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GLERL 1999 Milestone Reports
GOAL: SUSTAIN HEALTHY COASTS
OBJECTIVE: PROMOTE CLEAN COASTAL WATERS TO SUSTAIN LIVING MARINE RESOURCES AND TO ENSURE SAFE RECREATION, HEALTHY SEAFOOD, AND ECONOMIC VITALITY.
PM: Number of Coastal and Great Lakes States Provided with Improved Predictive Capabilities and Understanding of Environmental Processes.Milestone: Complete final report on Lake Michigan Mass Balance Hydrodynamic Modeling Project, a multi-agency Great Waters demonstration Project under the Clean Water Act designed to improve aquatic contaminant fate and transport modeling so as to improve management of contaminants. The hydrodynamic model is to be used with other modeling efforts to model the fate and transport and bioaccumulation of four different toxic contaminants.
Scientist: D. Schwab
In order to develop improved strategies for management and control of toxic chemicals in the coastal environment, in 1993 the USEPA Great Lakes National Program Office undertook a program to measure and model the transport, fate, and bioaccumulation of four particular chemicals in Lake Michigan: PCB's (industrial compounds once widely used in a variety of products, banned since 1982), trans-nonachlor (a chlorinated hydrocarbon originally registered as a pesticide in 1948, banned by EPA in 1988), atrazine (the most widely used herbicide in U. S. corn and sorghum production), and mercury (a toxic element which occurs both naturally and anthropogenically). The Lake Michigan Mass Balance Study (LMMBS) included a large monitoring program, including tributary inputs, atmospheric inputs, sedimentary processes, and biological processes, and also a modeling program.
The modeling framework for LMMBS (Fig.1) consists of a series of linked submodels which can be divided into three groups: computational transport models, mass balance models, and bioaccumulation models. The computational transport models include a hydrodynamic model to estimate the three dimensional velocity and temperature fields, a wave model, and a sediment and particulate transport model. A surface flux model is used to convert raw meteorological data into gridded estimates of heat and momentum flux suitable for use as forcing functions in the hydrodynamic, wave, and sediment transport models.
Fig. 1. LMMBS Modeling Framework. [Click to download EPS file]
The goals of this project were:
- Implement a surface flux model, a wave model, and a three dimensional hydrodynamic model for Lake Michigan
- Calibrate the models with measurements from wave buoys, current meters and thermistors from the GLERL 1982-83 Lake Michigan field program
- Use the model to simulate waves and three dimensional transport and thermal structure in Lake Michigan during the 1994-95 mass balance study field study period
- Couple the hydrodynamic model with a sediment resuspension and transport model being developed by EPA.
In this study, the POM (Princeton Ocean Model) hydrodynamic circulation model and the GLERL/Donelan wave model were applied to Lake Michigan for two 2-year periods: 1982-1983, and 1994-1995. The first 2-year period was chosen for the model calibration because of an extensive set of observational data including surface temperature observations at two permanent buoys, and current and temperature observations during June 1982 - July 1983 at several depths from 15 subsurface moorings. An example of the comparison between modeled and measured temperatures at a mid-lake station during the 1994-95 LMMBS field study period is shown in Figure 2.
The data collection phase of LMMBS provided information on atmospheric and tributary loadings, as well as in situ chemical concentrations for model validation for 1994-1995. The hydrodynamic models were applied for this entire period, and the results are being used to provide three dimensional transport fields for the EPA mass balance models. Mass balance models predict chemical concentrations in water and sediment, as well as the bioavailability of toxic chemicals. The food web bioaccumulation model (Fig. 1) will then be used to estimate the accumulation of chemical constituents in various elements of the food web, ranging from benthos and zooplankton to forage fish and the top predators (lake trout and coho salmon).
The Hydrodynamic Modeling project started in 1993 and was completed in 1998. All of the above goals were accomplished and a final report on the results (Schwab and Beletsky, 1998) along with a series of CDROMs containing numerical and graphical representations of the results, as well as documentation of the computer programs, were delivered to EPA in November 1998.
The eutrophication, sorbent dynamics, and transport and fate models will now be used by EPA in conjunction with the results of the computational transport models and the measured constituent loadings to simulate the seasonal cycle of primary production in the lake as well as the transport, intermedia exchange, phase distribution, and biogeochemical transformation of the target chemicals through the water column and the sediments. The models developed in this project will provide estimates of the physical environment in the lake with a spatial resolution of tens of kilometers and a temporal resolution of hours. These space and time scales are significant for many of the important chemical and biological processes that are being modeled as part of the LMMBS, particularly sediment resuspension and transport and lower food web modeling. Hydrodynamic models generally have very few system-specific adjustable parameters, so they are much easier to apply to new conditions, outside the conditions encountered during the project years. It is our conclusion that coastal pollution often has regional impacts and that hydrodynamic and water quality models are essential for assessing regional impacts. Promising areas of future research include coupling of near-field and far-field models, closer linkages between hydrodynamic and water quality models, and more coordinated sampling programs for physical, biological, and chemical parameters. It is our hope that the LMMBS modeling framework, which is based on the hydrodynamic models, will provide a sound basis for the development of management tools for Lake Michigan.
Fig. 2. Observed and simulated water temperature at mid-lake station for 1994-95 LMMBS field study period. Red represents the observed temperature in the bottom three panels.[Click to download EPS file]
References
Last updated: July 9, 2002 mbl