Five State Factors Control Progressive Stages of Freshwater Salinization Syndrome
Major ion concentrations in freshwaters are increasing in many world regions due to diverse causes such as: land use change, resource extraction, climate change, saltwater intrusion, and accelerated weathering. Freshwater Salinization Syndrome (FSS) refers to the interconnected direct and indirect effects of salinization on ecosystems and the built environment. Here, we propose there are progressive stages of FSS due to changes in salt ions, pH, and secondary mobilization of trace metals, nutrients, radionuclides, and contaminants and ecosystem level responses. Progressive stages of FSS are influenced by state factors such as: climate, geology, human activities, flowpaths, and time. We analyze empirical data demonstrating the importance of: (1) human activities such as inputs of salt ions and mobilization of chemical cocktails over decades in North American rivers, (2) flowpaths impacted by increasing and progressive salinization with multiple ions from small streams (along a few kilometers) to major rivers in North America (along hundreds of kilometers), (3) geology and links to human acceleration of erosion, weathering, ion exchange, acidification, and alkalinization rates (4) climate interactions such as rising river temperatures across North America, and evaporative concentration of ions and saltwater intrusion (5) time and salinization impacts on river restoration and recovery. We propose that state factors can influence progression of FSS in potential diagnostic stages: Stage 1 can be characterized by abnormally elevated concentrations of at least one or a few ions across one season; Stage 2 can be characterized by chronically elevated concentrations of at least one or a few ions across multiple seasons; Stage 3 can be characterized by local spread of increasing ions across space and time and formation of complex and distinct chemical mixtures or chemical cocktails; Stage 4 can be characterized by widespread and chronically elevated concentrations of ions across a region and secondary mobilization of chemical cocktails and major changes in ecosystem states, services, and functions. Our review and analysis suggest that FSS should be identified and managed appropriately across progressive stages of biological, geological, and chemical interactions. Analyzing diverse stages and state factors of FSS across world regions can improve evaluation of many freshwaters at risk and identifying and prioritizing proper local management strategies.