are some troubling discrepancies 

 between the Texas commercial land- 

 ings data reported by Chapman (1966) 

 and those presented by Armstrong 

 (1980). 



The differences are not due to a 

 14 year lag in sampling years, be- 

 cause the data discussed by Armstrong 

 (1980) were first presented by Cope- 

 land (1966) and may, in fact, be part 

 of the same data set (1956-62) used 

 by Chapman (1966). If the numbers 

 reported by Chapman are too high, 

 particularly the 450 kg/ha assigned 

 to Galveston Bay, then his argument 

 for a positive relationship between 

 freshwater input and fisheries yield 

 is not very compelling. 



It seems clear that while there 

 may be some estuaries in which there 

 is a good correlation (either posi- 

 tive or negative) between freshwater 

 discharge and fisheries yield, the 

 mechanism involved is probably some- 

 thing other than a simple fertilizing 

 effect of the river itself (eg. 

 Huntsman 1955; Barrett and Ralph 

 1977; Sheridan and Livingston 1979). 

 In fact, considering all of the fac- 

 tors that go into determining the 

 catch of finfish and shellfish in an 

 estuary, it is remarkable how similar 

 the area-based yields are from most 

 coastal marine systems. 



SEASONAL CYCLES 



There appear to be few systems 

 in which the seasonal cycle in pri- 

 mary production corresponds with the 

 cycle of river discharge (Figure 8). 

 With the exception of Narragansett 

 Bay and perhaps a few other areas 

 which have a strong winter-spring 

 phytoplankton bloom, the general 

 pattern seems to be for production 

 to peak during the summer, some 

 months after river discharge has de- 

 clined following spring runoff. Be- 

 cause the freshwater usually carries 



sediment with it, the offset in pro- 

 duction may be due to decreasing 

 turbidity as salinity rises or to a 

 combination of increasing solar radi- 

 ation and temperature (Figure 8) . In 

 the case of Narragansett Bay, the 

 freshwater input is very small and 

 initiation of the winter-spring bloom 

 has been shown to be due to light and 

 other factors rather than to river 

 discharge (Hitchcock and Smayda 1977; 

 Nixon et al. 1979) . 



It is possible to examine the 

 potential contribution of freshwater 

 nutrient inputs to the spring-summer 

 phytoplankton bloom in a more general 

 way. As river (or groundwater) flow 

 increases, fresh water will accumu- 

 late in the estuary, and the salinity 

 will decrease. As noted earlier, the 

 annual salinity excursion for many 

 estuaries appears to fall around 

 5 o/oo to 10 o/oo (Figure 5). A sa- 

 linity decline of 5 o/oo will repre- 

 sent an accumulation of varying 

 amounts of fresh water, depending on 

 the salinity of the nearshore and es- 

 tuarine water with which it is being 

 mixed (Table 4). If the concentra- 

 tions of dissolved inorganic nitrogen 

 (the major limiting nutrient in 

 coastal marine waters) in the river 

 water lie between 10 to 100 yM, the 

 amount of river-borne nitrogen per 

 unit volume of lower salinity estu- 

 arine water can be calculated and an 

 estimate made of the primary produc- 

 tion this amount of nitrogen could 

 support (Redfield 1934). The result 

 suggests that in most estuaries the 

 accumulation of "new" nitrogen from 

 fresh water is not likely to support 

 more than a few days of growth under 

 bloom conditions when production 

 rates often reach or exceed 500-1000 

 mg C/m /day. But the total primary 

 production cannot be calculated with- 

 out a knowledge of the turnover rate 

 and residence time of the nitrogen in 

 the estuary. 



188 



