Reconnaissance investigation of water quality, bottom sediment, and biota associated with irrigation drainage in the Salton Sea area, California, 1986-87

Water, bottom sediment, and biota were sampled during 1986-87 in the Salton Sea area to determine concentrations of trace elements and pesticides as part of the Department of Interior Irrigation Drainage Program. The sampling sites (12 water, 15 bottom sediment, and 5 biota) were located in the Coachella and Imperial Valleys. The focus of sampling was to determine if contaminants in irrigation drainage from Department of the Interior-sponsored irrigation projects have caused or have the potential to cause substantial harmful effects to humans, fish, or wildlife, or to reduce the suitability of water for beneficial uses. Results indicate that selenium is the major element of concern. Elevated concentrations of selenium in water were restricted to tile-drain effluent. The maximum selenium concentration of 300 micrograms per liter was detected in tile drain 6, and the minimum concentration of 1 microgram per liter was detected in a composite sample of Salton Sea water. The median selenium concentration was 19 micrograms per liter. In contrast to the water, the highest bottom-sediment selenium concentration of 3.3 milligrams per kilogram was in a composite sample from the Salton Sea. Concentrations of boron were elevated in tile-drain samples throughout the Imperial Valley. Boron concentrations were at levels in migratory waterfowl that could cause reproductive impairment. Elevated concentrations of chromium, nickel, and zinc were detected in the bottom sediment of the Whitewater River, but they were not associated with irrigation drainage. Organochlorine pesticide residues were detected in bottom sediment throughout the study area at levels approaching those measured more than 10years ago. More detailed studies will be needed to determine if these residues are affecting the waterfowl. In biota, selenium concentrations in tilapia and corvina ranged from 3.5 to 20 micrograms per gram dry weight; the mean concentration, 10.5 micrograms per gram, exceeds the 8.0-microgram-per-gram (dry weight) safe level for human consumption of fish. In waterfowl, selenium was detected in livers at concentrations as high as 27 and 42 micrograms per gram in black-necked stilts and cormorants, respectively. Selenium levels in waterfowl and fish approach levels of concern, but, to date, no studies have been done in the Salton Sea area to determine if selenium has caused adverse biological effects such as observed in other areas contaminated by selenium from agricultural drainwater. Mercury levels in waterfowl also were elevated. Concentrations in livers of cormorants and great blue herons ranged from 7.6 to 49 micrograms per gram. Shoveler ducks also had relatively high levels of mercury; concentrations in livers ranged from 2.2 to 11 micrograms per gram. These far-ranging and migratory birds likely accumulate the mercury outside the Salton Sea basin. INTRODUCTION Background During the past several years, there has been increasing concern about the quality of irrigation drainage that is, both surface and subsurface water draining irrigated land-and its potential effects on human health, fish, and wildlife. Elevated concentrations of selenium have been detected in subsurface drainage from irrigated land in the western part of the San Joaquin Valley in California. In 1983, incidences of mortality, developmental abnormalities, and reproductive failures among waterfowl and shorebirds were documented by the U.S. Fish and Wildlife Service at the Kesterson National Wildlife Refuge (Kesterson NWR) in the western San Joaquin Valley, where irrigation drainage was impounded in Kesterson Reservoir. In addition, potentially toxic trace elements and pesticide residues have been detected in other areas in the Western States that receive irrigation drainage. Because of concerns expressed by the U.S. Congress, the Department of the Interior started a program in late 1985 to identify the nature and extent of irrigation-induced water-quality problems that might exist in the Western States. In October 1985, an interbureau group known as the "Task Group on Irrigation Drainage" was formed within the Department. The Task Group subsequently prepared a comprehensive plan for reviewing irrigation-drainage concerns for which the Interior Department may have responsibility. Initially, the Task Group identified 19 locations in 13 States that warranted reconnaissance-level field investigations. These locations relate to three specific areas of Interior Department responsibilities: (1) irrigation or drainage facilities constructed or managed by the Interior Department, (2) national wildlife refuges that receive irrigation drainage, and (3) other migratory-bird or endangered-species management areas that receive water from Department-funded projects. Nine of the 19 locations were selected for reconnaissance studies that began in 1986. The nine areas are: Arizona-California: Lower Colorado-Gila River Valley area California: Salton Sea area Tulare Lake Bed area Montana: Sun River Reclamation Project area Milk River Reclamation Project area Nevada: Stillwater Wildlife Management area Texas: Lower Rio Grande-Laguna Atascosa National Wildlife Refuge area Utah: Middle Green River basin area Wyoming: Kendrick Reclamation Project area Each reconnaissance investigation was conducted by interbureau field teams composed of a scientist from the U.S. Geological Survey as team leader and additional U.S. Geological Survey, U.S. Fish and Wildlife Service, and U.S. Bureau of Reclamation scientists representing several different disciplines. The studies were directed toward determining whether irrigation drainage (1) has caused or has the potential to cause significant harmful effects on human health or on fish and wildlife, or (2) may reduce the suitability of water for beneficial uses. This report describes the results of the Salton Sea area reconnaissance investigation. The Salton Sea area is in the southeastern desert region of California and includes the Coachella and Imperial Valleys (fig. 1). This study focused primarily on the Imperial Valley because of its extensively developed irrigated agriculture, and because drainage from the Imperial Valley discharges directly into the Sallon Sea National Wildlife Refuge. Agriculture in the Salton Sea area is dependent on water from the Colorado River for irrigation. The diversion of this water to the Imperial and Coachella Valleys via the All-American Canal is regulated by the Kesterson Reservoir occupies only 1,283 of 5,900 acres within Kesterson National Wildlife Refuge. Data and observations from Kesterson National Wildlife Refuge referred to throughout this report usually were obtained from the small Kesterson Reservoir, which is part of the refuge. U.S. Bureau of Reclamation. Most soils in the major growing areas of the Imperial and Coachella Valleys are lacustrine deposits, which, under the influence of irrigated agriculture, have formed partly perched water tables. The presence of water close to land surface and the accumulation of salts from evaporation of water in the soils have required installation of underground tile drains hi fields throughout the Imperial Valley. The drains relieve waterlogging and salt buildup, thereby maintaining a successful agricultural environment. Water from these tile drains eventually discharges into the Salton Sea near the Salton Sea National Wildlife Refuge. Dissolved trace minerals (leached from the soil column) hi the drainwater have been recognized as being potentially harmful to human health and to various wildlife species in other irrigation projects such as Kesterson Reservoir in Kesterson National Wildlife Refuge. Determining the composition of drainwater and its effects on receiving-water quality and on biota were the main objectives of this irrigation-drainage study. Analysis of available data from the Salton Sea area indicated that contaminants from irrigation drainage in the Imperial and Coachella Valleys are adversely affecting the water quality and the health of the fish and wildlife using the Salton Sea National Wildlife Refuge. Existing and potential effects include: o High levels of selenium hi edible portions of fish hi the Salton Sea. An Imperial County health advisory has been issued limiting the consumption of fish caught in the Salton Sea to 4 ounces per 2-week period. o Selenium contamination of waterfowl in the Salton Sea area may reach levels that have been associated with reproductive failure. o Organochlorine pesticide residues hi rivers and drains may pose a threat to reproductive success of waterfowl. In addition to these concerns, (1) the Salton Sea is the terminus of three major rivers conveying over 1 million acre-ft/yr of irrigation return water; (2) the Salton Sea has few other sources of freshwater and has no outlet; (3) the salinity of the Salton Sea has increased over the past 80 years due to evaporation produced by the high average annual temperatures over the large surface area of the Salton Sea; and (4) the Salton Sea National Wildlife Refuge supports the most diverse bird populations of any national wildlife refuge and is the breeding ground for several endangered species. As a result, there is a high level of concern about the water quality of the Salton Sea and the future of its wildlife. Purpose and Scope This report presents results of a study to determine the impact of irrigation drainage from water supplied by the U.S. Bureau of Reclamation on downstream uses, especially the effect on fauna of the Salton Sea National Wildlife Refuge. The specific objectives of the study were to: (1) Determine concentrations of selected pesticides and trace elements in the water and bottom sediments of the Salton Sea and of streams and drams conveying agricultural effluent. (2) Determine concentrations of selected pesticides and trace elements hi the wildlife and fish of the Salton Sea National Wildlife Refuge. (3) Evaluate available data to determine if elevated leve