Evaluating Spatial and Temporal Dynamics of River‐Floodplain Surface Water Connectivity Using Hydrometric, Geochemical and Microbial Indicators

Abstract Water‐mediated linkages that connect landscape components are collectively referred to as hydrologic connectivity. In river‐floodplain systems, quantifying hydrologic connectivity is challenging yet enables descriptions of hydrologic function that emerge from complex, heterogeneous interactions of underlying geomorphic, climatic and biologic controls. Here, we quantify surface water hydrologic connectivity using field indicators and develop a connectivity strength metric across a river‐floodplain system. To measure connectivity strength, we analyzed hydrometric data, conservative tracers, and natural occurring geochemical and microbial tracers across streamflows. We developed empirical models of hydrologic connectivity and predicted daily connectivity strength values across sites and assessed the sensitivity of connectivity to streamflow variability. Some floodplain areas were consistently connected or disconnected to the river, while other floodplain areas exhibited variable connectivity strength through the season. Of the locations with intermittent connectivity, some disconnected quickly and others had a prolonged disconnection phase. At the river‐floodplain system scale, we found hydrologic connectivity always increased with streamflow while across‐system variance in connectivity peaked at intermediate streamflow. Floodplain locations with intermittent surface connectivity demonstrated inter‐annual variability in hydrologic connectivity as a function of climate variability. Our results suggest that intermediate flows are critical periods for seasonal connectivity regimes and understanding the influence of changing climate on full flow durations will be required to predict impacts on river‐floodplain connectivity.