Bly Creek ecosystem study - nitrogen exchange within a euhaline salt marsh basin of North Inlet, South Carolina

Abstract

Nitrogen exchange within the Bly Creek basin (North Inlet, South Carolina, USA) was studied during 34 tidal cycles between 20 June 1983 and 19 June 1984. Estimates of tidally mediated transport were made along with annual estimates of nitrogen input to the basin via streamwater, groundwater, and rainwater. Withln the basin, effects of the vegetated marsh, oyster reef community, and the tidal creek on material transport were assessed. There was a small, but statistically insignificant (a = 0.05) NH,+ export from the basin through the tidal creek of 433 kg N yr-' (0.65 g N m-' yr-l); inputs into the basin via streamwater, groundwater, and rain totalled 78 kg NH,+-N yr-'. The NH4+ mass balance suggests the basin is not a source or a sink for this constituent to the surrounding estuary. However, since the vegetated marsh surface imports ca l500 kg NH4+-N yr-l, the tidal creek subsystem must act as a source. It is suggested that remobilization of NH4+ within the tidal creek water column and/or benthic community produces the ammonium necessary to satisfy the input of this constituent to the vegetated marsh. There was also a small, insignificant import of nitrate + nitrite into the basin through the tidal creek of 158 kg N yr-' (0.23 g N m-'yr-'). The vegetated marsh is capable of removing all the nitrate + nitrite potentially imported into this system via tidal water, streamwater, groundwater, and rain. There was a significant (a = 0.05) dissolved organic nitrogen (DON) export from the basin of 7782 kg N yr-' or 11.7 g N m-2 yr-l, whereas there was a statistically insignificant import of particulate nitrogen (PN) (1541 kg N yr-' or 2.3 g N m-' yr-l). The vegetated marsh withm the basin appears to be the main source of DON material to the basin as a significant amount of DON was exported both during tidal inundation and via runoff during tidal exposure. Due to the lack of statistical significance in the tidally mediated PN flux, it is difficult to state whether the basin is a source or sink for this constituent. However, a negative association between tidally mediated PN flux and maximum tidal height suggests that the marsh surface is important in removing PN during high tide conditions.