Predicting bed suspension events in a moderate size shallow lake

Abstract

Cyanobacteria harmful algal blooms (cyanoHABs) and their potential to generate toxins are a significant concern to the ecology of lakes because of their potential to suppress the growth of pelagic consumers, and their ability to become negatively buoyant causing deep water-anoxia by decomposition. For humans, the concern is their tendency to accumulate at the shore where they smell bad and can produce toxins degrading recreational uses, or be entrained in drinking water supplies causing health and taste issues. CyanoHABs impact a significant and growing number of freshwater bodies globally and have become a priority issue for many government agencies such as the U.S. E.P.A. and the New York State Department of Environmental Conservation (NYSDEC). Estimates of the bed stress, gathered from an acoustic Doppler velocimeter (ADV), suggest incipient motion of sediment from the bed is possible as a result of near-bed induced stresses produced by turbulence. Elevated ADV beam amplitude levels are interpreted as possible indicators of sediment suspension in support of this hypothesis. An empirical model is constructed and used to predict suspension events using three years of meteorological forcing data. Suspension may be critical to cyanoHAB formation through transport of phosphorus into the illuminated water column where it can stimulate a bloom, and because living cyanobacterial cells that have settled to the lake bottom store phosphorus and when brought up to the illuminated surface waters may rapidly initiate a bloom even without taking up additional phosphorus.