Predicting impacts and recovery of marine-farm sites in Stewart Island, New Zealand, from the Findlay– Watling model

Abstract Data collected at marine farm sites on Stewart Island, New Zealand, were used to test the model for prediction of benthic impact of salmon net-pens proposed by Findlay and Watling wFindlay, R.H., Watling, L., 1997. Prediction of benthic impact for salmon net-pens based on the x balance of benthic oxygen supply and demand. Mar. Ecol.: Prog. Ser., 155, 147-157. . The model Ž uses the ratio of oxygen supply to the benthos based on Fickian diffusion and current velocities . Ž . above the seabed to oxygen demand based on rate of input of organic carbon to the benthos as a predictor of benthic response to input of organic matter from farms. Estimates of the rate of input of carbon and supply of oxygen to the seabed below an operating salmon farm in this study provided predictions of the severity of impact that compared reasonably well with the observed anoxic nature of the sediment and presence of patches of Beggiatoa-like growths. At a site where farming of salmon has recently ceased, the model predicted rates of mineralisation of organic y2 y1 Ž carbon in the sediments of 279-908 mmol m d depending on the method of summarising . data on current velocity . This was in reasonable agreement with the rates derived from the Ž observed decrease in the depth of the layer of waste over the period of a year 476-1206 mmol y2 y1 . m d and with rates derived from measurements of fluxes of several chemical species from Ž y2 y1 . the sediments 146-525 mmol m d . These results suggest that the model has utility beyond the locality for which it was originally developed and that it may also be useful for predicting Ž rates of recovery of farm sites. Accumulation of zinc and copper derived from food and . antifoulants in sediments below farms may significantly affect recolonisation of sediments by benthic organisms. q 2000 Elsevier Science B.V. All rights reserved