INTRODUCTION Winter snow and ice can have a significant impact on our mobility,whether on foot or by car.Alongside plowing,arguably the greatest tool in combating snow and ice is salt.The most commonly used salt for w...INTRODUCTION Winter snow and ice can have a significant impact on our mobility,whether on foot or by car.Alongside plowing,arguably the greatest tool in combating snow and ice is salt.The most commonly used salt for winter maintenance is Sodium Chloride(NaCl),the same salt used in food and water softeners,is applied to roads,sidewalks,and parking lots as it is an effective deicer when temperatures are between 0℃ and-12℃.Studies have shown that deicing with salt reduces accidents by 88%and injuries by 85%(Salt Institute 2017).The effectiveness of road salt,as well as its relative affordability,means that as much as four million tonnes may be applied annually in Canada for deicing(Environment Canada 2012).However,while salt is relatively inexpensive to purchase,there are a number of external costs that are becoming increasingly apparent.These include corrosion of vehicles and infrastructure like concrete,bridges,and water mains;damage and staining to the interior and exterior of buildings;impacts to roadside vegetation and soils;and the contamination of fresh water.In fact,the environmental impacts are such that it prompted Environment Canada to propose that winter salt be considered a toxic substance primarily due to the quantity that is applied annually(Environment Canada 2001).The Lake Simcoe watershed,approximately 3,400km2 in size,is situated just 20km north of Toronto,Ontario,with the southern portion of the watershed being considered part of the Greater Toronto Area(GTA),the most populous metropolitan area in Canada.As part of the GTA,the Lake Simcoe watershed has experienced and continues to experience considerable growth,and with this growth comes an increase in the amount of impervious surfaces requiring winter salting.Indeed,chloride has been showing a strong increasing trend in the urban creeks and in Lake Simcoe itself over the last 30 years.Even rural creeks are showing an increasing trend,albeit not as severe,nor are the concentrations of chloride reaching the same levels(LSRCA 2015).The highest chloride level recorded in a Lake Simcoe tributary was 6,120mg/l in the winter of 2013.Chloride guidelines for the protection of aquatic ecosystems utilize a guideline of 120mg/L for chronic exposure and 640mg/L for acute exposure(CCME 2011).While the high value recorded in the Lake Simcoe tributary greatly exceeds these guidelines,it is still drastically lower than values being recorded in larger,intensively urbanized catchments such as Cooksville Creek in Mississauga,Ontario,which sees concentrations in excess of 20,000 mg/L,the concentration of sea water,nearly every winter(Credit Valley Conservation personal comm).Similarly,in July of 2011 a small population of Atlantic blue crabs,a marine species,was found surviving in Mimico Creek in Toronto(Toronto Star:May 26,2012).That a marine species was able to survive in this fresh water creek in summer demonstrates that the impacts of winter salt are not just limited to winter but are impacting shallow groundwater and thus summer baseflow,maintaining high chloride concentrations year round.The same is being seen in some urban creeks in the Lake Simcoe watershed,with summer baseflow concentrations exceeding the chronic guideline and trending upwards(LSRCA unpublished).While not yet as extreme as rivers in the more densely urbanized parts of the GTA,these examples foreshadow what is in store for Lake Simcoe rivers if current winter salt practices continue along with the projected urban growth.During the winter of 2012 an estimated 99,300 tonnes of salt was applied in the Lake Simcoe watershed,an amount that equals nearly 250kg of salt per capita,or~3 times the average person’s body weight in salt.This estimate was generated through a survey of local road agencies along with the total area of commercial/institutional parking lots within the watershed.The exercise served to highlight a knowledge gap around application practices and rates in commercial/institutional parking lots.The majority of road agencies were found to record annual volumes,application dates and rates whereas literature values range from 10-40%of the salt applied in a catchment come from commercial/institutional parking lots(Perera et al,2009;Trowbridge et al,2010;Lake Simcoe Region Conservation Authority,2015),and a survey of winter maintenance contractors cite an average value of approximately 58g/m2/application(Fu et al,2013)(Figure 1).展开更多
文摘INTRODUCTION Winter snow and ice can have a significant impact on our mobility,whether on foot or by car.Alongside plowing,arguably the greatest tool in combating snow and ice is salt.The most commonly used salt for winter maintenance is Sodium Chloride(NaCl),the same salt used in food and water softeners,is applied to roads,sidewalks,and parking lots as it is an effective deicer when temperatures are between 0℃ and-12℃.Studies have shown that deicing with salt reduces accidents by 88%and injuries by 85%(Salt Institute 2017).The effectiveness of road salt,as well as its relative affordability,means that as much as four million tonnes may be applied annually in Canada for deicing(Environment Canada 2012).However,while salt is relatively inexpensive to purchase,there are a number of external costs that are becoming increasingly apparent.These include corrosion of vehicles and infrastructure like concrete,bridges,and water mains;damage and staining to the interior and exterior of buildings;impacts to roadside vegetation and soils;and the contamination of fresh water.In fact,the environmental impacts are such that it prompted Environment Canada to propose that winter salt be considered a toxic substance primarily due to the quantity that is applied annually(Environment Canada 2001).The Lake Simcoe watershed,approximately 3,400km2 in size,is situated just 20km north of Toronto,Ontario,with the southern portion of the watershed being considered part of the Greater Toronto Area(GTA),the most populous metropolitan area in Canada.As part of the GTA,the Lake Simcoe watershed has experienced and continues to experience considerable growth,and with this growth comes an increase in the amount of impervious surfaces requiring winter salting.Indeed,chloride has been showing a strong increasing trend in the urban creeks and in Lake Simcoe itself over the last 30 years.Even rural creeks are showing an increasing trend,albeit not as severe,nor are the concentrations of chloride reaching the same levels(LSRCA 2015).The highest chloride level recorded in a Lake Simcoe tributary was 6,120mg/l in the winter of 2013.Chloride guidelines for the protection of aquatic ecosystems utilize a guideline of 120mg/L for chronic exposure and 640mg/L for acute exposure(CCME 2011).While the high value recorded in the Lake Simcoe tributary greatly exceeds these guidelines,it is still drastically lower than values being recorded in larger,intensively urbanized catchments such as Cooksville Creek in Mississauga,Ontario,which sees concentrations in excess of 20,000 mg/L,the concentration of sea water,nearly every winter(Credit Valley Conservation personal comm).Similarly,in July of 2011 a small population of Atlantic blue crabs,a marine species,was found surviving in Mimico Creek in Toronto(Toronto Star:May 26,2012).That a marine species was able to survive in this fresh water creek in summer demonstrates that the impacts of winter salt are not just limited to winter but are impacting shallow groundwater and thus summer baseflow,maintaining high chloride concentrations year round.The same is being seen in some urban creeks in the Lake Simcoe watershed,with summer baseflow concentrations exceeding the chronic guideline and trending upwards(LSRCA unpublished).While not yet as extreme as rivers in the more densely urbanized parts of the GTA,these examples foreshadow what is in store for Lake Simcoe rivers if current winter salt practices continue along with the projected urban growth.During the winter of 2012 an estimated 99,300 tonnes of salt was applied in the Lake Simcoe watershed,an amount that equals nearly 250kg of salt per capita,or~3 times the average person’s body weight in salt.This estimate was generated through a survey of local road agencies along with the total area of commercial/institutional parking lots within the watershed.The exercise served to highlight a knowledge gap around application practices and rates in commercial/institutional parking lots.The majority of road agencies were found to record annual volumes,application dates and rates whereas literature values range from 10-40%of the salt applied in a catchment come from commercial/institutional parking lots(Perera et al,2009;Trowbridge et al,2010;Lake Simcoe Region Conservation Authority,2015),and a survey of winter maintenance contractors cite an average value of approximately 58g/m2/application(Fu et al,2013)(Figure 1).
