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Marine Ecology Progress Series

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MEPS 215:49-56 (2001)  -  doi:10.3354/meps215049

Primary production in estuarine oxic/anoxic interfaces: contribution of microbial dark CO2 fixation in the Ebro River Salt Wedge Estuary

Emilio O. Casamayor1,*, Josefina García-Cantizano2, Jordi Mas2, Carlos Pedrós-Alió1

1Departament de Biologia Marina i Oceanografia. Institut de Ciències del Mar-CSIC, Passeig Joan de Borbó s/n, 08039 Barcelona, Spain
2Departament de Genètica i de Microbiologia, Universitat Autònoma de Barcelona, 08193 Bellaterra (Barcelona), Spain

ABSTRACT: The present study assesses the contribution of dark carbon fixation to the primary production in the oxic/anoxic interface of a shallow estuarine environment that develops a salt-water wedge with the presence of sulfide. Primary production was partitioned into oxygenic photosynthesis, anoxygenic photosynthesis and dark fixation. The results show the importance of dark fixation in the oxic/anoxic interface with values higher than 5 mg carbon fixed per cubic meter and per hour in some cases. The average rate of primary production in the dark during the anoxic season for the Ebro River salt wedge resulted in 42 mg C m-2 d-1 in the interface. This represents at least twice the contribution of oxygenic photosynthesis to the primary production in such interface. Because this process is probably important in other salt-wedge or highly stratified estuaries with oxic/anoxic interfaces containing sulfide, the estimates of carbon fixation made so far for these systems may have been underestimated, and should therefore be revised taking into account the contribution of dark processes.

KEY WORDS: Primary production · Dark fixation · Thiobacilli · Salt wedge · Estuary · Sulfide · Oxic/anoxic interface

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