CARBON IN ESTUARIES 231 



matter) rrT 2 year l . No latitudinal trend is apparent, although a wide range of 

 latitude is spanned. 



Open Water 



Net production in the open waters of estuaries of the world may average 



— O — 1 



1000 to 2000 g (dry organic matter) m year . Where phytoplankton 

 production dominates, productivity is probably lower; where submerged 

 angiosperms or large attached algae are abundant, production would seem to be 

 higher, perhaps considerably higher. 



These limited data support the assertion that estuaries are "productive" of 

 net primary production. The wetlands or marshes are most productive, although 

 not spectacularly more productive than cane fields, rich woodlands, freshwater 

 marshes, or various communities of cultivated plants. 1 l 



Distribution of Net Production 



In estuaries there may be substantial imports of fixed carbon from uplands, 

 exchanges of carbon with coastal oceans, and exchanges with sediments. There is 

 no report of these exchanges available currently, although there is obvious need 

 for clarification of their magnitudes and function. Limited insight as to the 

 importance of the exchanges is available from an appraisal of the C budget of a 

 tidal salt pond on Long Island. Flax Pond is a 50-ha (hectare) marsh, open to 

 Long Island Sound (Fig. 3). Freshwater inputs are limited; it is flushed twice 

 daily by the tide. The study has been under way for about 1 year. 



The flux of dissolved organic carbon (DOC) through the single channel 

 connecting the marsh to Long Island Sound is potentially very large. Originally 

 we had assumed that there would be a large net flux into the Sound. This 

 appears questionable at present. Data compiled through the first 7 months of a 

 2-year sampling program show that between June and December there was a net 

 flux of fixed carbon into the marsh from Long Island Sound (Fig. 4). The largest 

 influx occurred during the summer and fall, especially September and October. 

 During 3 months a total quantity of C equivalent to 800 to 1000 g (dry organic 

 matter)/m was retained in the estuary. This is equivalent to the net production 

 of many vegetations. During winter and spring there appears to be a regular loss 

 of dissolved organic carbon. The balance for the year will probably be 

 approximately zero. The flux of particulate organic matter (POM) parallels that 

 of dissolved organic matter. The total quantities of particulate are about 10% 

 that of dissolved. The flux of large particulate matter (LPOM) in forms such as 

 Spartina stems appears to be still smaller. In Flax Pond it is less than 1% of the 

 POM. 



Measurement of C as total CO2 shows, as might be expected, a continuous 

 efflux of C from the estuary into the Sound, the total efflux approximating the 

 influx of DOC. 



