236 WOODWELL, RICH, AND HALL 



protein yields from managed estuarine regions equal or exceed protein yields 

 from managed terrestrial systems producing beef. 



THE CARBON BUDGET OF THE WORLD'S ESTUARIES 



Experience with Flax Pond suggests that there is not a large steady efflux of 

 fixed carbon from estuarine marshes into coastal waters. In such estuaries the 

 flux may be the opposite with the marsh removing fixed carbon from tidal 

 waters. Earlier experience seems to show that the dissolved organic matter of the 

 oceans (~1 mg/1) does not originate in the Amazon " and probably does not 

 originate in other estuaries. If this relationship applies generally, and 

 sediments are accumulating, net ecosystem production as we have defined it 

 must be positive for the estuaries of the world. Estuaries appear to be centers of 

 high primary production, high metabolism, and centers of sedimentation; they 

 may not normally be centers of outwelling of fixed carbon into coastal oceans. 



The magnitude of NEP in estuaries obviously depends on the division of the 

 carbon flux between metabolism and sedimentation. The rate of sedimentation 

 is controlled both by the rate of input of fixed carbon and the rise of sea level 

 against the land. The input of fixed carbon (NEP) can be appraised but crudely 

 at present. It is the net production of plants within the estuary (gross production 

 less respiration of autotrophs) plus the balance between influx and efflux 

 (Eq. 2). Net production can be estimated from the literature summarized above 

 for marshes and open water. 



The amount of primary production in marshes appears to vary with latitude. 

 Assuming that the world's marshes are divided equally among those having net 

 productions of 1000, 2500, and 5000 g (dry organic matter) nf 2 year 1 , the 

 annual net production of the world's marshes would be 1.09 X 10 1 5 g (dry 

 organic matter) (1.09 X 10 9 metric tons). If C is 0.45 of this dry matter, then 

 there would be 4.9 X 10 8 metric tons C entering the world's marshes annually as 

 net production. 



Estuarine waters are less productive but larger in total area. Assuming that 

 mean net production of estuarine waters is 1500g (dry organic matter) m 

 year , the world total is 2.04 X 10 metric tons (dry organic matter)/year, 

 equivalent to 9.18 X 10 8 metric tons C. Total net production of the estuaries 

 and estuarine marshes is thus 3.13 X 10 metric tons (dry organic matter)/year 

 or 1.41 X 10 9 metric tons C. An earlier estimate by Whittaker and Likens (cited 

 by Whittaker and Woodwell 24 ) suggests that world estuaries might contribute 

 4 X 10 9 metric tons (dry organic matter) as net production to a world total net 

 production of 164 X 10 metric tons. Thus, although estuaries as we have 

 defined them include an area of approximately 0.25% of the earth's surface, 

 their net production by this estimate is about 2% of the world net production. 



Direct, short-term measurements of rates of sedimentation are difficult to 

 make with accuracy. An appraisal of current data is beyond our scope, but such 



