WOLFE and RICE: CYCLING OF ELEMENTS IN ESTUARIES 



Murdoch, 1970) .' Quantification of the biomass 

 in each of the major biological components is a 

 primary objective of ecological research at the 

 Atlantic Estuarine Fisheries Center, and prelim- 

 inary estimates are currently available for the 

 dominant macroorganisms (Williams, Thayer, 

 Price, Kjelson, and Turner, Unpublished data). 

 Analytical data on the concentrations of iron, 

 manganese, zinc, and copper in these organisms 

 and in sediments and water are also available 

 or forthcoming (Cross et al., 1970; Cross and 

 Brooks, in press; Wolfe, 1970a; Cross, Lewis, and 

 Hardy") . Meaningful quantification of reservoir 

 size for any element in certain components, how- 

 ever, will be extremely difficult to achieve (espe- 

 cially for the "other" categories, e.g., filter-feed- 

 ing bivalves, deposit-feeding bivalves, carniv- 

 orous benthos, etc.) . It may be practical to eval- 

 uate the importance of these "catch-all reser- 

 voirs" only by manipulating trial values for bio- 

 mass and elemental concentrations during early 

 phases of model development. 



Pathways of elemental flux between reservoirs 

 also are tentatively identified in Table 2. Indi- 

 vidual transfer processes are designated in the 

 matrix of Table 2 by an "I", indicating an influx 

 of a metallic element from the reservoir at the 

 top of the table to the reservoir on the left. Flux- 

 es between biological reservoirs represent food 

 chain transfers of elements. Such transfers 

 usually involve one-way cyclic net flows (with 

 internal loops) through the food web of the eco- 

 system. At this time the feeding habits of many 

 of the listed species are incompletely known, and 

 the food web of Table 2 must be regarded partly 

 as the product of intuition and speculation. 



The flux of elements between the organisms 

 and the nonliving reservoirs is less readily ident- 

 ified, however, than the food web, because of un- 



" Williams, R. B., and M. B. Murdoch. 1970. A gen- 

 eral evaluation of fishery production and trophic struc- 

 ture in estuaries near Beaufort, N.C. In Center for 

 Estuarine and Menhaden Research Annual Report to the 

 Atomic Energy Commission. Filed at NMFS Atlantic 

 Estuarine Fisheries Center, Beaufort, N.C. 28516. [Pro- 

 cessed.] 



* Cross, F. A., J. M. Lewis, and L. H. Hardy. Con- 

 centrations of Mn, Fe, Cu, and Zn in four species of filter- 

 feeding bivalve molluscs. Unpublished manuscript filed 

 at NMFS Atlantic Estuarine Fisheries Center, Beaufort, 

 N.C. 28516. 



certainty about the relative abundance and im- 

 portance of diff'erent physical-chemical states, 

 e.g., the ionic forms versus organic complexes. 

 Physical-adsorption and ion-exchange processes, 

 operative on biological (and nonbiological) sur- 

 faces, obviously would contribute to the total flux 

 of an element; but since these processes are gen- 

 erally reversible, their importance to net trans- 

 fers (especially at higher trophic levels) remains 

 unknown. There must be a net influx of most 

 elements from the soluble ionic phase to most 

 organisms during their life span, however, sim- 

 ply because the surface area for adsorption in- 

 creases during growth. 



The significance of organic-metal complexes 

 is unknown. We suspect that dissolved organic 

 compounds constitute a mechanism for internal 

 feedback loops involving all organisms at all 

 trophic levels, except perhaps man. Thus, an 

 organism may accumulate specific organic-metal 

 complexes which undergo metabolic transforma- 

 tion, and the metals may in part be excreted as 

 different organic complexes which reenter the 

 cycle as nutrients for phytoplankton or hetero- 

 trophic microbes. We can only speculate now 

 on whether there is net production or net util- 

 ization of metal-organic complexes by organisms. 

 This ambiguity is indicated in Table 2 by a 

 "double I" (i.e., by I's at both relevant intersects 

 of the matrix) , representing ingestion or absorp- 

 tion of organic-metal complexes by most orga- 

 nisms with simultaneous excretion of other or- 

 ganic complexes which might be quite diff'erent 

 chemically. 



Fluxes between nonliving reservoirs are more 

 dependent upon reversible physical processes, 

 such as adsorption, ion-exchange, and sedimen- 

 tation-resuspension. The net direction of flux 

 may therefore depend on such variables as sa- 

 linity, pH, and turbulence. The association of 

 heterotrophic microbes with suspended partic- 

 ulate material probably results in a net influx 

 of most metals into this reservoir from soluble 

 sources with subsequent passage into detritus- 

 based food chains. The extent of reversibility 

 for the transfers (identified by "R" in Table 2) 

 varies also from element to element. Thus, ^''"Cs 

 may be transported into estuaries on bed-load 

 sediment and desorbed at higher salinities 



963 



