Anthropogenically Driven Changes in Chloride Complicate Interpretation of Base Cation Trends in Lakes Recovering from Acidic Deposition

• Published in: Environmental science & technology Vol. 41; no. 22; pp. 7688 - 7693
• Main Authors: Rosfjord, Catherine H, Webster, Katherine E, Kahl, Jeffrey S, Norton, Stephen A, Fernandez, Ivan J, Herlihy, Alan T
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 15.11.2007
• Subjects: Acids; Anions; Applied sciences; Calcium - chemistry; Cations; Chemical elements; Chlorides - analysis; Chlorine - analysis; Continental surface waters; Earth sciences; Earth, ocean, space; Engineering and environment geology. Geothermics; Environment; Environmental Monitoring - methods; Environmental Pollutants - analysis; Exact sciences and technology; Ion exchange; Lakes; Magnesium - chemistry; Models, Theoretical; Natural water pollution; Pollution; Pollution, environment geology; Salts - pharmacology; Surface water; Trends; Water - analysis; Water Pollutants, Chemical - analysis; Water Supply; Water treatment and pollution; Watersheds; United States; North America; America; USA, New England; USA, Maine; Atmospheric fallout; Pollutant behavior; Acid rain; Deicing salt; Ion composition; Acid precipitation; Hydrochemistry; Selfpurification; Surface water; Lakes; Acid neutralizing capacity; Water pollution; Anthropogenic factor; Northeast
• ISSN: 0013-936X; 1520-5851
• DOI: 10.1021/es062334f

Declines in Ca and Mg in low ANC lakes recovering from acidic deposition are widespread across the northern hemisphere. We report overall increases between 1984 and 2004 in the concentrations of Ca + Mg and Cl in lakes representing the statistical population of nearly 4000 low ANC lakes in the northeast U.S. Increases in Cl occurred in nearly all lakes in urbanized southern New England, but only 18% of lakes in more remote Maine had Cl increases. This spatial pattern implicates road salt application as the major source of the increased Cl salts. Among the 48% of the lake population classified as salt-affected, the median changes in Cl (+133 μeq/L) and Ca + Mg (+47 μeq/L) were large and positive in direction over the 20 years. However, in the unaffected lakes, Cl remained stable and Ca + Mg decreased (−3 μeq/L), consistent with reported long-term trends in base cations of acid-sensitive lakes. This discrepancy between the Cl groups suggests that changes in ion exchange processes in salt-affected watersheds have altered the geochemical cycling of Ca and Mg. One policy-relevant implication is that waters influenced by Cl salts complicate regional assessments of surface water recovery from “acid rain” related to the passage of the Clean Air Act.