WOLFE and RICE: CYCLING OF ELEMENTS IN ESTUARIES 



Table 3. — Role of nondynamic state variables. 



tuarine organisms. In addition, salinity pro- 

 vides a measure of bulk components of seawater, 

 e.g., Ca and K, which may compete directly with 

 trace components for adsorption sites of biologi- 

 cal accumulation, e.g., Sr and Cs. For example, 

 increasing salinity decreases the accumulation 

 rate and concentration factor for '"Cs in estu- 

 arine clams (Wolfe and Coburn, 1970) . Salinity 

 is correlated also with the concentration of '"Cs 

 in lower-salinity estuarine water, possibly as a 

 result of mass action on the sediment-water ex- 

 change equilibrium (Wolfe, 1971). Important 

 dissolved trace components include Fe, Al, and 

 Mn, whose concentrations depend less on salinity 

 than on watershed characteristics and runoff. 

 At the pH, Eh, and ionic strength characteristic 

 of seawater, these elements form insoluble hy- 

 droxides which flocculate and provide adsorptive 

 surfaces for other elements. Such a coprecipi- 

 tation process may be an important determinant 

 in the distribution of fallout '""Ru in estuaries 

 (Wolfe and Jennings, in press). 



For any given estuary the chemical environ- 

 ment and flushing characteristics are affected 

 greatly by the geological and chemical charac- 

 teristics of the watershed area, the type of es- 

 tuary (stratified vs. well-mixed, etc.), and the 

 physical size, shape, and orientation of the es- 



tuarine basin. Such characteristics must be con- 

 sidered when different estuaries are compared. 



A set of biological processes accompanies each 

 trophic interaction and determines the efficien- 

 cies for transfers of biomass between compo- 

 nents. These are feeding or ingestion rate, di- 

 gestion rate, assimilation efficiency, respiration, 

 and growth efficiency. Each of these character- 

 istics may be influenced in turn by various en- 

 vironmental factors, such as temperature and sa- 

 linity (Peters and Boyd, in press; Peters and 

 Angelovic, in press). 



Assimilation and respiration maintain the bio- 

 mass of the biological reservoirs for elements, 

 but the accumulation and retention of most me- 

 tallic elements are probably not directly correl- 

 ated with the assimilation and respiration of 

 carbon. For dynamic modeling of the cycling 

 of metallic elements in the estuarine biota, how- 

 ever, it is essential to consider the changes in 

 biomass as well as changes in concentration of 

 the element of interest. The interrelation of 

 •^^Zn-excretion and respiration has been examined 

 directly for pinfish, Lagodon rhomboides, (Hoss, 

 1971). Lowman et al. (1971) computed assimi- 

 lation efficiencies ("conversion factors") for the 

 transfer of several metallic elements from ocean- 

 ic phytoplankton to zooplankton, based upon 



967 



