90Y/90Sr and 234Th/238U disequilibria: Using dual chronometers to measure the effect of invasive dreissenid mussels on particle dynamics in Lake Michigan.

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In this project, researchers at the University of Wisconsin at Milwaukee will continue their research into the fluxes, pathways and residence times of particles and their associated nutrients and energy in nearshore waters of Lake Michigan. Their overall objective is to further explore the use of dual fast process chronometers (90Y/90Sr) and 234Th/238U disequilibria) as tracers of rapid particle dynamics. In Lake Michigan, dreissenid mussels now dominate these nearshore dynamics and the project objectives, therefore, focus on this influence. There are three specific objectives: (1) Examine what effect the in situ benthic mussel population density has on in situ particle (nutrient) removal from the water column. (2) Examine what effect an in situ benthic mussel population has on in situ particle (nutrient) removal under seasonally changing thermal conditions. (3) Examine the residence time of mussel-filtered particles (in the form of feces and pseudo-feces) and the inventory of 90Y and 234Th on the nearshore non-depositional lake bed. Broader Impacts: Coastal zones are under increasing nutrient and toxic stress, and developing and improving techniques for tracking suspended materials on short time-scales will have broad applicability in both Great Lakes and marine biogeochemistry. Understanding the transport of contaminants is also relevant to the heightened concerns over water security, particularly in the Great Lakes from which nearly 40 million people draw drinking water. The utility of radionuclides as tracers for following and quantifying environmental processes is an expanding field, and novel radionuclide techniques have wide potential application in limnology, oceanography, ground water and surface water hydrology, and terrestrial-aquatic system coupling. These tools are an essential component of the environmental research toolbox. Relatively few laboratories in the Great Lakes region are capable of making radiometric measurements; improving this capability has regional importance.