morning low of about 7.5 to 9 or even 10 during the day. At pH 9 there is no 

 free carbon dioxide in the interstitial water of the sediments and at pH 10 

 there is no bicarbonate either. Under these conditions the only sources of 

 carbon dioxide for photosynthesis are the respiration of heterotrophic organ- 

 isms in the immediate vicinity and diffusion from the air or the depths of the 

 sediments. 



Considering only the algal production and ignoring the Spartina, the 

 primary productivity of the salt marshes is comparable to that of many other 

 aquatic ecosystems, such as lakes and the oceans. It is lower than many 

 terrestrial and some flowing aquatic ecosystems. 



DISCUSSION 



Burbanck: 



Pomeroy: 

 Oppe nhe ime r : 



McHugh: 



Did you notice that the hydrogen sulfide formation in your 

 marsh seems to be limiting at all? 



That is something I have not done a thing with. 



Hydrogen sulphide apparently is not, because the algae will 

 grow right in the hydrogen sulfide layer. It is just as product- 

 ive as anywhere else. 



Just as a matter of curiosity, have you figured out this pro- 

 ductivity in terms of tons per acre ? 



Pomeroy: I cannot give you that offhand. 



Odum: Multiply grams per square meter by 10 and you get pounds 



per acre. 



Pomeroy: Well it is 200 grams per square meter per year. 



Odum: So that would be 2,000 pounds per acre. 



Chapman: What exactly do you mean by estuarine water ? You said that 



you covered it with estuarine water. Is it brackish? 



Pomeroy: I took water from the immediate situation so I wouldn't be sub- 



jecting these organisms to a sudden change in salinity. I am 

 sure they are tolerant to it but I didn't want to introduce this 

 possible variable, so I just collected water from the spot near- 

 by and took it to the laboratory, filtered it and boiled it, so I 

 would have no phytoplankton production and a minimum turbid- 

 ity in the water. 



Chapman: 



You do not know what the salinity was ? 



90 



