Selenium concentrations in Yuma Ridgway's Rails occupying managed and unmanaged emergent marshes at the Salton Sea

Yuma Ridgway's rail (Rallus obsoletus yumanensis, hereafter, "rail" are an endangered species for which patches of emergent marsh within the Salton Sea watershed comprise a substantial portion of habitat for the species' disjointed range in the southwestern United States. These areas of emergent marsh include: 1) marshes managed by federal (particularly the U.S. Fish and Wildlife Service's Sonny Bono Salton Sea National Wildlife Refuge (SBSSNWR), state (California Department of Fish and Wildlife), and local (Imperial Irrigation District) resource agencies that are sustained by direct deliveries of Colorado River water; and 2) unmanaged marshes sustained by agricultural drainage water. Management of rail habitat in this arid environment is complicated by increasingly limited availability of unimpaired freshwater owing by recent water management decisions associated with the Quantification Settlement Agreement, and risks posed by potentially harmful concentrations of selenium (Se) found in agricultural drainage water that can readily bioaccumulate in aquatic food webs. These data comprise selenium concentrations and associated locations and dates of the following matrices sampled to describe pathways of selenium exposure to rails occupying managed and unmanaged marshes: 1) unfiltered surface water, midge larvae (Chironomidae), water boatmen (Corixidae), mosquitofish (Gambusia spp.) and crayfish (Astacidae). Selenium samples were collected from 15 fixed sampling points each in managed and unmanaged marshes during late February, April, and June of 2016, which corresponded to rail pre-nesting, nesting, and fledgling reproductive life-stages, respectively. Two areas within the two treatment types (managed vs. unmanaged marsh) were of particular interest to help assess risks associated with changing Sea dynamics and different water management strategies: 1) a large unmanaged marsh (Morton Bay) unintentionally created in approximately 2008 when it became separated from the Salton Sea as water inflows began to drop and a berm formed from accumulated sediment; and 2) a restored marsh (HZ-9A) managed by the SBSSNWR, which is currently supplied with Colorado River water, but may be sustained in the future by a blend of clean (that is, low Se) Colorado River and agricultural drainage water with higher Se from the Alamo River.