A CONCEPTUAL ECOLOGICAL MODEL FOR CHESAPEAKE BAY 



Katherine A. Green 1 



INTRODUCTION 



PURPOSE 



The main objective of this project was the de- 

 velopment of a conceptual model of the Chesapeake 

 Bay ecosystem. The model indicates carbon and 

 nutrient pathways in the Bay. 



The Chesapeake Bay and adjacent wetlands 

 provide habitat for migratory birds and other wild- 

 life, maintain an aesthetically pleasing environ- 

 ment, and support recreational and commercial 

 fisheries. Resources are affected by biological inter- 

 actions and the physical and chemical processes of 

 Bay waters, as well as by water quality and the im- 

 pacts of human activities. 



For planning research to support management 

 decisions on renewable resources, Chesapeake Bay 

 should be viewed as an estuarine ecosystem. Such a 

 broad perspective is practical using a conceptual 

 model to indicate interrelationships among re- 

 sources and habitats. Within the ecosystem context, 

 key processes and potential indicator species can 

 be identified. 



A conceptual model, as an explicit statement 

 of the functioning of Bay ecosystem, will provide a 

 biologically realistic context for considering the 

 ramifications of changes in water quality. 



The information used to develop the concep- 

 tual model comes mainly from discussions with 

 scientists currently doing research on the Bay. 

 (Questions asked in interviews are listed in appen- 

 dix A). Some references are given, but the author's 

 principal role was synthetic, that is, combining 

 ideas and information from various sources into a 

 conceptualization of the ecosystem gestalt. Previous 

 models of the Bay ecosystem have been implicit 

 mental concepts. This report presents a concrete 



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11801 Rockville Pike, No. 802. Rockville, Md. 20852. 



ecosystem concept to facilitate the objective ex- 

 amination of assumptions. 



The project represents only 8 weeks of work 

 for interviews and writing. The model is general 

 and simplified for any given area of research. Its 

 utility lies in its holistic perspective, placing the 

 relationships among systems components into the 

 ecosystem context. 



This model, while necesarily limited in scope, 

 is a starting point for an ecosystem perspective on 

 the Bay, and should serve as a basis for discussion 

 on systems structure and relationships. 



The conceptual model is structured as a set of 

 box-and-arrow diagrams. Boxes represent system 

 components; arrows represent flows between com- 

 ponents or compartments. Components repre- 

 sented are carbon (C), nitrogen (N), and phos- 

 phorus (P), but the same basic structure could be 

 used for energy units. 



PHILOSOPHY 



An ecosystem is a system open in at least one 

 property, and in which at least one entity is living 

 (Dale 1970). Ecosystem behavior is regulated by 

 feedback loops, time lags, and external physical 

 factors (King and Paulik 1967). More generally, an 

 ecosystem consists of organisms including plants, 

 herbivores, carnivores, and decomposers, with asso- 

 ciated abiotic resources used by those organisms, 

 all located within a definable geographic area and 

 interrelated through a food web. It is an open sys- 

 tem, with radiant energy entering from, and matter 

 and energy lost to, the surrounding environment. 

 Energy is dissipated within an ecosystem, but 

 nutrients are recycled (Green 1975). 



A model should simplify the real system, while 

 preserving essential features (Levins 1966). Ecolo- 

 gical theory looks upon ecosystems as hierarchical 

 systems that can be subdivided for analysis, with 



