Lakes at Risk of Chloride Contamination

Abstract

Lakes in the Midwest and Northeast United States are at risk of anthropogenic chloride contamination, but there is little knowledge of the prevalence and spatial distribution of freshwater salinization. Here, we use a quantile regression forest (QRF) to leverage information from 2773 lakes to predict the chloride concentration of all 49 432 lakes greater than 4 ha in a 17-state area. The QRF incorporated 22 predictor variables, which included lake morphometry characteristics, watershed land use, and distance to the nearest road and interstate. Model predictions had an r 2 of 0.94 for all chloride observations, and an r 2 of 0.86 for predictions of the median chloride concentration observed at each lake. The four predictors with the largest influence on lake chloride concentrations were low and medium intensity development in the watershed, crop density in the watershed, and distance to the nearest interstate. Almost 2000 lakes are predicted to have chloride concentrations above 50 mg L–1 and should be monitored. We encourage management and governing agencies to use lake-specific model predictions to assess salt contamination risk as well as to augment their monitoring strategies to more comprehensively protect freshwater ecosystems from salinization.

Current water quality guidelines across North America and Europe do not protect lakes from salinization

“…In US Midwestern and Northeastern states alone, Dugan et al. ( 4 ) estimated that there are 2,000 lakes predicted to have Cl − concentrations >50 mg Cl − /L. In the next 50 y, many of those lakes will exceed the US threshold of 230 mg Cl − /L ( 3 ).…”

“…For instance, in regions that experience cold winters, millions of metric tons of inorganic road deicing salts are applied annually to protect the traveling public by improving road safety. After deicing salts dissolve in rainwater and snowmelt, they wash into adjacent surface and ground waters triggering a substantial increase in salinity ( 3 – 5 )—in some instances, a salinity level that is 25% the concentration of seawater ( 6 ). The application of fertilizers such as potash (potassium chloride [KCl]) and evapotranspiration during intensive irrigation in agricultural operations concentrate salts on the surface of agricultural soils, which are then transported into nearby fresh waters during precipitation events increasing freshwater salinity ( 7 ).…”

Salinization of Alpine rivers during winter months

“…For example, in the Alpine region of Tyrol, Austria, an average of 30,000 tons of salt (sodium chloride) are applied annually to approximately 2240 km of roads (Amt der Tiroler Landesregierung, press release). During periods of snow-removal from the roads (which is partly poured into rivers and stored next to them), and especially during melting and precipitation events, these salts might enter the rivers, as it has been shown for a northern Italian catchment (Nava et al 2020) and North American (Crowther and Hynes 1977;Dugan et al 2020) and Scandinavian streams (Ruth 2003). In all the cases, seasonal salinity cycles were synchronized with road salt applications.…”

Freshwater salinization syndrome: from emerging global problem to managing risks

“…Other studies have also demonstrated high levels of salt concentrations during winter months and widespread salinization in different regions of North America (Dugan et al 2017(Dugan et al , 2020. For example, winter concentrations of Clwere elevated above the United States Environmental Protection Agency (USEPA) acute aquatic life water-quality criteria concentration of 860 mg/L and above the USEPA chronic aquatic life water-quality criteria concentration of 230 mg/L in streams of the Midwestern USA, indicating potential for toxicity effects to aquatic life (Corsi et al 2010).…”