(though based on little evidence) is 

 that the amount of N, P, or Si being 

 delivered to various estuaries ought 

 to vary considerably (Jaworski, in 

 press), and that if this feature is 

 important in regulating primary pro- 

 duction, it might also be expected to 

 vary widely. 



SEASONAL VARIATION 



The inflow of freshwater varies 

 seasonally to a greater or lesser 

 degree in different estuaries as a 

 function of rainfall, temperature, 

 and watershed size and character- 

 istics. In many (perhaps all) 

 estuaries, a higher rate of 

 freshwater input is associated 

 with a higher rate of nutrient in- 

 put as well, but because there is 

 often some dilution of concentra- 

 tion during periods of higher dis- 

 charge, the total flux of nutrients 

 may be more constant during the 

 year than a simple inspection of 

 the yearly discharge cycle may 

 suggest. Overall, however, periods 

 of high discharge will bring about 

 an accumulation of fresh (presum- 

 ably high nutrient) water in the 

 estuary and result in a lowering 

 of the salinity. The annual varia- 

 tion in salinity differs consider- 

 ably among estuaries for all of the 

 reasons mentioned previously, but 

 an excursion of 5 to 10 percent is 

 not uncommon (Figure 5). If river 

 input is important in driving the 

 primary production of the estuary, 

 we might expect to see some en- 

 hanced production associated with 

 this period of increased discharge 

 and/or lowered salinity. 



SOME OBSERVATIONS ABOUT 

 ESTUARINE PRODUCTION 



REGIONAL VARIATION - A COMPARISON OF 

 SYSTEMS 



Primary Production 



In reviewing the various stud- 

 ies of primary production in estu- 

 arine systems, I have been impress- 

 ed by the remarkable similarity of 

 virtually all of the annual estimates 

 (Table 2). With few exceptions 

 (such as the highly eutrophic lower 

 Hudson River), there appears to be 

 somewhere between 150-400 gC/m /yr 

 fixed in shallow coastal waters when 

 an average is made over a whole estu- 

 arine system. Values higher than 

 these are certainly found in seagrass 

 and seaweed beds, but when their pro- 

 duction is apportioned over the 

 whole estuary and added to the 

 lower area-based phytoplankton pro- 

 duction that is usually found in 

 such shallow waters, the total pro- 

 duction seems to fall in with that 

 found in deeper plankton-based 

 systems. The same may be true of 

 estuaries with very productive in- 

 tertidal or shallow subtidal ben- 

 thic diatom communities, though 

 there are too few measurements of 

 this component to generalize with 

 any confidence. It seems to me 

 that this small variation in pro- 

 duction (approximately a factor of 

 2-3) compared with the very large 

 range in estuarine freshwater input 

 (orders of magnitude) suggests that 

 it is some other, more constant 



40 



