Nutrient Cycling and Water Quality on California Rangelands Randy Dahlgren Department of Land, Air and Water Resources University of California - Davis Core Research Team Barbara Allen-Diaz Rob Atwill Randy Dahlgren John Harper David Lewis Toby O Geen Mike Singer Ken Tate
Urban-Wildland-Agricultural Interface 80% of Reservoirs
Nutrient impaired waterbodies with possible grazing impacts
Nutrient Pollution Nitrogen - organic forms - ammonium (NH 3 /NH 4+ ) - nitrate (NO 3- ) Harmful Algal Blooms Organic N = Nitrogen = Hydrogen = Oxygen
Nutrient Pollution Phosphorus - organic forms - adsorbed to particles - dissolved phosphate (PO 3-4 ) 3- Organic P
Harmful Algal Blooms www.tankonyvtar.hu Nitrate in drinking water Water Quality Standard = 10 mg N/L Blue-baby syndrome (methemoglobinemia)
Ammonia (NH 3 ) Toxicity Aquatic Ecosystems Criterion Duration Acute (1-hr average) Chronic (30-d rolling average) 2013 Final Criteria TAN at ph = 7 & 20 o C 17 mg N/L 1.9 mg N/L TAN = NH 3 + NH 4 + Acute Toxicity at NH 3 ph 8.5 & 30 o C TAN = 0.33 mg N/L ph 7 = 0.5%
Nutrients (N/P) NH 3 /NH 4 /PO 4 Runoff
Nitrogen kg/ha/yr Atmospheric Nitrogen Deposition in California Atmospheric N deposition on California rangelands is often in the range: 5 10 kg/ha/yr
Mineral N (kg/ha/yr) 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 Sierra Nevada Foothills Watershed Annual N Export Load Most rangelands are sinks rather than sources for nitrogen Mean 1.6 0.0 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 Water Year
Natural Sources of Nitrogen Photo courtesy of Carson Jeffries Big Springs Shasta Valley Spring discharge = 90 cfs NO 3 -N = 0.48 mg/l PO 4 -P = 0.15 amorahquanyin.com mg/l
Northern California Volcanic Springs
0.4 Spring Water Nitrate and Phosphate 0.3 NO 3 -N (mg/l) 0.2 0.1 0.0 Up Sac Trout Up Sac Bridge Up Sac Moss Fall Lodge Fall Rainbow Crystal Big Lake Lava Crk Ja-she Trapral Casis 0.08 0.06 PO 4 -P (mg/l) 0.04 0.02 0.00 Up Sac Trout Up Sac Bridge Up Sac Moss Fall Lodge Fall Rainbow Crystal Big Lake Lava Crk Ja-she Trapral Casis
Scott Morford
Background nutrient levels are not zero Nutrient Background Level (mg/l) Eutrophication Concern (mg/l) TN 0.15 0.53 - NO 3 -N 0.005 0.040 (0.50) 0.30 TP 0.009 0.032 (0.15) 0.10 PO 4 -P (0.15) 0.05
Seasonal Pattern in Streamwater Nitrate in Non-grazed California Oak Woodlands 6 5 NO 3 (mg L-1) 4 3 2 1 0 J A J O J A J O J A J O J A J
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
0.25 0.20 Yuba River - Nitrate ~ 0.5 to 5 mg/l in oak woodland streams NO 3 -N (mg/l) 0.15 Nutrient assimilative capacity reduces nutrient concentrations to downstream 0.10 aquatic ecosystems 0.05 0.00 Oct Apr Oct Apr Oct Apr Oct Apr Oct 1999 2000 2001 2002 2003
State-wide Survey 24 streams 2000 and 2001 water years
5 4 Nutrient Concentrations n = 947 N / P mg/l (mg/l) 3 2 1 0 90 th 75 th 50 th 25 th 10 th * Eutrophication concern level * Total N NO 3 NH 4 Total P PO 4 * *
Grazing Treatments No grazing 1500 lb/ac RDM 1000 lb/ac RDM 500 lb/ac RDM
12 10 n = 156-277 Nitrate - Grazing NO 3 -N (mg/l) NO 3 (mg/l) 8 6 4 2 0 No Graze 1500 1000 500 Eutrophication concern level
9 Nitrate - 500 lbs/acre RDM Streamflow (cfs) NO 3 15 12 Streamflow (cfs) 6 3 9 6 NO NO 3 -N 3 (mg/l) 3 0 Nov Dec Jan Feb Mar Apr May 0
Coastal Creek Ammonia Ammonia and Flow for Site 1 during New Years Flood 400 Flow Site 1, 2006 350 NH3 Site 1, 2006 3 Flow (cfs) 300 250 200 150 100 chronic level 2 1 NH 3 /NH 4 N (mg/l) Un-Ionized NH3 (mg/l) 50 17 0 0 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 Slide courtesy of David Lewis
Grazing Management Buffer/Filter Strip
Flow-Through Wetlands Wetland
Wetland Treatment of Irrigation Tailwaters 100 Percent Reduction 80 60 40 20 0 E. coli Sediment Total N NO3-N Total P PO4-P
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?