Impacts of Climate Change on Phytoplankton Dynamics in Lake Michigan: A Biophysical Modeling Study

Physical factors such as water temperature, water column mixing, and light availability play critical roles in determining phytoplankton abundance and primary productivity in Lake Michigan. This study investigates the potential influence of climate change on these critical environmental factors and, consequently, on the dynamics of Lake Michigan's phytoplankton. To achieve this, we utilized an integrated modeling framework comprising a two-way coupled 3D lake-ice–climate system model (GLARM), a hydrodynamic model (FVCOM), and a nutrient-phytoplankton-zooplankton-detritus (NPZD) model, including a module representing the invasive quagga mussel (Dreissena rostriformis bugensis). Our methodology involved conducting historical simulations covering the period from 2005 to 2014 and projecting future scenarios for two distinct timeframes: the mid-21st century (2041–2049) and the late 21st century (2091–2099), based on the Representative Concentration Pathway 8.5 scenario, often referred to as the 'business as usual' scenario. The findings of our study highlight that changes in water temperature and mixing dynamics significantly alter the seasonal patterns of phytoplankton, particularly affecting the timing and intensity of winter-spring blooms as well as the vertical distribution. Specifically, our projections indicate a likely weakening and delay of mid-depth and offshore winter-spring blooms due to diminished winter stratification and altered spring turnover. Additionally, the onset of the deep chlorophyll layer is anticipated to occur 15-30 days earlier in the mid- and late 21st centuries, accompanied by an increased duration resulting from prolonged summer stratification. Our models also show an increase in primary production and a shift in spatial and temporal patterns under the influence of projected climate change scenarios.

Primary Presenter: Xing Zhou, Georgia Institute of Technology (xingzhou@mtu.edu)

Authors:

Pengfei Xue, Michigan Technological University  (pexue@mtu.edu)

Mark Rowe, NOAA - Great Lakes Environmental Research Laboratory  (Mark.Rowe@noaa.gov)

Peter Alsip, Cooperative Institute for Great Lakes Research, University of Michigan  (peterals@umich.edu)

David Bunnell, United States Geological Survey  (dbunnell@usgs.gov)

Tomas Höök, Purdue University  (thook@purdue.edu)

Edward Rutherford, NOAA - Great Lakes Environmental Research Laboratory  (ed.rutherford@noaa.gov)

Paris Collingsworth, Purdue University  (pcolling@purdue.edu)

Spencer Gardner, Purdue University  (gardn125@purdue.edu)