Management of marine construction works using ecological modelling

A system of bridges and tunnels between Denmark and Sweden is being constructed. The environmental management of the dredging and reclamation work includes planning using a mathematical model which can forecast the effect of different spill scenarios in order to minimize adverse effects on eelgrass beds. To develop the model, plots of eelgrass beds (4 m2) were covered with nets excluding 30, 60 and 90% of the light. Shoot density, leaf and root/rhizome biomass, and soluble carbohydrates in roots and rhizomes were observed in order to determine the response of the plants to shading. In selected plots, all aboveground biomass was harvested to assess the re-growth potential. The minimum level of soluble carbohydrates necessary for securing re-growth was 60–90 mg g−1. The inclusion of the subsediment parts of the eelgrass permits model runs beyond one growth season, and the prediction of re-growth after subsequent shading and winter dormancy. The model has been satisfyingly calibrated and validated. A feedback monitoring system has been developed based on field studies of eelgrass variables, a set of pre-fixed environmental criteria and forecasting of the effects of the construction works. The system facilitates planning and management of the dredging and reclamation operations, and mitigating actions during the progression of the work.