Effectiveness of estuarine adaptation strategies under future climate conditions.

Estuaries are among the most intensively used aquatic environments, where steep physical and biogeochemical gradients interact with dense human populations and valuable ecosystems. Intense human usage has historically led to ecological degradation and persistent use conflicts, in many temperate estuaries that host major inland ports such as the Elbe estuary in the North Sea. Climate change, with its associated effects on sea levels and global temperatures, represents a significant challenge for the functioning of these systems. The impact on estuarine hydrodynamics, sediment dynamics and water quality is, however, not yet fully understood. In this study, we utilise a coupled physical-biogeochemical model to assess the estuary's response to an extreme climate scenario, focusing on the evaluation of potential adaptation options that could mitigate the impact of the climate scenario. By comparing changes in key physical and biogeochemical state variables across interventions, we assess whether river engineering measures can alleviate risks such as elevated storm-surge levels, enhanced upstream particulate transport, and climate-driven degradation of ecological and water-quality conditions. Our findings demonstrate that targeted adaptation can effectively mitigate several adverse consequences of sea level rise and warming, emphasising the necessity to integrate climate projections and adaptation pathways into future estuarine management strategies.