Estimating Winter Deicing Salt Loading from Roads and Parking Areas into Ecologically Vulnerable Watersheds

Freshwater salinization is a threat to biodiversity conservation. Winter road deicing salt use is a dominant driver of freshwater salinization in north temperate regions that experience winter temperatures below 0 °C. In Canada, the identification and management of areas vulnerable to road salt contamination is the least-complied-with tenet of the Canadian Code of Practice for the Environmental Management of Road Salts. To aid delineation of salt vulnerable areas, we developed and applied a framework for identifying dominant road salt loading source areas relative to aquatic species at risk critical habitat. We estimated per-event road salt loading at the subwatershed scale from roads and parking areas to determine contributions from different land-use classes and road types. We spatially focused on a watershed containing Redside Dace (<i>Clinostomus elongatus</i>), a fish species listed as federally and provincially endangered in Canada and Ontario, respectively. Applying uncertainty analysis, we found that cumulative road salt inputs on parking areas dominated total subwatershed-scale inputs. We recommend enhanced management of smaller-scale private road salt use, as the cumulative effect of smaller-scale salt use can be the largest source of watershed road salt loading. Furthermore, we emphasize the need to include critical habitat explicitly in salt vulnerable area delineations.