Spatial and temporal trends of nutrients in Saginaw Bay (Lake Huron) during summer 2008

Synergistic effects of multiple stressors may result in unexpected impacts in aquatic ecosystems.  We seek to identify impacts of multiple stressors in Saginaw Bay, MI, a coastal system simultaneously impacted by stressors such as invasive species, changing land-use, and climatic change.  As part of a larger project we are investigating correlations among nutrients, algal blooms and invasive species.  High nutrient levels promote algae blooms which can lead to depleted oxygen, extremely low levels of soluble reactive phosphorus (SRP), and eutrophication.   Our initial investigations involved examining nutrients (i.e. total phosphorus, SRP, particulate C, N, P, dissolved organic carbon, TDP, NO₃, and NH₄) from 17 locations in the bay three times during 2008 to determine how well the spatial and temporal distribution of nutrients correlates with chlorophyll a and algal blooms.  We did not observe any apparent algal blooms during sampling.  However, we found both nutrient levels (particularly TDP and NH₄) and chlorophyll a to be highest in nearshore sampling stations compared with offshore sites and highest during the late summer.  Trends relating nutrient concentrations with phytoplankton productivity in Saginaw Bay will be discussed.  Understanding the factors contributing to eutrophication is a start to understanding impacts due to additional stressors.