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Utah Wetlands Foundation

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eutrophication, cyanobacteria, blue-green algae, Nodularia, birds, waterfowl, botulism, saline, Great Salt Lake, nutrients, hypereutrophic, cyanotoxins, HAB


Massive bird mortalities due to botulism occur in Farmington and Bear River Bays in the Great Salt Lake. During 2007 we investigated whether there could be a relationship between blooms of the toxic cyanobacteria, Nodularia spumengia and botulism outbreaks in Northern Shoveler ducks and other birds. Our limnological analyses indicated that Farmington Bay was hypereutrophic, with chlorophyll concentrations reaching more than 100 μg/L on most dates in the summer. The extreme eutrophication led to nighttime anoxia, even in sites as shallow as 30 cm. In 2007 cyanotoxin (nodularin) concentrations were moderately high (> 20 μg/L) in May and June, but declined when salinities rose above 50 g/L and Nodularia disappeared. Because of the high salinity, cyanobacterial densities were much lower in 2007 than have been observed previous and subsequent to the study. In 2007 bird mortalities were minimal and there was no major outbreak of botulism. Analyses of American Avocet and Northern Shoveler livers indicated that cyanotoxin levels were below levels of detection. Although cyanotoxin levels in Farmington Bay are well above those that have caused bird and mammal mortalities elsewhere, further analyses of bird mortalities during years of high cyanobacterial blooms and botulismrelated mortalities will be necessary to rigorously test the hypothesis that cyanotoxins initiate the botulism outbreaks.

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