MEPS 262:55-69 (2003)  -  doi:10.3354/meps262055

Contribution of denitrification to nitrogen, carbon, and oxygen cycling in tidal creek sediments of a New England salt marsh

M. Robert Hamersley1,3,*, Brian L. Howes2

1Department of Biology, Woods Hole Oceanographic Institution, 45 Water St., Woods Hole, Massachusetts 02543, USA
2School for Marine Science and Technology, University of Massachusetts, 706 S. Rodney French Blvd., New Bedford, Massachusetts 02744-1221, USA
3Present address: School for Marine Science and Technology, University of Massachusetts, 706 S. Rodney French Blvd., New Bedford, Massachusetts 02744-1221, USA

ABSTRACT: The contribution of denitrification to sediment metabolism was studied at 2 sites (muddy and sandy) in unvegetated tidal creek sediments from a small Cape Cod, USA, salt marsh receiving nitrate-enriched groundwater flows (32 mmol m-2 d-1). Simultaneous measurements of sediment N2, CO2, O2, and dissolved inorganic N fluxes were made over annual cycles. A total of 46% of the ammonium remineralized within the sediments was transformed to N2 by coupled nitrification-denitrification (Dn). Denitrifying and nitrifying bacteria contributed 15 and 18% to total sediment C and O cycling, respectively. C, N, and O2 cycling rates were limited by both temperature and the availability of labile organic matter. Muddy sediment C content was twice that of sandy sediments, but was half as labile, resulting in similar mean metabolic rates between sediment types (mean muddy and sandy O2 consumption rates were 62 and 58 mmol m-2 d-1, respectively; CO2 production was 58 and 46 mmol m-2 d-1; and Dn was 5.4 and 4.9 mmol N m-2 d-1). Sediment δ13C (-18.5 and -20.8‰) and the molar CO2:N flux ratio (6.1) at both sites are consistent with a sediment metabolism based on algal rather than macrophytic biomass, and groundwater nitrate was the dominant source of N supporting algal growth. Annually, Dn accounted for 72% of total denitrification, with the remainder accounted for by water column-supported denitrification. Since all the denitrified N originated from groundwater nitrate, algal uptake must have initially out-competed denitrification for water column nitrate, but nearly half of this algal N was subsequently remineralized and denitrified.


KEY WORDS: Salt marsh · Denitrification · Sediment metabolism · Groundwater nitrogen


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