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Marine Ecology Progress Series

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MEPS 504:13-26 (2014)  -  DOI:

Benthic nutrient fluxes and limited denitrification in a sub-tropical groundwater-influenced coastal lagoon

Rebecca J. Bernard1,2, Behzad Mortazavi1,2,*, Lei Wang1,3, Alice C. Ortmann1,3, Hugh MacIntyre4, William C. Burnett5

1The Dauphin Island Sea Lab, 101 Bienville Blvd. Dauphin Island, Alabama 36528, USA
2Department of Biological Sciences, University of Alabama, Tuscaloosa, Alabama 35487, USA
3Department of Marine Sciences, University of South Alabama, Mobile, Alabama 36688, USA
4Department of Oceanography, Dalhousie University, Nova Scotia B3H 4R2, Canada
5Department of Earth, Ocean and Atmospheric Science, Florida State University, Tallahassee, Florida 32306, USA
*Corresponding author:

ABSTRACT: Benthic processes in estuarine systems can alleviate nutrient over-enrichment by removing nitrogen (N) via denitrification, or further intensify eutrophication by supplying N back to the water column. The main objectives of this study were to (1) examine the magnitude and seasonality of benthic fluxes and denitrification, and (2) determine the relative importance of benthic versus submarine groundwater discharge (SGD) N fluxes in Little Lagoon, a shallow, sub-tropical, groundwater-influenced coastal lagoon in the North Central Gulf of Mexico. In the summer, when low water column nitrate (NO3-) concentration (<0.2 µM) occurred in tandem with high hydrogen sulfide concentration (>3000 µM), rates of net N2 fixation (61.7 ± 4.5 SE µmol N m-2 h-1) exceeded rates of net N2 efflux (51.6 ± 4.9 SE µmol N m-2 h-1). Unlike many estuarine systems where denitrification is coupled to nitrification, sulfidic sediments caused denitrification to primarily be supported by water column NO3- in Little Lagoon. Gene copy numbers indicated that markers for N2 fixation, sulfate reduction, and dissimilatory nitrate reduction to ammonium were more abundant than markers for denitrification and nitrification. SGD N fluxes were up to 42 times larger than the benthic rates, and both the benthos and SGD provided dissolved organic nitrogen to the water column. This study presents evidence of limited benthic N fluxes in supplying N to the water column compared to input associated with SGD.

KEY WORDS: Nitrogen cycle · Denitrification · Benthic flux · Sediment · Hydrogen sulfide · Submarine groundwater discharge

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Cite this article as: Bernard RJ, Mortazavi B, Wang L, Ortmann AC, MacIntyre H, Burnett WC (2014) Benthic nutrient fluxes and limited denitrification in a sub-tropical groundwater-influenced coastal lagoon. Mar Ecol Prog Ser 504:13-26.

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