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Soil as a reservoir for road salt retention leading to its gradual release to groundwater
Abstract
Road salt application elevates Na and Cl concentrations throughout the year in many surface water and groundwater systems. This study explores the role of soils in extending the lag time between road salt application and the delivery of Na and Cl to shallow groundwater in a temperate environment. Intact soil cores were collected near karst springs at both an urban and a rural site at distances of 1 m, 5 m, and 13 m from nearby roads that experience winter salting. Cores were manipulated in the lab to simulate various field conditions; treatments included irrigation with: 1) deionized (DI) water (DI group) as a control, 2) NaCl solution (salt group) to mimic prolonged exposure to road salt, or 3) NaCl followed by DI water (recovery group) to mimic winter road salting followed by dilute rainfall in spring. In the first NaCl irrigation of the salt and recovery groups, soils retained 62% of the applied Cl and 66% of the applied Na on average, which was largely stored in the porewater. Throughout the 5 week study, Ca, Mg, and K were elevated and the pH was depressed in leachate from salt group compared to DI group cores due to cation exchange. Likewise, cation exchange enhanced Na retention so that salt and recovery group cores retained half of the applied Na at the end of the experiment, compared to a quarter of the Cl. Na and Cl retention were greater for soils from the rural site, which is characterized by higher organic matter (OM) and sand content, faster infiltration, and lower bulk density than for the urban site, which has higher bulk density and more silt and clay. Furthermore, extractable Cl in field soils was positively correlated with soil water content, OM, and sand content, suggesting that these properties may control retention. We assume Cl retention to be the result of porewater retention, microbial uptake, and chlorination of soil OM. After the addition of 2000 mg Cl to the salt group cores, non-conservative Cl behavior ceased because the retention capacity of the soils had been exhausted. Recovery rates during DI flushes of recovery group cores indicate that these soils slowly release Na and Cl for at least 2.5–5 months following salt application. This gradual release from soils helps to explain the year-round persistence of high salt concentrations in some surface waters and groundwaters.
... Although salt runoff from impervious surfaces into streams is often considered the primary source of salt entering lakes (Dugan and Arnott 2023), chloride retention in stream sediments and riparian soils can result in a slow release to surface and groundwater (Robinson et al. 2017), which eventually can enter wetlands and lakes (Mackie et al. 2022). Despite the increasing interest in the salinization of freshwater systems, the role of soil as a repository and delivery system for salt is relatively unexplored. ...
... Chloride historically has been considered a conservative ion in substrates; as a consequence, few studies have focused on its retention in substrates, particularly in regard to road salt contamination (Bastviken et al. 2007). However, the limited number of studies that have investigated this topic found that chloride retention followed by release can occur (Öberg and Sandén 2005;Bastviken et al. 2007;Kincaid and Findlay 2009;Robinson et al. 2017). The mechanism accounting for release/retention is still unresolved. ...
... Organic matter content has been suggested as a possible factor, relating to the chlorination of organic matter within substrates by microbial activity (Öberg and Sandén 2005). Both Kincaid and Findlay (2009) and Robinson et al. (2017) found correlations between substrate organic matter and chloride retention, although the former could not draw conclusions from this association due to substrate organic matter's correlation with water content. Other potential mechanisms have also been suggested, such as ion exchange and substrate complexation, but no clear relationship has been identified (Bastviken et al. 2007). ...
Salinization in freshwater ecosystems has become an increasingly prevalent issue. Past studies indicate that increased salinity levels in lakes can impact biota, stimulate internal nutrient loading, and prevent seasonal turnover, potentially resulting in impairment to the lake ecosystem. Salt retention in soils and groundwater causes elevated salt concentrations in fresh water long after road salt was applied. We examined salt retention and release in soils collected near the tributaries flowing into and out of a salt-impacted urban lake. We distributed each soil sample into plastic trays and exposed them to three treatments, conducted in series: (1) non salt-contaminated water as a conditioning rinse; (2) salt-contaminated water to mimic salt de-icer runoff; and (3) non salt-contaminated water to determine salt release. We measured retention of chloride from each soil sample based on how much chloride was measured in water draining the soil (effluent). We observed considerable variability among sites presumably because of soil heterogeneity, although overall the soils in our study area retained a modest amount of chloride (mean of ∼29 mg/L) from simulated salt runoff events, even at short exposure times (
... Continued application of deicing agents has resulted in the accumulation of Cl − in the shallow subsurface Ludwikowski and Peterson 2018;Watson et al. 2002). Soil column experiments established the duration of Cl − retention within the soil to be several months, 2-5, despite flushing of the columns by simulated precipitation representing multiple volumes of porewater (Kincaid and Findlay 2009;Robinson et al. 2017). Retention times in soils are believed to be longer given variability of recharge events and the occurrence of dry periods (Robinson et al. 2017). ...
... Soil column experiments established the duration of Cl − retention within the soil to be several months, 2-5, despite flushing of the columns by simulated precipitation representing multiple volumes of porewater (Kincaid and Findlay 2009;Robinson et al. 2017). Retention times in soils are believed to be longer given variability of recharge events and the occurrence of dry periods (Robinson et al. 2017). Elevated Cl − concentrations measured in soils near roads in the subsequent fall attest to the persistence of Cl − in the environment (Lax and Peterson 2009;Mikkelsen et al. 1997). ...
... Existing studies have either focused on urbanized watersheds (Ostendorf 2013;Perera et al. 2013;Rivett et al. 2016;Stirpe et al. 2017) or do not resolve Cl − load between periods of storm and non-event flow (base flow) (Hubbart et al. 2017;Kelly et al. 2008;Nava et al. 2020;Oswald et al. 2019). To the authors knowledge only one study has examined storm and base flow Cl − load in a rural catchment, where it was found for a rural karst springshed that 32.4% of annual Cl − load was transported during storm flow (Robinson et al. 2017). However, given the large differences in hydrology between siliciclastic and karst catchments, it is unclear to what extent this result applies to Cl − load behavior in non-karst rural catchments. ...
Manual and high-frequency measurements (n = 535) of chloride (Cl−) along a low-order stream in an urban–agricultural watershed (8% urban, 87% agriculture) were conducted to investigate the importance of stormflow to Cl− transport. Sampling was conducted from February 2018 to February 2019; manual sampling occurred weekly, while stormflows were sampled at high frequency. Total Cl− export was nearly 780,000 kg, of which 42.1% occurred during winter. Stormflows, which represented 19% of the period, contributed 57.6% of the total Cl− load. The importance of stormflows varied seasonally; winter and spring storms exported nearly half of total Cl−, 29.1% and 18.2% respectively, while summer (8.2%) and fall storm (2.1%) events account for only ~ 10% of total export. A substantial portion of Cl− export, 43.4%, also occurred during baseflow, likely from accumulation of Cl− related to road salt and KCl fertilizer in groundwater. The results identified two periods of elevated Cl− concentrations: (1) flushing of road salt from impervious surfaces during and immediately following the cold season and (2) transport of salt accumulated from the dry season. Elevated discharges associated with summer and fall stormflows when road salt was not present did not generate similar Cl− loads, despite peak discharge values larger than those measured in the winter and spring. The lack of deicing application and a shift to stored Cl− during the summer stormflows created a discharge–load relationship that reached an asymptote where further increases in discharge do not correspond with increased Cl− load.
... These lakes differ from drainage lakes in that solutes are predominantly provided by groundwater and direct atmospheric deposition, residence times are long, and groundwater inputs are driven by landscape position relative to the water table (Webster et al. 2006). Seepage lakes are a window into groundwater flow paths and may be susceptible to long-term changes in water chemistry if aquifers are retaining anthropogenic solutes (Robinson et al. 2017;Baraza and Hasenmueller 2021). ...
... Based on observed trends, we added a storage component to Eq. 1. Although chloride is often considered a conservative solute, studies have shown that soil can store a limited amount of chloride (Kincaid and Findlay 2009;Robinson et al. 2017;Shannon et al. 2020). We modeled the terrestrial storage component as a sigmoid curve (s-curve), where at t = 0 (1950s) the rate of storage is high, that is, the most road salt is retained in the terrestrial landscape. ...
... Chloride retention in soils bucks the widely held view that chloride is a conservative ion that "goes where the water goes." Although, by now this paradigm should be shifting as the phenomenon of delayed leaching of chloride to groundwater and surface water has been noted by numerous studies Kincaid and Findlay 2009;Robinson et al. 2017;Oswald et al. 2019;Shannon et al. 2020). At the same time, the salinization of soils in the watershed may promote nitrate leaching ) and mobilize toxic heavy metals including lead, cadmium, and mercury; all of which may be more abundant due to vehicular traffic (Schuler and Relyea 2018). ...
The concentrations of conservative solutes in seepage lakes are determined by the relative inputs of precipitation vs. groundwater. In areas of road salt application, seepage lakes may be at high risk of salinization depending on groundwater flow. Here, we revisit a 1992 analysis on the salinization of Sparkling Lake, a deep seepage lake in Northern Wisconsin. The original analysis predicted a rapid increase in chloride concentrations before reaching a steady steady of 8 mg L−1 by 2020. Forty years of monitoring Sparkling Lake show that rather than reaching a dynamic equilibrium, chloride concentrations have steadily increased. We update the original box model approach by adding a soil reservoir component that shows the slow steady rise in chloride is the result of terrestrial retention. For freshwater rivers and lakes, chloride retention on the landscape will both delay chloride impairment and prolong recovery and must be considered when modeling future chloride contamination risk.
... 5 In particular, for sodium (Na) and chloride (Cl) transported through groundwater flow, soils can retain over 60% of the total amount of spilled NaCl. 6 Soils can slowly release NaCl over months, sometimes even beyond one year. 6,7 In Pennsylvania (PA), the most densely drilled state in the largest shale gas play in the world, ∼12000 shale gas wells have been drilled since 2004, often along ridges near streams with high water quality. ...
... 6 Soils can slowly release NaCl over months, sometimes even beyond one year. 6,7 In Pennsylvania (PA), the most densely drilled state in the largest shale gas play in the world, ∼12000 shale gas wells have been drilled since 2004, often along ridges near streams with high water quality. Spills and leaks are the most common pathway [8][9][10][11][12][13][14]33 that contaminants from the industry (other than natural gas itself) enter streams in the Appalachian Basin in PA and in other shale gas areas. ...
... 4,5 For example, salts retained by soils after a spill evaporates can slowly release during a time period of more than one year. 6,7 Month-long timeframes may be particularly important for streamwater quality impacted by groundwater flow related to spills into soil or sediments along a stream. ...
Chemical spills in streams can impact ecosystem or human health. Typically, the public learns of spills from reports from industry, media, or government rather than monitoring data. For example, ∼1300 spills (76 ≥ 400 gallons or ∼1500 L) were reported from 2007 to 2014 by the regulator for natural gas wellpads in the Marcellus shale region of Pennsylvania (U.S.), a region of extensive drilling and hydraulic fracturing. Only one such incident of stream contamination in Pennsylvania has been documented with water quality data in peer-reviewed literature. This could indicate that spills (1) were small or contained on wellpads, (2) were diluted, biodegraded, or obscured by other contaminants, (3) were not detected because of sparse monitoring, or (4) were not detected because of the difficulties of inspecting data for complex stream networks. As a first step in addressing the last problem, we developed a geospatial-analysis tool, GeoNet, that analyzes stream networks to detect statistically significant changes between background and potentially impacted sites. GeoNet was used on data in the Water Quality Portal for the Pennsylvania Marcellus region. With the most stringent statistical tests, GeoNet detected 0.2% to 2% of the known contamination incidents (Na ± Cl) in streams. With denser sensor networks, tools like GeoNet could allow real-time detection of polluting events.
... The length of time road salt will stay in surface soils before being leached into waterways depends on soil water residence time, soil characteristics and hydrologic flowpaths (Kincaid and Findlay 2009;Snodgrass et al. 2017). Robinson, Hasenmueller, and Chambers (2017) distinguish between two modes of ion retention: 1, conservative retention, where ions are held in pore water, and transport is governed by the degree of pore-water retention and 2, nonconservative retention, where sorption to organic and mineral particles, or uptake by plants (Lovett et al. 2005) and microbes (Bastviken et al. 2007), slows ion transport relative to pore-water residence time. While chloride ions are generally considered conservative, with retention being regulated by water residence time (Svensson et al. 2007), this does not equate to rapid flushing of chloride from soils. ...
... One study examining ion retention in urban and rural soils found that sodium and chloride retention lasted at least 2-5 months following salt application and that ions exhibited longer retention times in rural soils. The authors suggested that ion retention was expected to lengthen under nonlaboratory conditions due to less frequent flushing events and more complex movement pathways (Robinson, Hasenmueller, and Chambers 2017). ...
... With road salt application, the concentration of ions retained in soils will be driven by soil type, precipitation and time (Oswald et al. 2019). Time is influential in that a given soil may exhaust its nonconservative ion retention capacity over the course of a season or years of exposure (Robinson, Hasenmueller, and Chambers 2017). When soils act as salt reservoirs, the flow of salt to aquatic environments is slowed (Kelly et al. 2008;Kincaid and Findlay 2009). ...
Road salt application is a necessary component of winter road maintenance but comes with an environmental cost. Salts are transported via stormwater drainage or overland and soil throughflow to surface waterbodies, where excess ions create unfavorable or even uninhabitable conditions for freshwater organisms. Soils may retain salts during the process of overland and subsurface flow, thus acting as reservoirs that slow the transport of salt into freshwaters. Understanding the capacity and consistency of anthropogenic salt storage in urban soils may allow us to discover when and where deicing salt applications are most harmful. This article investigates the degree to which soils across a heterogeneous urban landscape retain salts. We measured the electrical conductivity (EC) of soils in an urban setting. Land covers included forests, grasslands, open spaces, low- and medium-density developments and along roadsides. We found that across land-cover types, soil carbon and porosity were correlated to EC in late summer, which suggests that pore space is an important and long-lasting reservoir for salt. In addition, more developed areas, had higher mean soil EC and greater EC variability within and between sites, with 75% of overall variance occurring within individual sites. We hypothesize that this within-site heterogeneity is driven by anthropogenic modifications to salt inputs and soil characteristics. The high EC variance in highly developed urban soils is a previously undiscussed phenomenon and highlights the fine-scale complexity of heterogeneous urban landscapes and the need for high-resolution sampling to accurately characterize urban ecosystems.
... Concentrations of Na + and Cl − increase in superficial and underground waters during winter, following the salting operations [14,20,36,42,43,[55][56][57][58][59][60][61]. Due to long retention times of these ions by soils and waters, this increase can continue during the summer period [56] and high concentrations in lakes and underground waters can be observed during several years [36,42,57]. ...
... Indeed, after salting operations, Na + concentration increases in the soil solution. Sodium enters in competition with other cations at the sites of ionic exchanges leading to an increase in Mg 2+ and Ca 2+ concentrations in the soil solution [19,41,56,61,63,66,[71][72][73][74][75]. Because of its stronger attraction to negatively charged soil particles, Mg 2+ may accelerate Na + leaching by displacing it in soils [23]. ...
... Road salt accumulation in soils depends on several parameters: the soil permeability and its density, and its mechanical properties influence the salt transport and the physicochemical processes. The Na + and Cl − ions can be retained in soils next to rural and urban roads in Missouri for 2-3 months after the end of the salting period, namely in soils containing organic matter, such as sandy soils [61]. According to Lundmark and Olofsson [81], soils with coarse particle size, which are more permeable, will have greater salt leaching down the soil profile. ...
... Après épandage de NaCl, la concentration en Na + augmente dans la solution de sol. Ce cation entre en compétition avec les autres cations présents au niveau des sites d'échanges ioniques entraînant, alors, une augmentation de la concentration en Mg 2+ et Ca 2+ dans la solution du sol (Howard et Haynes, 1993 ;Mason et al., 1999 ;Rosenberry et al., 1999 ;Norrström et Bergstedt, 2001 ;Bäckström et al., 2004 ;Green et al., 2008 ;Meriano et al., 2009 ;Nelson et al., 2009 ;Kim et Koretsky, 2013 ;Sun et al., 2015 ;Rhodes et Guswa, 2016 ;Robinson et al., 2017). Il peut également mobiliser les cations métalliques sorbés (Amrhein et al., 1992 ;Norrström et Jacks, 1998 ;Bäckström et al., 2004). ...
... L'accumulation des fondants routiers dans les sols dépend de plusieurs paramètres : la perméabilité du sol, sa densité, ses propriétés mécaniques influencent le transport des fondants, ainsi que les processus physico-chimiques. Robinson et al. (2017) ont montré que les ions Na + et Cl − pouvaient être retenus dans les sols de bord de route (rural et urbain du Missouri) entre deux et trois mois après la fin de la période de salage notamment dans les sols sableux contenant de la matière organique. Lundmark et Olofsson (2007) ont émis l'hypothèse que les sols ayant une granulométrie grossière, donc assez perméables, donnaient lieu à un plus fort lessivage des fondants vers le bas du profil du sol. ...
... Les concentrations en Na + et en Cl − augmentent dans les eaux superficielles et souterraines durant l'hiver, suite à l'application de fondants routiers (Demers et Sage, 1990 ;Mason et al., 1999 ;Godwin et al., 2003 ;Thunqvist, 2004 ;Kaushal et al., 2005 ;Kelly et al., 2008 ;Novotny et al., 2008 ;Daley et al., 2009 ;Corsi et al., 2010 ;Dailey et al., 2014 ;Corsi et al., 2015 ;Watmough et al., 2017 ;Robinson et al., 2017). Cette augmentation peut se poursuivre également durant la période estivale à cause d'un temps de rétention long des ions Na + et Cl − présents dans le sol et les eaux souterraines (Mason et al., 1999). ...
En conditions hivernales rigoureuses, l'application des fondants routiers (principalement du chlorure de sodium - NaCl) permet d'assurer la sécurité des usagers de réseaux. Toutefois, son utilisation généralisée entraîne des risques de contamination des écosystèmes aquatiques et terrestres. En milieu routier, le Na+ et Cl- sont transportés par les eaux de ruissellement vers des ouvrages de traitement tels que les bassins de rétention-décantation. Or, ces bassins n'ont pas la capacité de traiter efficacement cet apport de fondants sous forme dissoute. L'objectif de cette thèse est d'étudier le transfert de ces fondants au sein du système routier et de déterminer leur rôle dans la libération des polluants en période hivernale. Les caractéristiques du bassin situé à Azerailles (Lorraine, France) sur une route nationale moyennement fréquentée ont été étudiées, ainsi que les conditions météorologiques, les salages, la composition des matières en suspension (MES) et la concentration en éléments traces métalliques (ETM). Les résultats ont permis de montrer que entre 50 et 90 % du Cl- ont été collectés par le bassin. Il joue un rôle de tampon qui permet une libération du Cl- dilué durant la période de ruissellement suivant la période de salage. La présence de NaCl dans les eaux a joué un rôle sur la diminution de la qualité des matières en suspension, en mettant en évidence la présence de polluants organiques en période de salage. Elle entraîne également une modification de la chimie des eaux et une augmentation des polluants métalliques (zinc).
... For example, rivers draining semiarid and arid regions in South Africa can show enrichment in Na + concentrations relative to Cl − concentrations whereas rivers draining humid regions can show enrichment in Cl − concentrations relative to Na + owing to road salt and other pollution sources (Fig. 4). Retention of Na + and Cl − in groundwater can occur because of incomplete flushing of soils in the vadose zone, uptake by microbes and plants and ion exchange of Na + on soil exchange sites 84,85 . Overall, the attenuation effects of soil ion exchange, biological uptake and dilution effects of downstream water accumulation and/or precipitation events no longer drive salt concentrations below water quality limits. ...
... Cation exchange dictates how salts are stored and transported in soils and migrate vertically in the soil profile owing to leaching and capillary action. There can be substantial accumulation of anthropogenic salts in soils owing to retention of Cl − because of incomplete water flushing, uptake by microbes and plants, chlorination of organic matter, and ion exchange of Na + at soil exchange sites 84,85 . ...
... Very few studies, however, have examined benthic macroinvertebrate communities in the field and over an extended period of time, that is, years rather than days or months. There is some indication that background levels of Cl − may be increasing in streams in the northern United States and Canada because of incomplete flushing of road salt after winter storm events due to retention in soil and groundwater, resulting in the gradual release of Cl − into streams (Findlay & Kelly, 2011;Robinson et al., 2017;Wallace & Biastoch, 2016). Thus, over time it is possible that there may be either a general decline in the richness and/or abundance of the macrobiotic community or a change in the structure of the community (Wallace & Biastoch, 2016). ...
... Public works departments use salt on roadways, most of which convey runoff quickly to streams (Oswald et al., 2019). Some of this salt is retained in soils and groundwater and released gradually over the ensuing months (Oswald et al., 2019;Robinson et al., 2017), which is reflected in the contribution to median concentrations. ...
The use of deicing agents during the winter months is one of many stressors that impact stream ecosystems in urban and urbanizing watersheds. In this study, a long‐term dataset collected by citizen scientists with the Missouri Stream Team was used to evaluate the relationships between watershed urbanization metrics and chloride metrics. Further, these data were used to explore effects of elevated chloride concentrations on stream invertebrate communities using quantile regression. While the amount of road surface in a watershed was a dominant factor in predicting the maximum chloride measurement, the median chloride concentration was also strongly related to the amount of medium‐to‐high density development in the watershed, suggesting that non‐municipal salt use is an important contributor to increases in baseflow chloride concentrations. Additionally, chloride concentration appears to be one of the many factors that impact invertebrate density and diversity measurements, with decreases in invertebrate diversity corresponding with the U.S. EPA water quality criteria. Our findings suggest that the use of chloride‐based road salt on municipal roads as well as in non‐municipal settings is contributing to a loss of diversity and density of aquatic invertebrate communities in urban regions. This article is protected by copyright. All rights reserved.
... In wetland sediments where drainage is poor and road salt-enriched runoff may have long residence times, ion exchange (i.e., Na + displacement of Ca 2+ , Mg 2+ , and K + ) could alter spatial patterns of soil base cation availability. For example, organic-rich soils of wetlands may enhance Na + retention and displacement of other cations (Robinson et al. 2017), reducing plant mineral nutrition if macronutrients (N, Ca, Mg, and K) are leached from the ecosystem or if toxic levels of Na + accumulate in plant tissues. ...
... (a) Ground layer community composition was not distinct among distance zones; however (b), composition differed among wetland sites as evidenced by clustering among sites. Vector overlays show environmental factors that correlated with ground layer composition along axes (R 2 > 0.2). an important driver of Na + retention capacity, with soils high in organic matter and cation exchange capacity able to retain and store large quantities (Robinson et al. 2017). While organic-rich soils of roadside wetlands can mitigate road salt effects by trapping sodium, chronic exposure may jeopardize their capacity to perform key ecosystem services, as excessive levels of Na + cause degradation of soil structure via dispersion (i.e., disintegration of soil aggregates), reducing hydraulic conductivity and soil retention of Na + (Norrström and Bergstedt 2001). ...
Forested wetlands of the temperate north are increasingly exposed to deicing salts, but it is unclear how this may alter wetland biogeochemistry and plant community composition. To investigate potential effects of deicing salts on exurban forested wetlands in southern New England, we employed a multi‐site field study to describe spatiotemporal patterns of soil physiochemical, water quality, and vegetation characteristics with distance from road deicing salt source. We surveyed nine road‐adjacent, red maple‐dominated wetlands to quantify a suite of soil parameters (Na+, K+, Mg2+, Ca2+, pH, electrical conductivity (EC), heavy metals, N, P, and soil moisture), as well as surface and groundwater salinity, and vegetation communities. With increasing distance from roads along 165‐m transects penetrating into each wetland, soil salinity (EC, Na+) decreased, while soil base cation concentrations (Mg2+, Ca2+) increased, likely due to cation exchange (Na+ displacing other base cations). We also measured foliar chemistry and observed elevated Na+ and reduced Mg2+ of dominant species leaf tissue near roads, suggesting plant nutrient uptake responds to road salt‐related changes in soil physicochemical variables. Despite this, we did not detect differences in plant community composition (ground, shrub layers) along road salt‐induced soil chemistry gradients in the field, likely because surface and groundwater salinities were relatively low (maximum: 0.64 ppt). To determine at which field salinities we could potentially expect changes in wetland plant communities, we conducted a full‐factorial, manipulative seed bank experiment to examine how NaCl concentrations (0, 0.5, 1, 2, 4, and 8 parts per thousand (ppt)), frequency of salt exposure (pulse, constant), and water level (surface, 2 cm below surface) affected soil seed bank responses. Seedling richness was reduced at salinities exceeding 1 ppt, and seedling density was reduced above 2 ppt, but pulsing tended to alleviate salt‐induced reductions in seed bank responses. As salinization of freshwater ecosystems continues to increase, our results suggest that field salinity levels of exurban New England forested wetlands are nearing yet still typically below the threshold for which we expect to see strong plant community responses.
... The model made by Lax and Peterson (2009) indicated that 84-day NaCl application each winter for 11 years resulted in the soil systems reaching an equilibrium between Cl input and output: the unsaturated zone was characterised by permanently elevated concentrations of Cl, and this served as a constant source of groundwater and surface water contamination. Robinson et al. (2017) report that the storage capacity for salts in sandy soil increases with the amount of organic matter and that salt release from soil can take 2.5-5 months, depending on field conditions such as longer dry periods and deeper soils. Perera et al. (2013) noted that approximately 40% of applied chloride enters a shallow aquifer in the Highland Creek watershed (the City of Toronto, Canada). ...
... The increase of chloride ions in the environment following road salt application not only occurs directly as a consequence of the application per se, they can also migrate indirectly through the soil and groundwater pathways (Fig. 2). Regular use of NaCl as road salt influences the structure of nearby soils, with application resulting in the replacement of Ca, Mg and K with Na, and the depression of porewater pH (Robinson et al., 2017). Such decreases in pH result in the ammonium and dissolved organic matter being flushed from the soils, and the mineralization of organic-N and nitrification being decreased, even at low winter temperatures (Green et al., 2009. ...
Road salt (mainly NaCl) is commonly used during the winter to ensure road and pavement safety; however, the long-term application of NaCl has negative consequences on soil and the water environment. The aims of the present review were to evaluate the impact of road salt on catchment processes which accelerate the eutrophication of waters, and to identify a possible approach for reducing the impact of winter salt treatments of roads and sidewalks, on water body quality. The objectives were implemented in accordance with the ecohydrological approach, which recommends using hierarchical steps to solve problems. The first step was the monitoring of threats, in which the causes of high chloride (Cl) concentrations in groundwater and surface water were identified. The results indicate that long-term winter application of road salt increases the annual mean concentrations of Cl in rivers and lakes, due to Cl entering groundwater. The second step was a cause-effect analysis of the impact of NaCl on the abiotic processes in soil and water, and on the biotic response to chloride exposure. Chlorides appear to decrease the biodiversity of aquatic animals and plants but favour the growth of phytoplankton, especially cyanobacteria. Moreover, Cl reduces the self-purification processes of water by decreasing nutrient accumulation in macrophytes, decreasing the denitrification rate and reducing organic matter decomposition. The third step was to evaluate possible solutions for reducing the negative impact of NaCl on the environment, and to improve the effectiveness of alternative de-icing agents. An analysis of available literature indicates that a system-based approach integrating engineering knowledge with an understanding of biological and hydrological processes is necessary to indicate solutions for reducing environmental risks from road salt use.
... While it is possible for additional rainfall to wash away the salt, soil could retain sodium due to dry periods and water flowing vertically. (Robinson et al., 2017). As the control site along Fair Lane Drive at the EIC rain garden was located 4 meters away from the road, there was little opportunity for water mixed with salt pieces to be splashed into it, with what little salt there was percolating to the bottommost layer (253.9 ppm). ...
... Sodium content of plants is influenced by the same factors that affect soil salinity (Robinson et al., 2017). The sodium from the road salt enters the plant through the roots then distributed throughout the body. ...
For the past 70 years, municipalities in southeastern Michigan have used chloride as a deicer in winter months. This has resulted in increasing soil salinity and halophytes (salt tolerant plants) proliferating along roadsides. Three halophytes that have taken root in Michigan are common mugwort (Artemisia vulgaris), Bassia scoparia, and seaside goldenrod (Solidago sempervirens) were studied along with Canada goldenrod (Solidago canadensis) as a control. Roadside soil was collected to measure its sodium content, texture, moisture content, organic matter content, and pH. The sodium content of the halophytes stems, roots leaves, secondary stems, fruits, and flowers were also measured. Results have demonstrated all three species have adapted to saline environments as includer halophytes. The perennials seaside goldenrod and common mugwort were found to have contained more sodium than the annual Bassia scoparia. Sequestered sodium was highest in the leaves and stem of the seaside goldenrod, the secondary stems of common mugwort, and the fruit or leaves of Bassia scoparia. Soil sodium content was highest at soil by highways and lowest in residential areas. Additionally, salinity is affected by moisture content and soil texture. Lastly, the sodium content of plants increases with soil salinity. Halophyte sodium content was highest in those collected from roadsides while halophytes growing in soil with no to little salt contain no or little sodium as well. Common mugwort was found growing in soil with the highest salinity measured, seaside goldenrod the second most, and Bassia scoparia the least.
... While hydrological variability in urban watersheds has been extensively studied since the 1960s, 58 comparatively few studies have used high-frequency time-series data to investigate SC variability in urban streams. 26,27,56,58,105 SC variability in urban streams warrants further study given the likely negative effects on many freshwater organisms. ...
... 19,32,37,39,84 Retained Cl is subsequently released from soils and shallow groundwater over months to years. 27,42,105 Longer-term transport of Cl via deeper, slower groundwater flow results in export to streams over years to decades 31,32,34,109,111 with persistent Cl plumes observed near roads and associated infrastructure such as stormwater management basins. 27,112 In the Southeast, [Cl] is not increasing with a median interannual [Cl] change of 0.03 mg/L across the sites (median interquartile range = 0.32 mg/L). ...
Increasing specific conductance (SC) and chloride concentrations [Cl] negatively affect many stream ecosystems. We characterized spatial variability in SC, [Cl], and exceedances of EPA [Cl] criteria using nearly 30 million high-frequency observations (2- to 15-minute intervals) for SC and modeled [Cl] from 93 sites across three regions in the eastern United States: Southeast, Mid-Atlantic, and New England. SC and [Cl] increase substantially from south to north and within regions with impervious surface cover (ISC). In the Southeast, [Cl] weakly correlates with ISC, no [Cl] exceedances occur, and [Cl] concentrations are constant with time. In the Mid-Atlantic and New England, [Cl] and [Cl] exceedances strongly correlate with ISC. [Cl] criteria are frequently exceeded at sites with greater than 9–10% ISC and median [Cl] higher than 30–80 mg/L. Tens to hundreds of [Cl] exceedances observed annually at most of these sites help explain previous research where stream ecosystems showed changes at (primarily non-winter) [Cl] as low as 30–40 mg/L. Mid-Atlantic chronic [Cl] exceedances occur primarily in December–March. In New England, exceedances are common in non-winter months. [Cl] is increasing at nearly all Mid-Atlantic and New England sites with the largest increases at sites with higher [Cl].
... However, road salt runoff can also infiltrate roadside soils and leach into groundwater. This contaminated groundwater is then discharged into streams year round as baseflow, leading to elevated salt concentrations during summer and fall (Kaushal et al., 2005;Kelly et al., 2008;Kelly et al., 2012;Robinson et al., 2017;Snodgrass et al., 2017). ...
Land development and road salt usage drive long-term changes in major-ion chemistry of streamwater in six exurban and suburban watersheds, In urbanized areas, the "freshwater salinization syndrome" (FSS), which pertains to long-term increases in concentrations of major ions and metals in fresh surface waters, has been attributed to road salt application. In addition to FSS, the water composition changes as an influx of sodium (Na +) in recharge may displace calcium (Ca 2+), magnesium (Mg 2+), potassium (K +), and trace metals by reverse cation exchange. These changing ion fluxes can result in adverse impacts on groundwater and surface waters used for municipal supplies. Few datasets exist to quantify the FSS on a watershed scale or link its manifestation to potential controlling factors such as changes in urban development, land use/land cover (LULC), or wastewater treatment plant (WWTP) discharges in upstream areas. Here, we use two decades (1999-2019) of monthly streamwater quality data combined with daily streamflow for six exurban and suburban watersheds in southeastern Pennsylvania to examine the relations among Ca 2+ , Mg 2+ , K + , Na + , chloride (Cl −), sulfate (SO 4 2-), and alkalinity (HCO 3 −) concentrations and upstream controlling factors. Flow-normalized annual and baseflow (August ̶ November) concentrations for Ca 2+ , Mg 2+ , Na + , and Cl − increased in all six watersheds over the 20-year study, providing evidence of FSS's impacts on groundwater that sustains streamflow. Additionally, a redundancy analysis using 2019 flow-normalized values identified the following positive associations between solute concentrations and controlling variables: 1) Cl − , Mg 2+ , and Ca 2+ with impervious surface cover (ISC), 2) Na + and SO 4 2-with ISC and total WWTP discharge volume, and 3) HCO 3 − with agriculture and total WWTP discharge volume. From a human health perspective, 2019 flow-normalized Na + concentrations exceeded the U.S. Environmental Protection Agency's 20 mg L-1 threshold for individuals restricted to a low sodium diet. Furthermore, indices used to evaluate the corrosivity of source waters to drinking water infrastructure and inform municipal water treatment practices, such as the Chloride to Sulfate Mass Ratio and Larson Ratio, increased between two-and seven-fold over the 20-year time. Collectively, the results elucidate the causal factors of the FSS in suburban and
... Na is primarily delivered to mid-Atlantic riparian zones and streams through road salt runoff (Kaushal et al. 2005;Robinson et al. 2017;Moore et al. 2019;Hintz et al. 2022), especially at the Cooch milldam site, which is located just downstream of Interstate 95. As such, Na is consistently elevated across sediments at Cooch, and Na concentrations peak in upland-edge sediments at Roller where the other deicing agent, Mg, is also highly concentrated (Fig. 5). ...
Purpose
Riparian zones are important modifiers of nutrient flux between terrestrial and aquatic ecosystems. However, dams alter riparian zones—trapping fine-grained, organic matter-rich sediment and creating poorly mixed, low oxygen conditions—thereby affecting sediment biogeochemistry in poorly understood ways.
Methods
We characterized the impact of two relict US mid-Atlantic milldams (one from a primarily agricultural watershed and one from a mixed land use/urban watershed) on spatial patterns of bioavailable element concentrations (Mehlich-3 extractable P, K, Ca, Mg, Mn, Zn, Cu, Fe, B, S, and Na) in sediments upstream and downstream of milldams, with depth, and along transects running parallel and perpendicular to the stream.
Results
Element concentrations were not clearly correlated with grain size or organic matter content and, although generally higher, were not significantly more concentrated in upstream riparian sediments when similar (shallow, variably saturated) depths were compared. Pronounced differences were observed: upstream of milldams, sediment concentrations of Ca and Mg were highest in variably saturated shallow sediments, while Fe and Mn were highest in deeper, continuously saturated, low-oxygen sediments. Additionally, data was significantly different by milldam site, a result of differences in land-use histories (e.g., road salt and fertilizer application/runoff) and dominant bedrock geology.
Conclusion
Overall, results highlight the combined importance of milldams (and associated influences on groundwater hydrology and sediment redox conditions) and external drivers (other land-use legacies and bedrock geology) in influencing spatial patterns of bioavailable elements in riparian sediments.
... Обратный процесс уменьшения солесодержания в почвах от весеннего периода к осеннему реализуется за счет летнего рассоления почв с дождевыми осадками. Однако стоит учитывать, что избыток солей не просто пропадает из почв, а инфильтруется в подпочвенные грунты, что в ряде случаев -например, при залегании ниже проницаемых почв с высокими коэффициентами фильтрации -может приводить к изменению состава грунтовых вод [6]. В весенний период почвы обочин дорог увлажнены талым снегом, являющимся, в сущности, раствором противогололедных реагентов. ...
... Cl − concentrations are often of highest concern in winter months and early spring when roadway runoff enters streams as overland flow either directly or via storm drains (Interlandi and Crockett, 2003;Kaushal et al., 2005;Steele et al., 2010;Kelly et al., 2012;Corsi et al., 2015;Dugan et al., 2017;Moore et al., 2017;Dugan et al., 2020). However, road salts and salt-impacted runoff are often transported to the side of the road, where Cl − can infiltrate the soil, leach into groundwater, and be slowly released into streams over time (Kaushal et al., 2005;Kelly et al., 2008;Kelly et al., 2012;Robinson et al., 2017;Snodgrass et al., 2017). This legacy effect can also manifest in summer months with elevated Cl − concentrations in streams during seasonal baseflow conditions (Kaushal et al., 2005;Kelly et al., 2008;Corsi et al., 2015). ...
Roadway deicing agents, including rock salt and brine containing NaCl, have had a profound impact on the water quality and aquatic health of rivers and streams in urbanized areas with temperate climates. Yet, few studies evaluate impacts to watersheds characterized by relatively low impervious surface cover (ISC; < 15 %). Here, we use long-term (1997 ̶ 2019), monthly streamwater quality data combined with daily streamflow for six exurban and suburban watersheds in southeastern Pennsylvania to examine the relations among chloride (Cl⁻) concentrations and ISC. Both flow-normalized Cl⁻ concentrations and ISC increased over time in each of the six watersheds, consistent with changes in watershed management (e.g., ISC, road salt application, etc.). The watersheds that experienced the greatest changes in percent ISC (e.g., agriculture replaced by residential and commercial development) experienced the greatest changes in flow-normalized Cl⁻ concentrations. We also utilized a comprehensive mass-balance model (2011–2018) that indicated Cl⁻ inputs exceeded the outputs for the study watersheds. Road salt applied to state roads, non-state roads, and other impervious surfaces accounted for the majority of Cl⁻ inputs to the six watersheds. Furthermore, increasing Cl⁻ concentrations during baseflow conditions confirm impacts to shallow groundwater. Although flow-normalized Cl⁻ concentrations are below the U.S. Environmental Protection Agency's chronic threshold value for impacts to aquatic organisms, year-round exceedances may result before the end of this century based on current trends. Though reduced Cl⁻ loading to streams may be achieved by limiting the expansion of impervious surfaces in exurban and suburban watersheds, changes in baseflow concentrations are likely to be gradual because of the accumulated Cl⁻ in groundwater.
... Field studies aim to investigate the regulatory effect of an experimental factor in the interaction with natural conditions. Roadside soils are a type of soils exposed to significant stress, especially in northern urban areas, where the roads are treated with de-icing chemicals each winter, some of which end up staying on lawns (Robinson et al., 2017). As the urban areas rapidly grow and develop and traffic flows increase, the load on soil resources increases each day. ...
Mechanochemical modification of lignite in the presence of an eco-friendly oxidizer, sodium percarbonate, ensures one-step solvent-free oxidation of lignite organic matter. The product is characterized by high yield of humic acids and increases the content of phenolic and carboxyl groups. The study aimed to conduct in situ tests of mechanochemically oxidized lignite for restoring the highway divider lawn, with allowance for specific features of lawns maintained by public utility service providers. Adding oxidized lignite statistically reliably increased grass height and weight in the experimental sites compared to the control one. Applying oxidized lignite (30 g/m²) increased grass height and weight by ~ 40% and 25%, respectively, compared to those on the control site. Applying oxidized lignite (10 g/m²) together with N120P60K60 fertilizer and additional sowing of gramineous plant mixture increased grass height and weight by ~ 65% and 25%, respectively. Additional sowing of gramineous plants did not cause significant predominance of the gramineous component. The recommendations for the technology for maintaining lawns in this type of plots are provided.
... Na + and Cl − ions can easily travel with stormwater runoff from impervious surfaces to plants, receiving waters and soil, which stresses plants and animals, as it impacts water quality [8]. Chloride from deicing salt can be stored in shallow groundwater in winter and released into surface water bodies slowly [13,14], contributing to the impairment of the aquatic life and health of waterbodies with time [15,16]. Cl − is a relatively conservative constituent and its USA EPA acute and chronic freshwater aquatic life ambient water quality criteria are 860 mg/L and 230 mg/L, respectively. ...
Green infrastructure (GI) protects aquatic ecosystems from stormwater runoff caused by urban development. Bioretention (BR) is a typical GI system wherein stormwater runoff is routed to a soil basin planted with vegetation and has been shown to reduce deicing salt loads in surface runoff, but the removal mechanism of salt is poorly understood. This study explores the potential of different vegetation types to reduce deicing salt released from a BR by transpiration. Six engineered soil media columns were built in a laboratory greenhouse to simulate a 1012 m2 BR basin along Lorton Road, Fairfax County, VA, USA. The effect of vegetation type (Blue Wild Indigo and Broadleaf Cattail) and influent salt concentration on flow volume and salt mass reduction were quantified for multiple storm events. For all storm events, chloride inflow concentrations, and vegetation types, Cl− load reduction ranged from 26.1% to 33.5%, Na+ load reduction ranged from 38.2% to 52.5%, and volume reductions ranged from 11.4% to 41.9%. Different inflow salt concentrations yielded different removal rates of deicing salt, and for a given column, salt removal decreased over sequential storm events. For each influent salt concentration, columns planted with Broadleaf Cattail (BC) performed better for volume and salt mass reductions than columns planted with Blue Wild Indigo (BWI), which in turn performed better than the controls.
... Cl − concentrations are often of highest concern in winter months and early spring when roadway runoff enters streams as overland flow either directly or via storm drains (Interlandi and Crockett, 2003;Kaushal et al., 2005;Steele et al., 2010;Kelly et al., 2012;Corsi et al., 2015;Dugan et al., 2017;Moore et al., 2017;Dugan et al., 2020). However, road salts and salt-impacted runoff are often transported to the side of the road, where Cl − can infiltrate the soil, leach into groundwater, and be slowly released into streams over time (Kaushal et al., 2005;Kelly et al., 2008;Kelly et al., 2012;Robinson et al., 2017;Snodgrass et al., 2017). This legacy effect can also manifest in summer months with elevated Cl − concentrations in streams during seasonal baseflow conditions (Kaushal et al., 2005;Kelly et al., 2008;Corsi et al., 2015). ...
... There were two main reasons that caused a little deviation in the study's simulation results of water and salt. One was that the model assumed that soil water could infiltrate freely without the action of capillary suction in the process of infiltration, without considering the lag effect during migration [42]. The other was that the model defaulted to the complete dissolution of salt in soil water in the simulation process, even though there might be salt retention in the infiltration process [43]. ...
Nested Delft 3D and Hydrus 1D models were applied to simulate variations in the hydrological process of tidal creeks, soil water, and salt transport in the soil profile of the reconstruction area in the Yellow River Delta under six gate dam scenarios. The results showed that the gate dam set up near the sea area was more conducive to reducing the variation range of water depth in the reconstruction area. The water depth changes in scenarios with 6 m gate valves were higher than those with 3 m sluice valves in the same gate dam location. The variations in surface water salinity, cumulative flooding time, flooding frequency, and cumulative infiltration in each scenario were similar to those for water depth. Rapid changes in soil water and salt content occurred in each scenario in periods without flooding. The fluctuation of soil salt content in different soil layers was contrary to the changes in soil water content. The overall difference in the soil salt contents and soil water content of the soil profile in scenarios with a gate dam near the sea was relatively larger than that of those with a gate dam near the shore. Obvious differences in both the soil water content and soil salt content between scenarios with 3 m and 6 m gate valves were not observed. Our results contribute to the understanding of the function of gate dams in controlling soil water and salt content in coastal wetlands.
... For example, salt concentrations of up to 300 g/m 2 can be found in surface soils within 10 m of salinized roadways, with elevated salt concentrations continuing up to 100 m from roadways (Lundmark and Olafsson, 2007;Green et al., 2008;Findlay and Kelly, 2011). Salts are transported more slowly through soils and shallow groundwater than surface water, and there is increasing evidence that salt is retained in terrestrial environments long after winter application (Bastviken et al., 2006;Kelly et al., 2008;Robinson et al., 2017). The impacts of road salinization on amphibians are not limited to aquatic environments; they also may have extended repercussions across terrestrial environments. ...
Anthropogenic salinization is a pervasive pollutant in much of the northeastern United States because of the widespread use of chemical deicing agents on roads. Although studies have examined the physiological effects of salinization on amphibians across life stages, behavioral responses to salinization of habitats are less studied. In this study, we experimentally test how salinity and temperature conditions experienced as larvae affect behavioral and physiological responses as juveniles. We first experimentally test whether juvenile Wood Frogs (Lithobates sylvaticus) can detect and avoid road salt in terrestrial soils and whether this avoidance behavior differs depending on temperature and salinity conditions in which individuals were raised as larvae. We also experimentally test whether temperature and salinity conditions experienced as larvae affect desiccation rates in juvenile Wood Frogs. We found a significant correlation between larval salinity conditions and choice of soil, with frogs raised in high salt aquatic conditions spending the majority of time on high salinity soils and frogs raised in low salt aquatic conditions spending the majority of time on low salinity soils. This behavioral response was muted in frogs raised in elevated temperature conditions. We were unable to detect a correlation between larval treatment and desiccation rate. Our experiments demonstrate that Wood Frogs can detect and respond to salinity levels in terrestrial habitats and that this juvenile response depends on environmental conditions experienced as larvae.
... About 60% of highway salts enter surface water sources and about 40% enter soil and groundwater sources ( Perera et al., 2013, Schuler and Relyea, 2018, Green et al., 2008, Szklarek et al., 2021. The entry of salt-containing effluent into groundwater and soil causes the cationic exchange of Na + ion with Ca + 2 and Mg + 2 ions ( Robinson et al., 2017 ), thereby lowering the pH, and flushing heavy metals, nutrients, and organic matter, and reducing the retention of water in the soil ( Schuler and Relyea, 2018, Green et al., 2008, Szklarek et al., 2021, Rommel et al., 2020. Therefore, the runoff containing road salt reduces the efficiency of biofilter systems in heavy metals treatment ( Søberg et al., 2017 ). ...
Highway runoff is one of the most significant non-point sources of pollution for the terrestrial and aquatic environment with biological, physical, and chemical effects. Considering local characteristics, treatment practices, and determining factors are essential for highway runoff management. The aim of this paper is to survey the review of highway runoff management in Europe with emphasis on runoff characterization, treatment, and modeling approaches and identifying possible knowledge gaps exists based on our review. The results showed that highway runoff has spatiotemporal variation, which is the main factor in the regional selection of the best management practice (BMP). Also, recent studies have poorly deemed characterization of highway runoff in different climatic scenarios, performance assessment of the current BMPs, and uncertainty analysis in modeling approaches. Furthermore, economic and risk analysis, along with decision-making methods, provide an optimum plan for the design and operation of BMPs.
... porosity and flow in their littoral zones. More broadly, sediment pore size and hydraulic connectivity, which may be altered through urbanization (Bhaskar et al. 2015;Shannon et al. 2020), also impact the degree to which water and solutes can move from groundwater into surface waters following rain or storm events (Robinson et al. 2017). ...
Groundwater–surface water (GW–SW) interactions represent an important, but less visible, linkage in lake ecosystems. Periphyton is most abundant at the GW–SW interface and can rapidly assimilate nutrients from the water column. Despite the importance of periphyton in regulating whole‐lake metabolism, they are less well studied or monitored in comparison with planktonic taxa and pelagic systems. This is in stark contrast to studies of flowing waters and wetlands, where variability in GW–SW connectivity and periphyton productivity is more often incorporated into study designs. To bridge the gap between groundwater's influence on lake benthic communities, this synthesis aims to prime researchers with information necessary to incorporate groundwater and periphyton sampling into lake studies and equip investigators with tools that will facilitate cross‐disciplinary collaboration. Specifically, we (1) propose how to overcome barriers associated with studying littoral ecological‐hydrological dynamics; (2) summarize field, laboratory, and modeling techniques for assessing spatiotemporal periphyton patterns and benthic hydrological fluxes; and (3) identify paths for hydrological techniques to be incorporated into ecological studies, deepening our understanding of whole‐lake ecosystem function. We argue that coupling hydrological and periphyton measurements can yield dualistic insights into lake ecosystem functioning: how benthic periphyton modulate constituents within groundwater, and conversely, the extent to which constituents in groundwater modulate the productivity of periphyton assemblages. We assert that priming ecologists and hydrologists alike with a shared understanding of how each discipline studies the nearshore zone presents a tangible path forward for both integrating these disciplines and further contextualizing lake processes within the limnological landscape.
... The main hazards of Cl − are as follows: (1) Soil, water, and air: Heavy content of Cl − influences the soil structure and decreases the retention capacity and the porewater pH of soil [10,11]. Cl − may reduce the self-purification process of water. ...
The chloride ion (Cl−) is a type of anion which is commonly found in the environment and has important physiological functions and industrial uses. However, a high content of Cl− in water will do harm to the ecological environment, human health and industrial production. It is of great significance to strictly monitor the Cl− content in water. Following the recent development of society and industry, large amounts of domestic sewage and industrial sewage are discharged into the environment, which results in the water becoming seriously polluted by Cl−. The detection of Cl− has gradually become a research focus. This paper introduces the harm of Cl− pollution in the environment and summarizes various Cl− detection methods, including the volumetric method, spectrophotometry method, electrochemical method, ion chromatography, paper-based microfluidic technology, fluorescent molecular probe, and flow injection. The principle and application of each technology are described; their advantages, disadvantages, and applicability are discussed. To goal of this research is to find a more simple, rapid, environmental protection and strong anti-interference detection technology of Cl−.
... The increase in the Ca:C t ratio, as well as the Mg:C t ratio could also be coupled to the mobilizing effect of Na ions and their alkalizing properties. It is likely that Na + competes with other cations for ion exchange sites, consequently leading to their temporal increase in the soil solution 39,[44][45][46][47] . Increased levels of Ca and Mg correspond with previous studies showing that these elements occur in higher concentrations in close proximity to roadways 44,48 . ...
Roadways traverse many forest areas and they often have harmful effects on forest soils, including the modified stability of soil organic matter (SOM). Soil CO2 respiration is an important indicator of SOM biological stability. The aim of this study was to test the hypotheses that a roadway will (1) modify the composition of the cation exchange capacity of adjacent forest soils, and (2) significantly decrease the stability of SOM. Two study sites were established in Scots pine and Silver fir stands, located close to the S7 highway in central Poland, which was opened to traffic in 1984. From each site, samples were taken at 2, 12 and 22 m from the forest edge. Soil CO2 respiration was determined using closed chamber incubation with an alkali trap. We also conducted a comprehensive analysis of soil chemical properties. The stoichiometric ratios of chosen chemical parameters to total carbon (Ct) were calculated. In both sites, we observed increased soil pH and CO2 respiration in the vicinity of the highway, as well as increased ratios of exchangeable calcium (Ca), magnesium (Mg) and sodium (Na) to Ct. In the fir site, the humic and fulvic acids, the dissolved organic carbon (DOC) content and aluminum (Al) to Ct ratio were depleted in close proximity to the highway. We suggest that the combined effect of Ca and Na ions, originating from winter de-icing, caused the depletion of Al and hydrogen (H) in the soil close to the forest edge and, therefore, resulted in lower SOM stability expressed as the decreased DOC and pyrophosphate-extractable carbon content, as well as the release of CO2. We conclude that the changes of SOM stability with distance were the effect of modification of ion-exchange relationships (particularly base cations versus Al³⁺ with H⁺) rather than forest stand species or intrinsic SOM properties (like functional groups, the recalcitrance of bindings etc.). Our work supports earlier studies, confirming the significant impact of Al and H on SOM stability.
... The peak of road de-icing occurs in winter and early spring (Hofman et al., 2012;Pająk et al., 2015). This phenomenon poses a serious threat to the soil and can be responsible for the disruption of ion-exchange relations, colloid dispersion, or the deterioration of soil structure (Robinson et al., 2017;Sun et al., 2015). Another important risk of deicing is the effect of Na on heavy metal mobilization and their leaching to groundwater. ...
Intensified vehicular traffic causes increased heavy metal contamination of the environment. We investigated the heavy metal chemistry of soils located under silver fir stands in the vicinity of Poland's S7 roadway. Three sampling sites were located in fir stands in central Poland. Fieldwork included soil sampling of the organic (O) horizon and mineral (A) topsoil. We analyzed the soil pH, carbon (C) and nitrogen (N) concentration , and the HCl-extractable forms of sodium (Na) and heavy metals: copper (Cu), nickel (Ni), lead (Pb), and zinc (Zn). The stoichiometric ratios Cu:C, Ni:C, Pb:C, and Zn:C were also calculated. In all sites, a higher Na concentration was found in the 0-10 m from the forest edge. This zone was characterized by increased pH in the O horizon, increased Zn and Ni in the A horizon, and a decreased Pb in the O horizon. There was no clear pattern for the Cu concentration. The Ni:C and Zn:C ratios were correlated with pH, while Pb:C and Cu:C ratios were correlated with the clay minerals. HCl-extractable Ni and Zn concentrations in A horizon were greater near the roadway, revealing strong pH dependency. The roadway affects the geo-chemical background of the topsoil in the nearby fir stands. Mechanistically, we suggest that Na increases the soil pH and therefore enhances the ability of soil organic matter to bind Ni and Zn by releasing hydrogen from soil organic matter functional groups into the soil solution. A depleted Pb near the road was likely owing to the strong competition from Na.
... induce ion exchange affecting acidification and metal and nutrient leaching (Bäckström et al. 2004;Löfgren 2001), or biological, i.e. affect aquatic food webs (Hintz and Relyea 2019;Todd and Kaltenecker 2012;Van Meter et al. 2011). The application of road salt has been estimated to be substantial compared with deposition (Forczek et al. 2011), and there are indications of associated extra Cl retention in soil (Robinson et al. 2017;Kincaid and Findlay 2009;Perera and Gharabaghi 2013). ...
Chlorine (Cl) in the terrestrial environment is of interest from multiple perspectives, including the use of chloride as a tracer for water flow and contaminant transport, organochlorine pollutants, Cl cycling, radioactive waste (radioecology; ³⁶ Cl is of large concern) and plant science (Cl as essential element for living plants). During the past decades, there has been a rapid development towards improved understanding of the terrestrial Cl cycle. There is a ubiquitous and extensive natural chlorination of organic matter in terrestrial ecosystems where naturally formed chlorinated organic compounds (Cl org ) in soil frequently exceed the abundance of chloride. Chloride dominates import and export from terrestrial ecosystems while soil Cl org and biomass Cl can dominate the standing stock Cl. This has important implications for Cl transport, as chloride will enter the Cl pools resulting in prolonged residence times. Clearly, these pools must be considered separately in future monitoring programs addressing Cl cycling. Moreover, there are indications that (1) large amounts of Cl can accumulate in biomass, in some cases representing the main Cl pool; (2) emissions of volatile organic chlorines could be a significant export pathway of Cl and (3) that there is a production of Cl org in tissues of, e.g. plants and animals and that Cl can accumulate as, e.g. chlorinated fatty acids in organisms. Yet, data focusing on ecosystem perspectives and combined spatiotemporal variability regarding various Cl pools are still scarce, and the processes and ecological roles of the extensive biological Cl cycling are still poorly understood.
... Road salt eventually enters nearby surface water and groundwater aquifers (Kelly et al. 2008;Robinson et al. 2017), leading to harmful ecological effects (Morgan et al. 2012) and a deterioration of drinking water quality (Stets et al. 2018;Pieper et al. 2018). Cl − is not readily involved in oxidation-reduction reactions, does not form complexes under most groundwater conditions, and is not absorbed onto mineral surfaces. ...
The negative impacts of road salt (primarily NaCl) on freshwater ecosystems and ground and surface waters used for drinking purposes have been extensively documented. Besides direct increases in chloride (Cl−) and sodium (Na+) concentrations in receiving waters, these ions are responsible for a myriad of soil chemical changes and processes resulting in increased corrosivity of water and subsequent leaching of lead (Pb) and copper (Cu); mobilization of heavy metals in soils to ground and surface water including cadmium (Cd), chromium (Cr), Cu, Pb, nickel (Ni), manganese (Mn), and zinc (Zn); and radionuclide mobilization presenting increased risks to drinking water quality. This article summarizes literature describing the mechanisms and the implications of road salt on water corrosivity and mobilization of both metals and radionuclides on groundwater resources and public health.
... Numerous studies have examined the impact that humans have on karst areas (e.g., [4][5][6][7][8][9][10][11][12]). These studies highlight possible sources of pollutants, including the application of fertilizers and pesticides to fields [6,13,14], road salt [15], leaky septic systems [16,17], and wastewater [10,18,19]. Fertilizer application, either animal manure or synthetic fertilizer, is a significant source of nitrate as nitrogen (NO 3 -N) to aquifers [20]. ...
Surface water–groundwater interaction within a karstic system enhances contaminant transport, making karst aquifers susceptible to anthropogenic practices. Contaminated waters related to agricultural and animal husbandry in northwestern Illinois (USA) prompted this investigation. Six streams and five springs were sampled for 16 parameters to assess anthropogenic influences. Statistical analyses revealed differences in 13 of 16 parameters between the stream and spring waters. Rock–water interaction was identified as the dominant mechanism defining the chemistry for both waters, which were classified as Ca-Mg HCO3. Elevated nitrate as nitrogen (NO3-N), chloride (Cl-), sodium, and potassium concentrations indicate that human activities have influenced the quality of both water types. All streams and springs had NO3-N concentration exceeding background levels, with concentrations ranging from 2.9 to 14.5 mg/L and 2.9 to 30.1 mg/L, respectively. NO3-N/Cl relationships at individual locations showed elevated concentrations of NO3-N due to fertilizers,
while the spring waters were influenced by manure, septic effluent, or mixed sources. The presence of coliform supports the likelihood of animal or human waste influences on waters. Dissimilarities within their chemical fingerprints can be traced to aid in differentiating sources within the waters.
Human activities in urban areas disturb the natural landscape upon which they develop, disrupting pedogenic processes and ultimately limiting the ecosystem services urban soils provide. To better understand the impacts on and resiliency of urban soils in response to urban development, it is essential to understand the processes by which and degree to which soil physical and chemical properties are altered in urban systems. Here, we apply the source-tracing capabilities of Sr isotopes (87Sr/86Sr) to understand the impacts of urban processes on the composition of soils in eight watersheds in Austin, Texas. We evaluate natural and anthropogenic Sr sources in watersheds spanning a wide range of urbanization, comparing soils by variations in their natural (including mineralogy, thickness, soil type, and watershed) and anthropogenic (including irrigation, soil amendments, and fertilization) characteristics. A strong positive correlation between soil thickness and 87Sr/86Sr is observed among unirrigated soils (R2 = 0.83). In contrast, this relationship is not observed among irrigated soils (R2 = 0.004). 95 % of 42 irrigated soil samples have 87Sr/86Sr values approaching or within the range for municipal supply water. These results indicate soil interaction with municipal water through irrigation and/or water infrastructure leakage. Soils irrigated with municipal water have elevated 87Sr/86Sr values relative to unirrigated soils in seven of eight watersheds. We propose that original soil 87Sr/86Sr values are partially to completely reset by irrigation with municipal water via ion exchange processes. Our results demonstrate that in urban systems, Sr isotopes can serve as an environmental tracer to assess the overprint of urbanization on natural soil characteristics. In the Austin region, resetting of natural soil compositions via urban development is extensive, and the continued expansion of urban areas and irrigation systems may affect the ability of soils to retain nutrients, filter contaminants, and provide other ecosystem services that support environmental resilience.
Long-term road salt application has increased chloride (Cl-) concentrations in public drinking water wells in many cold climate communities. A range of Best Management Practices (BMPs) have been adopted to mitigate the impact of road deicing compounds on groundwater quality. Chronic increases in chloride levels have been observed in several municipal well fields within the southern Ontario Regional Municipality of Waterloo (RMOW). In response, the RMOW and City of Kitchener implemented a plan to reduce salt application on roads by 25% within the local capture zones of one of the impacted well fields, the Greenbrook Well Field. Here the influence of salt reduction BMPs on subsurface water quality are examined by documenting changes in pore water Cl- concentrations and stored salt mass in vadose zone core samples collected at sites near the well field both before and after the implementation of the BMPs. The data indicate that ~6 years after salt reduction measures were initiated, average pore water Cl- concentration and average cumulative stored chloride mass in the vadose zone had decreased by approximately 60% and 40%, respectively. Groundwater samples collected from shallow monitoring wells installed at each field site showed similar post-BMP reductions in shallow groundwater Cl- concentration (~35%). Long-term (1973-2022) trends in raw water Cl- concentration data from the deeper public drinking water supply wells clearly demonstrate a slow, time-lagged response of the municipal supply wells to the salt reduction BMPs. The combined results suggest that controlled reductions in road salt applications within vulnerable, capture zone regions of public supply wells can reduce the impact of road salt deicing practices on municipal groundwater supplies over time.
In connection with the growing deficit of water and problems in satisfying certain needs, stormwater ponds collecting runoff from impervious surfaces are increasingly often considered a potential water source. This paper evaluates the pollution level and variations in the quality of stormwater stored and pre-treated in reservoirs located next to new roads in the metropolitan area of Lublin (south-eastern Poland). Possibilities of water reuse were also assessed. The studies took into account changes in weather conditions and traffic intensity. Quality tests were carried out seasonally (16 measurement dates in total). Selected physical, oxygen, nutrient and salinity indicators were analysed. High variations in the concentration of total suspended solids, NH 4 ⁺ , NO 2 ⁻ , TP, PO 4 ³⁻ and Cl ⁻ were observed (74–216%). On some measurement dates alarming conductivity, pH, suspended solids, COD, TP and Cl ⁻ values were recorded. Variations in stormwater quality are greater at the first stage of using the system of ponds, and the mean level of pollution stabilises several years after its construction. Changes in traffic intensity have no significant effect on the degree of pollution of the stored water. The highly variable water pollution level makes it difficult to precisely identify periods in which the use of ponds poses the lowest risk. Stormwater management should be accompanied by thorough analyses of water quality (constant monitoring) and the evaluation of possible risks to the environment.
Soil-based filter media in green infrastructure buffers only a minor portion of deicing salt in surface water, allowing most of that to infiltrate into groundwater, thus negatively impacting drinking water and the aquatic ecosystem. The capacity of the filter medium to adsorb and fixate sodium (Na+) and chloride (Cl-) ions has been shown to improve by biochar amendment. The extent of improvement, however, depends on the type and density of functional groups on the biochar surface. Here, we use density functional theory (DFT) and molecular dynamics (MD) simulations to show the merits of biochar grafted by nitrogenous functional groups to adsorb Cl-. Our group has shown that such functional groups are abundant in biochar made from protein-rich algae feedstock. DFT is used to model algal biochar surface and its possible interactions with Cl- through two possible mechanisms: direct adsorption and cation (Na+)-bridging. Our DFT calculations reveal strong adsorption of Cl- to the biochar surface through hydrogen bonding and electrostatic attractions between the ions and active sites on biochar. MD results indicate the efficacy of algal biochar in delaying chloride diffusion. This study demonstrates the potential of amending soils with algal biochar as a dual-targeting strategy to sequestrate carbon and prevent deicing salt contaminants from leaching into water bodies.
Synoptic sampling of streams is an inexpensive way to gain insight into the spatial distribution of dissolved constituents in the subsurface critical zone. Few spatial synoptics have focused on urban watersheds although this approach is useful in urban areas where monitoring wells are uncommon. Baseflow stream sampling was used to quantify spatial variability of water chemistry in a highly developed Piedmont watershed in suburban Baltimore, MD having no permitted point discharges. Six synoptic surveys were conducted from 2014 to 2016 after an average of 10 days of no rain, when stream discharge was composed of baseflow from groundwater. Samples collected every 50 m over 5 km were analyzed for nitrate, sulfate, chloride, fluoride, and water stable isotopes. Longitudinal spatial patterns differed across constituents for each survey, but the pattern for each constituent varied little across synoptics. Results suggest a spatially heterogeneous, three‐dimensional pattern of localized groundwater contaminant zones steadily contributing solutes to the stream network, where high concentrations result from current and legacy land use practices. By contrast, observations from 35 point piezometers indicate that sparse groundwater measurements are not a good predictor of baseflow stream chemistry in this geologic setting. Cross‐covariance analysis of stream solute concentrations with groundwater model/backward particle tracking results suggest that spatial changes in base‐flow solute concentrations are associated with urban features such as impervious surface area, fill, and leaking potable water and sanitary sewer pipes. Predicted subsurface residence times suggest that legacy solute sources drive baseflow stream chemistry in the urban critical zone.
Increasing salinization of freshwater threatens water supplies that support a range of human and ecological uses. The latest assessments of Delaware River Basin (DRB) surface-water-quality changes indicate widespread salinization has occurred in recent decades, which may lead to meaningful degradation in water quality. To better understand how and when salinity transport occurs and implications for DRB streams, this study: 1) explores the variability of specific conductance (SC) trends spatially and seasonally from 1998 to 2018, and 2) investigates how trends relate to streamflow, land disturbance, and impervious surface area to better understand regional salinization drivers. We find widespread increases in SC across the DRB, with several sites in the lower basin exceeding thresholds for aquatic life and experiencing increasing frequencies of exceedance over time. In general, the greatest basin wide increases in SC occurred during low flow conditions, indicating that a legacy component resulting from subsurface retention and transport processes has driven observed changes in riverine SC. For a subset of sites in the lower basin, where impervious area and cumulative land disturbance are higher, the greatest SC increases occurred during high flow conditions in winter months. Given the patterns of SC and watershed changes across the basin, as well as strong relationships between SC trends and sodium and chloride trends, deicing salt appears to be a likely driver of observed SC change. Even if deicing salt application plateaus or declines in coming years, the continued release and transport of the legacy subsurface component may still contribute to elevated DRB riverine SC.
Deicing salt is an important component of road safety during winter storms. Stormwater infiltration best management practices aim to prevent the salt from polluting streams and waterways, but this may shift pollutants to groundwater resources. In response to limited field studies investigating groundwater quality impacts caused by input of salt from stormwater infiltration best management practices, we monitored water levels and quality of groundwater at various depths in an unconfined aquifer around a stormwater infiltration basin using in situ sensors coupled with grab sampling. Our observations revealed differences in groundwater chemistry with depth in the aquifer and processes that were driven by the seasonal changes in the chemistry of stormwater (salt-impacted in winter and fresh in non-winter) recharging the aquifer. Water-matrix interactions in the vadose zone beneath the basin affected the transport of sodium (Na) into groundwater following non-winter recharge. Sodium movement through the aquifer was delayed relative to chloride (Cl), indicating a longer residence time of Na in the vadose zone. Radium (Ra) concentrations were correlated with Cl concentrations, suggesting salt-impacted recharge caused desorption of Ra into groundwater because of increased salinity. Stormwater-influenced groundwater followed a preferential flow path due to heterogeneity of the aquifer materials, and water chemistry varied with time and location along the flow path. These results highlight the importance of well screen length, placement and depth, and frequency of observations when designing a monitoring network.
Secondary salinization of freshwater is becoming a growing environmental problem. Currently, there is few data available on the effects of salinisation on subterranean crustaceans that are vital for the maintenance of groundwater ecosystem functioning. In this study, the sensitivity of subterranean Niphargus amphipods to NaCl was investigated. We expected that cave-dwelling species would be more sensitive as surface-subterranean boundary species. Eight ecologically different Niphargus species were tested: four live at the boundary between the surface and subterranean ecosystems (N. timavi, N. krameri, N. sphagnicolus, N. spinulifemur), three live in cave streams (N. stygius, N. scopicauda, N. podpecanus), and one species (N. hebereri) lives in anchialine caves and wells. The organisms were exposed to five concentrations of NaCl for 96 h and afterwards the immobility, mortality, and electron transfer system (ETS) activity (a measure for metabolic rate of animals) were evaluated. As expected, the most tolerant species was N. hebereri dwelling in naturally high-salinity habitat. However, contrary to our expectations, the species collected at the surface-subterranean boundary were more sensitive as cave stream species when their immobility and mortality were assessed. Interestingly, the majority of Niphargus tested were more NaCl tolerant as can be deduced from currently available data for subterranean and surface crustaceans. We could not observe a clear trend in ETS activity changes between groups of surface-subterranean boundary and cave streams species after exposure to NaCl stress, but it appears that osmotic stress-induced metabolic rate changes are species-specific. This study shows that amphipods Niphargus can be a valuable subterranean environmental research model and further ecotoxicity research is of interest.
During winter, snow and ice on roads in regions with cold weather can increase traffic crashes and casualties, resulting in travel delays and financial burdens to society. Anti‐icing or deicing the roads can serve a cost‐effective method to significantly reduce such risks. Although traditionally the main priorities of winter road maintenance (WRM) have been level of service, cost‐effectiveness, and corrosion reduction, it is increasingly clear that understanding the environmental impacts of deicers is vital. One of the most important problems in this regard is environmental contamination caused by cumulative use of deicers, which has many detrimental effects on the aquatic systems. Among the deicers, the chloride‐based ones raise the most toxicological concerns because they are highly soluble, can migrate quickly in the environment and have cumulative effects over time. In this review, we summarize and organize existing data, including the latest findings about the adverse effects of deicers on surface water and groundwater, aquatic species, and human health, and identify future research priorities. In addition, the data provided can be used to develop a framework for quantifying some of the variables that stakeholders and agencies use when preparing guidelines and standards for WRM programs.
Practitioner points
Pollution from the increasing use of roadway deicers may have detrimental effects on the environment.
Of particular concern are the acute and cumulative risks that chloride salts pose to aquatic species.
Chloride salts are water‐soluble, very difficult to remove, highly mobile, and non‐degradable.
Deicers cause water stratification, change the chemicophysical properties of water, and affect aquatic species and human health.
Current guidelines may not be appropriate for environmental protection and need to be revised.
Anthropogenic freshwater salinization is increasing with global change. Rising freshwater salinity threatens ecosystem biodiversity, health, and services via toxicity to organisms and mobilization of nutrients and metals. Brining roads is one major source of freshwater salinization that continues to grow with rising urbanization. While the detrimental effects of salinization in streams are well-documented, high-frequency, temporal patterns in salt transport, particularly during winter road de-icing in mixed land use landscapes, are less understood. To address this knowledge gap, we analyzed high-frequency specific conductance as a proxy for salinity across 114 high-flow events from 2013 to 2018 in an impaired stream draining mixed agriculture−urban land use. The specific conductance was highest in winter (median = 947 μS cm −1) and decreased with first-order kinetics up to 90 days after brining (β 1 = −0.003), suggesting lasting impacts of road de-icing on water quality. Although hysteresis patterns suggested a transition from distal to proximal salt sources, they showed no clear correlation of flushing versus dilution to brining events. While seasonal brining increased salinity in receiving streams, unpredictable transport dynamics reduced the efficacy of hysteresis in characterizing salt transport dynamics. Thus, the complexity of mixed land use watersheds requires more spatially and temporally explicit monitoring to characterize stream salinization dynamics.
Increasing background salinity in watersheds has largely been attributed to road salt retention in groundwaters due to their long residence times. However, laboratory studies demonstrate that soils temporarily store salts, either in porewater or adsorbed onto particles. Field studies of road salt retention in soils are nevertheless rare, and mechanisms of salt transport across multiple hydrological reservoirs (e.g., from soil to groundwater) are unknown. Thus, we collected roadside soil porewater and karst spring water weekly for ~1.5 yr to determine salt transport through the vadose zone into the phreatic zone. We observed dual retention mechanisms of sodium (Na+) and chloride (Cl−) in soils due to slow porewater movement, causing ion movement through the soil as slow as 1.3 cm/day, and cation exchange processes, leading to initial Na+ retention followed by later release months after application. Cation exchange processes also caused base cation loss from exchange sites into mobile porewater. Rapid Na+ and Cl− delivery to groundwater occurred through karst conduits during the winter. However, elevated background levels of salt ions in groundwater during the non-salting months indicated accumulation in the catchment due to slower porewater flow in the soil and rock matrix and delayed Na+ release from soil exchange sites.
Anthropogenic impacts in groundwater ecosystems remain poorly known. Climate change is omnipresent, while groundwater salinization poses serious long-term environmental problems in arid and semi-arid regions, and is exacerbated by global warming. Both are present threats to the conservation of groundwater ecosystems, which harbour highly specialized species, with peculiar traits and limited geographic distributions. We tested the temperature and salinity tolerance of groundwater-adapted invertebrates to understand the effect of global warming and salinization in groundwater ecosystems. We used species representative of groundwater-adapted crustaceans: two copepods (harpacticoid and cyclopoid) and one syncarid, endemic to Australia. Our results show that 50% of the populations died at salt concentrations between 2.84 to 7.35 g NaCl/L after 96 h, and at 6.9 °C above the ambient aquifer temperature for copepods and more than 10 °C for syncarids. Both copepods were more sensitive to temperature and NaCl than the syncarid. We calculated a salinity risk quotient of 9.7 and predicted the risk of loss of 10% of syncarid and 20% of copepod population abundances under a worst-case scenario of global warming predictions for 2070. These results highlight that both salinity and temperature increases pose a risk to the ecological integrity of groundwater ecosystems.
The Vermont Department of Health and the U.S. Geological Survey analyzed the concentrations of chloride in groundwater samples collected from 4,319 domestic wells across Vermont between 2011 and 2018. Ninety of these wells were sampled twice and the remaining 4,229 were sampled once. This sample size represents approximately 4 percent of all wells in the State of Vermont. More than half of the wells sampled statewide had groundwater chloride concentrations less than 5 milligrams per liter, whereas more than 1 percent had groundwater concentrations greater than 250 milligrams per liter. Statistical analysis of this dataset revealed distinct patterns in the distribution of chloride in domestic wells. Wells closer (less than 100 meters) to a paved road had significantly higher concentrations of chloride than wells farther ( more than 100 meters) away. Also, wells in urban and in high population density areas, particularly Chittenden and Grand Isle Counties, had significantly higher concentrations of chloride and exhibited greater change in concentrations of chloride over time than wells in less populated areas. This evaluation addresses the distribution of chloride concentrations across the State, which may have adverse health impacts from water infrastructure corrosion and implications for deicing salt application at the State and local levels.
Soil and freshwater salinization are growing issues worldwide. Road salt, primarily sodium chloride (NaCl), is a significant contributor to this issue in North America. In this study, the ability of three native Canadian halophytes (Atriplex patula, Atriplex hortensis, and Atriplex canescans) to remove Na⁺ and Cl⁻ from contaminated soil was investigated. Field and greenhouse studies determined plant survivability in roadside areas, as well as Na⁺ and Cl⁻ extraction levels. The Atriplex spp. accumulated 18–55 mg Na⁺ g⁻¹ dry weight (DW) and 41–64 mg Cl⁻ g⁻¹ DW when grown for a two-month period in soil spiked with NaCl to simulate a very highly contaminated roadside. Using A. patula, it would theoretically take 6 growing seasons to remove all salt from an area contaminated with 1540 μg Cl⁻ g⁻¹, while A. hortensis and A. canescens would take 19 and 9 years, respectively. Salt content in shoot components (seeds, stem, leaves) was determined to provide further insight on phytoextraction processes. In all three Atriplex species, the leaves had the highest Cl⁻ concentration, followed by the seeds (bracteoles included), with the lowest concentrations found in the stem. These novel findings provide important information for road salt remediation and indicate that using Atriplex spp. may be a viable way in which to reduce the environmental impact of road salting.
This study explores the contamination potential of groundwater due to the use of sodium chloride (NaCl) in the wintertime. The research was conducted in two Iranian cities, Malayer and Hamedan, where groundwater is the major source of water for drinking and irrigating purposes. However, the amount of deicing salt used in the former is about 10 times less than that used in the latter. The assessment of geochemical dataset from 2004 to 2018 revealed no significant trend in the groundwater characteristics of Malayer where the water quality indices were in the range of WHO and USEPA permissible limits. In contrast, the indices had a continually increasing trend (~ 2.3% annually) in Hamedan’s supply wells over the same period and particularly near the urban areas that showed higher levels (> 5 times on average) than those observed in Malayer. This could mainly be ascribed to the influx of halite. Based on the USSL diagram, the water samples retrieved from the latter system were mostly classified as C3-S1 (decreasing the soil fertility) and even as C4-S2 (harmful for agriculture activities). Chloride contamination rates also reached 250 mg/L, which could negatively affect the water potability and threaten the aquatics microorganisms. In this region, a rather similar distribution of NaCl and arsenic was observed, implying mobilization of toxic trace metals with the increased salt encroachment into the aquifer. Based on such findings, it is suggested that in snow-influenced cities (e.g., Hamedan), new approaches for winter maintenance be considered to prevent the gradual deterioration of water resources.
Winter deicing salt application has led to water quality impairment as stormwater carries salt ions (Na⁺ and Cl⁻) through watersheds. Green infrastructure (GI) is a promising urban stormwater management practice, but its efficacy in managing salt is unknown. GI is not yet designed to remove salt, but may have potential to mitigate its loading to surface waters. Two roadside infiltration-based GI practices in Northern Virginia (bioretention and bioswale) were monitored year-round over 28 precipitation events to investigate the transport of salt through modern stormwater infrastructure. Stormwater runoff volumes and concentrations of salt ions entering and exiting each GI were monitored to determine reductions of salt ions. Both the bioretention and bioswale significantly reduced effluent surface loads of Cl⁻ and Na⁺ (76% to 82%), displaying ability to temporarily retain and infiltrate salts and delay their release to surface waters. Changes in bioretention soil chemistry revealed a small percentage of Na⁺ was stored long-term by ion exchange, but no long-term Cl⁻ storage was observed. Limited soil storage along with groundwater observations suggest the majority of salt removed from stormwater by the bioretention infiltrates into groundwater. Infiltration GI can buffer surface waters from salt, but are also an avenue for groundwater salt loading.
Winter snowmelt and stormwater runoff contain large concentrations of deicing salts. Past research has shown that NaCl has the potential to reduce the permeability of soils, defeating the purpose of green infrastructure. To understand the behavior of NaCl and its alternatives, our research compared three alternative deicing salts [sodium acetate (NaAc), calcium chloride (CaCl2), and calcium acetate (Ca(Ac)2)] to NaCl for their effects on infiltration, retention/release of metals, and fertility. The results suggest that chloride-based salts reduced the infiltration rate whereas the acetate-based salts had minimal impact. Calcium-based salts, especially CaCl, resulted in less copper uptake, compared to Na-based salts. After completing the infiltration tests, soils were tested for calcium, magnesium, potassium, pH, and phosphorus, total nitrogen (TN), total carbon (TC), sodium, and metals (copper and zinc). The soil test results confirmed that deicing salts resulted in less copper retention on the soil.
Releases of municipal waters, including drinking water and wastewater, can considerably alter urban stream chemistry. However, the relative contributions of drinking water versus wastewater to streams have not been quantified previously and are therefore the focus of this study. We sampled streams along a land use gradient that included watersheds with impervious surface areas (ISA) ranging from 1.6 to 62.6%. Samples were analyzed for F ⁻ , total B, δ ¹¹ B, and optical brighteners to determine municipal water inputs to streams. We observed low F ⁻ (75 ± 20 μg/L), B (29 ± 6 μg/L), and optical brightener (3.66 ± 0.76 RFU) levels in rural streams, but their concentrations increased with urbanization (up to 475 μg/L, 227 μg/L, and 22.09 RFU, respectively). The δ ¹¹ B values for drinking waters (16.52 ± 0.39‰) and wastewaters (untreated = 6.06 ± 0.88‰ and treated = 6.46 ± 0.93‰) were distinct, but there was poor correlation between δ ¹¹ B and ISA for the streams (R ² = 1 × 10 ⁻⁵ ; p = 0.99), likely due to variable lithology in the study area. We used inverse and three-component mixing models to quantify municipal water inputs to the streams. In densely urbanized watersheds, drinking water and wastewater can respectively contribute up to 54% and 16% of the total streamflow. In addition to our spatial sampling, we collected weekly samples at a suburban stream to test the effects of discharge and seasonality on municipal water tracer behavior. We found that tracer levels did not change significantly (p ≥ 0.28) with discharge or season, suggesting that municipal water inputs are fairly constant. Understanding the relative proportions of differing municipal water types to streams is crucial in guiding infrastructure improvements to conserve drinking water and reduce harmful wastewater releases. The unique chemical signatures of municipal waters aid in the widespread applicability of our multi-tracer method for identifying water sourcing to urban streams.
Chloride concentrations in northern U.S. included in this study have increased substantially over time with average concentrations approximately doubling from 1990 to 2011, outpacing the rate of urbanization in the northern U.S. Historical data were examined for 30 monitoring sites on 19 streams that had chloride concentration and flow records of 18 to 49 years. Chloride concentrations in most studied streams increased in all seasons (13 of 19 in all seasons; 16 of 19 during winter); maximum concentrations occurred during winter. Increasing concentrations during non-deicing periods suggest that chloride was stored in hydrologic reservoirs, such as the shallow groundwater system, during the winter and slowly released in baseflow throughout the year. Streamflow dependency was also observed with chloride concentrations increasing as streamflow decreased, a result of dilution during rainfall- and snowmelt-induced high-flow periods. The influence of chloride on aquatic life increased with time; 29% of sites studied exceeded the concentration for the USEPA chronic water quality criteria of 230 mg/L by an average of more than 100 individual days per year during 2006–2011. The rapid rate of chloride concentration increase in these streams is likely due to a combination of possible increased road salt application rates, increased baseline concentrations, and greater snowfall in the Midwestern U.S. during the latter portion of the study period.
Road salt deicers, especially NaCl and CaCl2, are increasingly applied to paved areas throughout the world. The goal of this study is to investigate the influence of high concentrations of these salts on wetland biogeochemistry. Sediment cores were collected in fall and spring from a freshwater wetland fringing an urban kettle lake (Asylum Lake, Kalamazoo, MI, USA), and incubated for 100 days in deionized water (control) or with treatments of 1 or 5 g/L CaCl2·2H2O or 5 g/L NaCl to simulate addition of road salt deciers. At monthly intervals, cores were sliced into three depths (0–5, 5–10, 10–15 cm) and pore waters extracted for analysis of pH, total alkalinity and dissolved Mn(II), Fe(II), PO
4−3, NH3, H2S, SO4−2, Na, K, Mg, and Ca. Changes in solid phase geochemistry were assessed by measuring the percent organic matter and the distribution of Fe and Mn among four operationally defined sediment fractions (exchangeable, carbonate, reducible, oxidizable) in the control and treatment cores. Addition of NaCl, and especially CaCl2, stimulated significant growth of microbial mats at the core sediment–water interface and led to decreased pH and increased concentrations of Mn(II), Fe(II) and exchangeable cations (Ca, Mg, K, Na) in the sediment pore waters. This study demonstrates that the influx of road salt deciers is likely to have a significant impact on biogeochemical cycling in wetland sediments.
A 15-month-long hydrogeologic investigation of a fen-wetland complex in northeastern Illinois, USA indicated the encroachment
of ground-water-borne anthropogenic contaminants into two of three high quality fens. Ground-water flow directions and chemical
evidence indicated that plumes of ground water with anomalously large concentrations of Na− and Cl− originated from a private septic system and from rock salt spread on an adjacent road. The contamination, in turn, had an
adverse effect on fen vegetation; within the plumes, diverse vegetation was replaced by the more salt-tolerant narrow-leaf
cattail (Typha angustifolia). Ground water of the third fen contained large concentrations of SO4
2− as high as 516 mg/L. The SO4
2− anomaly was observed on a transient and/or seasonal basis in the fen ground water and in an adjacent marsh and pond. Isotopically
light δ34S values in these waters indicated that the addition of SO4
2− resulted from the oxidation of pyrite within underlying peat and/or pyritic gravel. However, the large SO4
2− concentrations had no discernible effect on fen vegetation. The results of this investigation indicate how easily construction
of houses with private septic systems and deicing agents from roadway maintenance can contaminate fen ground water with relatively
large concentrations of Na+ and Cl−, resulting in a significant loss of biodiversity in fens.
Strong isotopic forcing of hydrologic systems in eastern Missouri, caused by the large seasonal variations in the values of meteoric precipitation, can be used to determine numerous characteristics of hydrologic systems including the residence time of the water. The normal annual average value of meteoric precipitation in this region is about −6.9‰, but during the period June 1997–May 1998, which incorporates an El Niño event, the average of precipitation was −9.4‰. Monthly averages are highly variable, ranging from −2.8‰ in August 1996 to −15.1‰ in January 1998, and define a cycloid-like annual pattern. This meteoric forcing gives rise to similar patterns of isotopic variation in springs and rivers, but with greatly reduced amplitudes. Thus the variations for the precipitation have an amplitude exceeding 10‰, yet the annual amplitudes of the variations in the unimpounded Meramec and Big Rivers are only about 3‰, and the amplitudes of several karst springs, including the `first magnitude' Maramec Spring, are even smaller at about 1‰. Most of the isotopic variation in streamflow can be explained by a simple exponential weighting of the preexisting rainfall events, such that the most recent precipitation more greatly influences the flow than earlier precipitation events, according to our formulation:
Five test runs were performed to assess possible bias when performing the loss on ignition (LOI) method to estimate organic matter and carbonate content of lake sediments. An accurate and stable weight loss was achieved after 2 h of burning pure CaCO₃ at 950 °C, whereas LOI of pure graphite at 530 °C showed a direct relation to sample size and exposure time, with only 40–70% of the possible weight loss reached after 2 h of exposure and smaller samples losing weight faster than larger ones. Experiments with a standardised lake sediment revealed a strong initial weight loss at 550 °C, but samples continued to lose weight at a slow rate at exposure of up to 64 h, which was likely the effect of loss of volatile salts, structural water of clay minerals or metal oxides, or of inorganic carbon after the initial burning of organic matter. A further test-run revealed that at 550 °C samples in the centre of the furnace lost more weight than marginal samples. At 950 °C this pattern was still apparent but the differences became negligible. Again, LOI was dependent on sample size. An analytical LOI quality control experiment including ten different laboratories was carried out using each laboratory’s own LOI procedure as well as a standardised LOI procedure to analyse three different sediments. The range of LOI values between laboratories measured at 550 °C was generally larger when each laboratory used its own method than when using the standard method. This was similar for 950 °C, although the range of values tended to be smaller. The within-laboratory range of LOI measurements for a given sediment was generally small. Comparisons of the results of the individual and the standardised method suggest that there is a laboratory-specific pattern in the results, probably due to differences in laboratory equipment and/or handling that could not be eliminated by standardising the LOI procedure. Factors such as sample size, exposure time, position of samples in the furnace and the laboratory measuring affected LOI results, with LOI at 550 °C being more susceptible to these factors than LOI at 950 °C. We, therefore, recommend analysts to be consistent in the LOI method used in relation to the ignition temperatures, exposure times, and the sample size and to include information on these three parameters when referring to the method.
Old assumptions that chloride is inert and that most chlorinated organic matter in soils is anthropogenic have been challenged by findings of naturally formed organochlorines. Such natural chlorination has been recognized for several decades, but there are still very few measurements of chlorination rates or estimates of the quantitative importance of terrestrial chlorine transformations. While much is known about the formation of specific compounds, bulk chlorination remains poorly understood in terms of mechanisms and effects of environmental factors. We quantified bulk chlorination rates in coniferous forest soil using 36Cl-chloride in tracer experiments at different temperatures and with and without molecular oxygen (O2). Chlorination was enhanced by the presence of O2 and had a temperature optimum at 20 degrees C. Minimum rates were found at high temperatures (50 degrees C) or under anoxic conditions. The results indicate (1) that most of the chlorination between 4 and 40 degrees C was biotic and driven by O2 dependent enzymes, and (2) that there is also slower background chlorination occurring under anoxic conditions at 20 degrees C and under oxic conditions at 50 degrees C. Hence, while oxic and biotic chlorination clearly dominated, chlorination by other processes including possible abiotic reactions was also detected.
Urban streams in the northeastern United States have large road salt inputs during the winter, increased nonpoint sources of inorganic nitrogen, and decreased short-term and permanent storage of nutrients. Restoration activities that re-establish connection between streams and riparian environments may be effective for improving urban stream water quality. Meadowbrook Creek, a first-order stream in Syracuse, New York, provides a unique setting to explore impacts of stream-floodplain connection because it flows along a negative urbanization gradient, from channelized and armored headwaters to a broad, vegetated floodplain with a riparian aquifer. In this study, we investigated how reconnection to groundwater and introduction of riparian vegetation impacted urban surface water chemistry by making bi-weekly longitudinal surveys of stream water chemistry in the creek from May 2012 until June 2013. We used multiple methods to measure groundwater discharge rates along the creek. Chloride concentrations in the upstream, disconnected reach were influenced by discharge of road salt during snow melt events and ranged from 161.2 to 1440 mg/L. Chloride concentrations in the downstream, connected reach had less temporal variation, ranging from 252.0 to 1049 mg/L, due to buffering by groundwater discharge, as groundwater chloride concentrations ranged from 84.0 to 655.4 mg/L. In the summer, there was little-to-no nitrate in the disconnected reach due to limited sources and high primary productivity, but concentrations reached over 1 mg N/L in the connected reach due to the presence of riparian vegetation. During the winter, when temperatures fell below freezing, nitrate concentrations in the disconnected reach increased to 0.58 mg N/L, but were still lower than the connected reach, which averaged 0.88 mg N/L. Urban stream restoration projects that restore floodplain connection may impact water quality by storing high salinity road runoff during winter overbank events and discharging that water year-round, thereby attenuating seasonal fluctuations in chloride. Contrary to prior findings, we observed floodplain connection and riparian vegetation may alter nitrate sources and sinks such that nitrate concentrations increase longitudinally in connected urban streams. This article is protected by copyright. All rights reserved.
Mass-balance calculations were used to quantify reactive transport processes and cation exchange in a plume of groundwater contaminated with septage-effluent wastewater on Cape Cod, Massachusetts. Of the chloride mass recharged to the aquifer in effluent, as much as 72% was accounted for using spatial moment analysis and finite-element integration of groundwater concentrations, which were sampled at ≤69 wells and supplemented by borehole electromagnetic-induction logging. Comparison of chloride transport and mass balances with transport and mass balances of other species indicated that reactive processes substantially altered concentrations of all major chemical constituents. Calcium in effluent was exchanged for magnesium on aquifer sediments. Potassium also was attenuated, possibly through exchange with magnesium, sodium, and/or hydrogen ions. Sufficient hydrogen ions were generated by microbial nitrification in the unsaturated zone to consume effluent alkalinity and lower the effluent pH from 7.2 to 5.0 in the recharged groundwater; the resultant acid conditions may have facilitated anion adsorption and silicate-mineral dissolution. Retardation factors (R) calculated from breakthrough curves indicated that calcium (R = 1.4−2.2) and boron (R = 1.3−2.1) were similarly retarded, whereas potassium experienced greater retardation (R = 1.8−5.2). Retardation of calcium, boron, and potassium was greater in the unsaturated zone than in the saturated zone; this may have resulted from spatial heterogeneity in exchange properties and preferential saturated-zone flow through coarse-grained sediments not present in the unsaturated zone. Although concentrations may stabilize and chemical reactions reach equilibrium at fixed points along paths in the plume, the mass-balance analysis illustrated that steady-state conditions will not be established throughout the aquifer and the cumulative mass of reacted constituents in the plume will increase until the plume reaches its discharge area. The analysis also indicates that retrospective study of dissolved concentrations in an established plume after many years of transport may not identify reactive transport and attenuation of plume constituents, if precise data on source concentrations (or masses) and the spatial distribution of solutes during plume development are not available. Finally, transport of the effluent-contaminated groundwater also altered the geochemistry of the aquifer, for example, through cation exchange, such that the introduction of clean, uncontaminated water into the aquifer will not immediately restore pre-plume conditions.
The cation exchange capacity (CEC) and specific surface properties were investigated in four particle-size fractions < 50 μm from three loess (one Kastanozem and two Phaeozems), a holocene (Fluvisol) and a basalt soil (Nitisol) before and after destruction of organic matter. Particle-size fractions were separated by sedimentation after chemical and physical dispersion of the soil samples. Illite, amorphous minerals, mixed layers, smectite and kaolinite were the predominant clay minerals. They were detected in all size fractions. The CEC increased with increasing organic matter contents and this effect was more pronounced in coarser fractions. The organic matter content per unit surface area was two or three times larger in coarse silt than in clay, irrespective of the soil type.Einfluss von Tonmineralen und der organischen Substanz auf die Kationenaustauschkapazität von SchlufffraktionenDie Kationenaustauschkapazität (KAK) und spezifische Oberflächeneigenschaften von vier Korngrößenfraktionen < 50 μm wurden in drei Lößböden (ein Kastanozem und zwei Phaeozeme) sowie je einem Boden aus holozänem Sediment (Fluvisol) und aus Basalt (Nitisol) vor und nach Zerstörung der organischen Substanz untersucht. Die Partikelgrößenfraktionen wurden durch Sedimentation nach erfolgter chemischer und physikalischer Dispergierung getrennt. Die überwiegenden Tonminerale waren: Illit, amorphe Minerale, Wechsellagerungsminerale, Smectit und Kaolinit. Sie waren in allen untersuchten Partikelgrößenfraktionen vorhanden. Die KAK-Werte nahmen mit steigenden Gehalten an organischer Substanz zu, insbesondere in den gröberen Fraktionen. Der Gehalt an organischer Substanz je Oberflächeneinheit war im Grobschluff zwei- bis dreimal größer als in der Tonfraktion.
The cation exchange capacity (CEC) of 18 samples (<2 mm) of five acid soils developed on granite or gneiss was measured before and after H2O2 treatment from pH-unbuffered extraction solution (1 N KCl). The pH in water of the soils ranged from 3.4-4.7. The samples were separated into seven fractions (<2μm, 2-20 μm, 20-50 μm, 0.05-0.2 mm, 0.2-0.5 mm, 0.5-1 mm and 1-2 mm) and the CEC of each measured. Thus the contribution of each size fraction and of organic matter to the CEC was obtained. From CEC measurements on the different fractions and particle size distribution data, a balance calculation was carried out to verify the methodology. According to the hypotheses used and soil characteristics, the CEC of organic matter was found to vary from 35 to 165 cmol(c) kg-1 and so represented from 10 to 85% of the total soil CEC in the upper soil horizons. In these sandy soils developed on granite or gneiss which were frequently affected by hydrothermal alteration, the CEC of silt and sand fractions was large. It can represent from 35 to 80% of the total soil mineral CEC. The specific contribution of the 0.2-2 mm fraction can reach 50% of the total soil mineral CEC with values ranging from 0.5-5.2 cmol(c) kg-1. The mineralogical description showed that hydrothermal white micas and neoformed smectites (precipitated during weathering) were present in all the fractions even in the coarsest ones. In some subsoils, albite grains containing smectite have a CEC as large as 21 cmol(c) kg-1. This study shows that the CEC of acid soils was not always located in the organic matter in the clay fraction. The sand fraction can contribute substantially to the soil CEC.
Pathways and fate of road deicing salt (NaCl) applied during the 1994–1995 winter were studied for a 14-km section of a major highway that crosses the Oak Ridges Moraine in southern Ontario. Total salt applications over the winter ranged from 29 to 74 kg m−1 of highway, and NaCl concentrations in snow banks adjacent to the roadway reached 9400 mg l−1 during the later stages of snow cover development. This salt was released to the ground surface during snowmelt. Sodium chloride (NaCl) loadings to soil from snow cover during the final melt phase were relatively uniform along the study section (3–5 kg NaCl m−1 of highway). However, the snowpack at all transects retained <50% of applied NaCl, and this shortfall probably reflected direct runoff and infiltration of saline meltwater from the road surface into the adjacent shoulder and right-of-way. Cation exchange with Ca2+ in near-surface soils most likely resulted in preferential retention of Na+ relative to Cl−, although total storage of NaCl in upper soil horizons by winter's end was <15% of deicing salt applications. An environmental tracer (18O) was used to trace movement of saline meltwater through the unsaturated zone underlying the highway. Average meltwater particle velocities at a site underlain by loam soils were 0.02 m d−1, and ca. 280 mm of water was displaced below a depth of 1.86 m over a 78-day period in the spring and summer of 1995. Sodium ion and chloride ion concentrations in water sampled in late summer 1995 at depths >2 m exceeded 500 mg l−1 and 1000 mg l−1, respectively. Approximately 75% of the net flux of NaCl below the upper soil was retained in the 0–2.8 m depth interval at this site, and results from more permeable soils traversed by the highway indicate an even greater penetration of the annual NaCl application into the unsaturated zone along the moraine. This saline water likely recharges groundwater in this portion of the Oak Ridges Moraine.
Increased application of chemical deicers for winter maintenance has resulted in increased concentrations of deicer constituents in the environment. The runoffs from the deicing operation have a deteriorating effect on soil and water quality. But the degree of impact is localized and it depends on various climatic factors and can also be attributed to the type of salts used and their storage conditions. This paper presents a review of the environmental impact of deicing chemicals.
The maintenance of safe-drivingconditions in snow and ice-affected areas in thewintertime includes the use of sodium chloride (NaCl)as de-icing salts. In this study, the impact of NaClon soil-colloid mobilisation and exchangeablebase-cation leaching has been evaluated. The chemistryof groundwater samples below an infiltration trenchfor highway runoff and leachate from column studiessuggested that soil-colloid mobilisation had occurred,as the exchangeable sodium (Na) concentration and theelectrical conductivity (EC) in the groundwater/columnleachate reached the threshold values for colloiddispersion. Generally, samples with no dispersionproblems had high Na and calcium (Ca) concentrations,suggesting that the initial effect of the de-icingsalt was to stabilise the colloids. In the columnstudy there was a good agreement between the degree ofcolloid dipersion problems and lead (Pb) concentrationwhen the pH value was above 7.0. Significant negativecorrelations between Na/CEC (cation exchange capacity)and Ca/CEC in roadside soils from three sitesindicated that Na preferentially displaces Ca from theexchange sites. However, the groundwater dataindicated that Na ions also displace potassium (K) andmagnesium (Mg). A positive effect of NaCl seen at onesite was an increase in the K concentration, which ishighly likely an effect of Na ions displacing fixed Kbetween the layers of 2:1 type clay minerals. In soilslacking these types of clay minerals, severe Kshortage may result from a high plant demand combinedwith the low K concentration in the readily availablefractions in the original soil and a highsusceptibility to leaching. The most significantimpact on soil exchange processes was found to occurwithin 6 m from the road.
This hydrogeochemical study concerns the distribution, origins and behaviour of groundwaters in Quaternary sediments of southern Ontario, Canada, containing elevated concentrations of chloride. Major-ion, minor-ion and trace-metal analyses of 37 potential chloride sources and over 400 well waters, 70 urban springs and 30 pore waters are reported. Source chloride concentrations ranged up to 230,000 mg L−1 for brines from southwestern Ontario; for groundwaters in Quaternary sediments, the chlorides range up to 700 mg L−1 for domestic wells, 2,840 mg L−1 for urban springs and 13,700 mg L−1 for shallow pore waters.Regional studies performed in support of the study suggest that very little chloride enrichment is associated with natural chemical evolutionary processes. Background concentrations are in the range 15–20 mg L−1 and these levels are exceeded in over half the wells in the area; potential sources include road salts, landfill leachates, agricultural fertilizers and saline bedrock waters. Most of these sources are found to be chemically pure with 2 or 3 major ions occurring to the virtual exclusion of all other constituents. Source trace-metal concentrations are low and none are diagnostic of origin. Only iodide and fluoride prove useful indicators of source. Iodide is especially useful for differentiating between road salts and saline bedrock waters, sources which are normally indistinguishable using major-ion criteria alone.From an inorganic water quality perspective, trace-metal concentrations in the chloride sources do not appear to be an environmental concern and only the primary chemical components constitute a serious threat to groundwater potability.
Inorganic chlorine (i.e. chloride; Clin) is generally considered inert in soil and is often used as a tracer of soil and ground water movements. However, recent studies indicate that substantial retention or release of Clin can occur in soil, but the rates and processes responsible under different environmental conditions are largely unknown. We performed 36Cl tracer experiments which indicated that short-term microbial uptake and release of Clin, in combination with more long-term natural formation of chlorinated organic matter (Clorg), caused Clin imbalances in coniferous forest soil. Extensive microbial uptake and release of Clin occurred over short time scales, and were probably associated with changes in environmental conditions. Up to 24% of the initially available Clin within pore water was retained by microbial uptake within a week in our experiments, but most of this Clin was released to the pore water again within a month, probably associated with decreasing microbial populations. The natural formation of Clorg resulted in a net immobilization of 4% of the initial pore water Clin over four months. If this rate is representative for the area where soil was collected, Clorg formation would correspond to a conversion of 25% of the yearly wet deposition of Clin. The study illustrates the potential of two Clin retaining processes in addition to those previously addressed elsewhere (e.g. uptake of chloride by vegetation). Hence, several processes operating at different time scales and with different regulation mechanisms can cause Clin imbalances in soil. Altogether, the results of the present study (1) provide evidence that Clin cannot be assumed to be inert in soil, (2) show that microbial exchange can regulate pore water Clin concentrations and (3) confirm the controversial idea of substantial natural chlorination of soil organic matter.
Transformation of chloride (Cl(-)) to organic chlorine (Cl(org)) occurs naturally in soil but it is poorly understood how and why transformation rates vary among environments. There are still few measurements of chlorination rates in soils, even though formation of Cl(org) has been known for two decades. In the present study, we compare organic matter (OM) chlorination rates, measured by (36)Cl tracer experiments, in soils from eleven different locations (coniferous forest soils, pasture soils and agricultural soils) and discuss how various environmental factors effect chlorination. Chlorination rates were highest in the forest soils and strong correlations were seen with environmental variables such as soil OM content and Cl(-) concentration. Data presented support the hypothesis that OM levels give the framework for the soil chlorine cycling and that chlorination in more organic soils over time leads to a larger Cl(org) pool and in turn to a high internal supply of Cl(-) upon dechlorination. This provides unexpected indications that pore water Cl(-) levels may be controlled by supply from dechlorination processes and can explain why soil Cl(-) locally can be more closely related to soil OM content and the amount organically bound chlorine than to Cl(-) deposition.
Ecological studies have demonstrated the adverse effects of road-salt, primarily NaCl, on water quality, flora, and fauna. In this study, we quantified changes in ionic composition and solute flux of water draining the Mohawk River Basin (9103 km(2)) in New York State, from 1952 to 1998. Using various statistical, graphical, and modeling techniques, we showed that concentrations ofNa+ and Cl- have increased by 130 and 243%, respectively, while other constituents have decreased or remained constant. The use of de-icing salt on roads within the watershed, which we estimate at 39 kg km(-2) day(-1), appears to be the primary mechanism responsible for reported increases, accounting for the increase in NaCl export from 16 to 46 kg km(-2) day(-1) over the 47-year period.Moreover, despite population decline within this rural upstate watershed, increased environmental stewardship, and The Clean Water Act, concentrations of Na+ and Cl- still increased during the 1990s.
The seasonal variations of some selected heavy metals (Cd, Cu, Pb and Zn) and principal anions in soil solutions were monitored as a function of distance from the road at two field sites in Sweden. During the winter, the conductivity, concentrations of dissolved sodium and chloride increased dramatically due to the application of deicing agents (i.e. NaCl). Due to ion exchange, the pH decreased one unit in the soil solutions, whereas the concentrations of total organic carbon decreased due to coagulation and/or sorption to stationary solids. The heavy metal concentrations increased during the winter, but through different mechanisms. Cadmium concentrations in the aqueous phase increased as a response to ion exchange, possibly also enhanced by the formation of chloride complexes. Similarly, the concentrations of zinc increased, due to ion exchange, with calcium and protons. The mechanisms of mobilisation for copper and lead were not that clear probably due to association with coagulated or sorbed organic matter in combination with colloid dispersion.
Deicing agents, primarily road salt, are applied to roads in 26 states in the United States and in a number of European countries, yet the scale of impacts of road salt on aquatic organisms remains largely under-studied. The issue is germane to amphibian conservation because both adult and larval amphibians are known to be particularly sensitive to changes in their osmolar environments. In this study, we combined survey, experimental, and demographic modeling approaches to evaluate the possible effects of road salt on two common vernal-pond-breeding amphibian species, the spotted salamander (Ambystoma maculatum) and the wood frog (Rana sylvatica). We found that in the Adirondack Mountain Region of New York (USA), road salt traveled up to 172 m from the highway into wetlands. Surveys showed that egg mass densities of spotted salamanders (A. maculatum) and wood frogs (R. sylvatica) were two times higher in forest pools than roadside pools, but this pattern was better explained by road proximity than by increased salinity. Experiments demonstrated that embryonic and larval survival were reduced at moderate (500 muS) and high conductivities (3000 muS) in A. maculatum and at high conductivities in R. sylvatica. Demographic models suggest that such egg and larval stage effects of salt may have important impacts on populations near roads, particularly in the case of A. maculatum, for which salt exposure may lead to local extinction. For both species, the effect of road salt was dependent upon the strength of larval density dependence and declined rapidly with distance from the roadside, with the greatest negative effects being limited to within 50 m. Based on this evidence, we argue that efforts to protect local populations of A. maculatum and R. sylvatica in roadside wetlands should, in part, be aimed at reducing application of road salt near wetlands with high conductivity levels.