Quantifying Nutrient and Energy Flows in Aquatic Food Webs

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Ecological systems are being modified by climate change. The Laurentian Great Lakes have the second fastest rates of warming in the world, and it is essential to develop new models and novel techniques that allow us to predict and measure the effects of climate change on aquatic ecosystems. We will address this challenge with the further development of non-steady state bioaccumulation models as well as the verification of the use of persistent organic pollutants (POPs) and mercury as environmental tracers to quantify energy and nutrient flow in aquatic food webs. These two research initiatives are interactive and interdependent in that non-steady state models have relatively high data requirements, needing information on growth rates, foraging strategies and seasonal metabolic processes that regulate contaminant uptake and elimination processes. We propose four projects. First we will investigate chemical accumulation dynamics in lake trout and salmon in the food web of Lake Huron which is in a state of collapse. We will use the non-steady state model approach to estimate energy requirements of the fish and measure the relative contribution of these fish to nutrient recycling and fate in Lake Huron. It is predicted that lake trout provide a critical role in nutrient recycling whereas salmon are primarily a nutrient loss vector. The decline in lake trout populations combined with the stocking of salmon is suggested to have contributed to the food web collapse in this system. The second study aims to expand the calibration of the non-steady state model from POPs to include mercury as an environmental tracer. Mercury exhibits a much higher assimilation efficiency than POPs, but little is known what regulates the assimilation of Hg from food in fish. We will examine the role of protein dynamics/kinetics to gain more insight as to what makes Hg a super-accumulator in fish. Thirdly, there is a strong relationship between fish consumption rates and body mass which follows the Three Quarter Power Law. We will use both POPs and Hg as