Assessing Nitrogen Dynamics Throughout the Estuarine Landscape

Assessing nitrogen dynamics in the estuarine landscape is challenging given the unique effects of individual habitats on nitrogen dynamics. We measured net N-2 fluxes, sediment oxygen demand, and fluxes of ammonium and nitrate seasonally from five major estuarine habitats: salt marshes, seagrass beds (SAV), oyster reefs, and intertidal and subtidal flats. Net N-2 fluxes ranged from 332 +/- 116 mu mol N-N-2 m(-2) h(-1) from oyster reef sediments in the summer to -67 +/- 4 mu mol N-N-2 m(-2) h(-1) from SAV in the winter. Oyster reef sediments had the highest rate of N-2 production of all habitats. Dissimilatory nitrate reduction to ammonium (DNRA) was measured during the summer and winter. DNRA was low during the winter and ranged from 4.5 +/- 3.0 in subtidal flats to 104 +/- 34 mu mol (NH)-N-15 (4) (+) m(-2) h(-1) in oyster reefs during the summer. Annual denitrification, accounting for seasonal differences in inundation and light, ranged from 161.1 +/- 19.2 mmol N-N-2 m(-2) year(-1) for marsh sediments to 509.9 +/- 122.7 mmol N-N-2 m(-2) year(-1) for SAV sediments. Given the current habitat distribution in our study system, an estimated 28.3 x 10(6) mol of N are removed per year or 76 % of estimated watershed nitrogen load. These results indicate that changes in the area and distribution of habitats in the estuarine landscape will impact ecosystem function and services.