Connectivity As a Driver of River-Floodplain Functioning: A Dynamic, Graph Theoretic Approach

Connectivity is a crucial property of the river-floodplain ecosystem. Reduction of connectivity, fragmentation and isolation effects, impacting ecological functions and biodiversity, is one of the most critical threats to floodplain systems. We use a graph theoretical approach for analyzing possible transport pathways in the system (directed, undirected, overland, seepage) and relate them to ecosystem functions in a river-floodplain system impacted by engineering structures (Danube River, Vienna, Austria). We studied essential ecological functions using indicators on sediment composition and quality, hydrochemical conditions, and macrophyte coverage. Our results indicate that sediment transport and composition are widely driven by directional flow and connectivity. In contrast, the exchange of water and nutrients is dominated by seepage exchange in the system. Macrophytes are dominating in water bodies which are not relevant for directed transport. The graph theoretical approach solely based on remotely sensed data can be used to classify floodplain water bodies related to their essential function and importance in the network and identify main deficits and potential restoration measures. It can, therefore, be an essential tool for prioritizing systems for management measures and restoration actions.