In my last post, I began talking about road salt and its environmental effects. In that post I showed a plot of increasing chloride in Lake Michigan due to road salt runoff. While the increase in the past 25 years was only 3 mg/L, that represents about 660,000 tons of chloride being added annually to the lake. Other lakes in northeastern Illinois have seen much larger increases in chloride concentrations.
Many lakes in Lake County have been monitored between April and October for dissolved solids since the late 1980s by the Lake County Health Department. Chloride concentrations have been routinely monitored only since 2005, but specific conductance, which is highly correlated with chloride concentrations, has been monitored from the beginning. As you can see in the figure below, specific conductance values have been increasing with time in most of these lakes:
The figure shows the annual median specific conductance values in selected lakes in Lake County. The chloride concentration for the most recent sample from Crooked Lake is reported. Data are from the Lake County Health Department.
In 2010, the median chloride concentration in the 22 lakes being monitored by the Lake County Health Department was 112 mg/L, with highest concentrations usually measured in the first sample collected (May). Interestingly, between 2005 and 2010, chloride concentrations have dropped in many of these lakes, which Michael Adam of the Lake County Health Department has attributed to dilution during the relatively wet summers in recent years:
The data are from the Lake County Health Department.
Michael has also told me that the increasing levels of dissolved solids in lakes at golf courses has forced their abandonment as sources of irrigation water due to the deleterious effects on grass. This in turn has led to drilling of new wells, increasing the amount of groundwater extracted from aquifers in Lake County. Another reminder of how the hydrological cycle is intimately connected. When we mess with one domain of the cycle, there is often a ripple effect on other domains.