Chemistry and evolution of desert ephemeral stream runoff

Abstract

The study investigates how water chemistry evolves as ephemeral stream runoff is formed through the interaction of sediments and precipitation in the Amargosa Desert region and by analogy other desert regions. In this study, thirty lysimeters were installed in the major arroyos in the Amargosa Desert to capture runoff water. The sampling process included sediment, precipitation, and runoff water chemistry. Innovative and low cost methods were used to measure the chemical composition of the resulting runoff and examined some of the important processes affecting the runoff chemistry. Results of the analytical and statistical analyses indicate that runoff salinity is low as a result of net salt accumulation in sediments. Chemical behavior between precipitation and runoff is classified as leached (TDS, alkalinity, Ca, Mg, K, Na, Ba, Cs, Li, Sr, Fe, Ni), nutrient (Br, As, SO42−, PO43−, NO3−, Rb, B, Cu, Zn, V), scavenged (U, F), and conservative (Al, Mo, Mn). Bromide behaves as a nutrient meaning the chloride/bromide ratio, a common tracer of groundwater sources, is not conservative. Runoff chloride, sulfate, and sodium are predominantly associated with concentrations of the same ions in sediment. Trace elements are more closely associated with precipitation chemistry.