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

Document Type

Presentation

Journal/Book Title/Conference

SETAC

Publication Date

2009

Keywords

eutrophication, cyanotoxin, Farmington Bay

Abstract

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.

This document is currently not available here.

Share

COinS