Assessing benthic impacts of organic enrichment from marine aquaculture

Impacts of salmon farming were evaluated from benthic sediment cores obtained at 22 stations in the Bay of Fundy, Canada. Eleven of the sites were under salmon net pens and 11 control locations were at distances greater than 50 m from net pens. The cores were analysed for several parameters including total sulphide, ammonium and oxygen uptake. Macrofauna were identified and enumerated. Oxygen and carbon dioxide exchange, total sulphide and Eh potential were the most sensitive variables for detecting differences between the experimental and reference sites. Total macrofauna and deposit feeder biomass based on organic carbon accumulation, ammonium gradients and Eh potentials were also indicators of organic enrichment. Model grain size, sediment water content, porewater salinity and sulphate concentration showed no significant differences between sites. The high variability in some sediment geochemical properties probably arose from the irregular deposition of uneaten food pellets and faecal waste.