DOES ROAD SALTING DAMAGE TO SOIL C AND N CYCLING CAUSE MORE THAN A SALT LOAD DAMAGE TO LOCAL STREAMS?

Road salts are used on highways to maintain traffic flow and safe driving conditions under sub-zero conditions. Salinity impacts on soils and soil solutions have been well documented. However, there is limited assessment on the effects on the nitrogen and carbon cycles after long-term soil exposure in the field to salinity induced by road salts. Road salt use disrupts natural cation exchange reactions, and therefore increases the pH of naturally acidic upland soils. An increase in pH of such soils has led to enhanced solubilization/mineralization of organic matter, as well as an increase in nitrification, ultimately leading to the loss of soil organic matter over time and nitrate leaching into adjacent surface waters. Furthermore, there is evidence for displacement of ammonium and hydrogen ions from the cation exchange sites by incoming sodium and calcium ions from road salts. Exchangeable calcium status remained higher than initially been predicted in impacted soils; this was attributed to the presence of gypsum in the road salt used at the study sites and more efficient retention of the divalent calcium ions. It was hypothesized that acidic soils would display a greater increase in pH and therefore greater impacts than less acidic soils. This was confirmed by the assessment of salting effects on calcareous soils. The calcareous soils showed a greater capacity to buffer against the incoming sodium ions and hence pH increase. Thus, the disruption to the nitrogen cycle that occurs as a consequence of road salting when roads run through naturally acid soil ecosystems becomes much less of an issue when the roadside soil ecosystems are calcareous.