Selenium hazards in the Salton Sea environment—Summary of current knowledge to inform future wetland management

First posted July 20, 2023 For additional information, contact: Director,California Water Science CenterU.S. Geological Survey6000 J Street, Placer HallSacramento, California 95819 Quaternary marine and continental shales in the western United States are sources of selenium that can be loaded into aquatic environment through mining, agricultural, energy production processes. The mobilization from agricultural irrigation has been recognized since 1930s; however, discovery deformities birds other wildlife using habitats during 1980s spurred studies to determine extent effects contamination. Through these early studies, researchers determined biota Salton Sea drainage basin was at risk legacy contamination Colorado River watershed.The its surrounding managed unmanaged wetlands provide vital inland habitat trophic support for diverse assemblages resident migratory wildlife, understanding regional hazards trust species is a priority many Federal State agencies. modern shallow, landlocked saline lake Riverside Imperial Counties (not shown) sustained by return perennial river inflow. Changes water transfer agreements under 2003 Quantification Settlement Agreement (QSA) have resulted reduced flow, declining levels, evolution areas where drains rivers no longer reach Sea. These some concern, but their potential increase largely unknown.From 2020, efforts document throughout region considerable amount data basin; long-term (greater than 20 years), consistent sampling program established, all collected different entities variety protocols analytical techniques. This lack coordination previously documented management plans led difficulty reliably assessing environment. report provides summary available disparate information water, sediment, identify gaps need filled understand on including federally endangered desert pupfish (Cyprinodon macularius) Yuma Ridgway’s Rail (Rallus obsoletus yumanensis; formerly Clapper Rail, Rallus longirostris yumanensis).Available show lowest concentration surface sources. All flowing elevated concentrations due evaporation evapotranspiration occurs fields associated delivery infrastructure or leaching irrigated farmland soils. lower because various biogeochemical processes recycle sediment volatilize it atmosphere; mechanisms not well defined, clear if cycling will change response possible changes oxidation state bottom waters as levels decline. Agricultural highest average concentrations, few sampled practices occurred (due QSA). Groundwater variable; wells south high 300 micrograms per liter (µg/L), whereas below detection wells. surface-water geothermal discharge zones around margins studied detail, published measurements features.Selenium wetland particulate organic matter lakebed, indicating removal primary mechanism keeping low column. Sediment higher inflowing rivers, lentic sites also may important sinks QSA), unknown sequestration column changed systems.We divided biological broad taxonomic categories, producers, invertebrates, herpetofauna, mammals, fishes, facilitate evaluation spatiotemporal trends observed Overall, were substantially greater algae samples compared vascular plant combined. Median several invertebrate taxa (Chironomidae, Formicidae, Corixidae, Corbiculidae Nereididae, Decapoda) exceeded maximum suggested dietary threshold 3.0–4.0 gram (µg/g) dry weight (dw) predators consuming invertebrates food webs. greatest number fish, distributions among locations showed range most U.S. Environmental Protection Agency criterion life (8.5 µg/g dw whole body, 11.3 fillets). median body fish locations, except bairdiella (Bairdiella icistia) drains, individual tilapia spp. (family Cichlidae, genera Tilapia, Oreochromis, hybrids) outlets, mosquitofish (Gambusia affinis) sailfin molly (Poecilia latipinna) drain outlets. avian combined years livers families waders Ibis Threskiornithidae) expected cause toxicosis (10–20 dw), egg above near 6.0 μg/g dw, which conservative value reproductive impairment.Most knowledge we identified interrelated, use integrated approaches address insight drivers behind hazards. Integrated could help cost-effective solutions serve multiple purposes. A comprehensive analysis hydrology, biogeochemistry, food-web inform predictive models bioavailability, uptake subsequent transfer, ultimately forming basis experimental manipulations minimize wildlife. Furthermore, comprehensive, laboratory plan would enable comparison Such suited fill preclude future options habitats, newly formed region.All compiled this two Survey releases: Groover others (2022) De La Cruz samples. releases include publicly Sea, Coachella Valleys. unpublished data.