Sustainable Adaptation Strategies Mitigate Climate Change Impacts in a Temperate Estuary

Estuaries are among the most heavily utilised aquatic natural areas, where strong physical and biogeochemical gradients meet a high density of fauna and a high population. The demands placed on estuaries have led to ecological degradation in the past, evidencing profound use conflicts. This applies to many estuaries of the southern North Sea coast hosting large harbours often deep inland, such as the Elbe estuary with the metropolitan region and port of Hamburg about a hundred kilometres from the open sea. Climate change, particularly sea level rise, poses enormous ecological, economic, and social challenges for this region. It is, however, unclear how exactly the estuary system will be challenged by potentially sharply rising mean sea level and global temperatures by the end of the century. Here, we use a coupled physical-biogeochemical model to derive the main climate change impacts under a simplified extreme climate scenario. In this model-based assessment study, we consider the human impact on potential future trajectories of key estuarine state variables, taking into account several scenarios for a sustainable adaptation of the estuarine geometry by means of river engineering. Our results show that sustainable adaptation measures can mitigate some of the adverse effects of sea level rise, highlighting the importance of integrating climate change projections into estuarine management plans.