Modeling the Impact of Water Quality and Food Web Structure on Bull Trout in Two Washington Reservoirs

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World Environmental and Water Resources Congress

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Mechanistic models of the hydrodynamics and water quality were developed for Lake Kachess and Lake Keechelus in the Yakima River basin of Eastern Washington. These models were coupled to a fish bioenergetics model and used to explore management strategies to improve water quality in the reservoirs affecting kokanee production. The models were also applied to evaluate the impacts of the proposed implementation of the Kachess Drought Relief Pumping Plant (KDRPP) projects. The public domain model, CEQUAL-W2 Version 4 (Cole and Wells, 2016) was adapted to model the reservoirs. CEQUAL-W2 is a 2-dimensional (longitudinal-vertical) hydrodynamic and water quality model capable of predicting water surface, velocity, temperature, nutrients, multiple algae, zooplankton, periphyton, and macrophyte species, fish bioenergetics, sediment diagenesis, dissolved oxygen, pH, alkalinity, multiple CBOD groups, multiple suspended solids groups, multiple generic constituents (such as tracer, bacteria, toxics), and multiple organic matter groups, both dissolved and particulate. The model is set up to predict these state variables at longitudinal segments and vertical layers. Comparisons of field data to model predictions were made for water level, temperature, NH4-N, NO3-N, PO4-P, total N, Total P, total organic carbon, alkalinity, zooplankton, pH, chlorophyll a, and dissolved oxygen at multiple reservoir sites at various depths.

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