Nitrate and sediment fluxes from a California rangeland watershed.
Long-term water quality records for assessing natural variability, impact of management, and that guide regulatory processes to safeguard water resources are rare for California oak woodland rangelands. This study presents a 20-yr record (1981-2000) of nitrate-nitrogen (NO(3)-N) and suspended sediment export from a typical, grazed oak woodland watershed (103 ha) in the northern Sierra Nevada foothills of California. Mean annual precipitation over the 20-yr period was 734 mm yr(-1) (range 366-1205 mm yr(-1)). Mean annual stream flow was 353 mm y(-1) (range 87-848 mm yr(-1)). Average annual stream flow was 48.1 +/- 16% of precipitation. Mean annual NO(3)-N export was 1.6 kg ha(-1) yr(-1) (range 0.18-3.6 kg ha(-1) yr(-1)). Annual NO(3)-N export significantly (P < 0.05) increased with increasing annual stream flow and precipitation. Mean daily NO(3)-N export was 0.004 kg ha(-1) d(-1) (range 10(-5) to 0.55 kg ha(-1) d(-1)). Mean annual suspended sediment export was 198 kg ha(-1) yr(-1) (range 23-479 kg ha(-1) yr(-1)). There was a positive relationship (P < 0.05) between annual suspended sediment export, annual stream flow and precipitation. Mean daily suspended sediment export was 0.54 kg ha(-1) d(-1) (range 10(-4) to 155 kg ha(-1) d(-1)). Virtually no sediment was exported during the dry season. The large variation in daily and annual fluxes highlights the necessity of using long-term records to establish quantitative water quality targets for rangelands and demonstrates the difficulty of designing a water quality monitoring program for these ecosystems.
Lewis
David J
DJ
University of California Cooperative Extension, Santa Rosa, CA 95403, USA.
Singer
Michael J
MJ
Dahlgren
Randy A
RA
Tate
Kenneth W
KW
D002140:California; D011232:Chemical Precipitation; D017753:Ecosystem; D004784:Environmental Monitoring; D019015:Geologic Sediments / Q000032:analysis*; D009566:Nitrates / Q000032:analysis*; D009584:Nitrogen / Q000032:analysis*; D011891:Rain; D045483:Rivers; D012621:Seasons; D013997:Time Factors; D014872:Water Movements; D014881:Water Supply
D009566:Nitrates; D009584:Nitrogen