Cycling of Elements in Estuaries

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 between 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 m~jor reservoirs of those metals, the mechanisms and pathways of elemental transformatIOn and rates of elemental 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 facilitate maximum use of the sea. This narrow interface 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 increasing industrialization are transported into and through this estuarine environment and may render the habitat unsuitable for desirable species, or may render certain species unfit for human 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 pressures demand that additional estuarine areas be challenged by an increasing multiplicity of additions and modifications whose combined ecological effects are yet unknown. Meaningful evaluation of the ecological stresses imposed by man's activities requires an improved understanding of the interactions between the wastes and the functional components of the ecosystem. Such understanding entails 1 National Marine Fisheries Service, Atlantic Estuarine Fisheries Center, Beaufort, NC 28516. Manuscript accepted April 19i2. fISHERY BULLETIN, VOL. iV. NO. J. 19i2. 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 producers of food, avenues of transportation, receptacles 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 ecosystems. No estuarine ecosystem has yet been studied in sufficient detail to permit accurate prediction 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 useful models for the cycling of contaminant metals (both radioactive and stable isotopes) in estuarine ecosystems. To understand the "cycling of elements" in a natural ecosystem necessitates identifYing the major reservoirs of those elements, determining