Soil Deposition of Road Salt on City Trees in Highland Park, IL
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The focus of this study was to determine the impact of road salt (NaCl) deposition in soils on tree health with respect to distance from the street. It was hypothesized that higher amounts of salt would be found in soils closer to the street, with decreasing concentrations at increasing distances from the roadway. The study streets were of similar layout and length, all located in the city of Highland Park, IL. Rice Street, Ivy Lane and Delta Avenue were chosen for their similarities, and data including health and location was collected from the City of Highland Park Forestry Department for roadside trees within the city’s right-of-way. Soil samples were then collected along a gradient for each street, and tested for salinity. These results showed the spatial distribution of salt along the roadsides, and were used for comparison with relative tree health. Analysis of overall trends showed that while salt concentrations were higher at the curb that at 25’ from the curb, the highest average concentrations were observed at 12.5’ from the curb. Because sidewalks on each street were located roughly 12’ from the curb, the increased amounts are likely due to private application. Increased levels were also observed where samples were collected along or near private driveways, again pointing to private applications. While excessive levels (above 400 ppm) were only occasionally observed, no point-source of deposition can be determined, although it is clear that private land-owners and city officials are each partly responsible. Furthermore, it is important to educate the public about the effects of NaCl and other deicers. Encouraging home and business owners to manually remove snow and use road salt in moderation may also prevent excessive accumulation and damage to vegetation.