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  • 06 Nov 2022 9:43 AM | Smart About Salt (Administrator)

    B.C. researchers investigating impact of road salt on Pacific salmon |

    B.C. university researchers and scientists are looking into the impact that road salt may be having on local Pacific salmon.

    Researchers at the University of British Columbia have teamed up with Simon Fraser University, British Columbia Institute of Technology and Fisheries and Oceans Canada scientists to monitor salt levels in more than 20 streams around the Lower Mainland.

    “We know that Pacific salmon are in decline and we don’t know all the factors involved. Could too much salt in their streams be a cause?” questioned Chris Wood, a UBC professor.

    “Even though adult salmon live in salt water, they grow up in fresh. When they’re ready for salt water, their whole body has to change to adapt.”

    Wood continued, “There’s evidence that quite moderate salt levels at young ages have caused mortality and stunted growth.”

    The research team will be measuring salt levels and review the data every two months.

    “While things like climate change are known causes of salmon decline, salt could also be a factor,” said Patricia Schulte, a UBC professor.

    “We know road salt use in Canada is increasing at about 2.5 per cent per year. In Vancouver, the city has 3,000 tonnes of salt in its yards for winter maintenance on streets and sidewalks.”

    Schulte said as snow and ice melt, salt from roads can run into streams and may be affecting salmon.

    The five-year project will be funded by a Natural Sciences and Engineering Research Council grant and will specifically be looking at Chum and Coho salmon.

    Woods said community members can do their part to help local salmon by using only a little amount of salt when salting driveways and sidewalks.

  • 02 Nov 2022 3:02 PM | Smart About Salt (Administrator)

    Do road salts trigger eutrophication? Reviewing twenty years of water quality data in an urban lake. | Water Institute Research | University of Waterloo (


    Urbanization and associated land use change is a global phenomenon with often negative impacts on water quality and aquatic ecosystems. In particular, urban development of watersheds has been blamed for worsening eutrophication in receiving lakes and wetlands. Increased loadings of nutrients, especially of phosphorus (P), are generally assumed to be the main driver of eutrophication. A high availability of P stimulates dense algal growth that, in turn, may severely deplete dissolved oxygen (DO). In the worst case, the development of a so-called anoxic “dead zone” may result in die-offs of most organisms, such as fish and plants. 

    In cold temperate regions, urbanization is typically accompanied by growing winter applications of deicing road salts that inevitably lead to the salinization of local waterways, lakes, and groundwater aquifers. A direct link between salinization and eutrophication of lakes has not yet been demonstrated, however. This study investigates water quality changes in a Canadian lake over a two-decade period. The long-term multi-variate dataset is used to delineate and explain general trends in water quality using a variety of statistical methods. The main outcome is that rising salinity is responsible for the observed intensification of eutrophication-like symptoms, with very low DO levels in the deeper waters of the lake persisting over increasingly longer periods of time during the year. Yet, no evidence was found for an increase in the external loading of P from the watershed to the lake.  


    Lake Wilcox is a small kettle lake located in Richmond Hill, Ontario with a watershed area of 2.39 km2 (Figure 1). The originally forested watershed has undergone significant development since the early 1900s when the land was converted to agriculture, followed by urban development since the 1980s. As a result, land surface imperviousness is now over 60% (Figure 2a). In the 1980s, harmful cyanobacteria became an issue and an aeration system was installed but later deactivated. In the early 2000s, several stormwater management (SWM) systems were installed in the lake’s catchment to address deteriorating lake water quality.  

    A variety of datasets for the period of 1996 to 2018 were collected for the study, including water quality monitoring data, climate data, and surveys and satellite images of land use. The dissolved oxygen (DO) time series data served to calculate values for the Anoxic Factor (AF), a measure of the changes in the intensity of deoxygenation of the lake’s deeper waters. Interannual variations in the stability of the water column stratification were assessed by calculating the water density from measured temperature and salinity data and comparing the Brunt-Väisälä or buoyancy frequency depth profiles for the month of August, that is, when the thermal stratification of the lake is highest.   

    Multiple statistical methods were used to characterize and interpret water quality trends. Temporal changes were assessed with the Mann-Kendall test (Figure 3) and Principal Component Analysis helped to group correlated variables and identify the main drivers of water chemistry changes. A Multiple Linear Regression model was also developed to explore the relationships between the principal components and the following potential predictor variables: watershed imperviousness (as a measure of urbanization), lake chloride (Cl−) concentration (as a measure of deicing salt usage), external P loading to the lake, water column stratification (using the Brunt-Väisälä frequency), and climate parameters (including, measures of temperature conditions and the intensity of extreme precipitation events that can play an important role in pollutant wash-off in urban areas).


    Although the external P inputs to Lake Wilcox have been generally declining, the lake is showing increasing eutrophic symptoms, most visible by the lengthening of the annual period during which the lower part of the lake (i.e., the hypolimnion) experiences low DO concentrations (i.e., hypoxic to anoxic conditions). The chloride concentration (and, hence, salinity) trend was explored as a potential explanatory variable because of the large increase in the lake water Cl concentrations (Figure 2b) at the same time hypoxia expanded (Figure 4).

    During the study period, the water chemistry of Lake Wilcox underwent significant changes, especially in terms of the concentrations of Cl, DO, total phosphorus (TP), and dissolved inorganic P (DIP). Changes in the ratios DIP:TP and DIN:DIP ratios (where DIN refers to dissolved inorganic nitrogen) were also observed. Chloride concentrations increased by a factor of 4, likely due to the increasing application of deicing agents as the watershed urbanized and connectivity to stormwater management infrastructure increased. While the results revealed decreasing trends for the external TP load to the lake and the TP concentrations in the lake, they showed little change in the DIP concentration, meaning that the lake DIP:TP ratios increased over time. This is important because DIP represents the most bioavailable fraction of TP. The longer annual periods of DO depletion of the hypolimnion and the corresponding increase of the AF likely intensified the P loading from the bottom sediments to the water column. It is well known that recycling of P from sediments, also known as internal P loading, is more efficient when the overlying water is anoxic.

    The results of the study show that the increasing salinity of Lake Wilcox due to the growing impervious land cover and accompanying increase in road salt application in the watershed has led to a strengthening of the lake's water column stratification. In turn, this has increasingly isolated the hypolimnion from the atmosphere and, hence, accelerated the depletion of DO and amplified the role of internal P loading, relative to the external loading. These changes in DO and P cycling are common symptoms of eutrophication. In Lake Wilcox, however, they appear to be more linked to the lake’s progressive salinization than to a higher external loading of P from the watershed.


    By increasing water density and stabilizing the stratification of the water column, salinity emerges as a major driver of changes in water quality in Lake Wilcox. These changes include the expansion of hypoxia and anoxia in the hypolimnion and the increased contribution of internal loading to the lake’s P budget. This is the first known study that directly links salinization with lake eutrophication symptoms.

    Salinization, in addition to climate warming, may be an overlooked driver of downward trends of hypolimnion DO concentrations in lakes worldwide. In cold-temperate regions, urbanization is usually accompanied by increased application of road salts as indicated by rising Cl concentrations observed in urban lakes of North America and northern Europe. The study further suggests that efforts to reduce eutrophication of water bodies in urbanizing areas by controlling external nutrient loadings may be offset by the enhanced internal P loading as DO depletion intensifies.

    Historical use of road salt in urban watersheds also created chloride legacies in soils and groundwater. These legacies could continue to supply excess Cl to receiving lakes even if winter salt applications were reduced or altogether halted. Protecting the health of urban lakes therefore calls for integrated management strategies and requires further work to understand the contributions of climate change, urbanization and salinization, and their interactions, to changes in lake water quality.

    Radosavljevic, J., Slowinski, S., Shafii, M., Akbarzadeh, Z., Rezanezhad, F., Parsons, C. T., Withers, W., Van Cappellen, P. (2022). Salinization as a driver of eutrophication symptoms in an urban lake (Lake Wilcox, Ontario, Canada). Science of The Total Environment, 846, 157336.

  • 18 Oct 2022 6:20 AM | Smart About Salt (Administrator)

    Snow can spread and worsen the effects of pollutants in the environment (

    By October, autumn’s arrival brings with it the promise of winter — and snow.

    And with it comes a quieter world, thanks to snow’s ability to absorb noise. This is because the spaces between snow crystals limit sound waves from bouncing around, creating a soundproofing effect.

    Snow also adsorbs other matters it comes into contact with. Adsorption is when substances adhere on surfaces of materials (usually liquids or solids). The adsorptive properties of snow are the reason for some of its unique features, including its loosely bound crystalline porous structure with finely divided individually shaped flakes with large surface areas.

    Its dynamic changes between ice and liquid states facilitate the absorption and release of pollutants, depending on prevailing surface and atmospheric conditions.

    As an analytical material chemist with a research background in adsorption, I am interested in understanding how various materials — like snow — adsorb certain substances, like persistent organic and vehicular exhaust pollutants.

    Snow and pollution

    In the winter, snow becomes a superabsorbent for a wide range of pollutants, including vehicular exhaust particulate matters, persistent organic pollutants (POPs), trace metals and chlorides from road salts.

    As snow subsequently moves around or melts, most of these pollutants find their way into underground pipes and aquifers.

    POPs are some of the most dangerous pollutants because they remain active, lasting for several years within their environments before finally degrading into other chemical forms. POPs, such as polychlorinated biphenyls, organochlorine pesticides and perflouroalkylated substances, have severe environmental impacts.

    They are classified under the Toxic Substances Management Policy as Track 1 substances in Canada, and are usually targeted for environmental removal.

    Just like POPs, very little is also known about how chemical pollutants from the exhausts of gasoline-powered vehicles interact with snow.

    In Canadian cities, snow is moved around through various means, including snow melts, during plowing, on tires of vehicles or even soles of pedestrian shoes. During transportation, changes in ground surface pressure and ambient temperature can also affect the adsorption rates of chemical pollutants on snow.

    Research conducted in Québec has shown that snow adsorbs significant amounts of organic pollutants and aerosol particles from exhaust pipes within 30 minutes of exposure. These researchers also observed the adsorption of aerosol particles with larger particulate sizes (approximately 50-400 nm) relative to smaller nanoparticles (less than 50 nm).

    Health effects

    POPs are introduced into the environment through agricultural and industrial practices. Most of them may have come from other anthropogenic sources but are unintentionally released from simple events like burning household waste.

    Burning industrial, municipal or medical wastes can also release dioxins and furans. Toxaphene and hexachlorobenzene could originate from uncontrolled insecticide and pesticide waste disposal. Upon exposure during winter, these chemical pollutants find their way into the snow, then into surface water and up the food chain. They can adversely affect aquatic life when subsequently introduced into the aquatic ecosystems.

    POPs and exhaust particulate matters can affect human health. They can cause allergies, hypersensitivity, birth defects and neurological disorders. Most POPs are carcinogens. Some of them may alter the nervous systems, leading to chronic health conditions. POPs can also affect reproductive health and disrupt the immune system. Some particulate matters cause lung inflammation and increase the risk of blood clotting.

    These severe impacts on human health and environment sustainability are why POPs are currently regulated under the Stockholm Convention, as adopted by Canada in 2001.

    Between applicable industries and environmental monitoring agencies, federal and provincial governments and us, everyone has a part to play. All hands must be on deck in providing sustainable regulations for these pollutants. And as we approach winter, measures should be developed to reduce the amount of pollutants that can accumulate and persist in snow.

    This article is republished from The Conversation, an independent nonprofit news site dedicated to sharing ideas from academic experts. It was written by: Ubong EduokWestern University. The Conversation has a variety of fascinating free newsletters.

  • 19 Sep 2022 6:41 AM | Smart About Salt (Administrator)

    Kincardine Awards Winter Road Salt Contract | Bayshore Broadcasting News Centre

    Kincardine Council has awarded Compass Minerals Canada a two-year contract for winter road salt.

    The municipality partnered with the County of Bruce and other municipalities to help ensure the best value for money.

    Council had to give final approval because inflation caused the price of road salt to go up.

    The contract is worth $100,000.

  • 07 Sep 2022 2:01 PM | Smart About Salt (Administrator)

    Landscape Trades

    Maintaining commercial properties in winter has become an incredibly challenging exercise in recent years. While the main concern of contractors is clearing parking lots and walkways of snow and ice to ensure the safety of patrons, they are also working to ensure, to the extent possible, that their treatment of the site reduces their exposure to slip and fall claims. Insurance premiums have skyrocketed over the past few years, and there are many stories of a single claim increasing premiums enough to put a small company out of business.

    Available training, such as that offered through the Smart About Salt Council, teaches contractors about best practices, including how much salt should be applied and in which conditions. However, it can be hard to put this knowledge into practice when you’re faced with real world conditions and pressure from property owners and the public.

    Given these concerns, contractors have good reason to be hesitant about making changes to their practices. To explore these issues, the Lake Simcoe Region Conservation Authority (the “Conservation Authority”) conducted a study at a large (14.2 hectare) commercial site to see if the best practices taught in training courses can be effective for both maintaining safety and limiting the amount of salt that’s applied. Two different contractors have been responsible for winter maintenance over the course of the study; the first was there from the start of the study in fall 2014 to spring 2018, and the second has been there since fall 2018. Both contractors focused on maintaining site safety while using different management practices, with the second contractor (2018 to present) utilizing recommended best practices and reducing salt use.

    It’s also important to note that neither contractor has had a slip and fall claim or complaint against them throughout the course of the study. The following sections will show that the use of best practices can provide numerous benefits to contractors, not the least of which is maintaining site safety. The failure to implement these practices, however, can potentially result in additional hazards, such as blowing snow, the freezing of melt water in drive areas, loose salt piles which can reduce traction, and reduced visibility; these can all increase a contractor’s exposure to liability.

    Of course, there are also environmental costs associated with using more salt to treat a site: high levels of chloride from winter salt have impacts on water resources and aquatic life. Careful thought about how to properly treat a site and close monitoring of on-site weather conditions can help contractors enhance the effectiveness of their practices and reduce or eliminate these issues.

    Salt use on the study site

    As noted above, the two contractors took different approaches to maintaining the site. These differences bear out in the data collected by the Conservation Authority over the years of the study. Figure 1 displays the average amount of salt applied in each event over each season (these numbers were calculated by the Conservation Authority through water quality measurements taken at the site’s single drainage outlet), with the first contractor shown in yellow, and the second shown in black. The first contractor applied an average of 12 tonnes (t) per event across all seasons, with an application rate of 81 g/m2, while the second applied an average of 10 t per event at a slightly lower rate of 70 g/m2. The first contractor noted that they used the same application rate regardless of the site conditions and expected weather, while the second tailored their application rates to the actual conditions of the site. This included noting the expected duration of the event and the forecasted amount and type of precipitation, which enabled them to apply less salt in most circumstances.

    The most notable difference in how the two contractors treated the site can be seen in the number of events they responded to in each season (Figure 2). The first contractor responded to more events in every season than the second contractor. The first contractor had an average of 68 event responses each season, while the second had significantly fewer, with an average of 42. As shown in Figure 2, seasonal precipitation was not notably lower for the period that the second contractor was managing the site and does not appear to be the reason they were able to respond to fewer events. They were able to undertake fewer applications at a time when municipalities in the area were increasing the number of applications each season. They attribute being able to respond to fewer events to keeping a close eye on the weather and conditions on the ground at the site, as widely available weather forecasts may not be accurate at a smaller scale.

    Factors affecting salt application

    There were some extenuating factors that affected the amount of salt applied and number of applications; the first, and most obvious of these is the weather. For example, 2015/2016 was a mild winter with fewer precipitation events and less precipitation overall. Because of this, the first contractor had slightly fewer applications, and it appears that the drivers elected to apply less salt given the conditions didn’t warrant heavy applications. The other major factor was the salt shortage of the 2017/2018 season. This was a North America-wide shortage that affected road authorities and contractors alike. Due to the shortage, the first contractor couldn’t purchase as much salt as they normally would for the season, forcing them to reduce their application rates, and eventually switch to the use of sand near the end of the season. These factors reduced the amount of salt used by the first contractor. If it weren’t for the mild winter and the salt shortage, the difference between the two contractors would likely have been even more pronounced than what was observed.

    Lessons learned

    This case study highlights the effectiveness of best practices and training programs in ensuring site safety and reducing the amount of salt applied on the site to achieve safe conditions. The potential benefits to the property owner and contractors who follow best practices include cost savings and records demonstrating that reasonable steps were taken to protect patrons from winter hazards. While there were no slip and fall claims for either contractor for the duration of the study, the second contractor was able to manage the parking lot using approximately 45 per cent of the salt used by the first contractor. The difference between the two is due mainly to fewer applications, as well as lower application rates.

    There can be considerable financial benefits for contractors who change their practices and apply less salt. In addition to fuel savings from sending plows and salters out less often, less wear and tear on vehicles, and less employee time spent treating the site, further benefits can be seen through cost savings on materials. Table 1 shows that, given the average number of applications and volume applied, the result is an annual savings in materials costs of over $37,000.

    As noted by the second contractor, training, an understanding of how to properly use salt in different conditions, and the implementation of best practices is vital when working to improve your methods. This highlights the importance of training for contractors and their staff. Understanding how the materials and the best practices work will help contractors ensure they are applying the right material, in the right amount, at the right time. Training courses are available for contractors in Ontario (such as Smart About Salt), and certification can also be obtained through these programs.

    Another important factor in ensuring salt is only applied when necessary is a thorough understanding of the current and forecasted weather conditions, as well as the on-site conditions. This can be achieved in part through subscriptions to detailed weather forecasts. The second contractor noted that they have a staff person check the site on days with weather or expected weather to determine the conditions and what actions may need to be taken; this person also decides whether further treatment is required after the initial treatment. While this may not be practical for all contractors, it is helpful in reducing person-hours and material costs incurred through treating a site unnecessarily. On-site camera technology has evolved to a point that it can be used to perform the same function. In addition, technologies such as pavement temperature and friction sensors mounted to plows, and automated salt delivery systems that control application rates by vehicle ground speed are also important tools that can ensure the right amount of material is being applied when it’s needed.


    This study highlights the importance of training, understanding the site conditions, and monitoring the local weather conditions. Implementing these practices results in savings in materials costs, including salt and fuel, as well as human resource and equipment costs. It can also help to prevent the contamination of our water resources. These benefits can be realized with relatively little effort on the part of the contractor, and without sacrificing the safety of parking lot users or increasing exposure to liability. For all these reasons, training and the use of best practices should be encouraged among all snow and ice management contractors.

    The Sustainable Technologies Evaluation Program (STEP) is a conservation authority-led initiative that fosters broader implementation of technologies that protect water resources and reduce our carbon footprint. The STEP Salt Working Group includes members from Lake Simcoe Region Conservation Authority; Toronto and Region Conservation Authority; Credit Valley Conservation; Ministry of Environment, Conservation and Parks; Region of Waterloo; Region of Peel; Toronto Metropolitan University; and the Smart About Salt Council.

    This case study has received funding and support from the Ontario Ministry of Environment, Conservation and Parks. Such support does not indicate endorsement by the Government of Ontario of the contents of this article.

  • 31 Aug 2022 7:24 AM | Smart About Salt (Administrator)

    Beet juice being eyed to battle winter roads | CTV News

    The city could be exploring a new method of treating slick winter roads that could beet the traditional sanding and salting.

    St. Boniface City Councillor Matt Allard has submitted a motion for a cost analysis of expanding the use of beet juice this winter instead of the usual dry applications.

    Allard said he drafted the motion after meeting with beet juice producers.

    “If you apply beet juice, it was explained to me that you can essentially create a layer between the snow and concrete, where you can essentially peel the snow off, which is something that doesn’t happen with sand and salt,” Allard told CTV News Winnipeg.

    Over the past few years, the city has been using around 100,000 litres of beet juice on roads, bridges and overpasses.

    Allard’s motion calls for a city-wide application of the solution on roads this winter.

    The study would also analyze the damage caused by sand and salt use to roadways, boulevards, trees, plows, and other city assets.

    He said although salt may be cheaper than some alternatives like beet juice, he wants to get a better understanding of its long-term effects.

    “I'm looking for a bigger picture analysis of how much damage is salt and sand doing to our streets. How much does it cost to clean up?” Allard said.

    “I don't think we've ever really looked at comparisons between different scenarios - more beet juice, more of this other product. I think there may be some efficiencies to be had if you look farther than just that one budget year."

    The issue will be debated at the Riel Community Committee hearing Tuesday.

  • 02 Aug 2022 11:32 AM | Smart About Salt (Administrator)

    New York wants local governments to buy American-made road salt. Why some believe that could be a costly move | Local News |

    Major local governments like Erie County buy tons of road salt every year to keep roadways safe and ice free during Western New York's frigid winters.

    But a state bill requiring that rock salt be purchased in only the United States has gotten the attention of highway superintendents around the state. The proposed law could cost Erie County hundreds of thousands of dollars, and other communities are facing the same type of increase.

    "It really boils down to two things: We’re concerned about the increased cost, as expressed in the letter, and we’re concerned that if you limit the number of suppliers, that we may have some problems getting supplies of road salt when we really need them at critical times during the winter," said Bruce Geiger, legislative representative for the New York State County Highway Superintendent's Association, which wants Gov. Kathy Hochul to veto the bill.

    The state's Buy American Salt Act, which has passed in the Assembly and State Senate, was co-sponsored by Sen. Timothy Kennedy, D-Buffalo.

    The concerns raised by the association led to changes in the bill that would allow local and state government to buy from foreign sources if the requirement to buy in the United States "would result in unreasonable costs." The bill also allows governments in New York to buy foreign salt if there is an insufficient domestic supply.

    That change should put everyone at ease, said representatives for Kennedy and other bill proponents.

    "The provisions of this bill would not apply if the American-mined cost is not reasonable, not in the public's best interest or not readily available," said Mario Cilento, president of the New York State AFL-CIO, in a statement to The Buffalo News. "This bill simply allows state and local governments to go above the lowest bid in order to support jobs right here in New York and in this country."

    New York State is home to two salt mines. One is owned by American Rock Salt, which produces 4 million tons of salt a year and is based in Livingston County. The other is the Cayuga Salt Mine in Tompkins County, owned by Minnesota-based Cargill.

    American Rock Salt is the larger of the two mines and is locally owned and operated, employing roughly 400 employees, said Chief Administrative Officer Mark Assini. The mine represents the single largest employer in Livingston County.

    "We are the largest salt mine in the United States," he said.

    Supplying rock salt in New York is not a problem, he said. But freighters docking in New York ports and bringing in rock salt from Egypt, Morocco and Chili is, he said.

    Those countries offer substandard pay and don't have the same regulatory oversight regarding environmental protection or miner safety, he said, citing Egypt in particular for human rights violations.

    Those imports have caused American Rock Salt to lose between 300,000 and 400,000 tons of salt business a year, he said.

    "That's a big deal for us," he said. "That's several weeks of work for our employees."

    Opponents of the bill cite two problems. The first is that for some New York counties near the Canadian border, like Erie County, the law makes it harder to purchase salt from Canada, which is geographically close and not comparable with overseas foreign suppliers.

    Erie County likes to have salt-buying options from multiple suppliers to safeguard against potential supply shortages, said Erie County Public Works Commissioner William Geary.

    Assini also conceded that the law was not meant to apply to countries like Canada, though he also said American Rock Salt is easily capable of supplying sufficient salt nationwide. The only snag that exists is the amount of salt that truckers can physically deliver.

    Geiger, of the highway superintendents association, also said he worried about the vague language that exists to allow governments to buy from foreign sources in certain circumstances.

    "Who makes that determination?" he said, expressing concern about municipalities' potential exposure to litigation.

    Geary said Erie County typically buys from domestic suppliers like American Rock Salt but also wants the flexibility of contracting with suppliers across the border. 

    A spokesman for Hochul said the governor is reviewing the legislation. Assini said he's hopeful the governor will sign the pro-American labor bill into law around Labor Day.

    Despite Erie County budget concerns expressed two weeks ago, the County Executive's Office said it has no opinion about the pending legislation. Officials with American Rock salt said the county contracted to buy salt from American Rock Salt earlier this month. An Ontario-based salt supplier, Compass Minerals, came in with a higher price this season. 

  • 29 Jul 2022 9:04 AM | Smart About Salt (Administrator)

    Road salt: The silent threat to urban lakes (

    The use of de-icing salts to clear roads and sidewalks in winter is a stressor of lake ecosystems. New research from the Ecohydrology Research Group at Waterloo University has shown that increasing lake salinisation linked to urban growth exacerbates water quality deterioration usually ascribed to the proliferation of algae driven by nutrient enrichment.

    Eutrophication is one of the leading causes of water quality impairment in lakes. It is driven by increased inputs of anthropogenic nutrients, mainly nitrogen (N) and phosphorus (P), which stimulate the growth of algae in the surface waters of lakes. Rapid proliferation of algae can result in so-called algal blooms which, in turn, negatively impact aquatic life and water quality. It is commonly accepted that P is the principal ‘limiting nutrient’ in freshwater lakes, meaning that the supply of P to a lake (rather than that of N) controls how much algae can be produced.1 Lakes receive P (and N) from diverse sources, including runoff from agricultural fields, seepage from septic tanks, as well as effluent from wastewater treatment plants, urban stormwater runoff, and industrial discharges. Stormwater runoff is especially important in urban areas where rainfall events flush nutrients and contaminants from residential lawns and impervious surfaces into streams and, eventually, in nearby lakes.

    In addition to high concentrations of P and N and algal blooms, the most telling symptom of eutrophication of a lake is the depletion of dissolved oxygen (DO) in the deeper part of a lake, also known as the hypolimnion.

    Road saltFig. 1: Anoxic bottom waters accompanying a strengthening of the water column’s stratification triggers internal phosphorus loading from the deposited sediments.

    Oxygen depletion occurs because, after they die, the algae sink to the bottom. Bacteria living at depth decompose the algal detritus by using the available DO. In a lake with low algal productivity, the downward mixing of DO into the hypolimnion can resupply DO faster than it is respired by the bacteria, and the hypolimnion remains oxygenated. In a eutrophic lake, however, DO consumption may overwhelm its resupply, and the hypolimnion becomes hypoxic. When this happens, fish and other aquatic wildlife are forced to move out and, in extreme cases, may even die. Thus, the logical way to mitigate lake eutrophication is to take measures to reduce the external inputs of P. The latter forms the basis for most existing strategies to mitigate lake eutrophication.2

    However, our recent work demonstrates that, in urban areas where roads, sidewalks, and parking lots must be cleared of snow and ice during winter, the application of de-icing salts also contributes to the depletion of DO in lakes.3 In essence, the wash-off of salt from the surrounding urban landscape causes the salinisation of the receiving lake. As the water becomes saltier and therefore denser, more and more energy is required to mix the water column and, therefore, the resupply of DO to the hypolimnion slows down. Thus, even if the external input of nutrients to the lake remains the same or decreases, the depletion of DO may become more severe. Moreover, much previous research has shown that, under waters depleted in DO, P deposited at the bottom of a lake is more efficiently recycled back to the water column (Fig. 1).

    Fig. 2: Location of Lake Wilcox in Ontario, Canada (a), and sketch of its drainage area (b).

    This release of P from deposited sediments is known as internal P loading. In lakes where the external P loading is reduced, but, where DO depletion of the hypolimnion persists, internal P loading may delay the return of the lake to a less eutrophic state.

    Oxygen depletion in Lake Wilcox, Canada

    Oxygen depletion driven by salinisation is exactly what we found for Lake Wilcox – a lake in the greater Toronto metropolitan area in Ontario, Canada (Fig. 2). The originally forested watershed of Lake Wilcox has undergone significant development since the early 1900s, when the land was first converted to agriculture. This was followed by urban development starting in the 1950s and further accelerating in recent decades. As a result, the impervious land cover in the watershed is now over 60% (Fig. 3a). By the 1980s, worsening eutrophication, including declining DO levels and the appearance of cyanobacteria, became a major issue. To combat increasing algal productivity and avoid harmful algal blooms (HABs), a suite of stormwater management systems, notably sediment-retention ponds, were constructed in the watershed starting in the early 2000s. Over time, more and more of the urban and suburban developments have been connected to the stormwater sewer system.

    Environmental and societal impacts on water quality

    We analysed 22 years of lake water chemistry data, from 1996 to 2018, to identify the roles climate change, urbanisation, and P and N inputs play in the observed changes in water quality and algal productivity. It quickly became clear that a major change in water quality was the large increase with time of the chloride concentration in the lake (Fig. 3b). As road salt primarily consists of rock salt, that is sodium chloride, the chloride concentration is a measure of the salt input to the lake. As seen in Fig. 3b, salinisation significantly accelerated after 2010, likely due to the increasing connectivity of the urban landscape to the stormwater sewer system, which facilitates the wash-off of salt toward the lake. At the same time, the data shows an expansion of the annual period where the hypolimnion exhibits no, or very low, DO concentrations (Fig. 4).

    SaltFig. 3: Fraction of impervious land cover in Lake Wilcox’s watershed (a) and in-lake surface water chloride concentrations (b) from 1996 to 2018.

    Further analysis of the data indicates that the external P input to the lake from the watershed has been declining since the late 1990s as a result of P retention in the stormwater management infrastructure – especially sediment retention ponds. Despite the lower external P inputs, the hypolimnion shows an enrichment in dissolved P, which is consistent with a ramping up of internal P loading. Overall, the temporal trends seen in the water chemistry data can be explained by the increasing amount of de-icing salts used in the urbanising watershed. The resulting salinisation decreases the chemical exchanges between the surface waters and the hypolimnion, therefore increasing the vertical differences in chemical composition of the water column – a condition lake scientists refer to as stratification.

    There are increasing reports of lakes in temperate climate zones experiencing declining DO concentrations and more pronounced water column stratification. Thus far, these changes have been ascribed to climate warming. Our results, however, suggest that, in cold and cold-temperate regions, salinisation may be an additional driver of these changes. Other researchers have observed rising chloride concentrations of lakes in urban watersheds of North America and Europe, generally following trends similar to the one observed in Lake Wilcox (Fig. 3b).

    Fig. 4: Mid-lake depth distributions of dissolved oxygen concentrations (DO) between 1996 and 2018. Note the lengthening of the yearly period of anoxia (blue colour) after 2005.

    Thus, the proposed salinisation-driven water column stratification and DO depletion may be widespread. Efforts to control the external P loading to such lakes may be offset by the enhanced internal P loading caused by growing DO depletion of bottom waters. Management strategies aiming to protect lakes against the impacts of eutrophication should therefore consider the role of salinisation in changes in lake water quality, including those that traditionally are associated to increasing external nutrient loading.


    1: O’Connell, D W, Ansems, N, Kukkadapu, R K, Jaisi, D, Orihel, D M, Cade-Menun, B J, Hu, Y, Wiklund, J, Hall, R I, Chessell, H, Behrends, T, and Van Cappellen, P (2020). Changes in sedimentary phosphorus burial following artificial eutrophication of Lake 227, Experimental Lakes Area, Ontario, Canada. Journal of Geophysical Research: Biogeosciences 125, 5713. DOI: 10.1029/2020JG005713

    2: Kao, N, Mohamed, M, Sorichetti, R J, Niederkorn, A, Van Cappellen, P, Parsons, C T (2022) Phosphorus retention and transformation in a dammed reservoir of the Thames River, Ontario: Impacts on phosphorus load and speciation. Journal of Great Lakes Research 48, 84-96, DOI: 10.1016/j.jglr.2021.11.008

    3: Radosavljevic, J, Slowinski, S, Shafii, M, Akbarzadeh, Z, Rezanezhad, F, Parsons, C, Withers, W, Van Cappellen, P (2022) Salinization as a driver of eutrophication symptoms in an urban kettle lake (Lake Wilcox, Ontario, Canada). Science of the Total Environment (in press). DOI:

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