Abstract
1.2 Summary
This report describes the present condition of benthic habitats and of important feeding guilds among benthic invertebrates in the project area from the planned Anholt Wind Farm in addition to an evaluation of impacts on habitats and feeding guilds related to operation of the wind farm. Basically, changes in current speed and sediment conditions are expected to affect the various functional groups such as filter-feeding bivalves being stimulated by high current speeds and high rates of plankton advection, while deposit-feeders being favored by low current conditions and high sedimentation rates.
1.2.1 Method
Based on modelled baseline condition in hydrography, water quality and, in situ monitoring of benthos and sediments /16/ statistical models were developed to explain the present distribution and biomass of different functional benthic groups. Models subsequently were used to predict changes in these benthic groups after establishment of the wind farm using predicted changes in the explanatory variables that included current speed, advection of plankton and sediment conditions.
Because of a limited spatial variability in external conditions, i.e. current speed, food advection and sediment characteristics within the project area the statistical models explaining variation in benthic groups had low predictive powers, between 15 and 23%. Accordingly, predictions of change in functional groups invariable are associated with a high uncertainty.
1.2.2 Predicted impacts on benthic habitats
Using the modelled changes in bottom current speeds, advection of food for filter- feeders and sedimentation a reduction of 5-6% in biomass of filter-feeders and, an increase of 10% in biomass of deposit-feeders were predicted within the wind farm area. The changes were caused by small reductions in current speeds due to flow obstruction by foundations, and by reductions in plankton advection partly caused by fouling blue mussels on foundations competing with the benthic filter-feeders for planktonic food. The predicted changes within the wind farm were mirrored by changes occurring outside the wind farm (but partly within the project area). Due to slightly higher current speeds outside the wind farm benthic filter-feeders are likely to increase and deposit-feeders likely to decrease in biomass. Overall, the predicted changes in benthic habitats and important benthic groups during the operational phase were very small and considering the relative large uncertainty associated with the predictions the impacts are likely to be insignificant.