Geomicrobiology at the Sevilleta

Predicting the metabolic energy available to aqueous microorganisms

By Samantha AdelbergMentors: Laura Crossey and Amy Williams

Water

• Sources of Water at the Sevilleta– Rio Grande– Precipitation– Groundwater Wells and Springs

Groundwater• 25 wells and springs• Minimal Knowledge• Some Previous Research

Research Question

• Water chemistries varying dramatically within the Sevilleta due to local geology

• But how much does the varying water chemistry affect the thermodynamics of the different springs and wells?

Thermodynamics• All reactions want to move towards an equilibrium

state• Natural waters such as the ones at the Sevilleta are not

in equilibrium• Energetically favorable for these reactions to move

from one state to another – Spontaneous reactions, - delta G

• But there is no set time limitAffinity = RT ln(K/Q)

Equilibrium constant

Gas constant

Temperature

Role of Microorganisms

• Act as catalysts in these reactions• Speed up the electron transfers• Must spend energy making enzymes that can

perform these reactions• Facilitate these reactions because they gain a

determined amount of energy through each transaction

• Amount of energy gained changes

Chemo-litho-auto-trophChemo-litho-auto-trophChemo-litho-auto-trophChemo-litho-auto-troph

Energy Source:Energy Source:Energy Source:Energy Source:Chemical reactionsChemical reactionsChemical reactionsChemical reactions

Electron Donor: Electron Donor: InorganicInorganic

Electron Donor: Electron Donor: InorganicInorganic

Carbon source: InorganicCarbon source: InorganicCarbon source: InorganicCarbon source: Inorganic

““Eater of”Eater of”““Eater of”Eater of”

Heterotroph PhotoautotrophChemolithoautotroph

Gib

bs F

ree

Ener

gy

Study Area: Sevilleta Springs and Wells

Methods• In the Field

– pH, conductivity , TDS, temp– Bottles for cations, anions, stable

isotopes, nutrients, delta 13C• In the Lab

– Alkalinity (endpoint titrations)– ICP: cations and trace elements– IC: anions– Nutrients

• Analysis– Geochemical modeling software

Phreeqc– Thermodynamics code to

determine electron affinity

PICTURE of LOCAL GEOLOGY

Cibola

San Acacia

Tomasino

Rio Salado Box Springs

Silver Creek

West Mesa

Deeply Derived Waters

San Acacia SpringRio Salado Box Springs

CoCorp Siesmic Line, Lewis and Baldridge 1994

Results

Reactions AFFINITIES (kJ/mol/e)

Electron Acceptor

9Fe2+ + NO2- + 10H2O -> 3Magnetite + NH4+ + 16H+ 108.3213633 Nitrite

2Fe2+ + NO3- + 2H2O -> Hematite + NO2- + 4H+ 65.70072061 Nitrate

Pyrite + NO3- + 2H+ -> 2Sulfur + Fe2+ + NO2- + H2O 42.97850923 Nitrate

Pyrite + 7NO3- + H2O -> Fe2+ + 2SO42- + 7NO2- + 2H+ 37.70280148 Nitrate

S + 3NO3- + H2O -> SO42- + 3NO2- + 2H+ 37.21998924 Nitrate

Top 5 Reactions for all Springs/Wells

What does this show?• What reactions can occur• The potential energy yield of the different

reactions• What niche spaces are available for use• Trends between the geology, water chemistry, and

affinity coefficients

Affinity Trends

• Chloride Dominated Waters (San A-C, RSB12) have nearly identical affinity coefficients

• P value = .94

The Chloride Dominated Waters

San Acacia Spring Rio Salado Box Spring

Affinity Trends• Geographically similar location (SdC1, TW)• Distinct water types– Sulfate Dominated (Cibola Spring)– Mixed Ion Water (Tomasino Well)

• P value = .925

PICTURE of LOCAL GEOLOGY

Cibola

Tomasino

Affinity Trends

• Bicarbonate Dominated Waters (WMW, SC2)• P value = .665

Nutrient Readings

C:N ratios limiting nutrients whose presence

greatly affects the health of a water system

> 14.6 severe N deficiency8.3 –14.6 moderate deficiency<8.3 no deficiencyOnly Tomasino Well does not have a

severe N deficiency

All Springs/Wells have high TOC readings which predict the presence of chemolithoheterotrophs

Spring/Well C:N

Fish & Wildlife Well 4635.96354

San Lorenzo Spring 2 76.86617

McKenzie Well 23.56353

Cibola Spring 426.27735

Canyon Well 25.24335

Gibbs Well 53.93346

Tule Well 1651.51884

Rio Salado (downstream) 1453.10889

Rio Salado Box spring11 293.03585

Rio Salado Box spring12 285.04539

Silver Creek seep 2 189.86399

San Lorenzo Spring 1 158.53682

Tomasino Well 9.65792

San Acacia brine pool 35.35470

Nunn Well 77.92092

West Mesa Well 66.00071

Canyon del Ojito Spring 39.41307

San Acacia spring 170.15187

Discussion• Nitrate is the dominant electron acceptor• Nutrient reading show that all but one

spring/well is deficient in N– This is probably because NO3 is being used nearly

entirely in these metabolic reactions• Surprisingly, in the springs/wells with O2, Nitrate

continues to have a higher energy yield– Perhaps because O2 is so limited that it isn’t optimal

for microorganisms to use this pathway• Feedback effect between microbs and water

Gib

bs F

ree

Ener

gy

Lower than atmos. pCO2 yet saturated with respect to calcite

Higher than atmos. pCO2 yet under saturated with respect to calcite

Higher than atmos. pCO2 and saturated with calcite

Crossey, unpublished

Why use thermodynamic modeling?• Future geomicrobiology research and sampling• Provides explanations• Similarities to Mid Ocean Ridge thermal vents

Rio Grande Rift; Crossey et al., in prep.

Lost City Hydrothermal area, Kelley et al., 2005

Continental spring systemsMarine vent systems

Acknowledgements - Laura Crossey - Amy Williams - Frankie Reyes- All the REU’s! - Jennifer Johnson - Scott Collins- Fish and Wildlife Services- NSF

- Sevilleta LTER- Ara Kooser - Brandi Cron - Amanda Martinez- Cathy!- Mehdi and Kim in the analytical

chemistry lab- Amanda Schaupp, my statistician!

QUESTIONS?