Harmful algal blooms in the Great Salt Lake (Utah): Salinity, nutrient and top-down controls

Agricultural, industrial and particularly secondary-treated domestic wastes from metropolitan Salt Lake City flow into Farmington Bay, a 280 km2 shallow estuary of the lake with salinities ranging from 0-90 g/L. Heavy nutrient loading causes hypereutrophic conditions (mean Chl. 166 µg/L), nighttime water column anoxia, odor problems and massive blooms of the cyanobacteria Nodularia spumigena. Mean cyanotoxin concentrations in the bay were 124 and reached 663 µg/L Microcystin LR equiv. in a year when salinities remained within Nodularia’s tolerance. Longitudinal transects and laboratory experiments indicate that Nodularia’s salinity tolerance is between 10 and 50 g/L. Additionally, bioassay experiments indicate that algal growth is controlled initially by nitrogen, but secondarily by phosphorus limitation of nitrogen fixation by Nodularia. Brine shrimp can reduce the algal blooms, but these grazers are in-turn limited by predacious corixids during summer. Bird use of the estuary is extraordinary, and mortalities occur, but these have not yet been linked to cyanotoxins. Fish use is limited to freshwater areas. These last factors contribute to a socio-political climate that is resistant to reducing eutrophication and HABs in the bay