nutrient cycling and water quality on california rangelands

Nutrient Cycling and Water Quality on California Rangelands

Core Research Team

• Barbara Allen-Diaz • Rob Atwill • Randy Dahlgren • John Harper

• David Lewis • Toby O’Geen • Mike Singer • Ken Tate

Randy Dahlgren Department of Land, Air and Water Resources

University of California - Davis

Urban-Wildland-Agricultural Interface

80% of Reservoirs

Nutrient impaired waterbodies with possible

grazing impacts

Harmful Algal Blooms

Nutrient Pollution

Nitrogen - organic forms - ammonium (NH3/NH4

+) - nitrate (NO3

-)

Organic N

= Nitrogen = Hydrogen = Oxygen

Phosphorus

- organic forms

- adsorbed to particles

- dissolved phosphate (PO43-)

Nutrient Pollution

3-

Organic P

Harmful Algal Blooms

www.tankonyvtar.hu

Blue-baby syndrome (methemoglobinemia)

Nitrate in drinking water Water Quality Standard = 10 mg N/L

Ammonia (NH3) Toxicity – Aquatic Ecosystems

Criterion Duration 2013 Final Criteria TAN at pH = 7 & 20 oC

Acute (1-hr average) 17 mg N/L

Chronic (30-d rolling average) 1.9 mg N/L

TAN = NH3 + NH4+

Acute Toxicity at

pH 8.5 & 30 oC

TAN = 0.33 mg N/L

pH 7 = 0.5%

NH3

Nutrients (N/P)

NH3/NH4/PO4 Runoff

Atmospheric N deposition on California rangelands is often in the range: 5 – 10 kg/ha/yr

Atmospheric Nitrogen Deposition

in California Nitrogen kg/ha/yr

Sierra Nevada Foothills Watershed Annual N Export Load

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5 19

81

1982

1983

1984

1985

1986

1987

1988

1989

1990

1991

1992

1993

1994

1995

1996

1997

1998

Water Year

Min

eral

N (k

g/ha

/yr)

Mean ≈ 1.6

Most rangelands are sinks rather than sources for nitrogen

amorahquanyin.com

Natural Sources of Nitrogen

Big Springs Shasta Valley Spring discharge = 90 cfs

NO3-N = 0.48 mg/L PO4-P = 0.15 mg/L

Photo courtesy of Carson Jeffries

Northern California Volcanic Springs

Up Sac Trout

Up Sac Bridge

Up Sac Moss

Fall Lodge

Fall Rainbow

Crystal

Big Lake

Lava CrkJa-sh

e

Trapral Casis

NO3-N

(mg/L

)

0.0

0.1

0.2

0.3

0.4

Up Sac Trout

Up Sac Bridge

Up Sac Moss

Fall Lodge

Fall Rainbow

Crystal

Big Lake

Lava CrkJa-sh

e

Trapral Casis

PO4-P

(mg/L

)

0.00

0.02

0.04

0.06

0.08

Spring Water Nitrate and Phosphate

Scott Morford

Nutrient Background Level (mg/L)

Eutrophication Concern (mg/L)

TN 0.15 – 0.53 -

NO3-N 0.005 – 0.040 0.30

TP 0.009 – 0.032 0.10

PO4-P 0.05

Background nutrient levels are not zero

(0.50)

(0.15)

(0.15)

J A J O J A J O J A J O J A J

NO

3 (mg L-1)

0

1

2

3

4

5

6

Seasonal Pattern in Streamwater Nitrate in Non-grazed California Oak Woodlands

Low Nutrient Demand High Nutrient Demand

California oak woodlands – annual grasslands are naturally susceptible to

seasonal nitrate leaching

Assimilative Capacity

Self-Purification Capacity – removal of pollutants during downstream transport

Assimilative Capacity

Yuba River - Nitrate

Oct Apr Oct Apr Oct Apr Oct Apr Oct

NO

3-N

(mg/

L)

0.00

0.05

0.10

0.15

0.20

0.25

1999 2000 2001 20032002

~ 0.5 to 5 mg/L in oak woodland streams

Nutrient assimilative capacity reduces nutrient concentrations to downstream

aquatic ecosystems

State-wide Survey 24 streams

2000 and 2001 water years

mg/

L

0

1

2

3

4

5

Total N NO3 NH4 Total P PO4

Nutrient Concentrations

90th

75th

50th 25th

10th

n = 947

N /

P (m

g/L

)

* * *

* Eutrophication concern level

Grazing Treatments No grazing

1500 lb/ac RDM

1000 lb/ac RDM

500 lb/ac RDM

Nitrate - Grazing

No Graze 1500 1000 500

NO

3 (m

g/L

)

0

2

4

6

8

10

12

n = 156-277

NO

3-N

(mg/

L)

Eutrophication concern level

Nov Dec Jan Feb Mar Apr May

Stre

amflo

w (c

fs)

0

3

6

9

Streamflow (cfs)

NO

3 (m

g/L)

0

3

6

9

12

15

NO3

Nitrate - 500 lbs/acre RDM

NO

3-N

(mg/

L)

Coastal Creek Ammonia

Ammonia and Flow for Site 1 during New Years Flood

0

50

100

150

200

250

300

350

400

12/25/05 12/26/05 12/27/05 12/28/05 12/29/05 12/30/05 12/31/05 1/1/06 1/2/06 1/3/06

Date

Flow

(cfs

)

0

1

2

3

Un-

Ioni

zed

NH

3 (m

g/L)

Flow Site 1, 2006

NH3 Site 1, 2006

Slide courtesy of David Lewis

NH

3/NH

4 –N

(m

g/L)

chronic level

17

Buffer/Filter Strip

Grazing Management

Flow-Through Wetlands

Wetland

E. coli Sediment Total N NO3-N Total P PO4-P

Perc

ent R

educ

tion

0

20

40

60

80

100

Wetland Treatment of Irrigation Tailwaters

Conclusions Most California rangelands are sinks rather than

sources for nutrients

Background nutrient levels are not zero

California oak woodlands – annual grasslands are naturally susceptible to seasonal nitrate leaching

Nutrient assimilative capacity reduces nutrient concentrations to downstream aquatic ecosystems

Rangeland streams rarely exceed nutrient thresholds for eutrophication, except during large storm events

Accurate nutrient monitoring of rangelands is extremely challenging given temporal variability

Questions?