Abstract
Over the past 70 years, nitrogen (N) enrichment in temperate coastal systems has been increasing with human population and shifts in land use. Managers currently seek new infrastructure tools to control N for restoring and protecting estuarine habitat. Recently, the use of bivalve aquaculture has been proposed, but few quantitative studies integrate both the mechanisms and extent which bivalves can mitigate the impact of nutrient enrichment in general. Specifically, in New England’s estuaries, oyster growth and filtration are well known; however, biodeposition from actively feeding bivalves has been shown to also modify the benthic-pelagic coupling of carbon (C) and N. The present study investigated the seasonal response of C and N cycling in sediments receiving labile organic matter through biodeposits from suspended aquaculture of eastern oysters, Crassostrea virginica, in two temperate estuaries. In addition to field measurements of sediment-water column exchange of oxygen (O2) and N, a long-term laboratory sediment incubation was conducted over 354 days, where sediments received daily additions of field collected biodeposits over the growing season (208 days).Further, a separate experiment incubated only the biodeposits to directly assess their decay rate at a constant temperature. Results showed similar seasonal trends in both the field and long-term laboratory incubation, with temperature being the primary factor inthe annual pattern of C and N mineralization. Of the biodeposits from the laboratory,19.4 – 22.8 % of C and 23.3 – 24.3 % of N was remineralized, including N loss through denitrification. The isolated biodeposits had a half-life for labile organic C of 18.6 – 21.2days. The transfer of organic matter from the water column to the sediments by oyster biodeposition will tend to lower water column total nitrogen levels and increase water clarity. While much of the C and N is remineralized during the oyster growing season, a fraction is held in the sediments and returned as inorganic forms in the fall, winter and early spring when the effects of N additions to estuarine waters are less.