Denitrification and nutrient assimilation on a restored oyster reef

Abstract

At a restored reef site and a control site in the Choptank River, Maryland, USA, we partially quantified the effect of oyster reef restoration on the removal of nutrients from the water column by determining seasonal fluxes of oxygen (O2), ammonium (NH4+), combined nitrate and nitrite (NO2+3), di-nitrogen (N2) and soluble reactive phosphorus (SRP) and by assessing the assimilation of nutrients by macrofauna. Fluxes of O2, NH4+, NO2+3 and SRP at the restored site were enhanced by at least one order of magnitude during all seasons. Seasonal denitrification rates at the restored site, measured as flux of N2-N, ranged from 0.3 to 1.6 mmol N2-N m-2 h-1, with August rates among the highest ever recorded for an aquatic system. In addition to oysters (131 oysters m-2; average shell height = 114 mm; age = 2 to 7 yr), the restored reef provided habitat for 24 585 other macrobenthic organisms per square meter compared to 2265 or - ganisms m-2 at the control site. Restoration enhanced the average standing stock of assimilated nutrients by 95 g N m-2 and 15 g P m -2. Nitrogen and phosphorus in shells of live oysters and mussels accounted for 47 and 48% of total nitrogen and phosphorus standing stocks, respectively. Our results demonstrate that oyster reef restoration can significantly increase denitrification rates and enhance nutrient sequestration via assimilation into bivalve shells. © Inter-Research 2013.