Underwater production reaches a peak rate of about 200 milligrams of 

 carbon fixed per square meter of marsh surface per hour (gross algal 

 production: the total primary product of photosynthesis) during 

 August and drops to about 50 milligrams in winter. For periods when 

 the marsh is exposed to air, a peak rate of about 150 milligrams is 

 reached in January. Production drops nearly to zero in March, and 

 gradually rises again through the rest of the year. 



Daily rates of production were estimated from the short-term (1 hour) 

 production measurements by correcting for day length and amount of time 

 various parts of the marsh are exposed to air and flooded with water 

 during a tidal cycle. From the daily production estimates, an estimate 

 of annual production was made which was weighted according to the amount 

 of marsh in the study area having certain elevation and Spartina 

 density. The mean annual production for Georgia salt marshes was estimated 

 to be 200 grams of carbon per square meter (gross algal production). 



Net algal production was estimated at probably more than 90 percent 

 of gross production. There is no evidence that the supply of carbon 

 dioxide is limiting to underwater photosynthesis, but it may sometimes 

 be limiting to photosynthesis in air. The pH of the surface of the marsh 

 sediments rises from an early morning low of about 7.5 to 9 or even 10 

 during the day. When only the algal production is considered and the 

 Spartina is ignored, the primary productivity of the salt marshes can 

 be considered comparable to that of many other aquatic ecosystems, such 

 as lakes and oceans, but lower than many terrestrial and some flowing 

 aquatic ecosystems. Considerable discussion follows presentation of 

 the paper. (G.S.) 



Keywords: primary productivity, algae, Spartina , Georgia 



II-C-2 



Pomeroy, L.R. 1959. Algal productivity in salt marshes of Georgia. 

 Limnology and Oceanography 4:386-397. 



Salt marshes support several populations of primary producers: 

 higher plants, algae on and in the sediments, and phytoplankton in 

 the estuarine water. Much work has been done on phytoplankton pro- 

 duction, and the production of Spartina alterni flora , the dominant 

 spermatophyte of Atlantic coast marshes, has been investigated; but the 

 possible role of the benthic microflora as producers has been largely 

 overlooked. 



This study is concerned with the productivity of the microscopic 

 algae of intertidal salt marshes and with the environmental conditions 

 that influence it. Most of the measurements of production and asso- 

 ciated factors were made in the marshes of the Duplin River, a tidal 

 creek adjacent to Sapelo Island, Georgia, 



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