The distribution of nitrate 

 in the upper Chesapeake Bay. . 

 ..suggests that the inflow of 

 the Susquehanna River. . . is 

 the major source ... (Carpenter 

 et al. 1969). 



The high fishery productivity 

 of the water adjacent the 

 river mouth is a result of nu- 

 trient contribution by the 

 Mississippi River... (Ho and 

 Barnett 1977). 



River inflow is clearly a ma- 

 jor source of substances to 

 the estuary (San Francisco 

 Bay) ... (Peterson 1979). 



Conclusions such as these seem in- 

 tuitively correct because the con- 

 centrations of nutrients, particu- 

 larly inorganic nitrogen and sil- 

 ica, are usually much higher in 

 fresh water than they are in coast- 

 al sea water (Figure 1). But the 

 situation is more interesting than 

 it first appears, and even this 

 simple relationship may be re- 

 versed. For example, in their stud- 

 ies of one of the world's major riv- 

 ers, Ryther et.al. (1967) found that: 



In the surface water influenc- 

 ed by the Amazon River compared 

 with the surrounding seawater, 

 the concentrations of nitrate, 

 phosphate, and planktonic organ- 

 isms were lower while the levels 

 of silicate were appreciably 

 higher. The direct over all ef- 

 fort of the river, therefore, is 

 to decrease the fertility of the 

 ocean into which it flows. 



low that the higher concentrations 

 of nutrients normally found in riv- 

 ers will make freshwater inputs 

 a major factor in estuarine nutri- 

 ent dynamics. And it will require 

 considerably more than a descrip- 

 tion of the freshwater-saltwater 

 nutrient concentration gradient to 

 properly assess the role of fresh 

 water in enhancing the productivity 

 of estuaries. 



I think it is important to 

 realize how confused we still are 

 about this fundamental problem of 

 estuarine (and nearshore) produc- 

 tivity, and how far we still are 

 from a full understanding of coast- 

 al marine nutrient dynamics. If 

 we keep our sense of humor and 

 some perspective on the real com- 

 plexity and challenge of the problem, 

 it can be humbling and amusing to 

 watch ecologists arguing that salt 

 marshes are valuable because they 

 "outwell" nutrients (which suppos- 

 edly make the estuary productive) 

 and because they provide "tertiary 

 treatment" which removes nutrients 

 from the estuary which supposedly 

 are making it eutrophic (Nixon 

 1980) . In a symposium focusing on 

 the importance of freshwater in- 

 puts, the tendency is to emphasize 

 the role of rivers in bringing 

 "good" nutrients into the estuary. 

 But in another context the emphasis 

 is likely to be on the harmful ef- 

 fects of "bad" nutrients from sew- 

 age or agricultural runoff. 



FRESHWATER INPUTS AND 

 OTHER HYPOTHESES 



While the behavior of the Ama- 

 zon may be a remarkable exception, 

 it still does not necessarily fol- 



Given the present state of know- 

 ledge, it should not be surprising 

 that a number of alternative hypothe- 

 ses have been developed which attempt 



33 



