Selenium in aquatic habitats at Imperial National Wildlife Refuge

Abstract

During 1991 and 1992, I studied environmental contamination of the aquatic communities at Imperial National Wildlife Refuge on the lower Colorado River. I collected composite samples of sediment, detritus, aufwuchs, aquatic plants, invertebrates, and fishes from 2 river sites, 5 backwater lakes, and 2 seepage lakes. Selenium concentrations (μg/g, dry weight) were elevated in sediment (geometric mean = 0.93, range = none detected (ND) to 4.1); detritus (4.50, 0.4-27.4); aufwuchs (4.85, 2.6-10.2); Najas marina (5.66, ND-21.0); Corbicula spp. (10.54, 5.8-26.5); Procambarus clarkii (7.70, 1.5-35.8); whole fishes (6.70, 1.6-17.2); and fish fillets (9.72, 5.8-22.6). Ninety-four percent of whole fishes and invertebrates (n = 185) contained concentrations of selenium that exceeded 3 μg/g, a concentration recommended by the U.S. Fish and Wildlife Service to protect aquatic birds from chronic selenium toxicity. Biological samples from seepage lakes had significantly lower (p ≤ 0.05) selenium levels than similar samples from backwater lakes. Selenium is incorporated into plants in backwater lakes and enters consumers primarily through the detrital food web.