CYCLING OF ELEMENTS IN ESTUARIES 



D. A. Wolfe and T. R. Rice' 



ABSTRACT 



Meaningful evaluation of the ecological stresses imposed by man's release of heavy metals 

 or radioisotopes into estuaries requires an improved understanding of the interactions be- 

 tween the waste materials and the functional components of the ecosystem. In this paper, 

 we review and discuss the types of information required for the development of useful 

 models for the cycling of contaminant metals (both radioactive and stable) in estuarine 

 ecosystems. With particular reference to the coastal plain estuaries of the southeastern 

 United States, we discuss the major reservoirs of those metals, the mechanisms and path- 

 ways of elemental transformation and rates of elem.ental turnover among reservoirs, 

 and the responses of these processes and reservoirs to environmental change. A concept- 

 ual systems model is presented as the preliminary phase in the development of dynamic 

 mathematical models of elemental cycling. 



Estuaries form the interface between the open 

 ocean and man's land base, which in the coastal 

 zone undergoes intensive development to facili- 

 tate maximum use of the sea. This narrow inter- 

 face is a highly productive environment used at 

 some stage of development by most of the marine 

 fishery organisms exploited by man. Waste 

 products of man's expanding population and in- 

 creasing industrialization are transported into 

 and through this estuarine environment and may 

 render the habitat unsuitable for desirable spe- 

 cies, or may render certain species unfit for hu- 

 man consumption. Man's impingement upon 

 estuaries has assumed many forms ; estuarine 

 habitats have already succumbed to industrial 

 and municipal pollution, to landfill and dredging 

 operations; and economic and population pres- 

 sures demand that additional estuarine areas be 

 challenged by an increasing multiplicity of ad- 

 ditions and modifications whose combined eco- 

 logical effects are yet unknown. 



Meaningful evaluation of the ecological stres- 

 ses imposed by man's activities requires an im- 

 proved understanding of the interactions be- 

 tween the wastes and the functional components 

 of the ecosystem. Such understanding entails 



' National Marine Fisheries Service, Atlantic Estuar- 

 ine Fisheries Center, Beaufort, NC 28516, 



Manuscript accepted April 1972. 

 FISHERY BULLETIN: VOL. 70, NO. 3, 



1972. 



knowledge of the general principles of ecosystem 

 operation, and not merely a description of the 

 ecosystem structure at one or more instants in 

 time. Man's continued and expanding variety 

 of demands on estuarine environments as pro- 

 ducers of food, avenues of transportation, recep- 

 tacles for wastes, and as sources of recreational 

 and esthetic pleasure make it imperative that we 

 understand the interactions of all the material 

 imports, whether of human or natural origin; 

 and all the outputs, including both tidal exports 

 and human exploitation of resources, to ensure 

 the continued viability of the resultant ecosys- 

 tems. No estuarine ecosystem has yet been 

 studied in sufficient detail to permit accurate pre- 

 diction of ecosystem response to contaminative 

 additions. Considerable insight may be gained, 

 however, from attempts to synthesize adequate 

 predictive systems models from fragmentary 

 data already available from ecological studies, 

 experimental biology, and experience with pre- 

 vious instances of pollution. In this paper, we 

 examine and discuss briefly the nature of the 

 information required for the development of use- 

 ful models for the cycling of contaminant metals 

 (both radioactive and stable isotopes) in estu- 

 arine ecosystems. 



To understand the "cycling of elements" in a 

 natural ecosystem necessitates identifying the 

 major reservoirs of those elements, determining 



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