Hence, this loss of SAV communities represents a convenient case study for 

 examining the emerging problem of managing and balancing the conflicting uses 

 of estuarine resources. The purpose of this paper is to describe a simulation 

 modeling framework which has served to organize, focus and elaborate a broad 

 empirical research program for investigating this problem. 



RESEARCH ORGANIZATION AND DESIGN 



Peception of Problem 



In figure 1 we have illustrated our perception of the important inter- 

 actions related to the decline of SAV, including (1) factors contributing to 

 the decline, (2) ecological consequences of the decline, and (3) socio-economic 

 ramifications of this ecosystem modification (Boynton et al., 1981). In this 

 cartoon SAV are shown to act as natural nutrient sinks and sediment traps, 

 both processes having economic analogs in terms of sewage treatment plants and 

 channel dredging operations, respectively. Furthermore, SAV communities are 

 suggested to be important sources of food and habitat promoting growth of fish, 

 shellfish, and waterfowl stocks which are harvested in commercial and 

 recreational endeavors. Various watershed activities are shown to influence 

 estuarine water quality (nutrient, sediment, and herbicide additions) via direct 

 discharges and runoff which are, In turn, regulated by rainfall and other 

 factors. Throughout this cycle some economic enterprises (e.g., agriculture) 

 may detrimentally influence SAV while others (e.g., fishing and dredging) are 

 affected by plant losses. While this presentation may be useful as an over- 

 view of the basic relationships involved in the problem, it does not indicate 

 the nature of such relationships. Hence, we need a more explicit framework 

 within which mechanistic connections are embodied. 



We recognized in this research project a rare opportunity to address 

 several scientific hypotheses of theoretical and empirical interest within a 

 broad context of resource management questions. However, to do so effectively 

 it was necessary to use a scheme whereby the complexity of this problem could 

 be dealt with in an organized, piece-wise simplified fashion. We, therefore, 

 developed a hierarchical approach for the overall research program which enabled 

 us to integrate highly controlled experiments (testing mechanistic hypotheses) 

 together with descriptive field measurements (characterizing the structure and 

 function of these SAV ecosystems). This allowed us to combine a spectrum of 

 research methods and scales of interest into a unified effort. We have discussed 

 the relative merits and philosophical underpinnings of this scheme elsewhere at 

 length (Kemp et al. , 1980). 



A variety of conceptual and simulation models were utilized to integrate 

 this research program. We reasoned that models could facilitate the coupling 

 of experimental findings on "causality" (i.e., influence) with the inherently 

 holistic perspective of descriptive in situ observations. Furthermore, 

 simulation models could be used to confer generality upon specific results at 

 either end of the controllability-realism spectrum (Kemp et al., 1980). This 

 would be done by constructing, calibrating, and verifying models with data 

 from a variety of systems. Thus, we concluded that simulation models could be 

 used to examine the possibility that altered water quality conditions contri- 

 buted to the decline of SAV in various regions of Chesapeake Bay. Such models 

 would help to Interpolate and extrapolate the results of experimentally inferred 



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