BENTHIC RESPIRATION AND NITROGEN RELEASE IN BUZZARDS BAY, MASSACHUSETTS

The decomposition of organic matter and the regeneration of nitrogen i n the sediments of Buzzards Bay, Massachusetts were examined by measur ing benthic fluxes of oxygen and dissolved inorganic nitrogen (DIN). B enthic respiration (O-2 consumption) rates measured from one site yiel ded an estimate of 65-80 g C m(-2) oxidized annually. Comparing the an nual release of DIN with the consumption of O-2 led to an estimate of N loss from the benthic-pelagic system, most likely as N-2 gas via den itrification, corresponding to 14-32% of the N remineralized from orga nic 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 (ch lorophyll a and phaeopigments). The rate of DIN release was also negat ively related to the particulate organic N (PON) pool as well. The rel ationship of benthic fluxes to sedimentary pigment concentrations sugg ested that pigments were good indicators of labile organic matter inpu t to sediments. Macrofauna appeared to have a direct negative effect, as well as a positive indirect effect on DIN release. Benthic respirat ion rates were not related to sedimentary particulate organic C (POC) or PON content, or macrofaunal abundances. Release rates of DIN were a lso 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 concentrat ions, macrofauna, and distance from the New Bedford sewage outfall wer e not related to the spatial patterns of benthic fluxes in Buzzards Ba y. The combination of seasonal and spatial observations indicate that the processes oxidizing organic matter in Buzzards Bay sediments are c ontrolled by temperature and the delivery of labile organic matter to the sediment surface. Benthic flux rates in Buzzards Bay were generall y low, but N recycling efficiency was high, relative to similar coasta l environments.