The Effects of a Recurrent Spring Plume on the Dynamics and Structure of the Lower Food Web in Southern Lake Michigan

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9726681 Gardner Research will be undertaken in response to an Announcement of Opportunity (NSF 97- 38)for Coastal Studies in the Great Lakes. This is a collaborative research project between investigators from ten academic and government research institutions. The research is being conducted under the auspices of the NSF Coastal Ocean Processes (CoOP) program and the NOAA Coastal Ocean Program. This collaborative, 5-year research program will focus on the importance of episodic events on nearshore-offshore transport and subsequent ecological consequences. The study seeks to 1) determine what processes control the cross-margin (inshore to offshore) transport of biological, chemical, and geological materials in the coastal margins of the Great Lakes, and to 2) develop and test scientific strategies for assessing, quantifying, and predicting the impacts of multiple stresses both natural and anthropogenic, in the Great Lakes or selected coastal sub-regions. A tight coupling between contaminated sediments and overlying water exists in lakes and coastal ecosystems through the process of sediment resuspension. Satellite observations in Lake Michigan illustrate an annually recurrent episode of nearshore-offshore transport, a 10 km wide plume of resuspended material extending over 200 km along the southern shores of the lake. Preliminary evidence indicates that this episodic event may be the major mechanism for cross-margin sediment transport in Lake Michigan. This type of event impacts recycling of biogeochemically important materials (BIMS), ecosystem responses, cross-isobath transport in the Great Lakes. The program results will be applicable to similar events in many coastal areas. This comprehensive, interdisciplinary study will implement an integrated observational program and numerical modeling effort to identify, quantify, and develop prediction tools for the winter-spring resuspension event and to assess the impact of this event on the transport and transformation of BIMS and on lake ecology. This component of the study focuses on structure and abundance of microbial food web organisms before, during, and after plume formation; measure Nitrogen cycling rates in relation to community and species-specific grazing rates of microzooplankton within, at the edge, and outside of the plume. Observations, experiments, and results will be coordinated with those from primary production and zooplankton grazing experiments and other studies of nutrient and physical processes to complete a conceptual model and provide data for the proposed coupled biological/physical model.