering

processes are also affected by mining activities and glaciation (Faure, 1991).

5.2.1. Sulfate

One of the most notable aspects of Rio Santa water is the high SO4 content at many

localities throughout the watershed. It was >50 mg/L in six of the sampled tributaries and at all

sites beyond the first 70 km of the Rio Santa. The average concentration in our samples was

77.6 mg/L for the Rio Santa, 93.5 mg/L for the tributaries, and 82.5 mg/L for the watershed as a

whole. This is significantly greater than the world average of 11.5 mg/L for river waters (Berner

and Berner, 1987), and consistent with previous measurements (e.g. Mark et al., 2005; Fortner et

al., 2011). High levels of dissolved SO4 contribute significantly to the overall high TDS within

the watershed.

There is a strong relationship between SO4 and total cations (Figures 5.3 and 5.4),

suggesting that sulfate oxidation is an important mechanism of chemical weathering in the

watershed. If sulfide oxidation were the only mechanism, milliequivalent per liter plots of SO4

versus total cations would fall on a 1:1 line with an intercept of 0. This is not the case, and in

particular, the intercept is not zero but 1.7 meq/L, indicating that there are additional sources of

cations and other processes contributing ions to surface waters.

There are numerous geologic sources of sulfide in the Rio Santa Watershed. This

includes the pyrite-rich Chicama Formation and medium-high sulfate epithermal metal deposits

Page 49: The origin and distribution of trace metals in the Rio Santa

39

within the Miocene Metallogenic Belt that is present across a range of lithologies in the

Cordillera Blanca, including mineralization at the sites of the large-scale Pierina and California

metal ore mines. Mining of the ore deposits exposes large quantities of finely ground sulfide

minerals to air and water, which can enhance their oxidation rate. Effluent from a mine

discharging into the Rio Yanayacu, sampled in 2007, had a SO4 concentration of 115.2 mg/L

(Appendix A.3).

SO4 is a primary species resulting from subglacial weathering reactions, even in

lithologies where only trace amounts of sulfides are present (see Section 5.5.2.) In addition to

near-surface chemical weathering reactions, SO4 may be contributed to surface waters via inputs

from geothermal springs. The TDS of thermal waters are generally higher than average surface

waters due to enhanced solubility and dissolution rates of minerals at high temperatures (Hem,

1985). The seismically active Cordillera Blanca is host to numerous hot springs. In the Rio

Santa Watershed, they are present in the subwatersheds of the Rios Tabla, Mancos, Marcara, and

Negro. In the Rio Negro (site S12.5 Olleros), the springs are located near the outlet to the Rio

Santa, while in other subwatersheds they are located further from the Rio Santa at higher

elevations. SO4 concentrations in the Olleros hot spring in 2004 and 2006 were 92.6 mg/L and

40.8 mg/L, respectively; there were 136.0 mg/L of SO4 in the Chancos hot spring (in the Rio

Marcara subwatershed) in 2006 (Appendix A.3.)

Page 50: The origin and distribution of trace metals in the Rio Santa

40

Figure 5.3. Plot of SO4 versus total cations in the Rio Santa. All values in meq/L.

Figure 5.4. Plot of SO4 versus total cations in the tributaries. All values in meq/L.

S2

S1

S4

S3 RSD

S3 RSU

S7 RSU

S11 RSU

S9 RSD

S14 RSD

S16 Conococha

S12.5 RSU

y = 0.8432x + 1.5871 R² = 0.8794

0

1

2

3

4

5

6

0 1 2 3 4 5 6

Cat

ion

s (m

eq

/L)

SO4 (meq/L)

Rio Santa: cations vs. SO4

S3 Tabla S10 Rio Mancos

S12.5 Olleros

y = 0.8438x + 0.7168 R² = 0.7713

0

2

4

6

8

0 2 4 6 8

Cat

ion

s (m

eq

/L)

SO4 (meq/L)

Tributaries: cations vs. SO4

Page 51: The origin and distribution of trace metals in the Rio Santa

41

The oxidation reactions of pyrite, FeS2, are well known and involve a complex series of

reactions that were described in detail by Banks et al. (1997), Akcil and Koldas (2005), and

others. The first step is oxidation of pyrite into dissolved ferrous iron, sulfate, and hydrogen:

2FeS2 (s) + 7O2 (g) + 2H2O (l) 2Fe2+

(aq) + 4SO42-

(aq) + 4H+ (aq) (7)

The acidity of the water is thus increased. In sufficiently oxidizing environments the ferrous iron

may be further oxidized to ferric iron:

2Fe2+

(aq) + O2 (g) + 2H+ (aq) 2Fe

3+ (aq) + H2O (l) (8)

If the pH is below 2.3, ferric iron will further oxidize the pyrite. At pH > 2.3, the majority of the

ferric iron will precipitate as iron hydroxides:

Fe3+

(aq) + 3H2O (l) Fe(OH)3 (s) + 3H+ (aq) (9)

The overall reaction for the oxidation of pyrite is:

FeS2(s) + 15

/4O2(g) + 7/2H2O(l) → 2SO4

2-(aq) + Fe(OH)3(s) + 4H

+(aq) (10)

Because pyrite is an acid insoluble mineral, this reaction will proceed regardless of pH. The

reaction rates are controlled by access to oxidizing agents and the presence of iron oxidizing

bacteria (Baker and Banfield, 2003).

Within the Rio Santa Watershed, the surface waters are well oxidized and Equations (7)

and (8) will proceed unhindered. Most surface waters have circumneutral pH values, indicating

that a source of alkalinity is neutralizing inputs of H+, thus buffering pH. At circumneutral pH

values, dissolved Fe is expected to precipitate, as in Equation (9). The presence of ochreous

deposits (Table 4.1) at some sites was indicative of this occurrence. The net result of Equations

Page 52: The origin and distribution of trace metals in the Rio Santa

42

(7) to (9) is dissolved SO4, Fe-oxyhydroxide precipitates, and increased acidity (buffered by

alkalinity.)

Figure 5.5. Plot of SO4 (mg/L) versus dO2 (% saturation) in the Rio Santa Watershed.

Increasing oxygenation of water causes enhanced SO4 mobility (Hem, 1985). In the Rio

Santa Watershed, SO4 concentrations tend to increase with increasing oxygenation (Figure 5.5).

The SO4 concentrations at Tabla, Olleros, and Mancos are notable for being significantly higher

than other sites with similar dissolved oxygen levels. This might be caused by SO4-rich inputs

from geothermal springs within these watersheds.

5.2.2. Alkalinity

The alkalinity of natural surface waters with 5.6 < pH < 9.5 can be assigned entirely to

HCO3 without serious error, in the absence of petroleum or natural gas associations or excessive

DOC (Hem, 1985). Bicarbonate is the second most abundant ion within the Rio Santa

S2

S3 Rio Santa Up

S7 Rio Santa Down S14 RS Down S16 Conococha

S12 RS Down

S3 Tabla

S7 Quitarasca

S10 Rio Mancos

S11 Marcara

S9 Llullan

S12.5 Olleros

0

50

100

150

200

250

300

350

50 55 60 65 70 75 80 85 90 95 100

SO4

(mg/

L)

dO2(% saturation)

SO4 vs. dissolved oxygen

Page 53: The origin and distribution of trace metals in the Rio Santa

43

Watershed. It may be derived through dissociation of atmospheric CO2 (Equation 11) and/or

dissolution of carbonate minerals (Equation 12):

CO2 + H2O ↔ HCO3- + H

+ (11)

CaCO3 ↔ Ca2+

+ CO32-

(+ H2O) ↔ HCO3- + OH

- (12)

HCO3 derived from carbonate dissolution is effective at neutralizing acidity from the oxidation of

pyrite, resulting in the precipitation of Fe-oxyhydroxides and maintenance of the aqueous system

at a circumneutral pH.

Below a pH of ~5.6, the majority of HCO3 in water is converted to H2CO3. This accounts

for the zero concentration calculated for Rio Olleros (pH=3) and near–zero concentration for Rio

Quilcay (pH=4.7). At these sites, any neutralization must be done by slower-acting silicates and

clays (Salomons, 1995). In the Rio Olleros, thick coatings of Fe-oxyhydroxides prevent the

dissolution of substrate minerals. Ochreous precipitates also coat the upper reaches of the Rio

Quilcay, but were not present at the downstream sampling site.

Carbonate buffering is a vital process for maintaining water quality in the Rio Santa

Watershed, where sulfide weathering adds high amounts of acidity to the surface waters. There

is carbonate mineralization in portions of the Chicama Formation and Goyllarisquizga Group,

which are present throughout the watershed (Wilson et al., 1967). Additionally, subglacial

weathering processes may contribute significant amounts of HCO3 from lithologies that contain

only trace amounts of carbonates (see Section 5.5.1.) Carbonate buffering is likely aided by

dilution of acidic tributary waters upon their mixing with the Rio Santa, particularly during the

wet season when flows are highest.

Page 54: The origin and distribution of trace metals in the Rio Santa

44

Concentrations of HCO3 are generally highest in the southern portions of the Rio Santa

Watershed, along the first 50 km of the river and in the tributaries along this stretch. In this

region, the Rio Santa and the lower tributaries flow through long stretches of low-gradient

Quaternary glaciofluvial sediments. The elevated concentrations may be due to greater

dissolution of carbonate minerals caused by increased water-rock residence time, and/or lower

rates of sulfide oxidation and associated acidity inputs. Northwards, HCO3 concentrations

generally decrease while SO4 concentrations generally increase.

5.2.3. Comparison with other rivers

In comparison to the mean composition of unpolluted natural waters, the Rio Santa has

similar concentrations of SiO2 and HCO3, notably higher levels of SO4 and Ca, and somewhat

elevated levels of other major ions, including Cl, F, Na, K, and Mg. The SO4 concentration and

pH of the Rio Santa are similar to levels documented in circumneutral waters draining from

pyrite-rich underground coal mines such as the Vryheld Mine in South Africa (Cravotta, 2008)

and the Cameron Mine in Pennsylvania (Azzle, 2002) (Table 5.1). The effluent from these

mines is unique from most mine drainage sites as alkalinity inputs are buffering against AMD-

acidification (Nordstrom, 2011a), in processes similar to those occurring in the Rio Santa

Watershed.

Page 55: The origin and distribution of trace metals in the Rio Santa

45

Table 5.1. Comparison of Rio Santa water with mean natural river water and that of the Vryheld

and Cameron mines.

Rio Santa

(Site S1)

Mean natural

river water

(Berner and Berner, 1987)

Vryheld Coal Mine

water

(Azzle, 2002)

Cameron Coal Mine

water

(Cravotta, 2008)

SiO2 12.4 8.71 2.52 20.0

SO4 203.0 5.3–16.8 376 510

Ca 64.2 13.4–23.8 71.2 53

HCO3 42.1 48.8 311 0.0

Cl 8.7 5.92 196 5

F 0.5 0.3 0.34 <0.1

Na 23.2 5.52 235 6.7

K 3.1 1.72 26.4 2.7

Mg 10.1 3.4–5.95 74.6 61

pH 8.0 n/a 9.03 4.0

5.3 Trace element chemistry

5.3.1. Dissolved metals in the Rio Santa Watershed

The large ore mining industry in the Cordillera Blanca and the Cordillera Negra are

indicative of the abundant metal-rich mineralizations in the Rio Santa Watershed. The

weathering of lithologies with high concentrations of metallic elements is likely give rise to

higher than average background concentrations of minor and trace elements in surface waters. It

is necessary to determine baseline levels of elements of concern before attempting to assess any

potential contamination issues. In addition to abundance in source rocks, baseline concentrations

of metals are determined by the weatherability of the rocks, pH, redox conditions, and sorption

or precipitation reactions (Nordstrom, 2011b). Anomalously high concentrations may be derived

from mining waste, industrial air-borne particles and aqueous effluents, and/or landfill and

sewage treatment runoff (Faure, 1991).

Page 56: The origin and distribution of trace metals in the Rio Santa

46

In the Rio Santa Watershed, the majority of indicator elements were present at most sites

at concentrations above detection limits, yet below 10 ug/L (Table 4.4). These are interpreted

primarily as naturally occurring concentrations arising from the chemical weathering of the

Jurassic Chicama Formation and deposits within the Miocene Metallogenic Belt. Most of the

indicator species cannot persist at high dissolved concentrations in the circumneutral waters

found at most sites within the watershed (Driscoll et al., 2004). The dramatic fluctuations in

bulk loads of dissolved trace metals in Figure 4.8 highlight the inability of metals to persist in

their dissolved forms in the pH conditions of the Rio Santa. The samples with anomalously high

dissolved concentrations were likely collected near to the source of contamination.

The spike in the dissolved As load at site S13 RSD is likely caused by the large tailings

pile at Ticapampa, located ~1 km upstream of the sampling site (Figure 4.8). The tailings have

been deposited along a bank of the Rio Santa and are actively eroded by the river. Previous

water sampling by Fortner (unpublished) directly adjacent to the tailings pile yielded maximum

dissolved As concentrations of 190.2 ug/L. Ochreous precipitates occur downstream of

Ticapampa. The strong tendency of As to adsorb to Fe-precipitates likely causes the rapid

decline in its downstream concentrations.

The locally high levels of Pb, Cd, Ni, and U at site S12 RSD, in Huaraz (population

120,000), are at least partly related to poorly enforced environmental standards within the city.

High volumes of garbage and industrial waste enter into the Rio Santa at this point (Figure 5.6).

The high levels of NO3 downstream of the city (Figure 4.5) are likely due to sewage inputs,

which highlight the lack of regulation regarding urban inputs into the river.

Page 57: The origin and distribution of trace metals in the Rio Santa

47

Figure 5.6. Urban garbage in the Rio Santa in the Miraflores district of Huaraz.

Although baseline levels of trace metals in the watershed may be attributed to weathering

of the metal-rich lithologies of the Cordillera Blanca, the sources of elevated levels of trace

metals are less apparent. As only one sample was collected from each tributary, sampling

resolution is too poor to pinpoint specific points of contamination within subwatersheds. The

subwatersheds are also highly variable in terms of geology, major ion compositions, size,

discharge, glaciation, mining activities, and population (Table 4.6).

In acidified tributaries, the metals may have originated far from the sampling site. In the

Rio Quilcay, the high concentrations of trace elements may have been derived from ARD from

the Chicama Formation at high elevations (as in Fortner et al., 2011). The Rio Olleros receives

metal-rich inputs from hot springs near its outlet to the Rio Santa. In tributaries with

circumneutral pH values and high trace element concentrations, such as Llullan, the source of

contamination was likely located close to the sampling site. In the case of Llullan, this is near

Page 58: The origin and distribution of trace metals in the Rio Santa

48

the mouth of the tributary, where the largest population lives. Intercomparison of multiple years

of data provides greater insight into potential contamination sources in circumneutral tributaries

(see Section 5.3.3.)

5.3.2. Aqueous trace metal relationships

Manganese is commonly present in Fe-bearing minerals and often co-occurs in natural

waters. In oxidizing conditions, both elements tend to precipitate out of solution, while in less-

oxidizing conditions, any Fe- and Mn- oxyhydroxides precipitates tend to dissolve. Fe is less

mobile than Mn and tends to precipitate more quickly and dissolve more slowly (Hem, 1985). In

Figure 5.7, the water at all sites (except Olleros; pH = 3.0) was circumneutral, but had varying

levels of dissolved oxygen (66 – 100% saturated.) There is an inverse relationship between %

oxygen saturation and dissolved concentrations of Fe and Mn. The samples with less oxidized

waters (< 75 %) tend to have higher levels of these elements and to come from sites where

ochreous precipitates were often observed. The oxidative dissolution of Fe- and Mn-

oxyhydroxides may give rise to the higher Fe and Mn concentrations. Conversely, the lower

concentrations at well-oxidized sites may be due to the precipitation of oxyhydroxides; as highly

oxygenated waters are often the most turbulent, the precipitates are more likely to remain

suspended in solution rather than to coat streambed surfaces.

Page 59: The origin and distribution of trace metals in the Rio Santa

49

Figure 5.7. Relationship between dissolved oxygen (% saturation) and concentrations of

dissolved Fe and Mn (ug/L). Fe at Olleros (8000 ug/L) is not plotted. Sites which had ochreous

precipitates plotted within in the blue shaded area.

Due to its higher aqueous mobility, Mn persists at a greater distance from the source than

Fe and occurs at higher concentrations in solution. This makes it a useful element for studying

the dynamics of dissolved trace metals within the watershed, especially at sites where direct

measurements of dissolved oxygen are not available (Hem, 1985).

Similar to Mn, other trace metals tend to be less mobile in oxidizing conditions. There is

a good correlation between increasing Mn (a proxy for decreasing oxygenation) and the

increasing concentrations of Al, Cd, Ni, Pb, and Zn (Figure 5.8). Conversely, As tends to

decrease at sites where Mn concentrations are higher (Figure 5.9). In more oxidizing conditions,

the charged arsenate ion predominates, and tends to strongly adsorb to Fe-oxyhydroxides and

other surfaces. In less oxidizing conditions, the more mobile, neutrally charged arsenite ion

predominates (Hem, 1985).

Page 60: The origin and distribution of trace metals in the Rio Santa

50

Figure 5.8. Dissolved Mn concentration (ug/L) versus concentrations of Al (mg/L) and Cd, Ni,

Pb, and Zn (all in ug/L).

Figure 5.9. Concentrations of dissolved Mn (ug/L) versus dissolved As (ug/L)

0

1000

2000

3000

4000

5000

0

50

100

150

200

250

300

0 200 400 600 800 1000 1200

Al (u

g/L)

Cd

, Ni,

Pb

, Zn

(u

g/L)

Mn (ug/L)

Relationship between trace metals and Mn

Zn

Pb

Ni

Cd

Al

0

5

10

15

20

25

30

35

0 200 400 600 800 1000 1200

As

(ug/

L)

Mn (ug/L)

Relationship between As and Mn

Page 61: The origin and distribution of trace metals in the Rio Santa

51

Table 5.2. Filtered and unfiltered concentrations of As (ug/L) in the Rio Santa Watershed, July

2008.

Site Filtered Unfiltered pH

Conococha 4.7 3.1 8.96

Jangas 3.5 21.2 7.62

Rio Santa @ Huaraz 20.3 29.4 8.06

Rio Santa 2 <d/l 53.7 8.62

Rio Santa Ticapampa 18.1 66.1 7.6

Rio Santa Ucashaca 4.2 9.2 8.52

Ticapampa 190.2 533.2 6.62

Yan <d/l 4.5 n/a

Catac Bridge 3.1 12.0 8.22

Unpublished data supplied by S. Fortner, Wittenberg University, USA. Analysis is same as in

Fortner et al. (2011). Non-detection is indicated by <d/l.

Filtered and unfiltered samples were collected in July 2008 and analyzed for As using the

methods presented in Fortner et al. (2011). Arsenic concentrations were greater in unfiltered

samples than in filtered (Table 5.2), indicating that the majority of As is adsorbed to particulate

phases or has co-precipitated with other species. Given the pH-Eh conditions of the Rio Santa

Watershed, it is likely that dissolved trace element concentrations presented in this study are

significant underestimates of the true amounts of these species in the aqueous environment.

However, as long as the Rio Santa maintains its strong buffering capacity and circumneutral pH

conditions, these species will continue to remain in the particulate phase and not be of concern to

human health.

5.3.3. Temporal variations in trace metals

In July 2008 and 2011, trace metal samples were collected at site Quilcay Out [site 24 in

Fortner et al. (2011)] (Figure 5.10). The levels of dissolved Co, Cu, Mn, Ni, Sr, and Zn were

similar in both samples. In 2011, there was a notable decrease in Fe and an increase in Pb.

Page 62: The origin and distribution of trace metals in the Rio Santa

52

Fortner et al. (2011) determined that significant amounts of Pb are sorbed to Fe in the Rio

Quilcay; therefore, a decrease in Fe may have caused more Pb to remain dissolved in solution.

Figure 5.10. Dissolved metal concentrations (ug/L) at site Quilcay Out in July 2008 and July

2011.

Table 5.3. pH at sites in Rio Santa Watershed in 2008 and 2011 (for Figure 5.11).

Sample S9 Llullan S13

Yanayacu

S12.5

Olleros

S11

Marcara Conococha S9 RSD

2008 6.7 8.8 3.43 6.85 9 7.9

2011 7.3 7 3 7.4 7 n/a

Comparison of trace metal concentrations in 2011 to an unpublished dataset compiled in

2008 (Appendix A.1) shows that, similar to Quilcay Out, there is consistency at other sites in the

Rio Santa Watershed (Figure 5.11). Most elements that were present at low levels in the 2008

samples also occurred in low levels in the 2011 samples. They are indicative of background

metal concentrations, which may arise from natural rock weathering, enhanced weathering in

tailings piles, and/or regular anthropogenic inputs. This inter-annual comparison shows that,

1.0

10.0

100.0

1000.0

10000.0

Co Cu Fe Mn Ni Pb Sr Zn

Co

nce

ntr

atio

n (

ug/

L)

Dissolved Metal

Quilcay Out: dissolved metals

July 2008

July 2011

Page 63: The origin and distribution of trace metals in the Rio Santa

53

despite strong spatial variations within a watershed, there may be temporal consistency in

background trace element concentrations

Figure 5.11. Dissolved metal concentrations (ug/L) at various sites in July 2008 and July 2011.

Page 64: The origin and distribution of trace metals in the Rio Santa

54

. Discharge data for 2008 at these specific sites is unavailable, as this study performed

the first complete survey of discharge within the watershed. However, in general there is strong

interannual consistency in dry season discharge in the Rio Santa (see Section 5.5.1; Appendix

A.5). Additional years of discharge and trace metal measurements are required to assess

interannual trends with greater confidence.

As discussed in Section 5.3.1, large anomalies may be indicative of point sources of

contamination. The most probable example of this is Mo in the Rios Llullan and Yanayacu. In

Llullan, the concentration changed from 11.5 ug/L to 720 ug/L between 2008 and 2011. At

Yanayacu, the concentration changed from 4.2 ug/L to 55 ug/L in the same time span. Mo is a

common by-product of metallic ore mining, particularly Cu-sulfides (Hem, 1985). It tends to

remain in solution in oxidizing conditions across a wide range of pH values, although at

circumneutral pH values it may react with Pb to form a relatively insoluble precipitate mineral

(Faure, 1998). In both sample years, Pb concentrations and Eh-pH conditions remained

relatively similar, suggesting that the change was due to a net increase in Mo within the

tributaries. The increases in its concentration may be related to up-river mining activities.

Large-scale mining of Cu-bearing sulfides occurs at the Paron Gold mine in the Llullan

watershed; mining activities are also ongoing in the Yanayacu watershed and there are large

tailings piles near the sampling site. Additional undocumented small-scale mining activities may

also be occurring near the sampling sites.

5.3.4. Implications for water quality

Drinking water standards for maximum dissolved concentrations set by WHO (2008) and

Health Canada (2010) are exceeded at three sites along the Rio Santa and in the Llullan and

Quilcay tributaries (Table 5.4). Trace metals are most bioavailable in their dissolved forms.

Page 65: The origin and distribution of trace metals in the Rio Santa

55

They tend to bioaccumulate and are potentially toxic to human health at high concentrations

(Driscoll et al., 1994). The potential toxicity of the water is of concern because populations

reside along the river at all sites except for Quilcay Out and may use the water for irrigation,

livestock, and/or domestic consumption (INEI, 2007).

Table 5.4. Select dissolved trace element concentrations at sites in Rio Santa Watershed.

Sample As Cd Mo Pb U

WHO Guideline

(Health Canada Guideline)

10

(10)

3

(5)

70

(none)

10

(10)

15

(20)

S12 RSU 0.2 56.7 40 74 53

S13 RSD 30 0.2 1.4 0.1 0.2

S16 Conococha 11.8 <0.01 1 0.1 0.1

S9 Llullan 2 5.5 720 3.8 180

Quilcay Out 0.02 27.3 0.3 82 14

Grey shaded boxes represent values that exceed guidelines set by WHO (2008) and Health

Canada (2010).

Long term ingestion of low levels of As may cause chronic illnesses and skin problems.

At higher doses it may be fatal (ATSDR, 2007a). Cadmium tends to decrease bone density and

to bioaccumulate and cause deterioration in the kidneys (ATSDR, 2012). Similarly, kidney

damage can also result from ingesting aqueous U (ATSDR, 2013). Lead is toxic for the nervous

system. Low level, long term exposure causes reduced mental alertness, while high levels cause

severe brain damage and death (ATSDR, 2007b). Molybdenum is regulated by WHO (2008) but

not Health Canada (2010). Its health effects are still debated although there is evidence that it

causes infertility in cattle and is harmful to humans at high concentrations (Eisler, 1989).

In addition to potentially toxic metals, the acidity and ochreous precipitates in the Rio

Quilcay, Rio Negra, and some sites within the Rio Santa are likely to put significant stress on

Page 66: The origin and distribution of trace metals in the Rio Santa

56

lotic systems. The ochreous coatings eliminate habitats and significantly reduce biodiversity

within the stream system (Gray, 1997). Studying the diversity and abundance of organisms is an

important additional step for ongoing water quality monitoring efforts in the Cordillera Blanca.

5.5. Temporal variations in water chemistry

5.5.1. Temporal variations

There are large spatial variations in hydrochemistry throughout the Rio Santa Watershed.

They are caused by differences in lithology, glaciation, discharge, and anthropogenic activities.

Temporally, there is a dichotomy between dry and wet season hydrochemical conditions.

However, there is evidence of site-specific consistency on diurnal and interannual time scales.

Near the headwaters of the Rio Quilcay, Burns et al. (2011) took hourly samples over a 24

hour period to study the diurnal variability of water chemistry. Relatively minor diurnal

variations in pH (from 3.3 – 3.7) and specific conductance (from 349 – 466 µS/cm) were

observed. A plot of conductivity versus SO4 for the 2011 sampling data shows a strong linear

relationship between the two parameters (Figure 5.12) (Appendix A.2). Based on this

relationship, the diurnal conductance variations are equivalent to ~25 mg/L variations in daily

SO4 concentrations. Variations are attributed to changes in glacial melt volumes caused by daily

temperature and radiation cycles. Burns et al. (2011) predicted that the buffering effect of

groundwater would decrease diurnal fluctuations with greater distance from glacial headwaters.

Page 67: The origin and distribution of trace metals in the Rio Santa

57

Figure 5.12. Relationship between SO4 (mg/L) and conductivity (µS/cm) in Rio Santa

Watershed, July 2011. Based on data from Burns et al. (2011)

Figure 5.13. pH values at synoptically sampled sites in July 2005-2007.

y = 2.884x + 81.034

0

200

400

600

800

1000

1200

0 50 100 150 200 250 300 350

Co

nd

uct

ivit

y (u

s/cm

)

SO4 (mg/L)

Conductivity vs. SO4

2

3

4

5

6

7

8

9

10

0 2 4 6 8 10 12 14 16

pH

Site

Interannual pH Variations

2005

2006

2007

Page 68: The origin and distribution of trace metals in the Rio Santa

58

Figure 5.14. SO4 concentrations at synoptically sampled sites in July 2004-2007. 5% error bars

are shown.

Figure 5.15. Ca concentrations at synoptically sampled sites in July 2004-2007. 5% error bars

are shown.

0

20

40

60

80

100

120

0 2 4 6 8 10 12 14 16

SO4 (

mg/

L)

Site

Interannual SO4 Variations

2004

2005

2006

2007

0

5

10

15

20

25

30

35

40

45

50

0 2 4 6 8 10 12 14 16

Ca

(mg/

L)

Site

Interannual Ca Variations

2004

2005

2006

2007

Page 69: The origin and distribution of trace metals in the Rio Santa

59

Table 5.5. Legend of site numbers for Figures 5.13-5.15.

Number Site

1 Buin

2 Colcas

3 S16 Conococha

4 Jangas

5 Llan Lakes Out

6 S9 Llullan

7 S11 Marcara

8 S14 Pachacoto

9 Q1

10 Q3

11 Quilcay Out

12 Ranrahirca

13 Rio Santa 1

14 Rio Santa 2

15 Rio Santa Low

16 S13 Yanayacu

At the interannual time scale, there is surprisingly good year-to-year consistency. Figure

5.13 displays the pH at synoptically sampled sites in the summers of 2005 through 2007

(Appendix A.3), including many sites that were examined in this study. Site-specific pH values

remain within ~1 unit over time. At the majority of sites, SO4 concentrations remain within 10

mg/L from year to year with maximum variations of ~30 mg/L, which are comparable to diurnal

SO4 variations noted by Burns et al. (2011) (Figure 5.14). Similarly, Ca concentrations tended to

vary within ~15 mg/L over the time span, with maximum variations of ~20 mg/L (Figure 5.15).

All the above samples were collected in July of each year, during the height of the dry

season. The similar year-to-year concentrations indicate that baseline water conditions within

the Rio Santa Watershed are consistent from year to year, with no major anomalies in SO4, Ca,

or pH. This suggests that inter-year comparisons of water chemistry in this study are valid and

aberrations may be considered as significant.

Page 70: The origin and distribution of trace metals in the Rio Santa

60

5.5.2. Case study: Chemical weathering in the Querococha Basin

A detailed examination of weathering processes in the Querococha Basin yields greater

insight into potential weathering dynamics of the Cordillera Blanca as a whole. The Querococha

Watershed has two main subbasins of comparable size and similar lithologies. They are

dominated at higher elevations by granitic-plutonic rocks and the Chicama Formation, and

Quaternary glaciofluvial sediments along the valley bottoms. The northern basin, Q2, contains

the Yanamarey glacier and its proglacial zone; the southern basin, Q1, has been completely

deglaciated (Figure 5.16). Monthly discharge and major ion samples were collected at the outlet

streams of Q1 and Q2, the outlet stream of the Yanamarey glacier (YAN), and the distal outlet of

the Querococha Basin (Q3) on a monthly basis from May 1998 – April 1999 by Mark and

Seltzer (2003) (Appendix A.4). This data was reanalyzed to calculate monthly and annual

denudation rates of SiO2, total cations (i.e. CDR), and individual ions in the subglacial,

proglacial, deglaciated, and distal zones. In order to examine processes occurring in each

specific zone, calculations for the Q2 proglacial zone exclude discharge and ion load inputs from

YAN; similarly, calculations for the distal Q3 zone exclude inputs from Q1 and Q2.

Page 71: The origin and distribution of trace metals in the Rio Santa

61

Figure 5.16. Map of the Callejon de Huaylas. Inset is a map of the Querococha Basin. YAN =

subglacial, Q1 = deglaciated, Q2 = proglacial, Q3 = distal valley. From Mark and Seltzer

(2003).

The annual chemical weathering rate in the subglacial zone (YAN) is nearly twice that of

the proglacial zone (Q2) and over five times greater than in the deglaciated valley (Q1) (Figure

5.17). Chemical weathering rates fluctuate throughout the year (Figure 5.18). Subglacial

weathering peaks in October, at the start of the wet season. Proglacial weathering has a small

peak in October, although its maximum is near the end of the wet season in March, when

proglacial weathering exceeds that of the subglacial area. Comparison of Figures 5.18 and 5.19

shows that specific discharge rates are the primary control on chemical weathering rates.

Discharge and precipitation are strongly correlated in deglaciated and distal areas. Subglacial

discharge is decoupled from precipitation, reaching its annual peak at the start of the dry season,

Page 72: The origin and distribution of trace metals in the Rio Santa

62

four months before peak runoff. Proglacial discharge is intermediate between the two, with peak

CDR corresponding to maximum glacial melt and to maximum precipitation (Figure 5.21).

Figure 5.17. Annual chemical weathering rates in the Querococha Watershed, April 1998 – May

1999. As some monthly data is missing, these results are underestimates. YAN = subglacial, Q1

= deglaciated, Q2 = proglacial, Q3 = distal valley.

Figure 5.18. Monthly CDR in the Querococha watershed, April 1998 – May 1999. Data is

missing for February. YAN = subglacial, Q1 = deglaciated, Q2 = proglacial, Q3 = distal.

YAN Q1 Q2 Q3

0

10

20

30

40

50

60

Subbasin

CD

R (

t/km

2 /yr

)

Querococha: chemical weathering rates

0

1

2

3

4

5

6

7

8

May Jun Jul Aug Sept Oct Nov Dec Feb Jan Mar Apr

CD

R (

t/km

2 /m

on

th)

Month

Monthly chemical weathering variations

YAN

Q1

Q2

Q3

Page 73: The origin and distribution of trace metals in the Rio Santa

63

Figure 5.19. Specific discharge and precipitation in the Querococha watershed, April 1998 –

May 1999. Discharge data is missing for February. YAN = subglacial, Q1 = deglaciated, Q2 =

proglacial, Q3 = distal valley.

Chemical fluxes in glacial meltwater do not reflect the composition of the catchment

lithologies but rather reflect the type of chemical weathering reactions that are occurring.

Tranter (2003) describes the series of subglacial chemical reactions that occur. The first is the

hydrolysis of carbonate and silicate minerals when very dilute meltwater meet fresh glacial flour.

Calcium carbonate is the most common carbonate mineral:

CaCO3 (s) + H2O (l) → Ca2+

(aq) + HCO3-(aq) + OH

- (aq) (13)

The dilute water also favors the exchange a single dissolved divalent cation for two monovalent

cation ions from mineral surfaces. Hence, some Ca2+

and Mg2+

released from Equation (13) will

exchange for Na+ and K

+. Sulfide oxidation is the dominant reaction in subglacial environments.

It primarily occurs in subglacial areas where fresh rock is first in contact with water. Microbial

mediation enhances the reaction rate by several orders of magnitude. The reaction proceeds in a

series of steps, with an overall equation of:

FeS2 (s) + 15O2 (g) + 14H2O (l) → 4Fe(OH)3 (s) + 8SO42-

(aq) + 16H+ (aq) (14)

Page 74: The origin and distribution of trace metals in the Rio Santa

64

The reaction lowers the pH of the water, which enhances carbonate dissolution. The dissolution

of carbonates and oxidation of sulfides by the dilute waters is so effective that Ca and SO4 tend

to be the dominant exported ions, despite usually occurring only in trace amounts in the

substrate. Although silica is a dominant mineral in most basins and its dissolution reactions

dominate non-glaciated fluvial basins, it is weathered very slowly in subglacial environments

due to low water temperatures (Tranter, 2003):

Silicate mineral(s) → clay mineral(s) + cations(aq) + Si (aq) (15)

Weathering dynamics in the proglacial zone are not as well studied as in the subglacial

zone. The proglacial zone is a region of potentially high geochemical activity due to the

presence of abundant comminuted sediments that are continually being reworked by runoff

(Tranter, 2003) although vegetation and soil development are likely to increasingly affect

weathering dynamics with distance from the glacial margin (Anderson et al., 2000).

One of the first studies of proglacial weathering dynamics was by Anderson et al. (2000)

at the Bench Glacier, Alaska. In the immediate proglacial area, carbonate dissolution and sulfide

oxidation were the principal chemical reactions, with rates as high as three times greater than

those occurring subglacially. Further down the valley, where sediments were older, these

reactions declined as sulfide and carbonate minerals became exhausted. Silicate dissolution

increased down-valley due to warmer water temperatures. The overall chemical weathering rate

for the proglacial valley was lower than in the subglacial area (Anderson et al., 2000). Similar

results were found by Wadham et al. (2000) at the Finsterwalderbreen Glacier in Svalbard.

Page 75: The origin and distribution of trace metals in the Rio Santa

65

Figure 5.20. YAN (subglacial) major chemical weathering products, April 1998 – May 1999.

February data and December SO4 data are missing.

Figure 5.21. Q2 (proglacial) major chemical weathering products, April 1998 – May 1999.

February data and SO4 data for December and January are missing.

May Jun Jul Aug Sept Oct Nov Dec Feb Jan Mar Apr

0

50

100

150

200

De

nu

dat

ion

Rat

e (

t/km

2 /m

on

th)

Subglacial: chemical weathering reactions

Ca

Si

SO4

May Jun Jul Aug Sept Oct Nov Dec Feb Jan Mar Apr

0

10

20

30

40

50

60

70

De

nu

dat

ion

Rat

e (

t/km

2 /m

on

th) Proglacial: chemical weathering reactions

Ca

Si

SO4

Page 76: The origin and distribution of trace metals in the Rio Santa

66

Figure 5.22. Q1 (deglaciated) major chemical weathering products, April 1998 – May 1999.

August and February data and December, January, and April SO4 data are missing.

Figure 5.23. Q3 (distal) major chemical weathering products, April 1998 – May 1999. February

data and December SO4 data are missing.

The waters draining YAN are acidic (pH <5), therefore HCO3 resulting from carbonate

hydrolysis will be converted into CO2. Herein, all Ca is attributed to carbonate weathering for

evaluation purposes.

May Jun Jul Aug Sept Oct Nov Dec Feb Jan Mar Apr

0

1

2

3

4

5

6

7

De

nu

dat

ion

Rat

e (

t/km

2 /m

on

th) Deglaciated: chemical weathering reactions

Ca

Si

SO4

May Jun Jul Aug Sept Oct Nov Dec Feb Jan Mar Apr

0

0.5

1

1.5

2

2.5

3

3.5

De

nu

dat

ion

Rat

e (

t/km

2/m

on

th)

Distal: chemical weathering reactions

Ca

Si

SO4

Page 77: The origin and distribution of trace metals in the Rio Santa

67

Sulfide oxidation is the most dominant chemical reaction in the subglacial zone.

Carbonate dissolution is of secondary importance, and silicate dissolution is the least significant

reaction (Figure 5.20). These reactions are similarly occurring in the proglacial zone, but at

lower rates. The most marked decline is in the rate of sulfide weathering (Figure 5.21).

Weathering rates are even lower in the deglaciated terrain. In this zone, carbonate dissolution

tends to dominate over sulfide oxidation. Silicate dissolution assumes an increasingly important

role in weathering reactions due to the decline of carbonate and sulfide weathering (Figure 5.22).

In the distal zone, weathering reactions occur in similar proportions to the deglaciated terrain, yet

at lower rates (Figure 5.23)

Numerous studies have suggested that high physical weathering rates can generate high

chemical weathering rates (e.g. Lyons et al., 2005; Anderson et al., 2002). The shift in

weathering dynamics between subglacial, proglacial, and deglaciated terrains is likely related to

declines in physical weathering with ongoing glacial recession. In the subglacial zone, the

constant abrasion of the overlying glacier maintains a continual supply of fresh, comminuted

debris in the subglacial zone. These are mixed with older sediments in the proglacial zone, with

the supply of fresh sediments dwindling with increasing distance from the glacier terminus. The

influx of glacially-derived fresh sediments has ceased entirely in the deglaciated zone. Sulfide

oxidation and carbonate dissolution occur rapidly in glacial areas, causing SO4, Ca, and HCO3

exports to decline as mineral supplies are exhausted as physical weathering declines. Silica

dissolution is inefficient in the glacial area due to low water temperature; its decline with

deglaciation is less pronounced.

In comparison with other glacierized watersheds, the cation denudation rate below the

Yanamarey glacier is nearly the highest globally observed (see Figure 5.24), which is likely

Page 78: The origin and distribution of trace metals in the Rio Santa

68

attributable to the sulfide-rich bedrock. Subglacial sulfide mineral oxidation is so effective that

it is a dominant weathering process even in lithologies where these minerals are present in even

trace amounts. The abundant supply of sulfide minerals below the Yanamarey glacier allows for

higher than average rates of sulfide oxidation and contributes to the high overall chemical

weathering in this basin. Most glacial meltwaters have a pH between 7 and 10 (Tranter, 2003);

the high amounts of sulfide weathering cause Yanamarey meltwater to have a pH of < 5.

Carbonate dissolution rates are enhanced in acidic conditions, resulting in a high flux of Ca and a

corresponding cation denudation rate that is higher than average.

Figure 5.24. Denudation rates of dissolved cations and dissolved silica versus annual specific

discharge for a variety of different catchments, including the different zones of the Querococha

basin. Modified from Anderson (2007).

YAN

Q1

Q2

Q3

Page 79: The origin and distribution of trace metals in the Rio Santa

69

Weathering rates in the proglacial zone are also higher than most glaciated basins (Figure

5.24), due to the abundant sulfide mineralization of comminuted debris that are deposited in this

zone by meltwater, which allows the weathering processes described above to continue at a high

rate. The deglaciated zone plots near the low end of glacial cation fluxes, within other

deglaciated terranes.

In terms of silicate flux, YAN plots among other glaciated basins with similar specific

discharge (Figure 5.24). Because low temperatures slow silicate weathering rates, glaciated

basins tend to have lower silicate flux than other watersheds with similar specific discharge. Q1,

Q2, and Q3 plot at the low end of the group consisting of deglaciated and non-glaciated basins,

which have higher water temperatures and therefore greater SiO2 weathering rates. The

relationship between specific discharge and silicate weathering rates is apparent in the non-

glaciated portions of the Querococha basin. Their low values in relation to other basins in the

world may be related to the strongly seasonal discharge, particularly in the Q1 basin, when dry

season weathering is limited.

Page 80: The origin and distribution of trace metals in the Rio Santa

70

5.5.3. Chemical weathering rates in the Cordillera Blanca

Figure 5.25. Dry and wet season CDRs for the Callejon de Huaylas, calculated for July 2005,

July 2006, July 2007, and January 2009. (Based on data in Appendix A.5.)

Figure 5.26. Dry and wet season concentrations at Rio Santa Low, the outlet of the Callejon de

Huaylas, measured in July 2005, July 2006, July 2007, and January 2009 (Data in Appendix

A.5.)

Page 81: The origin and distribution of trace metals in the Rio Santa

71

Cation denudation rates within the Callejon de Huaylas (samples named Rio Santa Low,

near the La Balsa hydroelectric dam) are very consistent during the dry season from year-to-year,

ranging from 1.06 - 1.11 t/km2/month between 2005 and 2007. The wet season CDR in January

2009 was 3.7 t//km2/month, more than three times greater than the dry season rate (Figure 5.25).

Discharge in the dry season ranged from 30.9 - 34.2 m3/s (Appendix A.5). By contrast,

discharge during the wet season in 2009 was 230 m3/s (Appendix A.6). Despite the significantly

greater cation flux, the Rio Santa is more dilute in the wet season than in the dry season (Figure

5.26). From 2004 to 2008, wet season discharge was lower than in 2009, with an average flow

of 123.9 m3/s. Thus, the 2009 CDR may be an over estimate of typical winter weathering rates,

and average wet season flow may be slightly less dilute than indicated.

5.5.4. Implications of changing hydrology on water chemistry

Glaciers play a key role in the current hydrologic regime and water compositions in the

Rio Santa Watershed. Weathering rates are higher in basins with glaciers than in those in which

glaciers have disappeared because glaciers maintain stream flow year round and provide a

continual supply of fresh, finely ground sediments. The efficiency of sulfide and carbonate

weathering in glacierized basins contributes to the high levels of SO4, HCO3, and Ca throughout

the watershed.

The Querococha case study demonstrates that specific discharge is the strongest control

on chemical weathering rates. With ongoing glacier recession, dry season discharge will

decrease and there will be a corresponding increase seasonal variability, with more of the annual

discharge occurring in the wet season. There will be a temporal shift in chemical weathering

Page 82: The origin and distribution of trace metals in the Rio Santa

72

from year-round, as occurs in the YAN-Q2 basin, towards a predominantly wet season

weathering regime, as occurs in the Q1 basin.

With ongoing glacial retreat, subglacial weathering reactions will initially increase due to

higher annual melting rates, followed by a gradual decline after glaciers have passed their peak

annual discharge. Proglacial zone weathering rates are controlled by fresh sediment inputs and

meltwater from the subglacial zone, therefore a similar evolution of weathering will occur in this

zone. Weathering profiles in glaciated basins will gradually become more similar to those seen

in Q1: overall weathering rates will decline and the importance of sulfide and carbonate

weathering in relation to silicate weathering will decrease. Wet season weathering rates are

significantly higher than dry season rates, although river water tends to be more dilute at this

time. This seasonal pattern will be amplified with time.

The changing hydrological dynamics will affect trace metals in different ways, depending

on their source. Persistent low levels of dissolved metals throughout the watershed suggest that a

significant amount of these species is derived through the natural weathering of sulfide minerals.

These baseline concentrations may initially increase as dry season glacial meltwater enhances

weathering fluxes in glaciated basins. After peak annual discharge, there will be a gradual

decline in naturally weathered trace metals.

As dry season discharge declines, the watershed will become less effective at buffering

against direct contamination inputs from industrial waste, mining effluents, or mine tailings

deposited directly into the rivers. There is likely to be an exacerbation of current pollution issues

in the Rio Santa at Ticapampa and Huaraz, and new problem areas may develop.

Page 83: The origin and distribution of trace metals in the Rio Santa

73

During the dry season, evaporative concentration may enhance the formation of ochreous

precipitates. Dissolved trace metal levels may decline if they are coprecipitated or adsorbed to

the ochreous coatings, or, they may remain in solution and become increasingly concentrated by

evaporation (e.g. Nordstrum, 2009). A complex combination of both outcomes is likely, due to

the differing aqueous behavior of individual metals (e.g. Olias et al., 2004). At the start of the

wet season, there will be greater potential for sharp increases in trace metal concentrations as

precipitates dissolve and mine workings and isolated surface water bodies are flushed. As the

wet season progresses, levels of dissolved trace metals will likely decline due to the significant

dilution capacity of the Rio Santa at peak flows (e.g. Younger and Blachere, 2004).

The net effect of these different processes will likely lead to decreasing discharge,

increasing ochre precipitation, and acidification of water in the Rio Santa Watershed during the

dry season, particularly in the upper Rio Santa and its tributaries where the impact of glacier

recession will be most conspicuous. Potentially toxic trace metal concentrations may increase

throughout the summer and/or undergo a pronounced spike early in the wet season as metals are

flushed through the hydrologic system. Dilution of trace metals will likely reduce contamination

issues as the wet season progresses.

Page 84: The origin and distribution of trace metals in the Rio Santa

74

6. Conclusions

The oxidation of sulfide minerals and dissolution of carbonates exerts a strong control on

water composition in the Rio Santa Watershed, where waters are characterized by high SO4, Ca,

and HCO3. The pH at most sites is maintained at circumneutral values by the watershed’s

capacity to buffer against acidity inputs. Acidity derived from the weathering of sulfide minerals

is diluted and neutralized by alkalinity derived from carbonate dissolution. At some sites, acidity

inputs have overwhelmed the neutralization capacity of the river and the positive feedback cycle

of AMD/ARD has been initiated. The Rios Olleros and Quilcay are examples of tributaries in

which this process is occurring. They are characterized by high SO4, low pH, and high dissolved

metal concentrations. The streambeds are coated by ochreous precipitates that prevent efficient

carbonate dissolution and maintain the low pH within these tributaries.

There is a risk that AMD/ARD processes will commence in other areas of the watershed

if sulfide weathering rates increase beyond a critical threshold, after which carbonate dissolution

no longer provides sufficient neutralization (e.g. Banks et al., 1997; Salomons, 1995). Sulfide

weathering may increase due to the acceleration of mining activities and production of tailings.

Additionally, as annual glacial discharge initially increases due to greater rates of melting, rates

of subglacial production of finely ground fresh sediments will accelerate, with an associated

increase in subglacial and proglacial sulfide oxidation rates.

Glacial retreat is changing the hydrologic regime in ways that may affect the acid-base

balance within the watershed. As dry season discharge declines, the buffering capacity of the

Rio Santa will decrease. There will be less river water available for dilution of acidic effluents

released directly from mines or downstream of in-river tailings piles.

Page 85: The origin and distribution of trace metals in the Rio Santa

75

Trace metals are derived from natural and mining-accelerated weathering of various

lithologies throughout the watershed. They tend to be present in dissolved forms at

concentrations between detection limit and 10 ug/L at most sites. There are significant increases

in concentrations and bulk loads of dissolved trace metals in the Rio Santa at Ticapampa and

Huaraz. The sharp drops in downstream bulk loads indicate that metals do not persist in their

dissolved forms at high concentrations in the circumneutral waters of the Rio Santa. It is likely

that dissolved trace metal concentrations are lower than particulate trace metal concentrations

throughout most of the watershed. As sulfide weathering is accelerated, potential acidification of

the watershed may have serious environmental consequences as particulate-phase metals

redissolve into their toxic aqueous form.

To assess climate change or mining-related changes to trace metals within the watershed,

a strong baseline record of current concentrations is required. Sampling should be repeated over

a multi-year period and multiple times per year. Future sampling efforts should include non-

filtered trace metal samples, in order to quantify the amount of particulate metals within the

watershed. Greater spatial resolution is required to better define potential sources of current

contamination issues.

The Cordillera Blanca, with its multitude of tropical glaciers, has been a focus of research

on the impacts of climate change on water resources (e.g. Vergara et al., 2007). In particular,

this research has focused on physical hydrology and the quantity of water available for domestic,

agricultural, hydroelectric, and mining uses. The research presented here shows that quantity is

only part of the story - although not polluted along its entire length, there are numerous point

sources of contamination, both natural and anthropogenic. While these ‘hot spots’ are generally

treated naturally by the hydrologic system (through precipitation and dilution), they are cause for

Page 86: The origin and distribution of trace metals in the Rio Santa

76

great concern. Water that is polluted beyond a critical threshold is effectively removed from use,

further stressing fresh water resources. As discussed in this thesis, with receding glaciers and

decreasing melt runoff, potentially toxic trace metals will likely put further stress put on water

quality. Combined with increasing population and mining activities, these issues will only

exacerbate in the future. The outstanding question that cannot be easily answered is, "what will

be the extent of water quality degradation and what will be the timing or rate of these changes?"

Page 87: The origin and distribution of trace metals in the Rio Santa

77

7. References

Agency for Toxic Substances and Disease Registry (ATSDR). 2007a. Toxicological profile for

Arsenic. Atlanta, GA: U.S. Department of Health and Human Services, Public Health

Service.

Agency for Toxic Substances and Disease Registry (ATSDR). 2007b. Toxicological profile for

Lead. Atlanta, GA: U.S. Department of Health and Human Services, Public Health

Service.

Agency for Toxic Substances and Disease Registry (ATSDR). 2012. Toxicological Profile for

Cadmium. Atlanta, GA: U.S. Department of Health and Human Services, Public Health

Service.

Agency for Toxic Substances and Disease Registry (ATSDR). 2013. Toxicological Profile for

Uranium. Atlanta, GA: U.S. Department of Health and Human Services, Public Health

Service

Akcil, A., & Koldas, S. 2005. Acid Mine Drainage (AMD): causes, treatment and case studies.

Journal of Cleaner Production, 14 (2006), 1139-1145

ANA. 2010. Inventario de glaciares Cordillera Blanca. Huaraz, Peru: Unidad de Glaciologia y

Recursos Hidricos.

Ames, A., Dolores, A., Valverde, P., Evangelista, D., Javier, W., Gavnini, J., Zuniga V., &

Gomez, J. 1989. Glacier inventory of Peru, Part 1, 105. Huaraz, Peru: Hidrandina.

Anderson, S.P., Drever, J. I., Frost, C.D., & Holden, P. 2000. Chemical weathering in the

foreland of a retreating glacier. Geochimica et Cosmochimica Acta, 64 (3), 1173-1189.

Page 88: The origin and distribution of trace metals in the Rio Santa

78

Anderson, S.P. 2005. Glaciers show direct linkage between erosion rates and chemical

weathering fluxes. Geomorphology, 67 (1-2), 147-157.

Anderson, S.P. 2007. Biogeochemistry of Glacial Landscape Systems. Annual Review of Earth

and Planetary Sciences, 35 (1), 375-399.

Araneda, R. 2003. Alto Chicama Project, Quiruvilca District La Libertad Department, Peru.

Presented at ProEXPLO Conference, Lima, Peru, May 2003.

Azzie, B.A. (2002) Coal mine waters in South Africa: Their geochemistry, quality and

classification. Unpublished. PhD thesis, University of Cape Town, South Africa.

Banco Central de Reserva del Peru. 2009. 2008 Annual Report: Banco Central de Reserva del

Perú. Lima, Peru.

Baker, B.J., & Banfield, J.F. 2003. Microbial communities in acid mine drainage.

Microbiology Ecology, 44 (2003), 139-152.

Banks, D., Younger, P.L., Arnesen, R., Iverson, E.R., & Banks, S.B. 1997. Mine-water

chemistry: the good, the bad and the ugly. Environmental Geology, 32 (3), 157.

Baraer, M., Mark, B.G., McKenzie, J. M., Condom, T., Bury, J., Huh, K., Portocarrero, C.,

Gomez, J., & Rathay, S. 2012. Glacier recession and water resources in Peru’s

Cordillera Blanca. Journal of Glaciology, 8 (207), 134-150.

Baraer, M., McKenzie, J. M., Mark, B. G., Bury, J., & Knox, S. 2009. Characterizing

contributions of glacier melt and groundwater during the dry season in a poorly gauged

catchment of the Cordillera Blanca (Peru). Advances in Geosciences, 22 (2009), 41-49.

Bebbington, A. & Williams, M. 2008. Water and Mining Conflicts in Peru. Mountain Research

and Development, 28, 190-195.

Page 89: The origin and distribution of trace metals in the Rio Santa

79

Berner, E.K., & Berner, R. A. 1987. The Global Water Cycle. Upper Saddle River, NJ:

Prentice-Hall.

Burns, P., Mark, B.G, & McKenzie, J.M. 2011. A multi-parameter hydrochemical

characterization of proglacial runoff, Cordillera Blanca, Peru. The Cryosphere

Discussions, 5 (5), 2483-2521.

Bury, J. T., Mark, B. G., McKenzie, J. M., French, A., Baraer, M., Huh, K. I., Zapata Luyo, M.

A., & Lopez, R.J.G. 2010. Glacier recession and human vulnerability in the

Yanamarey watershed of the Cordillera Blanca, Peru. Climatic Change, 105 (1-2), 179-

206.

Cobbing, E. J., Pitcher, W. S., Wilson, J. J., Baldock, J. W., Taylor, W. P., & McCourt, W.

1981. The geology of the western cordillera of northern Peru. Overseas Memoir of

Institute of Geological Sciences, 5, 143.

Cobbing, E. J. & Sanchez, A. W. Mapa geologico del cuadrangulo de Huaraz. (Map.) 1996.

1:100,000. Insitituto Geologico Minero y Metalurgico, Peru.

Cravotta, C.A. 2008. Dissolved metals and associated constituents in abandoned coal-mine

discharges, Pennsylvania, USA. Part 1: Constituent quantities and correlations. Applied

Geochemistry, 23, 166-202.

Driscoll et al., 1994. Trace metals cycling and speciation. In: B. Moldan & J. Corny (Eds.).

Biogeochemistry of small catchments: a tool for environmental research. New York,

NY: John Wiley & Sons.

Eisler, R. 1989. Molybdenum hazards to fish, wildlife, and invertebrates: a synoptic review.

U.S. Fish Wildlife Service Biology Report, 85, 1-19.

Page 90: The origin and distribution of trace metals in the Rio Santa

80

Faure, G. 1991. Principles and applications of geochemistry. R. A. McConnin (Ed.). Upper

Saddle River, NJ: Prentice Hall.

Fortner, S. K., Mark, B. G., McKenzie, J. M., Bury, J. B., Trierweiler, A., Baraer, M., Burns, P.

J., & Munk, L. 2011. Elevated stream trace and minor element concentrations in the

foreland of a receding tropical glacier. Applied Geochemistry, 26, 1792-1801.

Fortner, S.K., Wittenberg University. 2008. (Trace metal sampling in Rio Santa Watershed,

July 2008). Unpublished raw data.

Garbarubi, J. R., Hayes, H.C., Roth, D.A., Anteriler, T.I., Brinton, Taylor, H.E., 2005. Heavy

metals in the Mississippi River. In: R.H. Meade (Ed.), Contaminants in the Mississippi

River. Richmond, VA: U. S. Geological Survey.

Gray, N.F. 1997. Environmental impact and remediation of acid mine drainage: a management

problem. Environmental Geology, 30, 62-71.

Harris, D. L., Lottermoser, B. G., & Duchesne, J. 2003. Ephemeral acid mine drainage at the

Montalbion silver mine, North Queensland. Australian Journal of Earth Science, 50,

797–809

Hem, J.D. 1985. Study and interpretation of the chemical characteristics of natural water. USA:

United States Geological Survey.

INEI. 2007. The 2007 national census: XI of population and VI of houses. Lima, Peru: Institute

of National Statistics and Information.

Johnson, D.B. 2003. Chemical and microbiological characteristics of mineral spoils and

drainage waters at abandoned coal and metal mines. Water, Air, and Soil Pollution, 3, 22-

66.

Page 91: The origin and distribution of trace metals in the Rio Santa

81

Kaser, G., Juen, U., Georges, C., Gomez, J., & Tamayo, W. 2003. The impact of glaciers on the

runoff and the reconstruction of mass balance history from hydrological data in the

tropical Cordillera Blanca, Peru. Journal of Hydrology, 282, 130-144.

Kaser, G., and Osmaston, H.A. 2002. Tropical Glaciers. In: UNESCO international

hydrogeology series. Cambridge, UK: Cambridge University Press.

Lyons, W. B., Carey, A. E., Hicks, D. M., and Nezat, C. A. (2005). Chemical weathering in

high-sediment-yielding watersheds, New Zealand. Journal of Geophysical Research.

110.

Mark, B. G. & Seltzer, G. O. 2003. Tropical glacier meltwater contribution to stream discharge:

a case study in the Cordillera Blanca, Peru. Journal of Glaciology, 49, 271–281.

Mark, B.G. & McKenzie, J.M. 2007. Tracing increasing tropical Andean glacier melt with

stable isotopes in water. Environmental Sciences and Technology, 41, 6955-6960.

Mark, B.M., McKenzie, J.M., & Gomez, J. 2005a. Changes to Water Resources in a Tropical

Mountain Watershed: a Hydrochemical Assessment of Glacier Meltwater Impact to

Streamflow. Open Science Conference: Global Change in Mountain Regions. Perth,

Scotland, UK, 2-6 October 2005.

Mark, B.G., McKenzie, J.M., & Gomez, J. 2005b. Hydrochemical evaluation of changing

glacier meltwater contribution to stream discharge, Callejon de Huaylas, Peru.

Hydrological Sciences Journal, 50 (6), 975-987.

McMahon, G., Evia, J. L., Pasco-Font, A., & Sanchez, J. M. 1999. An environmental study of

artisanal, small, and medium mining in Bolivia, Chile, and Peru, World Bank Technical

Paper 429. Washington, DC: The World Bank.

Page 92: The origin and distribution of trace metals in the Rio Santa

82

MEM. 2008. Electrical statistics 2008. Lima, Peru: Ministry of Energy and Mines.

Nordstrom, D.K. 2009. Acid rock drainage and climate change. Journal of Geochemical

Exploration, 100, 97-104.

Nordstrom, D.K. 2011a. Mine waters: acidic to circumneutral. Elements, 7, 393-398.

Nordstrom, D.K. 2011b. Hydrogeochemical processes governing the origin, transport and fate of

major and trace elements from mine wastes and mineralized rock to surface waters.

Applied Geochemistry, 26, 1777-1791.

Olias, M., Nieto, J.M., Sarmiento, A.M., Ceron, J.C., & Canovas, C.R. 2004. Seasonal water

quality variation sin a river affected by acid mine drainage in the Odiel River (South

West Spain). Science of the Total Environment, 333, 267-281.

Painter, J. 2007. Deglaciation in the Andean Region. New York, NY: United Nations

Development Program.

Petford, N., & Atherton, M. 2006. Na-rich Partial Melts from Newly Underplated Basaltic

Crust: the Cordillera Blanca Batholith, Peru. Journal of Petrology, 37 (6), 1491-1521.

Raiswell, R. 1984. Chemical models of solute acquisition in glacial meltwaters. Journal of

Glaciology, 20, 49-57.

Racoviteau A.E., Arnaud, Y., Williams, M.W., & Ordonez, J. 2008. Decadal changes in glacial

parameters in the Cordillera Blanca, Peru, derived from remote sensing. Journal of

Glaciology, 54 (108), 499-510.

Salomons, W. 1995. Environmental impact of metals derived from mining activities: Processes,

predictions, prevention. Journal of Geochemical Exploration, 52, 5-23.

Page 93: The origin and distribution of trace metals in the Rio Santa

83

Sullivan, P. J., & Yelton, J. L. (1988). An evaluation of trace element release associated with

acid mine drainage. Environmental Geology (New York), 12 (3):181-186.

Taylor, B.E. 2007. Epithermal gold deposits. In: W.D. Goodfellow (Ed.), Mineral Deposits of

Canada: A Synthesis of Major Deposit-Types, District Metallogeny, the Evolution of

Geological Provinces, and Exploration Methods. Ottawa, Canada: Geological

Association of Canada, Mineral Deposits Division.

Tranter, M. 2003. Geochemical weathering in glacial and proglacial environments. Treatise on

Geochemistry, 5, 189-205.

USGS. 2006. Shuttle Radar Topography Mission, 3 arc second scenes srtm_21_13 &

srtm_21_15. Version 2.0. Global Land Cover Facility, University of Maryland.

College Park, Maryland. 2000.

USGS. 2010. 2008 Minerals Yearbook, The Mineral Industry of Peru. U.S. Geological Survey.

USEPA Region 9 Laboratory. 2004. Standard operating procedure: Trace metal clean sampling

of natural waters. Richmond, CA: United States Environmental Protection Agency.

USEPA Region 9 Laboratory. 2000. Standard operating procedure: Trace metal labware

cleaning procedures. Richmond, CA: United States Environmental Protection Agency.

Vergara, W., Beed, A. M., Valencia, A. M., Bradley, R. S., Francou, B., Zarzar, A., Gunwaldt,

A., & Haeussling, S. M. 2007. Economic impacts of rapid glacial recession in the

Andes. EOS, 88 (25): 261-264.

Wadham, J. L., Cooper, R. J., Tranter, M., & Hodgkins, R. 2001. Enhancement of glacial solute

fluxes in the proglacial zone of a polythermal glacier. Journal of Glaciology, 47 (158),

378-386.

Page 94: The origin and distribution of trace metals in the Rio Santa

84

Younger, P.L., & Blachere, A. 2004. First-flush, reverse first-flush and partial first-flush:

Dynamics of short- and long-term changes in the quality of water flowing from deep

mine systems. In: Price, W.A., Bellefontaine, K. (Eds.), Proceedings of the 10th

Annual

British Columbia ML/ARD Workshop, Performance of ARD Generating Wastes,

Material Characterization and MEND Projects.

Wilson, J.J., Reyes, L., & Garayer, J. 1967. Geologica de los cuadrangulos de Mollembamba,

Tayamba, Huaylas, Pomabamba, Cuaraz y Huari. B.G. P. (Ed.). Lima, Peru.

World Health Organization. 2008. Guidelines for drinking-water quality. Geneva, Switzerland:

World Health Organization.

Page 95: The origin and distribution of trace metals in the Rio Santa

85

Appendix

Appendix A.1. Trace metal concentrations in Rio Santa Watershed in July 2008.

As Cd Cr Cu Fe Mn Mo Ni Pb V Zn

Buin 1.3 0.0 1.6 0.6 159.7 13.7 2.1 1.1 0.3 0.5 1.3

Conococha 12.2 0.0 0.5 0.3 434.1 53.5 0.8 2.1 0.2 0.2 0.8

Cordillera Negra1 3.3 0.0 0.9 0.3 115.3 21.2 0.1 0.6 0.0 0.1 1.7

Cordillera Negra 0.9 0.0 0.1 0.3 26.7 31.0 0.6 0.2 0.0 0.2 2.8

Negra Low 23.6 0.1 8.9 2.7 13.1 5.5 36.2 0.0 0.4 4.3 6.0

Olleros 0.4 0.2 0.8 2.8 4,328.2 499.3 0.0 57.8 0.6 0.0 110.2

Olleros Hot Spring 8,593.2 0.0 3.8 66.0 3,319.0 266.3 0.4 14.7 0.2 1.2 40.8

Rio Santa @ Ticapampa 14.4 0.3 2.5 4.0 169.9 73.3 1.8 47.5 1.1 2.3 75.8

Ticapampa 346.1 1.2 39.9 9.9 246.9 331.7 0.7 1.6 0.9 0.1 192.8

Ishinca B 0.5 0.1 0.0 0.4 53.8 8.8 1.8 0.3 0.3 0.1 3.0

Jangas 4.0 0.2 3.5 1.8 31.9 191.6 1.4 5.0 0.2 0.1 62.4

Llullan 2.1 0.1 0.5 0.7 72.8 20.6 11.5 0.4 0.2 0.1 6.9

Marcara 1.8 0.3 1.1 0.5 75.5 179.2 1.1 5.3 0.2 0.2 33.5

Mi Casa 0.2 0.1 0.3 0.5 109.8 3.5 3.9 1.7 0.0 0.1 196.8

Nev Pastoruri 0.4 0.6 0.5 2.4 943.6 983.9 0.0 37.7 1.5 0.0 80.2

Pariacs 0.5 0.1 0.0 0.2 51.3 36.6 1.9 1.3 0.0 0.1 5.5

Puente Choquechaca 5.1 0.1 4.2 1.2 15.4 46.4 3.1 2.0 0.2 0.3 14.5

Recuey 0.4 3.0 0.2 31.8 46.8 582.5 0.0 2.1 5.3 0.0 676.3

Rio Colloca 12.0 0.0 0.1 0.2 4.0 1.4 1.9

0.0 0.3 0.7

Rio Santa Huaraz 20.6 0.2 3.3 1.3 123.3 152.4 1.8 3.8 0.2 0.1 24.0

Rio Tucco 1.7 0.0

0.9 14.3 4.1 0.6 0.2 0.0 0.0 3.5

RioSanta1 4.9 0.0 0.6 1.1 25.1 15.6 0.6 0.3 0.0 0.1 2.3

RioSanta2 2.6 0.3 2.3 1.2 26.9 160.1 0.9 7.8 0.1 0.0 32.7

Ranrahirca 0.8 0.2 0.3 2.6 101.4 56.6 4.7 0.6 0.4 0.1 31.0

RS Ucashaca 5.5 0.0 0.5 0.7 15.6 10.7 0.7 0.3 0.0 0.1 1.1

Santa Bridge Catac 4.0 0.1 0.9 0.7 21.5 61.2 0.6 2.0 0.2 0.1 7.9

Santa Low 5.4 0.1 3.8 1.2 15.9 45.0 3.2 1.8 0.2 0.3 10.4

Yanayacu 2.6 0.0 0.1 0.2 40.0 4.1 4.2 0.4 0.0 0.2 1.3

Unpublished data supplied by S. Fortner, Wittenberg University, USA. Analysis methods were

the same as in Fortner et al. (2011).

Page 96: The origin and distribution of trace metals in the Rio Santa

86

Appendix A.2. Concentration of SO4 (meq/L) and conductivity (µS/cm) in the Quilcayhaunca

basin in July, 2009.

Site

SO4

(meq/L)

Conductivity

(µS/cm)

Cuchillacocha Out 3.15 478

Lower Lake (Tupla) Out 3.08 495

Jatun 2.70 390

Cuchi Con 2.23 304

Tulpa Low 2.04 281

V2 Ab Pacsa 2.01 258

Tulp Ab Conf 2.01 259

Cay High 1.44 226

Cay Ab Conf 2.85 391

Quil Bel Conf 2.18 296

Casa de Agua 2.14 293

Park Entrance 1.85 228

Quilcay 1.48 241

Jatun Upper Conf 1.48 176

Jatun Mid 1.09 133

Cay L1 2.04 421

Cay Red 11.69 314

Cay L2 1.71 242

Cay L3 5.19 130

South Waterfall 1.20 179

North Waterfall 0.19 53

J Spring 0.34 88

Cay Spring 0.13 26

Quil Spring 0.67 116

Data from Burns et al. (2009).

Page 97: The origin and distribution of trace metals in the Rio Santa

87

Appendix A.3. Synoptically sampled pH, Ca, and SO4 in the Rio Santa Watershed for July 2004

– 2007.

Name pH Ca SO4

2005 2006 2007 2004 2005 2006 2007 2004 2005 2006 2007

Buin 7.5 8.5 8.9 21.5 12.70 30.60 29.69 29.64 21.04 44.40 25.51

Colcas

8.1 8.1 19.3

19.00 13.73 29.46 0.00 30.81 28.49

Conococha 9.1 8.2 8.6 19.6 19.60 15.10 19.03 4.63 3.47 4.37 2.43

Jangas 7.2 7.9 8.0 27.9 20.90 22.90 39.42 61.74 53.19 61.55 60.81

Llan Out 7.1 7.3 7.3 6.0 5.27 5.15 9.10 8.33 8.24 8.52 7.57

Llullan

7.8 7.7 7.6 7.81 6.57 12.12 10.00 9.52 8.53 10.55

Marcara 6.9 7.9 7.8 15.5 11.40 12.20 18.26 46.02 37.25 42.21 37.72

Pachacoto 7.2 8.2 7.8 22.1 19.30 24.60 40.91 65.36 50.14 67.10 58.16

Q1 7.6 8.3 8.1 9.5 10.60 9.51 14.40 7.89 6.83 6.40 5.41

Q3 7.3 8.4 8.0 7.4 6.71 7.02 6.10 14.34 13.09 13.15 11.12

Quilcay 4.7 4.4 5.0 18.1 11.80 13.60 10.39 73.27 69.35 84.36 92.50

Ranrahirca

8.0 7.9 18.0 9.40 11.00 5.24 36.31 17.45 22.45 21.45

Rio Santa 1 8.6 7.0

28.7 30.50 29.00

19.10 18.43 16.92 0.00

Rio Santa 2 8.1 7.5 22.9 24.40 35.80 23.75 63.24 67.98 68.05 62.17

Rio Santa Low

8.4 42.0

39.15 71.16 0.00 0.00 77.37

Yanayacu 7.2 8.0 7.7 5.7 5.74 5.55 5.60 6.00 5.54 5.81 6.04

Methods and partial dataset are published in Mark et al. (2007). Concentration data is given in

mg/L.

Page 98: The origin and distribution of trace metals in the Rio Santa

88

Appendix A.4. Monthly concentration (mg/L) and discharge (m3/s) in the Querococha Basin

from April 1998-April 1999. Month Ca Si Mg K Na Cl SO4 HCO3 Discharge

YA

N

Apr 9.29 3.23 1.11 0.45 1.41 0.02 37.85 0.00 0.60

May 8.36 3.05 1.10 0.39 1.34 0.06 36.97 0.00 0.24

Jun 8.73 3.41 1.14 0.44 1.87 0.06 38.52 0.00 0.10

Jul 9.79 3.16 1.26 0.47 1.30 0.00 41.15 0.00 0.11

Aug 9.21 3.07 1.19 0.42 0.87 0.05 39.80 0.00 0.08

Sep 8.93 3.26 0.95 0.35 0.96 0.04 33.72 0.00 0.10

Oct 10.10 2.99 1.17 0.49 1.57 0.06 39.18 0.00 0.31

Nov 9.97 2.85 1.31 0.51 3.95 0.05 43.81 0.00 0.20

Dec 10.10 2.77 1.20 0.41 0.53 0.12 0.00 0.00 0.14

Jan 12.70 2.79 1.58 0.54 0.66 0.08 52.99 0.00 0.11

Feb

Mar 14.50 2.90 1.63 0.60 0.89 0.05 53.67 0.00 0.07

Apr 14.50 3.19 1.59 0.50 0.94 0.05 53.62 0.00 0.03

Q1

Apr 5.83 2.68 0.39 0.35 5.02 0.19 4.87 27.10 0.60

May 6.85 3.16 0.60 0.40 4.77 0.24 5.40 30.08 0.37

Jun 8.92 3.21 0.72 0.49 6.14 0.17 7.56 38.15 0.14

Jul 9.54 3.49 0.81 0.52 7.02 0.20 9.86 39.89 0.09

Aug

Sep 9.40 3.21 1.00 0.64 2.46 0.15 11.00 27.25 0.07

Oct 7.60 3.07 1.02 0.47 7.91 0.33 18.47 26.64 0.20

Nov 6.98 2.94 0.62 0.46 1.45 0.19 6.08 21.17 0.22

Dec 5.41 2.39 0.50 0.32 1.00 0.17 0.00 22.17 0.21

Jan 4.38 2.54 0.34 0.38 0.95 0.12 0.00 18.16 1.31

Feb

Mar 4.39 2.64 0.34 0.40 0.95 0.08 3.11 14.47 1.33

Apr 5.30 2.61 0.39 0.35 0.98 0.09 0.00 21.22 0.68

Continued on page 89.

Page 99: The origin and distribution of trace metals in the Rio Santa

89

Appendix A.4. (Continued.) Monthly concentration (mg/L) and discharge (m3/s) in the

Querococha Basin from April 1998-April 1999.

Month Ca Si Mg K Na Cl SO4 HCO3 Discharge

Q2

Apr 6.00 2.90 0.68 0.35 1.15 0.06 18.28 2.09 2.59

May 7.10 3.12 0.99 0.39 1.13 0.07 23.54 0.36 1.12

Jun 8.81 3.10 1.02 0.48 1.43 0.10 26.26 3.21 0.42

Jul 8.39 3.42 1.13 0.52 1.63 0.09 29.76 -1.38 0.26

Aug 9.19 2.95 1.45 0.51 1.66 0.08 36.97 -6.33 0.34

Sep 10.20 2.49 1.35 0.39 1.30 0.08 34.41 -1.67 0.43

Oct 8.86 2.61 1.09 0.45 1.14 0.14 31.11 -3.32 1.24

Nov 8.30 2.99 1.04 0.42 1.11 0.09 29.71 -3.66 0.71

Dec 7.64 2.76 0.90 0.35 0.95 0.15 0.00 30.76 1.27

Jan 5.59 3.20 0.62 0.36 1.04 0.14 0.00 23.51 2.10

Feb

Mar 5.71 3.40 0.60 0.37 1.04 0.23 14.44 4.84 2.17

Apr 6.50 3.49 0.67 0.38 1.14 0.08 0.00 26.93 1.19

Q3

Apr 6.52 3.23 0.61 0.42 1.32 0.11 12.62 10.89 3.34

May 6.84 3.05 0.63 0.44 1.19 0.09 13.40 10.74 1.40

Jun 7.37 3.41 0.71 0.44 1.41 0.10 14.24 12.35 0.60

Jul 7.30 3.16 0.71 0.45 1.35 0.10 14.35 11.80 0.27

Aug 7.18 3.07 0.73 0.44 5.42 0.18 15.57 20.67 0.34

Sep 7.65 3.26 0.72 0.44 1.49 0.09 14.07 13.82 0.33

Oct 7.98 2.99 0.80 0.55 1.60 0.37 16.82 11.68 0.90

Nov 7.22 2.85 0.73 0.50 1.24 0.20 16.00 9.24 1.24

Dec 7.08 2.77 0.72 0.45 1.17 0.11 0.00 28.99 1.23

Jan 6.48 2.79 0.67 0.44 1.17 0.10 0.00 26.84 4.23

Feb

Mar 6.16 2.90 0.61 0.45 1.19 0.13 12.92 9.16 4.96

Apr 5.59 3.19 0.55 0.44 1.36 0.09 0.00 24.10 2.17

Data published, in part, in Mark and Seltzer (2003). Blank spaces indicate data is n/a.

Page 100: The origin and distribution of trace metals in the Rio Santa

90

Appendix A.5. Concentration (mg/L) and discharge (m3/s) at Rio Santa Low, the outlet of the

Callejon de Huaylas.

Date Ca Na Mg K SO4 Si Discharge

July 2005 33.60 14.00 5.97 3.07 66.61 3.55 34.15

July 2006 28.10 20.30 5.58 3.78 74.33 4.62 32.48

July 2007 39.15 10.04 7.29 3.86 77.40 3.97 30.89

July 2008 28.58

January 2009 19.48 2.67 4.52 1.47 32.18 3.40 230.47

Discharge data collected by Duke Energy. Methods and partial concentration data are published

in Mark et al. (2007) and Baraer et al. (2012). Discharge for January is the average of January

and February volumes; discharge for July is the average of June and July volumes. Blank spaces

indicate data is n/a.

Appendix A.6. Wet season discharge data at Rio Santa Low, the outlet of the Callejon de

Huaylas.

Year Discharge

2005 101.65

2006 101.19

2007 123.76

2008 169.03

2009 230.47

Values presented are the average of January and February volumes. Data collected by Duke

Energy.