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

Abstract

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 microeq/L) and Ca + Mg (+47 microeq/ L) were large and positive in direction over the 20 years. However, in the unaffected lakes, Cl remained stable and Ca + Mg decreased (-3 microeq/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.

Atmospheric CO2 consumption by chemical weathering in North America

“…Road salting would originally leave a halite molar Na/Cl ratio of 1, but actually this ratio is reduced by substantial proportions of CaCl 2 in street salt (e.g. Bowser and Jones, 2002;Szramek and Walter, 2004;Rosfjord et al, 2007), and because of cation exchange in soils (Lofgren, 2001;Rosfjord et al, 2007). Road salting is particularly important in the northeastern US, where it even influences small, rural streams (Transportation Research Board, 1991;Kaushal et al, 2005).…”

Mapping of road‐salt‐contaminated groundwater discharge and estimation of chloride load to a small stream in southern New Hampshire, USA

“…Ion exchange processes also can occur in clean sand and gravels (Granato et al , 1995). The positively charged sodium ion displaces calcium, potassium, and magnesium on cation exchange sites on soil particles (Granato et al , 1995; Rhodes et al , 2001; Jackson and Jobbagy, 2005; Ramakrishna and Viraraghavan, 2005; Rosfjord et al , 2007). To a lesser extent, chloride ions bind to soil particles through chlorination of organic matter and ion exchange processes (Rhodes et al , 2001; Bastviken et al , 2006).…”

Multiple land use activities drive riverine salinization in a large, semi‐arid river basin in western Canada

“…The salinity of freshwater ecosystems is generally determined by the concentration of calcium (Ca 21 ), magnesium (Mg 21 ), potassium (K 1 ), sodium (Na 1 ), chloride (Cl 2 ), sulphate (SO 22 4 ), carbonate (CO 22 3 ) and bicarbonate (HCO 2 3 ) ions (Cañedo-Arg€ uelles et al 2013). Temporal increases in one or more of these ions (or some measure of overall salinity) have been reported in lakes (Rosfjord et al 2007;Likens and Buso 2009;M€ uller and G€ achter 2011;Winter et al 2011), and in streams and rivers (Jolly et al 2001;Parr and Mason 2003;Thunqvist 2004;Kaushal et al 2005;Corsi et al 2015). Increased salinity in freshwater ecosystems has been linked to a number of deleterious impacts including shifts in aquatic community composition (Collins and Russell 2009;B€ athe and Coring 2011;Porter-Goff et al 2013), alteration of biogeochemical processes (L€ ofgren 2001;Swan and DePalma 2011), and the degradation of potable water supplies (Kaushal 2016).…”

“…There is increasing evidence that the application of road salt for winter road maintenance is a major cause of salinization in cold, humid surface waters (Godwin et al 2003;Thunqvist 2004;Rosfjord et al 2007;Kelly et al 2008;Novotny et al 2009;M€ uller and G€ achter 2011). The most common de-icing agent used for winter road maintenance in North America is NaCl and its use has increased significantly in the last 50 yr to 60 yr (Jackson and Jobb agy 2005;Ramakrishna and Viraraghavan 2005).…”