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
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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
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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?