Preliminary Analyses of Selenium Bioaccumulation in Benthic Food Webs of the Great Salt Lake, Utah

Benthic organisms and substrates in the Great Salt Lake, Utah, were sampled during one week in June 2006 to test collection methodologies for biostromes and soft substrates and to get preliminary information on the selenium concentrations of benthic organisms. The sampling was focused on biostromes, as these solid reef-like structures cover 23% of the oxic benthic area of the lake and are the principal habitat for brine fly (Ephydra cinerea) larvae and pupae that are fed upon by some birds utilizing the lake. Samples were taken at depths of 1-5 m along two transects–one near Bridger Bay and another in the southern area of Gilbert Bay. The biostromes were sampled with a pumped-bucket device operated by a SCUBA diver whereas the soft sediments were sampled with a Ponar grab. Water samples and adult brine flies were also collected. The pumped-bucket sampler effectively sampled brine flies on horizontal surfaces of the biostromes, but not on the sides of the mounded ones encountered in the southern part of Gilbert Bay. Brine fly larvae and pupae were far more abundant on the biostromes than on the soft substrates, with respective mean densities of 240/m 2 , 530/m 2 and 9,140/m 2 on mud, sand and biostromes. In 2006 the mean selenium concentration in the combined organic matter-inorganic substrates in the biostromes was 1.7 ± 0.9 μg/g dry weight. Additional samples collected in 2007 yielded selenium concentrations of 0.3 ± 0.1. However, when the inorganic carbonates were removed, the remaining organic matter had selenium concentrations of 1.0 ± 0.1 μg/g dry weight. Mean Se concentrations in larvae, pupae and adult brine flies in 2006 were 1.3, 1.5 and 1.8 μg/g dry weight, respectively. A 2-way ANOVA indicated that selenium concentrations were significantly higher in Bridger Bay than in Gilbert South (p < 0.000), and in pupae than in larvae (p = 0.046), but the differences were not large. Although there was over a thousand-fold bioconcentration between Se dissolved in the water and in the periphyton of the 3 biostromes, the limited data suggested that there was no further bioconcentration between the periphyton and the brine flies. Although biostromes cover only 18% of the area where phytoplankton can grow in Gilbert Bay, we estimated that the attached periphyton on them have approximately 68% of the chlorophyll contained in the lake's phytoplankton. Consequently, the biostromes represent a significant feature of primary production. The limited data from …