The Impact of a Recurrent Coastal Plume on
Phosphorus Dynamics and Production in Lake Michigan

J. Cotner and T. Johengen

The proposed work will examine the influence of a major episodic event on phosphorus (P) availability and dynamics in the southern basin of Lake Michigan. Efforts will focus on a recurrent coastal plume that develops in the spring. Understanding the impact of episodic events on P availability has important implications for ecosystem structure and function because primary productivity in this system is P-limited.
The goal of this project is to determine the importance of the recurrent coastal plume to transport, composition and biological availability of P. To achieve this goal, we will address the following objectives: (1) To determine the potential sources, distributions and fluxes of P in the recurrent coastal plume; (2) To determine the impact of P associated with the recurrent coastal plume on phytoplankton and bacterioplankton production in Lake Michigan; and (3) To determine the impact of biotic utilization and settling on P composition and availability within the plume.
These objectives will be fulfilled by examining the geochemical composition and mineralogy of suspended particles, and the effects of these particles on biological processes. Specifically, we will examine the impact of these suspended particles on microbial (heterotrophic bacteria and phytoplankton) community productivity and nutrient limitation through a combination of bioassays (growth rate measurements, alkaline phosphatase activity), nutrient chemistry and stoichiometry, and P regeneration rates.
The proposed work will address both NSF and NOAA goals. It will contribute to the understanding of the processes controlling transport of a potentially limiting nutrient (P) from nearshore to offshore regions and especially the impact of sediment-water interactions and biological transformations. It will also provide insight into the potential impact of major episodic events that deliver large quantities of non-point source material on nutrient cycling and productivity in the Great Lakes.