ARS | Publication request: Nutrient and sediment transport on flood irrigated pasture in the Klamath Basin, Oregon

Submitted to: Rangeland Ecology and Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 19, 2009
Publication Date: June 30, 2010
Citation: Ciotti, D., Griffith, S.M., Kann, J., Baham, J. 2010. Nutrient and sediment transport on flood irrigated pasture in the Klamath Basin, Oregon. Rangeland Ecology and Management. 63:308-316.

Interpretive Summary: For many years, the Upper Klamath Lake (UKL) in southern Oregon has experienced excessive algal growth and nutrient enrichment that has led to the decline of some native fish species. While Upper Klamath Lake would have been considered eutrophic over 100 years ago, settlement of the drainage and modern land uses, including agricultural, may have accelerated the lake’s eutrophic status and impaired aquatic life. The UKL sub-basin was listed on the 1998 Oregon 303(d)1 list for dissolved oxygen, chlorophyll-a, and pH. Water quality problems are attributed to the lake’s production of blue green algae. Reducing nutrient inputs such as phosphorus and nitrogen is the most practical way to reduce algal growth and attain the water quality standards for pH and dissolved oxygen. Since nutrient loading in UKL is enhanced by the drainage of irrigation water from agricultural properties adjacent to the lake, we studied nutrient and sediment transport at two irrigated cattle pastures in the Klamath Lake Basin. We found that cattle disturbance to drainage canals and first flush of nutrients during flood irrigation caused the greatest nutrient transport at the site scale and these mechanisms were likely important contributors to nutrient export from the Wood River Valley during the summer irrigation season.

Technical Abstract: Excessive eutrophication in Upper Klamath Lake (UKL), Oregon is in part linked to high phosphorus input from adjacent watershed tributaries. Little is known of the specific nutrient and sediment source areas and transport mechanisms on flood irrigated pastures in the Wood River Valley, an important drainage basin to UKL. Sub- and surface -water samples and flow measurements were taken from irrigation headwater and tailwater locations at two pasture sites (2 ha and 70-ha). Water samples were analyzed for concentrations of sediment, dissolved organic carbon (DOC), total dissolved nitrogen (TDN), total dissolved phosphorus (TDP), orthophosphate (OP), ammonia (NH4+-N) and nitrate (NO3--N). The mean concentration of TDN and TDP in irrigation headwater was significantly lower (0.20 mg TDN L-1 and 0.06 mg TDP L-1) than in surface irrigation tailwater.