Characterisation of the environmental impact of a turbot (Scophthalmus maximus) re-circulating production system using Life Cycle Assessment

The environmental impacts of a water re-circulating system for fish farming were studied through the case study of an inland turbot farm located in Brittany (France). Life Cycle Assessment methodology was used to evaluate the potential environmental impact through the following indicators: Eutrophication Potential, Acidification Potential, Global Warming Potential, Net Primary Production Use and Non Renewable Energy Use. Two methods were used to assess the farm's nitrogen, phosphorus and solids emissions: nutrient measurement accounting and nutrient balance modelling. The two methods gave similar results for solids and phosphorus emissions, while for nitrogen the measurement-based approach resulted in half the emissions predicted by the model. The uncertainty regarding the potential gaseous nitrogen emissions led us to assess impacts according to three scenarios, differing with respect to emissions of N2, N2O and NH3. This approach illustrates that the uncertainty concerning nitrogenous emissions to the atmosphere leads to uncertainty with respect to the production system's Eutrophication Potential and its Global Warming Potential. The comparison of our results with similar results for large rainbow trout production in a flow-through system points out the impacts associated with the high level of energy consumption in the studied re-circulating system (i.e. Non Renewable Energy Use, Global Warming potential, Acidification Potential). The nitrogenous gas emissions of re-circulating systems require further studies, in order to precisely identify the substances involved and the technological solutions allowing reduced impacts.