'Comparative analysis of eutrophication in three bays of the Great Salt Lake.'
Wayne Wurtsbaugh (email@example.com), Utah State University; Amy Marcarelli (firstname.lastname@example.org), Department of Biological Sciences, Michigan Technological University, Houghton, MI
The Great Salt Lake is bordered by an extensive metropolitan area that discharges its secondary-treated wastewaters to the ecosystem. To compare how three bays of the lake respond to different levels of nutrient loading we measured eutrophication parameters over several years. Farmington Bay, which receives the most direct and highest nutrient loading, was hypereutrophic with mean summer total phosphorus levels of 0.4 mg/L and chlorophyll levels of 141 ?g/L. In contrast, Bear River Bay which receives less metropolitan wastes, had phosphorus levels of 0.21 mg/L and chlorophyll levels of 22 ?g/L. The largest part of the lake, Gilbert Bay, had high phosphorus (0.32 mg/L) and nitrogen concentrations (4.7 mg N/L—the limiting nutrient), but chlorophyll levels were only 17 ?g/L, in part because of strong top-down control on phytoplankton by brine shrimp grazers. Cyanotoxin concentrations in Farmington were extremely high (> 50 ?g/L) and far exceeded World Health Organization criteria when salinities were in the 2-5% range that permitted the cyanobacteria Nodularia spumigena to bloom. The toxin concentrations in Farmington Bay were well above those found to have caused bird mortalities in other systems. Farmington Bay’s high phytoplankton production led to super-saturated oxygen concentrations during the day, but very low oxygen concentrations at night as a result of respiration and phytoplankton decomposition. In Gilbert Bay, oxygen levels were near saturation and varied little over 24 hours. Additionally, the bottom waters of approximately 50% of the area of both Farmington and Gilbert Bays were devoid of oxygen, contained high concentrations of toxic hydrogen sulfide, and consequently could not support aquatic invertebrate life. These “dead zones” are due to the combined effect of the stable salt-stratification caused by diking, and the phytoplankton that fall into these lower layers and decompose. The implication of eutrophication in the bays is discussed relative to the Beneficial Uses of these distinct ecosystems.