Extreme Eutrophication and Cyanotoxin Levels in Farmington Bay, A Polluted Embayment of the Great Salt Lake, Utah

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eutrophication, cyanotoxin, Farmington Bay


The Great Salt Lake of Utah is surrounded on its eastern and southern shores by 1.4 million people, with projections of 5 million by 2050. Agricultural, industrial and particularly secondary-treated domestic wastes from this population flow primarily into Farmington Bay, a 280 km2 shallow "estuary" with a mean depth near 0.5 m. Fish are rare but bird use is extensive and massive mortalities of waterfowl and shorebirds have occurred in the bay. Phosphorus loading rates of >2 g m-2yr-1 cause hypereutrophic conditions: Secchi depths are usually 0.6 mg/L, mean Chl. a is 179 ug/L and the combined trophic state index (TSI) is 85. Brine shrimp grazing can ameliorate (Secchi >1 m) the hypereutrophic conditions, but these grazers are rarely abundant due to predation from air-breathing corixid insects and/or the severe water quality in the bay. Surface water salinities in the bay range seasonally and with drought cycles from 0.2 - 9% and exert primary control on the biotic community. A 15% salt wedge also enters from the main lake. Nocturnal anoxia in the entire water column is common. Anoxic and reducing conditions within the salt wedge produce hydrogen sulfide concentrations >8 mg/L, and when windstorms mix this H2S into the overlying water, the entire water column has gone anoxic for >2 d. At salinities of 1-5%, field sampling and bioassays have demonstrated excessive growth of the nitrogen-fixing cyanobacteria (Nodularia spumigena). These produce concentrations of the cyanotoxin nodularin that frequently exceed the WHO's health advisory limit and have exceeded 100 ug/L. In comparison to Farmington Bay, the trophic states in the main lake (Gilbert Bay) and shallow Bear River Bay are much lower (respective mean Chl. of 18 and 32 ug/L). The eutrophication is discussed relative to the sociopolitical climate that until recently has largely neglected water quality issues in North America's largest salt lake.

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