Modelling the impact of aquaculture on early diagenetic processes in sea loch sediments

We present a novel approach for the simulation of the impacts of finfish aquaculture on sedimentary redox dynamics, based on the coupling of a fish farm waste deposition model (DEPOMOD) and a knowledge-based reactive transport model (RTM) of early diagenesis. The integrated model was applied to a salmon fish farm located in a Scottish fjordic sealoch. The major diagenetic processes of the reaction network were first identified on the basis of literature information and historic data. Next, the organic carbon (OC) flux at a pristine site near the farm was estimated by fitting the vertical profiles of pore water and solid-state chemical species measured in the field. DEPOMOD was then used to predict the fluxes of OC due to the release of uneaten feed and faeces at various distances away from the farm. These fluxes were added to the background ‘natural’ fluxes and used as forcing functions for the RTM. Comparison of the simulated transient profiles with data collected at an impacted site revealed that the RTM model satisfactorily predicted the transient dynamics of the system. We discuss the use of the model for cost-effective environmental impact assessments, site selection and the optimization of husbandry practices.