Salinization of inland waters
Freshwater salinization is an increase in dissolved ions in ground and surface waters. Salinization is a growing agent of global change that causes a constellation of interrelated and interactive symptoms. Symptoms of salinization include contaminant mobilization, loss of biodiversity, corrosion of infrastructure, and human health risks. Direct and indirect effects of salinization can be grouped together as Freshwater Salinization Syndrome (FSS), which impacts multiple biological, physical, geological, and chemical systems. A key component of Freshwater Salinization Syndrome is the mobilization of harmful chemical cocktails, or distinct mixtures of elements, in response to different amounts and types of salt ions in the environment. Here, we review the drivers, impacts, and management of Freshwater Salinization Syndrome (FSS) and its chemical cocktails. First, we characterize the diverse chemical combinations of Na+, Ca2+, Mg2+, K+, Cl-, SO42-, HCO3-, CO32-, which form distinct chemical cocktails of salt pollution from agriculture, road salt, potash mining, oil and gas extraction, and industrial activities. We then review the current causes, consequences, and ecosystem implications of increasing salt ions across inland waters such as groundwater, streams and rivers, lakes, and engineered water systems, and we explore areas of further research. Our review encompasses the built environment where wastewater can be an overlooked source of freshwater salinization due to the use of many household products containing different salt ions. We explore emerging human health implications as a component of Freshwater Salinization Syndrome such as: (1) saline dust from lake drying and diseases, (2) mobilization of radionuclides in groundwater and cancers, (3) arsenic mobilization and saltwater intrusion, (4) hypertensive disorders and sodium restricted diets, and (5) mobilization of trace metals from soils and piped infrastructure. We discuss the formation and mobilization of harmful chemical cocktails of Cu, Pb, Cd, Zn, As, Ra, U, Mn, and other contaminants as driven by salt ions and a combination of geochemical processes such as: chlorocomplexation, ion exchange, changes in pH and adsorption and solubility of metals, sodium dispersion of organic matter in soils, shifting redox conditions with saltwater intrusion and complex biogeochemical interactions, and extensive changes in the abundance and forms of ligands in response to freshwater salinization. Finally, we evaluate the pros and cons of diverse strategies for managing Freshwater Salinization Syndrome across inland waters using ecosystem, watershed, engineering, stormwater management, and policy based approaches. If left unmanaged, salinization of inland waters can spread across progressive stages, alternative stable states, and contribute to losses in critical services and functions provided by natural and engineered water systems along its trajectory.