River-estuary system, particulates

Table 5-2 presents plutonium levels detected in several surface waters and groundwaters. The Pacific Ocean was sampled for plutonium and Northern Pacific concentrations were, on the average, greater than those detected in the Southern Pacific for both plutonium-239, -240 and plutonium-238 (Miyake and Sugimura 1976). The plutonium content of the particulate matter in three South Carolina estuarine systems was investigated by Hayes et al. (1976). The Neuse and Newport River estuaries received plutonium only through atmospheric fallout the Savannah River estuary received effluent from the Savannah River Plant. Concentrations detected in the three estuaries are comparable. 

Moreover, both river induced up-welling and river discharge of nutrients create a fertile environment which enhances the primary production of organic matter in off-shore direction of estuaries. It can be predicted from these observations that heterogeneous reactions between dissolved and both mineral phase and biota will be predominant in estuaries and coastal zones. These reactions will primarily affect those elements and compounds which are located at the particulate surface. The determination of surface properties of particles appear to be an important key to understand the interactions of trace elements and organic compounds between particulate and dissolved phases in estuarine and coastal systems. 

Estuarine water column particulates, primarily derived from rivers, adjacent wetland systems, and resuspension events, have been shown to be important in controlling the fate and transport of chemicals in estuaries. In particular, mineral surfaces on these particles have been shown to be important in binding organic molecules, gels, and microaggregates. 

Sea water contains a much lower concentration of dissolved organic matter than river water. More than half of this dissolved organic load is of a humic nature. These dissolved organic acids tend to flocculate as the salinity increases (10). Hair and Bassett (11) have observed an increase in the particulate humic acid load of an estuary as one approaches the sea. Although no studies of the distribution of humic materials throughout an estuarine system have been performed, it would appear that estuaries and their sediments in particular, act as a major sink for the dissolved and particulate humic materials. Nissenbaum and Kaplan (12) have observed that terrestrial humic materials are not deposited at great distances from shore in the marine system. A study of the flux of particulate carbon through the Chesapeake Bay comes to a similar conclusion (13). 

In the hypothetical terrestrial system depicted in Fig. 14-4, the P eroded from the land is eventually transported to the estuaries. As in lakes, soils, and rivers, many chemical and biological processes act to control the transport of P within and from the estuary (Lucotte and d Anglejan, 1988 Jonge and Villerius, 1989). Dissolved P may be removed from solution onto the particulate phase and deposited in the sediments. On the other hand, the change in the solution composition may cause P to be released from the particulate load. The P that is transported from the estuaries to the ocean in particulate form will rapidly settle to the sea floor and be incorporated into the sediments. The dissolved P will enter the surface ocean and participate in the biological cycles. Determining what proportion of P that is transported out of the estuary is reactive is a critical step in the elucidation of the marine P budget (Froelich et al., 1982). 

Other inputs of fixed N to the marine environment include terrestrial runoff and atmospheric precipitation, the N isotopic compositions of which are poorly constrained (Figure 2). Dissolved and particulate (5 N in pristine river systems ranges mostly from 0%o to 5%o. However, biological processes along the flow path and in estuaries (in particular, by denitrification see below) can alter the of the... 

Coatzacoalcos estuary had extremely elevated Hg levels during the 1970s. A possible explanation for such elevated Hg values may be that water samples in early studies were not hltered. The waters of this system are characterized by having a high suspended particulate load that corresponds with the sediment load in the river, the tidal regime, and the discharge of effluents from a nearby petrochanical complex. 

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