The Contribution of Benthic Nutrient Regeneration to Primary Production in a Shallow Eutrophic Estuary,Weeks Bay,Alabama |
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| Authors: | Behzad Mortazavi Ashley A Riggs Jane M Caffrey Hélène Genet Scott W Phipps |
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| Institution: | (1) Department of Biological Sciences, University of Alabama, Tuscaloosa, AL 35401, USA;(2) Dauphin Island Sea Lab, 101 Bienville Boulevard, Dauphin Island, AL 36528, USA;(3) Center for Environmental Diagnostics and Bioremediation, University of West Florida, 11000 University Parkway, Pensacola, FL 32514, USA;(4) Weeks Bay Reserve, 11300 U.S. Highway 98, Fairhope, AL 36532, USA |
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| Abstract: | Benthic oxygen, dinitrogen, and nutrient fluxes (NH4+, NO3−, and PO43−) were measured monthly during a 1-year period at two locations in Weeks Bay, a shallow (1.4 m) and eutrophic estuary in Alabama.
Gross primary productivity (GPP), ecosystem respiration (R), and net ecosystem metabolism were determined from high-frequency
dissolved oxygen measurements. Peak water column NO3− (55 μM) and chlorophyll a (138 μg/l) concentrations were measured during spring and fall, respectively. Sediments were a net source of NH4+ (102 μmol m−2 h−1) and PO43− (0.9 μmol m−2 h−1) but a sink for NO3− (−30 μmol m−2 h−1). Benthic N2 fluxes indicated net N fixation (12 μmol N m−2 h−1). Sediment oxygen demand (0.55 g O2 m−2 day−1) accounted for <10% of R (7.3 g O2 m−2 day−1). Despite high GPP rates (4.7 g O2 m−2 day−1), the estuary was net heterotrophic. Benthic regeneration supplied, on average, 7.5% and 4% of primary productivity N and
P demands, respectively. These results contrast with the conventional view that benthic regeneration accounts for a large
fraction of phytoplankton nutrient demand in shallow estuaries. |
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