Differential Effects of Bivalves on Sediment Nitrogen Cycling in a Shallow Coastal Bay

• Published in: Estuaries and coasts 2018-06, Vol.41 (4), p.1147-1163
• Main Authors: Smyth, Ashley R., Murphy, Anna E., Anderson, Iris C., Song, Bongkeun
• Format: Article
• Language: English
• Subjects: Agricultural practices; Ammonium; Ammonium compounds; Annual variations; Aquaculture; Bivalvia; Clams; Coastal ecosystems; Coastal environments; Coastal Sciences; Denitrification; Earth and Environmental Science; Ecology; Ecosystems; Environment; Environmental Management; Excretion; Farm management; Fluxes; Freshwater & Marine Ecology; Marine molluscs; Metabolism; Mineral nutrients; Mineralization; Mollusks; Nitrate reduction; Nitrates; Nitrogen; Nitrogen compounds; Nitrogen cycle; Organic matter; Oxides; Oyster reefs; Oysters; Reduction; Reefs; Seasons; Sediment; Sediments; Strategic management; Uptake; Water and Health; Water column
• ISSN: 1559-2723; 1559-2731
• DOI: 10.1007/s12237-017-0344-9

In coastal ecosystems, suspension-feeding bivalves can remove nitrogen though uptake and assimilation or enhanced denitrification. Bivalves may also retain nitrogen through increased mineralization and dissimilatory nitrate reduction to ammonium (DNRA). This study investigated the effects of oyster reefs and clam aquaculture on denitrification, DNRA, and nutrient fluxes (NOx, NH₄⁺, O₂). Core incubations were conducted seasonally on sediments adjacent to restored oyster reefs (Crassostrea virginica), clam aquaculture beds (Mercenaria mercenaria) which contained live clams, and bare sediments from Smith Island Bay, Virginia, USA. Denitrification was significantly higher at oyster reef sediments and clam aquaculture site than bare sediment in the summer; however, DNRA was not enhanced. The clam aquaculture site had the highest ammonium production due to clam excretion. While oyster reef and bare sediments exhibited seasonal differences in rate processes, there was no effect of season on denitrification, or dissimilatory nitrate reduction to ammonium (DNRA) or ammonium flux at the clam aquaculture site. This suggests that farm management practices or bivalve metabolism and excretion may override seasonal differences. When water column nitrate concentration was elevated, denitrification increased in clam aquaculture site and oyster reef sediments but not in bare sediment; DNRA was only stimulated at the clam aquaculture site. This, along with a significant and positive relationship between denitrification and sediment organic matter, suggests that labile carbon limited nitrate reduction at the bare sediment site. Bivalve systems can serve as either net sinks or sources of nitrogen to coastal ecosystems, depending mainly on the type of bivalve, location, and management practices.