Biostromes, brine flies, birds and the bioaccumulation of selenium in Great Salt Lake, ,Utah

Benthic organisms and substrates in Great Salt Lake, Utah, were sampled to measure selenium concentrations of prey organisms of the birds that utilize the lake for nesting and during migrations. The sampling was focused on stromatolite biostromes, as these solid reef-like structures cover approximately 23% of the oxic benthic area of the lake and are the principal habitat for brine fly (Ephydra cinerea) larvae and pupae. Samples were taken at depths of 1-5 m along two transects in Gilbert Bay where salinities ranged from 116–126 g l. Periphyton on the biostromes had chlorophyll levels of 700 mg m, and contained approximately 68% of the chlorophyll in the lake’s phytoplankton. Consequently, the biostromes represent a significant component of the lake’s primary production. A 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 the bay. Brine fly larvae and pupae were far more abundant on the biostromes than on the soft substrates, with respective mean densities of 9100 m, 530 m and 240 m, on biostromes, sand and mud. Total brine fly biomass on biostromes averaged 5.9 g m, which is about 30% of the biomass present in brine shrimp (Artemia franciscana) in the water column. The mean selenium concentration in the combined organic matter-inorganic substrates of biostromes sampled in 2007 was 0.3 ± 0.1 g g dry weight. However, when the inorganic carbonates were removed with acid, the remaining organic matter had selenium concentrations of 1.0 ± 0.1 g g dry weight. Mean Se concentrations in larvae, pupae and adult brine flies were 1.3, 1.5 and 1.8 g g dry weight, respectively, but the differences were not significant. Although there was a 2500X bioconcentration factor between total dissolved Se (mean = 0.40 g l) in the overlying water and in the periphyton of the biostromes, the limited data suggested that there was little biomagnification between the periphyton and the brine flies. A review of the diets of birds utilizing Great Salt Lake and other saline lakes suggests that brine fly produced on biostromes are an important diet component for goldeneye ducks (Bucephala clangula), American avocets (Recurvirostra americana), black-necked stilts (Himantopus mexicanus) and California gulls (Larus californicus) and perhaps other birds utilizing the lake. Consequently the benthic food web may be important route for uptake of metal contaminants in these birds in Great Salt Lake. The high selenium concentrations in goldeneye ducks that feed on brine flies suggests that proposed increases in the loading of this contaminant should be reviewed carefully by managers. High mercury levels in goldeneyes suggest that the food web on the lake’s biostromes may be an important pathway for other metals into birds.