altered both the chemical properties of the estuarine water and the 

 physical and chemical properties of the sediment in Chesapeake Bay. 

 Similar areas of interest occur throughout the United States and the 

 world, each with their own erosional and hydrological characteristics. 



3. A major study of the dissolved and particulate trace-element 

 burden of streams is required. There is good evidence that organic 

 particles, especially, act as a major carrier of trace metals to the sea 

 where subsequent estuarine processes may release the metals to sea- 

 water. On the basis of sediment and water studies it is clear that as 

 much as 80% of the content of some trace elements and organic particles 

 are released to the estuarine water. The release mechanism is not known. 

 It may in part be released by ion exchange, in part by biological degrada- 

 tion of the organic carrier of the metals, processes that also occur in 

 the open ocean. 



4. The fate of metals and silica in estuarine waters must be assessed 

 to understand not only the pathway of these elements brought to the 

 estuary by streams, but also the modifying role of open-ocean seawater 

 when it encounters the coastal zone. We know that in areas where the 

 supply of organic matter from the continent is great and biological produc- 

 tivity in the adjacent marine environment is high, organic matter accumu- 

 lates rapidly in the sediment, and sulfate reduction occurs. Silica is 

 deposited rapidly by diatom productivity in the same areas. The high 

 sulfide-ion concentration results in the sequestering, as sulfide, of many 

 trace metals released in the sediment from in-situ organic degradation. 

 The result of this process is to extract many metals from seawater, 

 reducing their concentrations in open seawater. This is especially true 

 for mercury, lead, gold, and silver. Iron and manganese (and possibly 

 other metals) may be exceptions to this because of the higher solubilities 

 of the sulfides of the doubly charged ions of these two elements. Hence, 

 a flux of iron and manganese out of an estuary is possible. These pro- 

 cesses are now mainly understood intuitively on the basis of the com- 

 position of sediments and thermodynamic arguments. Experimental 

 and direct observational confirmations are required. 



One aspect of trace-element studies in estuaries, including both 

 radioactive and stable nuclides, involves the transfer of minor elements 

 from polluted rivers and estuaries to the sediments. One can observe 

 the disappearance of lead, cadmium, and similar metals from the water 

 column near shore at a rate faster than can be accounted for by dilu- 

 tion. Analysis of sediment cores reveals that the sediments are a sink 

 for these pollutants. However, the processes of transfer are difficult 

 to define. The chemical forms of the accumulated metals in the sediments 

 may not be related to those in the water column because of the rapid 

 transport and mixing of the sedimentary material. The sampHng problem 



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