Influence of environmental conditions on late-summer cyanobacterial abundance in Saginaw Bay, Lake Huron

The relationships among environmental conditions and phytoplankton assemblages were characterized during late summer (2003-2005) in Saginaw Bay, Lake Huron. Differences among sampling stations, arising primarily from spatial disparities in water-column optical properties and nutrient availability, were evident. Cyanobacteria and diatoms dominated phytoplankton assemblages, with the greatest total chlorophyll a concentrations occurring at the innermost portions of the Bay. Microcystis abundance was greatest in the Bay's upper reaches and decreased with increasing distance from the mouth of the Saginaw River. A suite of variables, indicative of annually-distinct meteorological and hydrological conditions and phosphorus-laden inflows, were identified to (collectively) best ‘group’ stations in a manner consistent with that of phylogenetic-group chlorophyll a concentrations and cyanobacterial biovolumes. However, a great deal of variability between abiotic and biotic patterns remained unexplained and several abiotic variables singularly corresponded with Microcystis abundance. Taken together, it appears that multiple environmental conditions (including annual/episodic meteorological patterns, seasonal/intermittent riverine inflows, annual phosphorus loading, etc.) interact with taxon-specific physiological traits to holistically influence late-summer phytoplankton abundance throughout inner Saginaw Bay.