Dissolved reactive phosphorus release from sediments beneath a freshwater cage aquaculture development in West Scotland

Sediments below Atlantic salmon (Salmo salar) smolt cage rearing units in Loch Tralaig, a small freshwater loch in Western Scotland, were studied to assess the potential for waste products, such as fish faeces, uneaten or egested feed pellets, to release dissolved reactive phosphorus (DRP) from sediments.Replicate cores were incubated in the dark at 10 °C for 10 days, with the overlying water column constantly aerated. In a parallel experiment, cores were incubated under the same conditions, but with a 5 % formalin solution added to the overlying water to inhibit microbial activity.Results indicated that DRP release rates from unsterilised aerobic sediments beneath cages is an order of magnitude higher than those at a control site. Biotic activity is therefore seen to be of little influence in controlling aerobic release of DRP from undercage sediments.