Impact of Floods on Salinity Levels in Freshwater Ecosystems

In a warmer climate, hydrologic extremes (e.g. floods) are projected to increase in many regions around the world. The impact of flooding events on salinity levels, however, remain inadequately quantified, hence limiting our understanding of potential climate change impacts on water quality. Here, we investigate the impacts of floods on salinity in rivers and streams using daily observations of discharge and specific conductance (SC) from 33 USGS stations across the contiguous United States. The stations span a wide range of climatic, topographic and land surface properties, and they represent natural flow conditions with minimal human disturbance. In particular, we address the following questions: What are the factors that cause salinity (SC) to respond distinctively to different flood events? What is the impact of catchment memory (i.e. antecedent conditions) on salinity response to floods? How properties of floods (e.g. magnitude, frequency...etc.) and catchment attributes (climate, soil, vegetation ...etc.) interact to define the resilience and resistance of stream salinity to floods? We address the aforementioned questions using a wide range of statistical and nonlinear dynamics methods, including analysis of conditional statistical distributions and examining system trajectories in the phase space. Finally, we highlight the implications of our findings for vulnerability and resilience of freshwater ecosystems in a future climate.