INVESTIGATING THE SOURCE WATERS, SALINITY, NUTRIENTS, AND SELENIUM IN THE SALTON SEA WILDLIFE AREA

Our study of the Niland Wister Unit Wetlands along the eastern shores of the Salton Sea focused on the hydrology and hydrochemistry of the area. We investigated salinity, selenium, phosphorus, nitrate levels, and the origins of water inputs. The primary water sources included imported Colorado River water, local agricultural drainage, and a minor contribution from native groundwater through natural springs and mud features. The Colorado River water showed salinity levels between 700 and 750 mg/L total dissolved solids (TDS). In contrast, salinity in agricultural drain water was highly variable, ranging from 1,400 to 8,000 mg/L TDS. Selenium concentrations in Colorado River water averaged 1.3 µg/L, whereas agricultural drainage displayed a broader range, from 2 to 41 µg/L, frequently surpassing the aquatic standard of 5 µg/L. There was a notable positive correlation between TDS and selenium, suggesting evaporative concentration processes in the shallow aquifer beneath the agricultural fields and showing no evidence of nitrate-facilitated oxidation of selenium. Isotopic analyses using stable water isotopes indicated that most agricultural drain water followed an evaporation line derived from Colorado River water. Unique among local mud features, the Niland moving mud pond, characterized by high levels of TDS (approximately 17,500 mg/L) and enriched in carbon dioxide and hydrogen sulfide gases, appears to source predominantly from evaporated Colorado River water. This pond has shown lateral movement towards the Salton Sea, likely responding to hydraulic gradients influenced by the lake's recession. Our hydrogeological model proposes that the groundwater at the Niland moving mud pond was recharged during historical events, such as the 1906 flood or through more recent seepage from unlined canals and fields. This groundwater interacted with evaporites from ancient playa deposits and absorbed gases from deep magmatic sources as it migrated, eventually surfacing at the mud pond. This study provides insights into the complex interactions of imported water, agricultural practices, and geological features influencing the hydrochemistry of the Salton Sea wetlands.