Detailed Study and Assessment of Irrigation Drainage in the Salton Sea Area, Imperial Valley, California

Problem: Selenium concentrations exceeding criteria for the protection of aquatic life have been found by the NIWQP (National Irrigation Water - Quality Program) in irrigation drainage throughout the Imperial Valley. Elevated levels of selenium and DDT and (or) its metabolites also have been reported by the Department of the Interior's interagency NIWQP in fish and water birds in the Salton Basin, including at and near the Sony Bono Salton Sea National Wildlife Refuge. Historical data also have documented the long-term environmental implications of increasing salinity, variable water-surface elevations, and nutrient loading to the Salton Sea.

Objective:

1. Determine the extent and severity of existing and potential irrigation-induced water-quality problems in the Salton Basin, especially those on Federal lands or in areas receiving water from Federal water projects, and ensure the protection of endangered and threatened species in these areas.

2. Provide the scientific basis needed for development of realistic alternatives to mitigate or remediate identified environmental problems and thereby ensure the continued health of the Salton Basin ecosystem.

Relevance and Benefits: More than 90 percent of historical wetlands in California, an important segment of the Pacific Flyway, have been lost to agriculture and urbanization in the last 150 years. In this context, formation of the Salton Sea by accidental flooding of the Colorado River in 1905-07 and its continued sustenance, largely from agricultural runoff, takes on special importance. Degradation from increasing salinity and uncontrolled fluctuations in water level of this terminal quasi-marine lake has long been a concern. More recently, dieoffs of large numbers of fish and birds have indicated broader causes of ecological degradation, including excessive nutrients and perhaps other toxicants and pathogens. Congress has recognized the importance of this resource by designating $3 million for the construction of wetlands in the Imperial Valley and $5 million (in FY 99 alone) for scientific studies in the Salton Sea, and by financial support for projects that upgrade infrastructure in the U.S.-Mexico transboundary region. The NIWQP has a long history of advisory support and technical studies in the Salton Basin and will continue in both roles as long as requested.

Approach: The approach has been adjusted continuously in response to changing perceptions of environmental problems and with the source and amount of funding for the NIWQP. Currently, emphasis is on the following:

1. Construct and monitor wetlands to improve the quality of irrigation drainage in the Imperial Valley and the New River and provide habitat that could supplement that lost by proposed inter-basin water transfers and declining ecological value of the Salton Sea.

2. Monitor the effectiveness of nitrogen and selenium removal from agricultural drain water at a constructed subsurface biodigester on the Lewis Drain in the Imperial Valley.

3. Determine the current and historical levels of contaminants, especially nutrients and selenium, in the Salton Basin by means of physical and chemical analyses of sediment in the Salton Sea.

4. Serve in an advisory role with the Bureau of Reclamation and Fish & Wildlife Service to advocate and ensure that Federal interests of the NIWQP are represented to other local, State, Federal, and international agencies mandated by Congress to protect and enhance the economic and ecological health of the Salton Basin.

Progress and Significant Results in FY 1999:

1. Design of two wetlands and a proposed monitoring program have been nearly completed incorporating recommendations from the NIWQP and the Bureau of Reclamation to the Citizens Committee New River Task Group.

2. Comparative analyses of influent and effluent from the Lewis Drain project indicates no reduction in targeted chemicals, possibly because the organic carbon in subsurface drain water necessary to support microbial reduction is recalcitrant.

3. Analyses of water samples and sediment grab samples from 11 locations and sediment cores from 2 locations in the Salton Sea suggest that nitrogen levels in the Salton Sea have increased by about an order of magnitude since the inception of widespread fertilizer use in the 1950s. During that same period, phosphorus concentrations have increased only a little, apparently reflecting that elements proportionately greater contribution from natural sources and perhaps unique mineralogical controls on its sequestration in bottom sediment.

4. Positive outcome of participation at monthly meetings of the New River Task Group is given in item 1. Periodic attendance by the USGS at monthly meetings of the Salton Sea Science Subcommittee, an interagency entity recently created to recommend and oversee scientific investigations to save the Salton Sea, has been less influential.

Plans for FY 2000:

1. Design and monitoring plans for two proposed wetlands in Imperial Valley will be submitted in a grant application to the EPA by the Imperial Irrigation District (the lead agency) early in the fiscal year to permit wetland construction and installation of plants to be completed before hot weather ensues.

2. After suitable approvals are received, methanol will be added (by the Imperial Irrigation District and Bureau of Reclamation) to the drain water to provide a source of biodegradable organic carbon, and NIWQP monitoring will be done to test its effectiveness in reducing nitrogen and selenium .

3. Complete chemical analyses of cores collected in 1999 and report results at conferences and in publications. A joint proposal with the Geologic Division for expansion of nutrient studies in the Salton Basin will be submitted to the Salton Sea Science Subcommittee.

4. Attendance and technical input at meetings of the New River Task Group, the successor to the Salton Sea Science Subcommittee, and binational interests in the Lower Colorado River Basin will continue.