Benthic respiration and nitrogen release in Buzzards Bay, Massachusetts

Abstract

The decomposition of organic matter and the regeneration of nitrogen in the sediments of Buzzards Bay, Massachusetts were examined by measuring benthic fluxes of oxygen and dissolved inorganic nitrogen (DIN). Benthic respiration (O 2 consumption) rates measured from one site yielded an estimate of 65-80 g C m −2 oxidized annually. Comparing the annual release of DIN with the consumption of O 2 led to an estimate of N loss from the benthicpelagic system, most likely as N 2 gas via denitrification, corresponding to 14-32% of the N remineralized from organic matter decomposition. Using path analysis, benthic flux rates of O 2 and DIN over a seasonal cycle in Buzzards Bay were determined to be related to water temperature and sediment photosynthetic pigments (chlorophyll a and phaeopigments). The rate of DIN release was also negatively related to the particulate organic N (PON) pool as well. The relationsbip of benthic fluxes to sedimentary pigment concentrations suggested that pigments were good indicators of labile organic matter input to sediments. Macrofauna appeared to have a direct negative effect, as well as a positive indirect effect on DIN release. Benthic respiration rates were not related to sedimentary particulate organic C (POC) or PON content, or macrofaunal abundances. Release rates of DIN were also unrelated to POC pools. Benthic flux rates measured at 12 sites in Buzzards Bay during August 1989 varied by less than a factor of 2 for benthic respiration and less than a factor of 3 for DIN release. The only environmental factor that emerged from path analysis as related (negatively) to the spatial pattern of benthic flux rates in August was water depth. Other factors, such as organic pools, pigment concentrations, macrofauna, and distance from the New Bedford sewage outfall were not related to the spatial patterns of benthic fluxes in Buzzards Bay. The combination of seasonal and spatial observations indicate that the processes oxidizing organic matter in Buzzards Bay sediments are controlled by temperature and the delivery of labile organic matter to the sediment surface. Benthic flux rates in Buzzards Bay were generally low, but N recycling efficiency was high, relative to similar coastal environments