WOLFE and RICE; CYCLING OF ELEMENTS IN ESTUARIES 



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(Wolfe, 1971) ; whereas *^^Zn may be irreversibly 

 adsorbed onto estuarine sediments (Johnson, 

 Cutshall, and Osterberg-, 1967) . The actual flux 

 of any given element throug-h the complex inter- 

 woven network of pathways tentatively identi- 

 fied in Table 2 is in a state of dynamic equilibri- 

 um afl^ected by system imports and exports and 

 by a number of environmental variables, to be 

 discussed in the following sections. 



INPUTS AND OUTPUTS OF ELEMENTS 

 TO AND FROM ESTUARIES 



System inputs and outputs consist of the phys- 

 ical translocation of elemental reservoirs (sedi- 

 ment, water, and biotic components) across the 

 boundaries of the estuarine system (Table 2), 

 and fluxes of other materials (nonreservoirs) 

 which influence the distribution or movement of 

 elements among the system reservoirs. Rainfall 

 is a dominating system input, which introduces 

 small amounts of some elements directly as aero- 

 sols (Gorham, 1961), but exerts its greatest in- 

 fluence in the form of runoff". The volume and 

 flow rate of runoff in turn determine the amount 

 and composition of elements leached from the 

 land and the size of the bed load of eroded sedi- 

 ment transported into the estuary. The volume 

 and flow of runoff" also interact with the tidal 

 volume to affect the flushing rate for the estuary. 

 Tidal flushing continuously removes from the 

 estuary a fraction of the dissolved and suspended 

 materials, including the planktonic reservoirs. 

 The tidal volume also represents an input of 

 ocean water, but since seawater contains less of 

 most metallic elements than estuarine waters, 

 net loss from the estuary probably results. If, 

 on the other hand, the coastal or estuarine waters 

 contained an excess of uncomplexed organic ma- 

 terial, seawater might represent an input of sol- 

 uble ionic metallic elements which could accumu- 

 late in the estuary through sedimentation, or be 

 removed from the estuary as organic complexes, 

 either by flushing or bioaccumulation. 



Variable wind speed and direction affect water 

 circulation patterns particularly in shallow estu- 

 aries and thereby vary the "normal" flushing 

 characteristics of an estuary. Circulation within 



965 



