CARBON IN ESTUARIES 



G. M. WOODWELL, P. H. RICH, and C. A. S. HALL 



Biology Department, Brookhaven National Laboratory, Upton, New York 



ABSTRACT 



A crude estimate of the area of the world's estuaries indicates a total area of about 

 1.7 x 10 6 km 2 of which 3.8 x 10 s km 2 is marsh and 1.4 x 10 6 km 2 is open water. Despite 

 the large amount of research on estuaries in recent decades, there is little basis for an 

 evaluation of equations that define relationships between net primary production, gross 

 production, and various segments of total respiration in estuaries. A survey of the literature 

 suggests that net primary production of estuarine marshes ranges from low rates averaging 

 1000 g (dry organic matter)/year in high latitudes to as much as 5000 g in the tropics. An 

 average middle-latitude net production for the shallow water of estuaries seems to be about 

 1500g (dry organic matter)/year. World net production of estuaries by this estimate is 

 probably about 3.1 x 10 9 metric tons of organic matter annually or 2% of the total for the 

 biota. Large exchanges of fixed carbon occur between estuaries and other water bodies. 

 Most of the exchange occurs as "dissolved" organic matter. Sedimentation may also account 

 for large amounts of net production. Rates of sedimentation of organic matter are probably 

 fixed by the rate of rise of water against the land. The standing crop and productivity of fish 

 in estuaries exceed those for all other natural water bodies. 



Estuaries are commonly considered by scientists and many laymen as among the 

 most vital elements of the interacting series of ecosystems that is the biosphere. 

 They are, we say, "highly productive" and "essential" to maintenance of 

 important coastal and oceanic fisheries. But when asked for a definition of 

 "estuary" or for a measure of their size as a segment of the biosphere or for an 

 appraisal of their total metabolism or their role in the world carbon or sulfur 

 cycles, we must equivocate. Biologists, strangely enough, have been slow to 

 measure the biosphere. 



What are estuaries? What are their functions in the carbon budget? And what 

 is their future? 



Definitions seem simple, including the dictionary definition: "a passage 

 where the tide meets the river current. . .a firth." Most students of estuaries 



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