Freshwater Salinity Regimes

Freshwater salinization of rivers is increasing across the globe due to non-point source loading of ions from accelerated weathering and anthropogenic activities such as agricultural and urban land-use. Although we are gaining a better understanding of decadal trends in river salinization, our understanding of annual regimes—namely the timing, magnitude, and duration of characteristic annual patterns—of salinization in rivers draining diverse western U.S. landscapes and their relationship to catchment attributes is limited. Here, we classify annual salinization regimes in 246 stream locations through hierarchical clustering of publicly available time series of specific conductance and discharge. We found two emergent salinization regimes, one characterized by an early-fall peak in SC/Q (73% of sites) and the other characterized by a late-winter or early-spring peak (28% of sites). Using a random forest classifier, we found that soil salinity and the proportional watershed area of open water were the most important catchment attributes for predicting cluster membership. Advancing our understanding of the dynamics of salinization in rivers will improve our ability to estimate and mitigate the effects of excess salinity on lotic freshwater ecosystems and ecosystem services.