Methods to identify areas susceptible to irrigation-induced selenium contamination in the western United States

Assessing the effectiveness of land and water management practices on nonpoint source nitrate levels in an alluvial stream–aquifer system

“…Within the root-soil zone, NH 4 can undergo nitrification to NO 3 , which then can be denitrified to N 2 depending on water content and availability of organic carbon (OC). Both O 2 and NO 3 can undergo autotrophic chemical reduction in the presence of pyrite (FeS 2 ), which is present in bedrock shale formations and shale outcrops in many alluvial river valleys in the western United States (Seiler, 1995;Seiler, 1997). Carbon (C) and N cycling in the soil-plant system also is included, with organic C and N present in decaying roots and after-harvest plant stover added to the soil organic matter pool following plowing and harvest and apportioned to a fastdecaying pool (Litter L N ) and a slow-decaying pool (Humus H N ).…”

The Influence of Nitrate on Selenium in Irrigated Agricultural Groundwater Systems

“…Also, SeO 4 can be produced through oxidation of residual Se by O 2 or NO 3 (Fig. 1), for example in the oxidation of FeSe 2 within geologic formations: (Seiler, 1995(Seiler, , 1997. Methods of removing soluble Se species from environmental waters include (i) reducing SeO 4 , which sorbs weakly (Ahlrichs and Hossner, 1987;Neal and Sposito, 1989) to SeO 3 , which sorbs strongly (Ahlrichs and Hossner, 1987;Balistrieri and Chao, 1987) via the process in Eq.…”

“…[3] and [4] are likely the cause of Se contamination of surface water in regions underlain by marine sedimentary rocks such as shale. The National Irrigation Water Quality Program study, conducted between 1986 and 1993 in 26 irrigated regions within 14 states of the western United States, demonstrated that toxic levels of Se concentration in agricultural drainage waters typically occur when irrigated aquifer systems are underlain by marine shales (Seiler, 1995, 1997).…”

Methods for evaluating potential sources of chloride in surface waters and groundwaters of the conterminous United States

“…Animal waste, as a point source at animal-feeding operations or as a diffuse source when spread on fields, is a source of chloride, nutrients, hormones, pharmaceuticals, bacteria, and viruses (Ruhl, 1999;Hooda and others, 2000;Arnon and others, 2008;Showers and others, 2008). Irrigation water contains chloride and other contaminants, evapotranspiration can concentrate contaminants, and infiltration of excess irrigation water in agricultural suburban and urban areas may mobilize nutrients, herbicides, pesticides, fungicides, selenium, and other constituents (Wagner and others, 1996;Seiler, 1997;Seiler and others, 1999;Paul and others, 2007). Return flows from oil and gas development wells commonly contain high concentrations of chlorides as well as radioactive constituents and hundreds of organic chemicals that may be toxic, carcinogenic, mutagenic, or endocrine disrupting (Kharaka and others, 2005;Zielinski and Budahn, 2007;Colborn and others 2010;Wilson and Van Briesen, 2013; Kassotis and others, 2014;Vengosh and others, 2014).…”