Three-dimensional management model for lake Washington, Part II: Eutrophication modeling and skill assessment

Abstract

The CE-QUAL-ICM 3-dimensional eutrophication model was applied to Lake Washington for the period 1995–1997. Transport processes were obtained from the companion CH3D-WES hydrodynamic model. The model activated 18 state variables in the water column, including physical variables; phytoplankton; multiple forms of carbon, nitrogen, and phosphorus; dissolved oxygen; and fecal coliform. The water column was coupled to a sediment diagenesis model that computed sediment-water fluxes of dissolved oxygen, methane, ammonium, nitrate, and phosphate, based on computed inputs of particulate organic matter. The model successfully computed the annual cycles and spatial distributions of key water quality components. Nutrient loads were calculated and nutrient budgets were constructed as part of the model exercise. Load sources included river inflows, distributed loads, sewer overflows and atmospheric loading. The Sammamish River was identified as the largest source of nutrients to Lake Washington, followed by the Cedar River and other distributed sources. The majority of the nutrient load is deposited in the sediments. A lesser amount leaves via Lake Union. Our nutrient loads were 30% (nitrogen) to 60% (phosphorus) higher than the loads from the late 1970s. © 2006 Taylor & Francis Group, LLC.