Modeling Study of Phytoplankton Responses in Lake Michigan to a Changing Climate

Physical factors such as water temperature, water column mixing, and light are crucial for the phytoplankton abundance and primary production in Lake Michigan. The potential impacts of climate change on these factors could significantly affect the dynamics of Lake Michigan's phytoplankton. In this study, we employed an integrated modeling framework to project the impact of climate change. This framework included a two-way coupled 3D lake-ice–climate system (GLARM), a hydrodynamic model (FVCOM), and a nutrient-phytoplankton-zooplankton-detritus (NPZD) model, further enhanced by a compartment representing the invasive quagga mussel (Dreissena rostriformis bugensis). Our approach encompassed historical simulations for the period 2005–2014, as well as two sets of future projections for the mid-21st century (2041–2049) and the late 21st century (2091–2099), utilizing the Representative Concentration Pathway (RCP) 8.5 scenario. Our findings indicate that changes in water temperature and water column mixing significantly influence the seasonal patterns of phytoplankton abundance and primary production. These changes notably alter the timing and magnitude of the winter-spring phytoplankton bloom and the depth of the chlorophyll layer. Furthermore, the model predicts an increase in primary production under the projected climate scenarios, with significant variations in both spatial and seasonal patterns.