Green Bay Mass Balance
Preliminary Management Summary
Prepared by: Robert F. Beltran
With the assistance of: William Richardson, Director,
A publication of the Green Bay/Fox River Mass Balance Study Management Committee
Produced by the Illinois-Indiana Sea Grant Program
This report presents the Green Bay/Fox River Mass Balance Study experience as a model and a lesson in large scale interagency cooperation to apply the mass balance approach. The report will incorporate the fundamentals of the mass balance approach and identify some lessons learned in the Green Bay experience while looking forward to the implication for future -- and even larger scale -- effort to apply a mass balance approach to the management of toxics for an entire Great Lake.
The Green Bay/Fox River Mass Balance Study is intended to evaluate the feasibility of mass balance modeling for toxic substances as a basic planning and management tool in restoring Great Lakes water quality. Successful application of the methodologies employed in the Study offer an accurate basis for pollution control and a foundation for setting objectives for Lakewide Management Plans and Remedial Action Plans.
OBJECTIVES OF THE GREEN BAY/FOX RIVER MASS BALANCE STUDY
The Green Bay/Fox River Mass Balance Study was conducted as a pilot to test the feasibility of using a mass balance approach to assess the sources and fates of toxic pollutants spreading throughout the Great Lakes food chain. It was intended to validate and refine monitoring and analytical assumptions made by the coordinating agencies, and to rigorously test the models. Specific objectives included:
SELECTION OF GREEN BAY
Green Bay was selected over other potential sites for the Great Lakes mass balance pilot project for six primary reasons:
GREEN BAY AND THE FOX RIVER
Green Bay can be characterized as a long, relatively shallow extension of northwestern Lake Michigan. Fourteen tributaries drain about 15,675 mi.2 of watershed in both Wisconsin and Michigan, comprising about one third of the total Lake Michigan drainage basin. The southern portion of the Bay and its largest tributary, Wisconsin's Fox River, have been acknowledged as a polluted water system, and have been designated by the United States and the International Joint Commission as a Great Lakes Area of Concern. The Fox River Valley is heavily industrialized and contains the worlds largest concentration of pulp and paper mills. The Bay nevertheless remains a major recreational resource in the region, providing excellent boating and outstanding walleye fishing, despite fish consumption advisories established by the states.
CONDITION OF THE BAY
Green Bay is impacted by three categories of contaminants: nutrients, metals, and organic toxicants. Each deserves a brief discussion:
This eutrophication has had distinct effects upon the Bay:
Since 1970, some $338 million in wastewater quality improvements have helped alleviate the worst of these events.
However, past studies have given us some information on their concentrations:
Improvements in industrial processes and wastewater treatment have reduced most external sources of metals to the River and Bay. These contaminants nevertheless continue to cycle into the system from their reservoir in the sediments.
For Green Bay, specifically, there is cause for concern:
THE MANAGEMENT DILEMMA
Acting in response to the environmental problems evident in Green Bay and the Fox River, public agencies, the private sector, and individual citizens have reacted on a broad front to identify and reduce loadings of both nutrients and toxicants.
Agencies utilized the authorities granted them under the landmark federal environmental statutes -- the Clean Water Act, the Clean Air Act, Superfund legislation, and others -- to regulate discharges from both active sources and waste sites. In the watersheds, land management and agricultural agencies at all levels worked with private landowners to abate nonpoint source contributions. Municipalities, industries, and environmental agencies constructed waste treatment facilities and remediated waste sites, and implemented new approaches to waste materials handling, reduction, treatment, reuse, and recycling. Literally billions of dollars, public and private, have been and are now being spent to save the Bay.
Still, problems persist in the Green Bay system. Fish consumption advisories remain in place. Contaminant levels in Green Bay biota continue to decline, but for a number of substances, this decline appears to be leveling off. Bottom dwelling organisms, the base for a large component of the food chain, continue to be particularly exposed via the sediments, which persist as a continuing reservoir of contaminants to the system.
In addition, predator fish, birds, and fish-eating mammals may be suffering from reproductive, development, and cognitive disorders. While no "smoking gun" has been found, a number of respected researchers have pointed out strong correlations between such factors as reduced hatching success or deformities and levels of PCBs and other contaminants in the studied populations.
From the outset, the Management Committee recognized that no single agency had sufficient resources nor expertise to manage, fund, and conduct the entire project. The fundamental operating principle was that each involved agency, program, laboratory, and investigator would benefit from the products of the other parties. Each piece of the project would then fit together to build the whole and each would "own" the whole.
It was also recognized that a project plan should follow an agreed to process including:
The principal question concerned the feasibility of using a mass balance approach to manage toxic chemicals in the Great Lakes. However, more specific environmental questions for Green Bay concerned the continuing, chronic problems associated with PCBs. The specific management questions which directed the remainder of the project included:
Considering the management questions, the modeling committee determined that the Green Bay Model could build on the basic model framework that had been previously developed for Saginaw Bay and for the Great Lakes. This would involve a time variable model, as shown in Figure 1, starting with a water transport model coupled to a nutrient driven eutrophication model. The eutrophication model generates organic carbon-related solids which are input to a solids model. Output of the solids model form an input to the contaminant exposure model the output of which forms the input to the food chain model.
Each model produces output in the form of concentrations computed at different locations in the Bay and at future times. The calculated concentrations are compared to data which, for this study, was collected in 1989. The model is calibrated by changing model process coefficients so that the computed concentrations match the measured concentrations. Future concentrations are predicted by calculating conditions beyond the calibration period.
The more specific model framework is shown in Figures 2 and 3. Figure 2 shows the interactions occurring between air and water, water and sediment, and the food chain. The model, in essence, links the sources of the contaminant to the mass in water, sediment, and biota in space and time. Therefore the model, once calibrated and deemed valid, can be used to compute future concentrations under any altered load condition.
PCBs enter the Green Bay system from the atmosphere, and from tributaries, primarily the Fox River. There exists a reservoir of PCBs in bottom sediments which may re-suspend with sediments during storm events, and then desorb and become available to the food chain. PCBs are lost from the system through volatilization to the atmosphere, burial to deep sediment, and possible transport to Lake Michigan.
The computer model program keeps track of the mass of PCBs in space and time. It is called a "mass balance model" because the principal thermodynamic law of conservation of mass is maintained at all times. Thus, if mass is lost from one physical, chemical, or biological component of the model it must be gained in another.
A conceptual view of the food chain bioaccumulation model is shown in Figure 3. Chemical accumulation results from direct uptake from water and from food chain transfer with feeding. The bioaccumulation model is based upon a mass balance equation for each organism in the food chain. The model simulates the accumulation of chemical concentrations along each step of the aquatic food chain in response to the organisms' chemical exposure via food, water, and sediments. Calculation of this exposure is itself based upon the simulation provided by the aquatic mass balance model.
These inputs to the organism are balanced by elimination processes, and are diluted within the organism as a result of growth. Green Bay field data was used to refine the mathematical assumptions derived from earlier experimentation. For PCBs, food chain transfer has been shown to be highly effective, resulting in increasing chemical concentrations at higher trophic levels.
The food chain model is depicted in more detail in Figure 4. A separate computer program uses output from the physical/chemical model to quantify the available contaminant in the water column. This form of toxicant is available to each level of the food chain and "bioconcentrates" the chemical. In addition, each level preys on the lower level and "bioaccumulates" more of the chemical. The chemical may return to the water via death or excretion. The speed at which the uptake and excretion occur are important factors in the model and must be determined through experimentation and refined by calibration to field data.
Design of the Monitoring Plan
The model "requires" field data for two primary purposes:
In addition the model requires site-specific "rate" information to include as model coefficients. The rate data can be obtained in three different manners, all employed in the Green Bay project:
THE MASS BALANCE RATIONALE
Mass Balance Defined
More precisely, a mass balance model is an accounting device to ensure that differences between inputs and outputs during any particular interval of time, within any particular volume in space, are equal to the net sum of the production, retention, and decay processes within the volume. In practice, there are many complex processes that influence the transport, transformation, and fate of toxic chemicals in the Great Lakes.
Mass balance models can be run at any of several levels, or tiers. A screening model -- a preliminary approach --utilizing existing data, can be run at very minimal cost to give very rough ideas of the magnitude of a lakes toxicants problem. A loadings model -- an intermediate approach -- can be used to identify whole lake total maximum daily loadings (TMDLs). A full mass balance study -- a complete approach -- is needed, however, to set specific wasteload allocations for individual sources.
The suite of toxicants to be modeled exerts a profound influence upon the study's budget. For example, the Green Bay effort (designed as a pilot to tell us how much we need to know) involved analysis for all PCB congeners, but another study might look only at total PCBs, quartering the analytical expense.
The degree of complexity actually incorporated in any particular model (and the level of confidence it obtains) depends upon:
Mass Balance Capabilities
Mass balance modeling has four special strengths:
1. Models establish a framework for organization and synthesis of data.
2. Models provide a basis for managers to minimize costs and enhance information flow.
3. Models are useful tools for understanding processes that lie behind the data.
4. Models demonstrate linkages between inputs and system responses.
Modeling can likewise be employed to calculate loading reductions needed to stabilize water column or biota contaminant levels at some given level. This information can also be used as a basis for establishing target loads (total maximum daily loads, or TMDLs) , wasteload allocations, and permit limits as interim goals for the ultimate attainment of zero discharge and virtual elimination of toxic substances. This approach was used to determine the phosphorus loadings targets identified in the Supplement to Annex 3 of the 1978 Great Lakes Water Quality Agreement.
Mass Balance Limitations
1. Toxic chemical mass balance models conceptually oversimplify natural processes.
Our imperfect understanding of these processes forces the model to represent a simplification of reality. Nevertheless, the modeling approach forces scientists to assign values quantifying process rates -- reducing ambiguity and subjectivity. If values are not well-known, further experimental research is conducted to increase confidence. In the final analysis, the model is tested by its ability to simulate and predict actual occurrences. To test the validity of the model, extensive surveillance data are required.
2. Mass balance models have extensive data requirements.
If ultimate validation of the model is needed, it is also necessary to obtain future actual ambient data as a basis for comparison with the model predictions.
The model must incorporate values for a wide range of variables, loading of chemicals, circulation, basin morphometry, temperatures, etc. to produce an output predicting water column. Linkage to a food chain model demands the products of the water-sediment-air model and requires data on the forage base, biotic body burdens, and fish migration patterns to produce a projection of load response contaminant concentration trends in fish.
Realistic load estimates are the basis of any mass balance effort, and comprise the preponderance of its costs. Since loading mass is dependent upon loading rates from many sources over a specified time period, it is critical to characterize, in a "snapshot" of one or more years, the loading from the multitude of tributaries, point sources, and nonpoint sources. These sources include the atmosphere, groundwater, waste sites, urban and agricultural runoff, and sediment deposits.
The more extensive the chemical analysis, the longer the period modeled. The more statistically representative the acquired data points are of the loading regimes, the greater will be the reliability and precision will be of the final product. In other words, the quality and quantity of the data determines the quality of the model results. This equates to the considerable expense involved in an intensive monitoring program. Much of this expense may later be recouped in two ways:
3. There are no rigorous methods for quantifying model prediction uncertainty.
4. Mass balance modeling exercises can challenge the support infrastructure.
MASS BALANCE -- IN SUMMARY
While mass balance modeling cannot make absolutely precise and accurate predictions, the concept remains sound and has been thoroughly field validated. The expense of the higher level models is primarily incurred due to greatly increased resolution of ambient monitoring and analysis. These costs, however, are largely or entirely offset by enabling managers to initiate less expensive, more refined routine monitoring programs. Substantial cost reduction may be affected by fitting the level of modeling to the need.
The approach provides a rational basis for setting load reduction targets and priorities, as well as management and regulatory policy. The alternative of setting arbitrary reduction targets and conducting follow-up ambient trend monitoring to determine target adequacy proves to be much more fiscally and environmentally expensive. Inordinate efforts may be expended to control and correct the least consequential sources. Given the response lag of most environmental systems, the poor efficacy of such misdirected resources may not be evident for many years.
THE GREEN BAY PLAYERS
Responding to provisions of the 1978 Great Lakes Water Quality Agreement and the resolutions of the 1986 Mackinaw Island "Large Lakes of the World" international conference, the USEPAs Great Lakes National Program Office (GLNPO) initiated planning among the environmental agencies in 1986. An agreement was reached to share overall coordination between the GLNPO and the Wisconsin Department of Natural Resources (WDNR).
USEPA Great Lakes National Program Office (GLNPO)
USEPA Office of Research and Development (ORD)
Environmental Research Laboratory Duluth (ERL)
Large Lakes Research Station (LLRS)
USEPA Region V Water and Waste Management Divisions
US Geological Survey (USGS)
Wisconsin Department of Natural Resources (WDNR)
National Oceanic and Atmospheric Administration Great Lakes Environmental Research Laboratory (NOAAGLERL)
Michigan Department of Natural Resources (MDNR)
University of Wisconsin Sea Grant Institute
US Fish and Wildlife Service
US Coast Guard
US Department of Energy Argonne National Laboratory (USDOEANL)
Illinois State Water Survey
Wisconsin State Lab of Hygiene
University of Michigan (U of MI)
University of Wisconsin Milwaukee (UWM)
University of Minnesota (U of MN)
University of Notre Dame
University of California Santa Barbara (UCSB)
Green Bay Remedial Action Plan Implementation Committee
The Study has operated through a three-tiered committee structure:
The Management Committee deals with administrative and budgetary matters:
The Technical Coordinating Committee addresses scientific and technical issues:
Four technical committees address specific study tasks: Modeling; Biota; Field and Technical Operations; and Field and Analytical Methods.
Planning the Field Program
In March, 1988, the Modeling Committee prepared the planning document, Report on Project Planning for the Green Bay Physical-Chemical Mass Balance and Food Chain Models. This report provided detailed information for use in selecting a final monitoring plan including costs for alternative levels of complexity and precision. The final design was based on a series of discussions among managers, modelers, and those responsible for monitoring and experimentation.
In March, 1989, the Green Bay Mass Balance Management Committee approved the Green Bay/Fox River Mass Balance Study Plan: A Strategy for Tracking Toxics in the Bay of Green Bay, Lake Michigan. The plan was partitioned into six major divisions reflecting particular requirements of the model. Each division was subdivided into study components. Study participants were each assigned an appropriate specific study component:
III. Active Pools and Interface
V. Quality Assurance and Data Management
Working from the precept that the project would build upon existing knowledge, the Management Committee sought to contain costs and to leverage existing activities. Only essential monitoring and experimentation would be funded. Four toxicants, themselves representative of larger groups of chemicals, were selected for investigation:
PCBs (total, homologs, and congeners) -- toxic metals: lead is available in an organic form; cadmium as an ion. Based upon the Technical Coordinating Committee and the Modeling Subcommittee, WASP IV was selected as the computer program for the toxicant fate model. A transport model was coupled to eutrophication, solids, exposure, and food chain models. Walleye, brown trout, and carp were specified as target species.
The physical-chemical model simulates and predicts concentrations of the modeled toxicant in the sediment and water given a specific loading (input) to Green Bay from any source.
The models and computer programs have been combined into a unified model, WASP IV, the computer program chosen for the Green Bay model. The simulated concentrations of the dissolved chemical species in the water are then used as input to WASTOX, the food chain model.
THE GREEN BAY/FOX RIVER MASS BALANCE STUDY PLAN
In March, 1989, the Green Bay Mass Balance Management Committee approved the Green Bay/Fox River Mass Balance Study Plan: A Strategy for Tracking Toxics in the Bay of Green Bay, Lake Michigan.
The plan was partitioned into six major divisions reflecting particular requirements of the model. Each division was subdivided into study components. Study participants were each assigned appropriate specific study components to accomplish:
Identify and quantify sources of contaminants entering the system.
Identify and quantify pollutants leaving the Bay.
III. Active Pools and Interfaces
Characterize principal contaminant reactors within the Bay.
IV. Biota characterize biotic pathways of contaminants WDNR/LLRS
V. Quality Assurance and Data Handling USDOEANL/GLNPO/U. of MN
VI. Administration GLNPO/WDNR
A multitude of reports have been produced from this study. Cooperative efforts to share technology, explore alternative management scenarios, and build consensus on remedial choices are ongoing. Preliminary results are available for a few studies.
Individual researchers will also be publishing results and follow-up studies independently in scientific journals.
A less quantifiable product of the Green Bay/Fox River Mass Balance Study is its contribution to the "state of the art" of modeling. The very scale, duration, and intensity of the study; its extensive field calibration; and continuing empirical verification will validate certain modeling assumptions and will better quantify others. This will serve to not only improve our understanding of critical exchange and transformation processes, but will help to reduce both model uncertainty and data requirements.
Model Development and Project Results
Four primary models were developed and linked:
Reports and other products from the Green Bay Project have or will be produced as follows:
Lower Fox River Mass Balance Model
The Lower Fox River Mass Balance Model is a transport and fate model for PCBs in the Fox River between DePere Dam and the River mouth at Green Bay. The Model simulate point and nonpoint sources, sediment (including episodic transport of in-place PCBs during floods), volatilization, and dispersion (due to Bay induced seiching). These factors all affect the mass balance of PCBs along the lower seven miles of the River. The model was calibrated using chloride, suspended solids, and PCB concentration data from samples collected at DePere Dam, the River mouth, and at five sampling stations in the lower River, as part of the Mass Balance Study.
The function of the model is twofold. First, it predicts the transport of PCBs from the Fox River to Green Bay. This prediction then becomes a load to the Green Bay Mass Balance Model. Accuracy in this prediction is critical because transport from the Fox River provides the largest source of PCBs to Green Bay.
The mass balance modeling approach incorporates, refines, and goes beyond conventional tributary loading estimates. Model predictions account for factors affecting PCB transport at both low flow (mixing due to seiches) and high flow (sediment bed erosion) that confound the loading estimates. Furthermore, the mass balance model can predict future PCB transport from the Fox River over the long duration necessary to simulate water quality management scenarios.
The second function of the model is to predict water column concentrations of PCBs in the Fox River. These concentrations are used by the Green Bay bioaccumulation model to define PCB water exposure for fish that seasonally reside in the River.
Output of the Lower Fox River Mass Balance Model in terms of 1989 loading of PCBs to Green Bay is shown in Figure 4 . This data formed part of the input for the Green Bay Model.
GREEN BAY RESULTS
In the final analysis the validity and credibility of the model is determined by its ability to simulate existing conditions. Ideally, the model would be validated by predicting some future occurrence and testing the prediction with an independent data set. In this situation, an independent data set does not exist. However, the model output in Figure 5  shows that the model does match the data collected in 1989. This fact provides enough credibility at this time to use the model for management purposes.
PCB Mass Budget
The first management question regarded the PCB loadings to the Bay. An accounting of all PCB inputs and fluxes provides an answer. As summarized in Figure 4 , the majority of PCBs enter the Bay via the Fox River. However, in 1989 there is an equal flux from the bottom sediment to the water column. Considerable loss of PCB occurs to the atmosphere via volatilization and transport to Lake Michigan. (Figure 6).
As the project evolved and interim results became available, it grew evident that the major management consideration for Green Bay and Fox River concerns the in place, contaminated sediment. An approximately 25 to 30 thousand kg reservoir of PCBs exists in deposits below DePere Dam. Also, an additional 3 to 4 thousand kg reservoir of PCB contaminated sediments resides in Little Lake Butte des Mort, above DePere Dam. Resuspension and diffusion of PCBs from these deposits above and below the dam appear to be the major sources of PCBs to Green Bay.
Under normal meteorological and hydrological conditions these sediments slowly deplete either through transport downstream, slow biodegradation, and perhaps permanent burial. The question remains, however, as to the possible disruption of these deposits and transport downstream and into Green Bay. It is unclear under what conditions significant quantities would be released and what would be the downstream consequences.
The Management Committee asked the Modeling Committee to address these questions near the projects conclusion. Additional resources and efforts are being expended to provide the answers. The results will be presented separately, and at the December 1992 Conference.
CHALLENGES FACED AND LESSONS LEARNED
A primary original intent of the participants was to challenge themselves, both organizationally and technically. They sought to test their ability to develop and calibrate mass balance models at the level of precision necessary to make sound toxic regulatory and management decisions and to do that within the context of the complex jurisdictional framework which exists on the Great Lakes.
The Project's success can be attributed to several factors:
THE MANAGEMENT SCENARIOS
The Management Committee requested the modelers to prepare several alternative management scenarios. Some alternatives in this suite were selected in part to demonstrate distinct contrasts among management approaches. Others were selected specifically to identify best management alternatives and to enable managers to better ascertain cost effectiveness among those alternatives. For each scenario, the Fox River Modeling Team provided its results to the Green Bay Water/Sediment Modelers and to the Green Bay/Fox River Food Chain Model.
Weather conditions are an important driver for the scenarios. This was the basis for the selection of the 100 year, 60 day high flow event for Scenario 2. To provide realism, the modelers utilized the past 60 years weather and flow records to simulate the weather for the next 60 years.
The scenario results are not presented here. Some scenarios were still being developed as this publication was being finalized for delivery at the December 34, 1992 Green Bay/Fox River Management Summary Meeting. An addendum to be provided at the meeting will present complete results of the final runs since the Green Bay/Fox River Food Chain Model is the last link in the chain of models, and is only touched upon here. Interpretation of Food Chain Model results for all scenarios will also be presented separately at the meeting.
STUDY FINDINGS AND CONCLUSIONS
As this document goes to print, the effort to define, identify, and evaluate the effects of various management scenarios is still underway. An addendum will present the full range of model scenario results, not presented here because some elements of the modeling effort must await the completion of other, precursor elements. Their results must be scrutinized and validated in the light of environmental results. Inevitably, these and other environmental management scenarios will be implemented. The choice is whether to select and implement them by design or to accept the scenarios that serendipity and misfortune deal out by default.
The Green Bay/Fox River Mass Balance Model is a tool to be used. While that means managers will be able to draw certain conclusions by pulling the study results off the shelf and reviewing the existing scenario runs. Much of the real power, however, resides in a manager's ability to ask the modelers to rerun the model using new parameters reflecting newly conceived or previously unanticipated circumstances. Any conclusions listed here now, and for a considerable time to come, must therefore be considered preliminary.
WATER/SEDIMENT QUALITY MODEL FINDINGS
Two classes of findings emerged in the scenarios:
The water and sediment models for Green Bay and the Fox River targeted total PCB concentration endpoints in the water column and sediments after the time periods, and under the management schemes defined in the six scenarios. While the models looked specifically at a suite of PCB phases in the water and sediment, for management purposes, they are here, with few exceptions, grouped generally into water or sediment phases.
FOOD CHAIN MODEL FINDINGS
As previously stated, only the most preliminary results of the Green Bay/Fox River Food Chain Model are available as this document goes to print. More complete data will be made available at the Management Summary Meeting and in the addendum to this report.
The Green Bay Food Chain Model results are particularly important to decision-makers, since the food chain is the vehicle for bioconcentration of PCBs and many other substances to reach toxic levels in the biota; it is this trait that makes even the comparatively low levels of PCBs found in the Green Bay water column a matter of concern.
The Model was run using field-collected Green Bay PCB data for phytoplankton, zooplankton, three forage fish, and two top predator fish species. The Food Chain Model was then linked to and driven by results from the Fox River and Green Bay Water Quality Models. Substantive decreases in water column total PCBs predicted by the water quality models suggest parallel, but delayed, decreases in PCB concentrations within the Green Bay food chain under several management scenarios. This predicted reduction applies to Green Bay top predator fish. At this writing, specific scenario results are still being analyzed.
PRELIMINARY MANAGEMENT CONCLUSIONS
Not all results are yet available as this report goes to press. Conclusions must be drawn in light of the remaining scenarios, and further analysis is certainly called for and will be made available at the Management Summary Meeting. At this writing, however, the following is evident based upon the 1989 field year and the scenarios so far run under the model:
There are four primary sources of total PCBs to Green Bay. These may be divided into internal sources (1) and external sources (2). The overwhelming internal source is Green Bay sediments. The external sources are, in order of importance, the Fox River (primarily its sediments), Lake Michigan (its water column), and the atmosphere. While Green Bay also loses PCBs to both the atmosphere and Lake Michigan, only the atmosphere takes on more total PCBs from the Bay, overall, than it contributes.
It is not the function of this document nor of the presenters to come to ultimate conclusions for the environmental managers, even were all of the scenario and analytical results now available. Clearly, however, managers and investigators alike must combine model results with intuition and common sense, available resources, and statutory and popular mandates. Once a scenario is chosen for action, the task will be to accomplish it.
A factor to keep in mind while ruminating these results is that the Green Bay/Fox River Mass Balance Study was performed as a prototype. Its results are not likely to be mirrored elsewhere, but its approach and methods have established a framework that is imitable in greater and lesser water bodies everywhere.
Any conclusions will warrant further validation through continued monitoring to ensure that the model coincides with our real-time and real-life experience. The modeling and monitoring community will need to continue to refine both the models and the validity of the data used to drive them.
ON THE HORIZON -- WHAT'S NEXT
Use of the mass balance approach is becoming recognized as an effective means of determining contaminant reduction objectives as called for under the Great Lakes Water Quality Agreement, and as an important tool in the lakewide management planning process. Its cost is a function of the level of certainty desired to support management decision-making and the concurrent level of monitoring needed to describe toxicant loading to the system. Regardless of the chosen level of certainty, the models are valuable tools in the design of more cost-effective monitoring programs and in the organization, interpretation, and application of environmental data.
Groundwork has already been laid for a Lake Michigan mass balance study to begin in 1992. This exercise will require less intensive monitoring than Green Bay:
Lake Michigan's Green Bay is a large, primarily shallow freshwater estuary having many of the characteristics of a whole Great Lake. It suffers from many of the same nutrient and toxicant problems as the rest of the Great Lakes system, including eutrophication and a biotic population impaired by PCBs, pesticides, and metals. The dynamics of loading, transport, and fate of those contaminants are complex and are readily understood only with the assistance of complex mathematical models based upon quality monitoring data.
Despite the complexities of such models, major costs are associated primarily with enhanced monitoring. These costs can be at least partially recouped through resulting refinements in subsequent monitoring programs. Various levels of modeling can be performed, depending upon the specific objectives of the exercise and the acceptable confidence levels needed. Use of the models makes it possible to set realistic, defensible loading reduction targets and to design and operate more cost-effective monitoring networks.
The Green Bay/Fox River Mass Balance Study was the first effort to conduct a large-scale, multi-parametric mass balance model for toxicants in a large freshwater body. The Study utilizes a combination of nutrient and toxicant models with a bioaccumulation model. It employs an unprecedented Multi-agency team approach over a scheduled five-year period.
Challenges encountered in the Green Bay/Fox River Mass Balance Study have established an experience base for future efforts in whole lake modeling, and have afforded the opportunity to learn what works and what doesn't work in a large-scale, intensive toxicant monitoring and analysis project.
This report was prepared, in part, using information derived from the following:
Bierman, Victor J., Jr. et al.,Development and Validation of an Integrated Exposure Model for Toxic Chemicals in Green Bay, Lake Michigan Final Report, Nov. 1992, (Unpublished).
Bierman, Victor J., Jr., Strength and Weaknesses of a Mass Balance Approach for Toxic Chemicals in the Great Lakes. In R.L. Eshenroder, J.H. Hartig, and J.E. Gannon. Lake Michigan: An Ecosystem Approach for Remediation of Critical Pollutants and Management of Fish Communities, Great Lakes Fisheries Commission Special Publication 912, 58 p.
DeVault, David, and H.J. Harris/U. S. Environmental Protection Agency, Great Lakes National Program Office, The Green Bay/Fox River Mass Balance Study (Study Plan), April, 1989.
Harris, H.J. (Untitled), Unpublished report.
Kreis, Russel G., Personal correspondence, Nov. 1992.
Richardson, William L., P.E., Influence of Modeling in Planning Large Scale, Integrated Water Quality Studies, (Unpublished).
Richardson, William L., P.E., Personal correspondence, Nov. 1992.
University of Wisconsin Green Bay, The State of the Bay - 1990.
U.S. Environmental Protection Agency, Office of Water, The Green Bay Mass Balance Project, Sept. 1990.
Funding for this report was made possible by a grant from USEPA, Great Lakes National Program Office, to NOAA, National Sea Grant College Program. The project was administered by the Illinois-Indiana Sea Grant Program.
Editorial assistance for this report was provided through the Illinois Indiana Sea Grant Program by Robin Goettel, Nancy Riggs, and Tracy Reder.
Design and formatting was provided through the University of Illinois, Office of Conferences and Institutes by Jean Deichman.
Photos to be provided by Dave Crehore, Wisconsin Department of Natural Resources and LTI-LimnoTech, Inc.
Maps provided by LTI-LimnoTech, Inc., and by Robin Jourdan and Kay Morrison, Computer Sciences Corporation, Large Lakes Research Station, Grosse Ile, Mich.
Special thanks for management and technical contributions to USEPA Office of Research and Development, Environmental Research Laboratory, and Large Lakes Research Station, USEPA Region V Water and Waste Management Divisions, Wisconsin Department of Natural Resources, U.S. Geological Survey, U.S. Fish and Wildlife Service, National Oceanic and Atmospheric Administration, Michigan Department of Natural Resources, and University of Wisconsin Sea Grant Institute.