Freshwater salinization syndrome: from emerging global problem to managing risks

Abstract

Freshwater salinization is an emerging global problem impacting safe drinking water, ecosystem health and biodiversity, infrastructure corrosion, and food production. Freshwater salinization originates from diverse anthropogenic and geologic sources including road salts, human-accelerated weathering, sewage, urban construction, fertilizer, mine drainage, resource extraction, water softeners, saltwater intrusion, and evaporative concentration of ions due to hydrologic alterations and climate change. The complex interrelationships between salt ions and chemical, biological, and geologic parameters and consequences on the natural, social, and built environment are called Freshwater Salinization Syndrome (FSS). Here, we provide a comprehensive overview of salinization issues (past, present, and future), and we investigate drivers and solutions. We analyze the expanding global magnitude and scope of FSS including its discovery in humid regions, connections to human-accelerated weathering and mobilization of ‘chemical cocktails.’ We also present data illustrating: (1) increasing trends in salt ion concentrations in some of the world’s major freshwaters, including critical drinking water supplies; (2) decreasing trends in nutrient concentrations in rivers due to regulations but increasing trends in salinization, which have been due to lack of adequate management and regulations; (3) regional trends in atmospheric deposition of salt ions and storage of salt ions in soils and groundwater, and (4) applications of specific conductance as a proxy for tracking sources and concentrations of groups of elements in freshwaters. We prioritize FSS research needs related to better understanding: (1) effects of saltwater intrusion on ecosystem processes, (2) potential health risks from groundwater contamination of home wells, (3) potential risks to clean and safe drinking water sources, (4) economic and safety impacts of infrastructure corrosion, (5) alteration of biodiversity and ecosystem functions, and (6) application of high-frequency sensors in state-of-the art monitoring and management. We evaluate management solutions using a watershed approach spanning air, land, and water to explore variations in sources, fate and transport of different salt ions (e.g. monitoring of atmospheric deposition of ions, stormwater management, groundwater remediation, and managing road runoff). We also identify tradeoffs in management approaches such as unanticipated retention and release of chemical cocktails from urban stormwater management best management practices (BMPs) and unintended consequences of alternative deicers on water quality. Overall, we show that FSS has direct and indirect effects on mobilization of diverse chemical cocktails of ions, metals, nutrients, organics, and radionuclides in freshwaters with mounting impacts. Our comprehensive review suggests what could happen if FSS were not managed into the future and evaluates strategies for reducing increasing risks to clean and safe drinking water, human health, costly infrastructure, biodiversity, and critical ecosystem services.

Impacts of Road Deicing Application on Sodium and Chloride Concentrations in Philadelphia Region Drinking Water

“…Similarly, Leslie and Lyons ( 2018 ) attributed a winter‐time spike of chloride concentrations in Columbus, Ohio tap water to the application of roadway deicing agents. Furthermore, winter‐time seasonal peaks in sodium and/or chloride concentrations have also been observed in surface water bodies used for drinking water purposes throughout the northeastern and midwestern United States (Dailey et al., 2014 ; Kaushal et al., 2018 , 2021 ; Kelly et al., 2008 ).…”

Salinity Affects Freshwater Invertebrate Traits and Litter Decomposition

“…Mass loss estimation excluded the leaching period, which has been shown to be affected by salinity associated parameters [5,23] and there were no invertebrate shredders colonizing the leaves. We may thus assume that mass loss was mainly due to microbial degradation, and that the 61% lower mass loss in treatment 15.3 mS cm −1 was a result of decreased microbial activity on leaf litter.…”

“…How freshwater organisms and ecosystem processes will respond to the increasing salinization of coastal freshwaters, predicted by the Intergovernmental Panel on Climate Change [1], is a fundamental quest for an integrated biodiversity and conservation management of coastal ecosystems at risk. Studies on a wide variety of lakes, rivers, and wetlands have shown salinity effects on freshwater organisms and on ecosystem structure and function [3][4][5][6]. Regarding freshwater animals, salinity may have lethal effects once a threshold is exceeded, or sub-lethal effects, reducing both organism and population fitness, and resulting in the decline of richness with increasing salinity [3,6].…”

“…Most studies have assessed the effect of dryland and secondary salinization [3,12], although seawater intrusion (primary salinization) already contributes significantly to coastal salinization [5]. Natural seawater varies in ionic composition and differs from salinized freshwater sources and dryland salinity [5], and ionic composition has been shown to significantly affect the results obtained in other salinization studies (e.g., [15,16]). Thus, the effects of primary salinization on organisms and on ecosystem processes requires special consideration.…”

Relation between Road-Salt Application and Increasing Radium Concentrations in a Low-pH Aquifer, Southern New Jersey

“…Increasing mineral dissolution and salinity can enhance the mobility of Ra by introducing competing or complexing ions . Studies in coastal regions experiencing seawater intrusion have shown that Ra concentrations correlate positively with salinity. , Outside of coastal areas, salinization of fresh water has been attributed to long-term applications of road salt, which also has been reported to mobilize Ra. , We use the term “road salt” to indicate rock salt and brine used for road-deicing and anti-icing. Rock salt (halite, NaCl) used for road applications can include minor amounts (∼10 g/kg) of Mg and Ca with trace amounts (<50 mg/kg) of Ba and Sr. , Salt brines used for anti-icing may also contain mixtures of NaCl, CaCl 2 , and MgCl 2 .…”