ABSTRACT 



This paper provides a broad overview of a system of simulation models 

 developed in conjunction with empirical research programs to study the de- 

 clining abundance of submerged aquatic vegetation (SAV) in Chesapeake Bay and 

 the effects of this decline on ecological and socio-economic processes. A 

 hierarchical organization of models and submodels allowed the simplification 

 needed for tractability while maintaining sufficient detail for examining 

 mechanisms of ecological interaction. Two models of the SAV ecological 

 subsystem are presented. First, the Autotroph Model was used to investigate 

 consequences of shifting competition for light and nutrients among 4 groups of 

 primary producers (SAV, phytoplankton, epiphytes and benthic microalgae). 

 This model, which has been calibrated and verified against independent data 

 sets, was used to extrapolate from controlled experiments to consider effects 

 of nutrient enrichment. The second of these, the Nekton Model, was developed 

 to test possible effects of declining SAV on the trophic structure and relative 

 abundance of 3 fish groups. The model's design utilizes certain elements of 

 traditional fish population models within the generic structure of an ecosystem 

 model. An SAV resource management model was developed by aggregating the details 

 of these and other ecological submodels and is linked to a suite of simulation 

 models which relate human activities to estuarine processes and societal values 

 in the Bay region. We argue here that this management modeling framework 

 allows results of scientific research to be integrated into political and 

 socio-economic networks toward balanced uses of those estuarine resources 

 related to SAV. 



INTRODUCTION 



Estuaries such as Chesapeake Bay are complex and dynamic ecological 

 systems which benefit human societies in many ways. On one hand, these coastal 

 ecosystems provide a bountiful source of fisheries production and diverse 

 recreational ooportunities . On the other hand, natural biogeochemical 

 processes witl#n these systems are capable of transforming many wastes emanat- 

 ing from human activities into useful components of regional and global cycles. 

 In some cases low levels of waste inputs (such as nutrients and organics) can, 

 in fact, enhance estuarine productivity. However, in many of these environ- 

 ments waste loading rates are such that they detract significantly from the 

 estuary's value as a source of fisheries and recreation. Hence, a serious 

 problem evolves wherein legitimate but competitive uses of the natural resource 

 are in direct conflict with one another. 



In the last two decades, Chesapeake Bay has undergone some documented 

 changes. One such change has been the drastic decline of submerged aquatic 

 vegetation (SAV) which once dominated littoral zones throughout the estuary. 

 Coincident with this loss of aquatic plants, there have been significant changes 

 in water quality (including increased levels of turbidity, nutrients and 

 agricultural herbicides), as well as declines and shifts as in various fisheries 

 (Boynton et al. , 1979). Stevenson and Confer (1978) postulated that many of 

 these alterations in water quality are attributable to increased waste loadings 

 to the Bay from both sewage outfalls and diffuse sources, and that such deteri- 

 orating conditions have led to the loss of ecosystems associated with these 

 submerged plants. Moreover, it was hypothesized that the decline of SAV has 

 contributed to detrimental changes in fisheries production (Boynton et al . , 1979). 



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