Development and Calibration of Lake Whatcom Water Quality Model

A water quality model of Lake Whatcom, Washington was developed as part of a Total Maximum Daily Load Study. Lake Whatcom is a large natural lake which was first listed on the 1998 Washington State 303(d) list of water bodies that do not meet the criterion for dissolved oxygen. Located next Bellingham, it is approximately 10 miles long, has a surface area of approximately 5000 acres, and a maximum depth of over 100 meters. Residence time is approximately 5-10 years. Lake Whatcom is within a relatively small watershed, and the lake's surface area is large in comparison to the size of its watershed. Eutrophication processes in the lake have been facilitated by the availability of nutrients, leading to concerns about development within the watershed. The lake is being modeled using the Corps of Engineer's model CEQUAL-W2, which is a two-dimensional model consisting of directly coupled hydrodynamic and water quality transport models. Primary physical processes simulated were surface heat transfer, short-wave and long-wave radiation and penetration, convective mixing, wind and flow induced mixing, inflow density stratification as impacted by temperature and dissolved and suspended solids. Major chemical constituents and biological processes simulated include: atmospheric exchange on DO, photosynthesis, respiration, organic matter decomposition, nitrification, and chemical oxidation of reduced substances; uptake, excretion, and regeneration of phosphorus and nitrogen and nitrification-denitrification under aerobic and anaerobic conditions; carbon cycling and alkalinity-pH-CO2 interactions; trophic relationships for 3 phytoplankton species; and the accumulation and decomposition of detritus and organic sediment. For this application phosphorus and nitrogen organic matter compartments were added specially to represent the phosphorus (P) and nitrogen (N) mass contained in dissolved and particulate organic matter and the sediments. Thus the stoichiometry of the organic matter is variable and the user is able to set dynamic values of N and P in all tributaries associated with organic matter and to track these quantities within the domain of the CE-QUAL-W2. There were also sufficient data to model 3 phytoplankton species: diatoms, greens, and blue-greens. The project is managed by the Washington Department of Ecology who plans to make recommendations for reduction and allocation of pollutant loads.