Modeling the effects of human influences on water quality and quantity in the Zarrineh River Basin,Iran

This study aims to analyze the environmental and economic impacts of land use change and water abstraction in the Zarrineh River basin, which is Lake Urmia’s main inflow source in the north-west of Iran. The Soil & Water Assessment Tool (SWAT) is used to model water quantity and quality in the basin. Environmental Kuznets Curves (EKC) are used to assess the relationship between environmental degradation and the development of the agricultural sector. Two scenarios were employed to identify the effects of dam construction and land use change on stream flow, evapotranspiration, groundwater recharge and nitrate loads in the area. The SWAT model showed a satisfactory to very good performance for monthly stream flow at most of the gauges in calibration and validation periods as well as a reasonable performance for nitrate loads. The estimated EKC indicates that the environmental degradation in the inverted U-shape that has passed its peak and the rate of degradation has decreased. Based on the scenarios, the dam has a strong impact on nitrate loads in the basin and water inflow into Lake Urmia. Results verify that human influences have had negative impacts on the Zarrineh River basin. In particular, the extensive development of the agricultural sector has not only drastically reduced the inflow of water to Lake Urmia accelerating the drying up of the lake, but it has also increased nitrate loads. Therefore, it can be recommended to take counter measures within the catchment area to improve the ecological status of Lake Urmia.     

Determining the Main Factors in Declining the Urmia Lake Level by Using System Dynamics Modeling

Urmia Lake in Iran is the second largest saline lake in the world. This ecosystem is the home for different species. Due to various socio-economical and ecological criteria, Urmia Lake has important role in the Northwestern part of the country but it has faced many problems in recent years. Because of droughts, overuse of surface water resources and dam constructions, water level has decreased in such a way that one quarter of the lake has changed to saline area in the last 10 years. The purpose of this research is to determine the main factors which reduce the lake’s water level. To this end, a simulation model, based on system dynamics method, is developed for the Urmia Lake basin to estimate the lake’s level. After successful verification of the model, results show that (among the proposed factors) changes in inflows due to the climate change and overuse of surface water resources is the main factor for 65% of the effect, constructing four dams is responsible for 25% of the problem, and less precipitation on lake has 10% effect on decreasing the lake’s level in the recent years. In the future, the model also can be used by managers as a decision support system to find the effects of building new dams or other infrastructures.     

Tonle Sap Lake: Current status and important research directions for environmental management

Tonle Sap Lake (TSL) in Cambodia is the largest freshwater body in South‐East Asia and one of the most productive ecosystems in the world. The lake and its ecosystems are widely under threat, however, due to anthropogenic activities occurring inside and outside its basin (e.g., water infrastructure development; land use change), being poorly understood in most aspects. This study provides an updated review of the state of knowledge of the TSL ecosystem, as well as important research directions for sustainable lake environmental management of Tonle Sap Lake by focusing on four major topics, including climate change and hydrology, sediment dynamics, nutrient dynamics and primary and secondary production. The findings of this study suggest anthropogenic activities in the TSL basin, as well as the Mekong, in combination together with climate changes, are key contributing factors in the degradation of the TSL ecosystem. Insufficient accurate data, however, precludes quantitative assessment of such impacts, making it difficult to quantitatively assess and accurately understand the ecosystem process in the lake ecosystem. More efforts are recommended in regard to environmental monitoring in all sub‐basins around TSL, assessing seasonal changes in nutrient and sediment inputs corresponding to water level and flow changes, assessing cumulative impacts of water infrastructure and climate change on the ecosystem dynamics, and elucidation of ecosystem processes within the lake's internal system.     

A New Non-stationary Hydrological Drought Index Encompassing Climate Indices and Modified Reservoir Index as Covariates

Due to accelerating climate variability and intensified anthropogenic activities, the hypothesis of stationarity of data series is no longer applicable, questioning the reliability of the traditional drought index. Thus, it is critical to develop a non-stationary hydrological drought index that takes into account the joint impacts of climate and anthropogenic changes in a drought assessment framework. In this study, using the Generalized Additive Model for Location, Scale and Shape (GAMLSS), a new Non-stationary Standardized Runoff Index (NSRI) was developed combining climate indices (CI) and modified reservoir index (MRI) as explanatory variables. This novel index was applied to the hydrological drought assessment of the Hanjiang River basin (HRB) in China, and its reliability was assessed by comparing with the traditional Standardized Runoff Index (SRI). Results indicated that the optimal non-stationary model with CI and MRI as covariates performed better than did other models. Furthermore, NSRI was more robust in identifying extreme drought events and was more effective in the study region than the conventional SRI. In addition, based on the method of Breaks for Additive Seasonal and Trend (BFAST), it was found that there were two change points in 1981 and 2003 for the NSRI series at four hydrological stations in the HRB, which indicated that hydrological drought in the basin had a prominent non-stationary behavior. Our findings may provide significant information for regional drought assessment and water resources management from a changing environment perspective.

     

Synthesis review on groundwater discharge to surface water in the Great Lakes Basin

Groundwater in the Great Lakes Basin (GLB) serves as a reservoir of approximately 4000 to 5500 km³ of water and is a significant source of water to the Great Lakes. Indirect groundwater inflow from tributaries of the Great Lakes may account for 5–25% of the total water inflow to the Great Lakes and in Lake Michigan it is estimated that groundwater directly contributes 2–2.5% of the total water inflow. Despite these estimates, there is great uncertainty with respect to the impact of groundwater on surface water in the GLB. In terms of water quantity, groundwater discharge is spatially and temporally variable from the reach to the basin scale. Reach scale preferential flow pathways in the sub-surface play an important role in delivering groundwater to surface water bodies, however their identification is difficult a priori with existing data and their impact at watershed to basin scale is unknown. This variability also results in difficulty determining the location and contribution of groundwater to both point and non-point source surface water contamination. With increasing human population in the GLB and the hydrological changes brought on by continued human development and climate change, sound management of water resources will require a better understanding of groundwater surface–water interactions as heterogeneous phenomena both spatially and temporally. This review provides a summary of the scientific knowledge and gaps on groundwater–surface water interactions in the GLB, along with a discussion on future research directions.     

Multi-Objective Surface Water Resource Management Considering Conflict Resolution and Utility Function Optimization

In the present research, a multi-objective model is developed for surface water resource management in the river basin area which is connected to the lake. This model considers different components of sustainable water resource management including economic, social and environmental aspects, and simultaneously tries to resolve conflicts between different stakeholders by means of non-symmetric Nash bargaining, which is linked to the multi-objective optimization method. This study proposes a new methodology to improve Nash Conflict Resolution through finding the optimum degree of the utility function. The proposed model is examined in the Zarrineh River basin in Iran. The results show that the amount of available resources or volume of reservoirs play a significant role in determining the optimal degree of the utility function and efficiency of the proposed method in such a way that the higher amount of resources or the larger reservoirs will result in the higher optimal degree of the utility function. In the proposed multi-objective model, two different amounts of surface water inflow are considered. The first assumed amount is the long-term average flow rate and the second one is equal to 80% of the first mode, which is reduced based on the estimated impacts of climate changes. This multi-objective allocation model could supply 100 and 97.5% of the environmental demand of Lake Urmia in the first and second situations, respectively.     

Deriving and Evaluating Bathymetry Maps and Stage Curves for Shallow Lakes Using Remote Sensing Data

Urmia Lake as a most vital water bodies in Iran, has been shrinking since the late twentieth century and its area has dramatically decreased. To develop and apply any plans to survive the lake, qualitative and quantitative analysis and any modeling, deriving physical information such as volume, area and their changes are very crucial. The objectives of this study were therefore, intended firstly, to study the bathymetry of Urmia Lake with a more satisfactory approach using Landsat- LDCM satellite image and in situ measurement data. The polynomial model was developed to predict the water depth in Urmia Lake area. This model was developed with the input series of reflectance values from blue, green, red and NIR bands in the Landsat- LDCM satellite imagery for Urmia Lake taken on 12 April 2013 of the sampling sites from actual depth measured were taken on the same date. Also, using a large archive of Landsat imagery (TM, ETM+ and LDCM), a counter of equivalent elevation were established for deriving the bathymetry of desiccated areas by mapping the edges of the lake and finally assembled with bathymetry derived from polynomial model. In-situ depth measurements were used to evaluate resultant derived bathymetric map. This comparison shows reasonable agreement between the Landsat-derived depths and those measured in the field with RMSE of 0.27 cm and R² = 0.91. The maximum and mean depths measured were 4.9 and 11 m respectively. The maximum depth measured was located at the upper part of the lake. As well as, developed multi-regression equation used for deriving another bathymetry map using Landsat- LDCM satellite image taken on Sep. 2015 for salt deposition monitoring. Results indicates that about 64 cm salt deposition has occurred during the last two years. Secondly, to make stage curves of lake, multi-temporal changes of water body have been derived from Landsat, MODIS and AVHRR satellite images sets since 1972. In this regard, the area of Urmia Lake at different level was estimated base on object oriented and pixel base classification using 78 satellite images. Finally, stage curve (volume- area- level relations) was derived from bathymetry map.     

Investigating the restoration of Lake Urmia using a numerical modelling approach

We assessed the effectiveness of multiple hydrologic restoration scenarios for Lake Urmia, as well as the variation of its salinity regime under no intervention, using a 2D shallow water model. Tested scenarios, proposed by Urmia Lake Restoration Program Committee, include: Preservation of current lake status (no intervention), complete closing of Shahid Kalantari causeway, dyke construction in the southern part of Lake Urmia, water transfer from Zarrinehrood River to Siminehrood River and reduction of agricultural water consumption by best agricultural practices. Results indicate that neither the closure of the causeway nor the construction of the southern dyke would significantly improve lake conditions when compared to preservation of current lake status. The water transfer alternative doesn’t seem to have any effect on the current lake conditions either. However, the reduction on water diversions by improving agricultural practices in the lake's basin leads to a partial restoration of the lake in terms of water level, surface area and volume. If current conditions persist, salinity in the northern part of Lake Urmia will reach supersaturation levels (340?g/L), generating further salt deposits.     

Climatic and anthropogenic impacts on water and sediment generation in the middle reach of the Jinsha River Basin

Response of water and sediment generation to climate change and anthropogenic activities is becoming a hot topic in the middle reach of the Jinsha River Basin. In this research, coefficients of variation and concentration degree (i.e., C_v and C_d) and double mass curve (DDC) were adopted to examine the changes in water and sediment discharge and their relationships with precipitation. The contribution rates of climatic and anthropogenic factors to water and sediment discharge were assessed through comparisons between the measured and predicted values in the baseline and postbaseline periods in the basin. The main results were: (a) the water and sediment discharges of the basin showed a decreasing trend from 2006 to 2014, with peak points of C_v and C_d of sediment discharge of the basin in 2009 and 2010, respectively; (b) the precipitation had a major influence on water discharge variations, and the peak point of the DDC of the cumulative precipitation and sediment discharge was consistent with the cumulative water and sediment discharge; and (c) under annual and flooding season scales, the contribution rates of anthropogenic factors to water discharge were 63.060% and 70.457%, respectively. The contribution rates of anthropogenic factors on sediment discharge were 84.790% and 85.541%, respectively. The impacts of anthropogenic factors on water and sediment discharge were more significant than the impacts of precipitation, in which the construction and operation of cascade hydropower stations (CHS) were believed to play a crucial role.     

Lake Urmia restoration success story: A natural trend or a planned remedy?

Lake Urmia is the second-largest hypersaline lake in the world. There has been a drastic water level drop of 7.2 m from 1995 to 2016. Beginning in October 2013, the Lake Urmia Restoration Plan (LURP) launched a 10-year program. An increase in water level and a relative improvement in Lake Urmia condition has been observed since 2017. It is an undecided and controversial issue whether the recent positive trend of Lake Urmia has been due to the LURP activities or it is a natural contribution of climate factors variations. To shed some light on this issue, we examine three other lakes, adjacent to the Lake Urmia basin, with similar rainfall variability to investigate their status during the same period. Van (Turkey), Mosul, and Tharthar (both in Iraq), are evaluated as well as Lake Urmia. Three decades of remotely sensed data including precipitation ($P$), water level ($\mathit{WL}$), and lake extent ($A$) were considered for the mentioned lakes. A significant correlation was observed between standardized $\mathit{WL}-P$, and $A-P$ over the long-term period, especially for the recent three years ($R$² = 0.63–0.87). We show that the cumulative precipitation in the antecedent months played a major role in the improvement of these lakes' situation but with different time lags (up to 6 months for Van and Mosul lakes and up to 36 months for Lake Urmia and Tharthar lake). These findings could inform the planners of LURP to adopt strategies for achieving a sustainable state of Lake Urmia based on a more realistic outlook.     

Impact of Urbanization on the Hydrology of Ganga Basin (India)

Large scale emigrations from rural areas to urban areas and population growth have been uninterrupted and accelerating phenomena in parts of Ganga basin, where urbanization is increasing at an unprecedented rate. Urban agglomeration is causing radical changes in groundwater recharge and modifying the existing mechanisms. Majority of the cities are sited on unconfined or semi confined aquifers depend upon river water and groundwater for most of their water supply and disposal of most of their liquid effluents and solid residues to the rivers and ground. There has also been an inevitable rise in waste production. Drainage of surface water has been disrupted as the small natural channels and low lying areas have been in filled, often with municipal waste. Total water potential of the Ganga basin including surface water potential and ground water potential is around 525.02 km³ and 170.00 km³ respectively. Basin supports approximately 42% of the total population in India. Water tables are declining at approximately an average of 0.20 m per year in many parts of the basin and there is a trend of deteriorating groundwater quality. The demand of water has been increased many folds and most of the areas are highly reliant upon the groundwater to meet this increasing demand for water, but unfortunately degradation of groundwater both in terms of quantity and quality has deteriorated the situation. Studies shows that change in climate may increase temperature by 2 to 6°C and can reduce precipitation up to 16%, which could reduce the groundwater recharge by 50%. In densely populated Ganga basin urban drainage consumes a high proportion of the investments into urban infrastructure and needs integrated approach for the sustainable development of water management, water education regarding conservation and pollution caused by urbanization.     

Using satellite data to extract volume–area–elevation relationships for Urmia Lake,Iran

Urmia Lake in the northwest of Iran is the second largest hyper-saline lake worldwide. During the past two decades, a significant water level decline has occurred in the lake. The existing estimations for the lake water balance are widely variable because the lake bathymetry is unknown. The main focus of this study is to extract the volume–area–elevation (V–A–L) characteristics of Urmia Lake utilizing remote sensing data and analytical models. V–A–L equations of the lake were determined using radar altimetry data and their concurrent satellite-derived surface data. Next, two approximate models, a power model (PM) and a truncated pyramid model (TPM), were parameterized for Urmia Lake and checked for accuracy. Results revealed that in comparison with the satellite-derived reference volume–elevation equation, the PM slightly over-predicts the volume of Urmia Lake while the TPM under-estimates the lake storage. Variations of the lake area and volume between 1965 and 2011 were examined using the developed V–A–L equations. Results indicated that the lake area and volume have declined from the historical maximum values by 2200 km² and 33 km³, respectively. To restore Urmia Lake to a level to maintain ecological benefits, 13.2 km³ of water is required. This study demonstrates the use of remote sensing data of different types to derive V–A–L equations of lakes. Substituting satellite-derived V–A–L equations for common empirical formulas leads to more accurate estimations of a lake water balance, which in turn, provides insight to water managers for properly assessing and allocating water resources to downstream ecosystems.     

Drying Urban lakes: A consequence of climate change,urbanization or other anthropogenic causes? An insight from northern India

Urban lakes in many places around the world are rapidly becoming vulnerable because of such factors as urbanization, climate change, anthropogenic pollutant inputs, etc. The influence of such forcing factors on lakes hydrology must be correctly recognized and addressed in order to protect them over the long term. Facing similar challenges, Sukhna Lake, an urban lake in northern India, has apparently dried up frequently in the recent past. Numerous hypotheses were subsequently proposed to isolate the possible factors affecting the lake and its water budget, including the potential impacts of land use changes, climate change, anthropogenic activities and other natural processes. Using meteorological data, lake‐catchment information and a hydrologic model, these hypotheses were comprehensively analysed. Relevant data on rainfall, wind, temperature, lake inflows, groundwater, lake physical characteristics, catchment land uses, soil texture, etc., were gathered for the analysis. A temporal trend analysis of factors relevant to these hypotheses was undertaken to identify critical drivers of hydrological changes. A sensitivity analysis also was performed, using the lake water budget, to determine and prioritize the predominant factors affecting the lake, leading to the creation of an annual lake water budget for the period from 1971 to 2013, highlighting the lake inflows and outflows. The lake annual inflow (catchment run‐off) was computed by adopting a rainfall–run‐off model based on the SCS‐curve number. Lacking any anthropogenic water withdrawals, the outflow was quantified by estimating the evaporation loss (using the FAO‐based Penman–Monteith Equation). The results of the present study  indicate that the process of siltation and the construction of check dams in the catchment, rather than urbanization and climate change, were the dominating reasons contributing to changes in the lake hydrology, and affecting the lake most in recent years.     

基于数字遥感影像的呼伦湖水量平衡分析

利用多源、多时相的数字遥感影像和呼伦湖周边地区水文气象资料,采用基于卷积神经网络的高分辨率图像重构方法研究了1999—2019年呼伦湖面积、库容变化情况。结果表明:2003—2012年呼伦湖的面积逐年减小,湖泊水量逐年下降,2003—2012年补给呼伦湖的乌尔逊河与克鲁伦河的多年平均径流量分别为1.30亿m³与1.41亿m³,分别只有1991年以前多年平均径流量的21%与24%;而2003—2012年呼伦湖平均水面年蒸发量为17.5亿m³,平均年湖面降水量为3.25亿m³;地下水补给呼伦湖的年平均水量为5.3亿m³,主要来自新生代玄武岩地下水,哈拉哈河源头火山玄武岩地下水通过熔岩管道集中外泄,据此推断补给呼伦湖的地下水来自跨流域的外源水。     

A New Method for Joint Frequency Analysis of Modified Precipitation Anomaly Percentage and Streamflow Drought Index Based on the Conditional Density of Copula Functions

In this study, a new method was proposed to model the occurrence of related variables based on the conditional density of copula functions. The proposed method was adopted to investigate the dynamics of meteorological and hydrological droughts in the Zarinehroud basin, southeast of Lake Urmia, during the period 1994–2015. For this purpose, the modified precipitation anomaly percentage and streamflow drought indices were extracted. Finally, the joint frequency analysis of duration-duration and severity-severity characteristics of meteorological and hydrological droughts was analyzed. Analysis of 7 different copulas used to create the joint distribution in the Zarinehroud basin indicated that the Frank copula had the best performance in describing the relationship between the meteorological and hydrological drought severities and durations. By examining the results of the bivariate analysis of duration-duration of meteorological and hydrological droughts at different stations, the expected meteorological and hydrological drought durations were estimated in the years ahead. For example, at Chalkhmaz station, 4- to 7-month duration for the hydrological drought and 9- to 12-month duration for the meteorological drought is expected in the years ahead. The joint frequency analysis of drought characteristics allows to determine the meteorological and hydrological drought characteristics at a single station at the same time using joint probabilities. Also, the results indicated that by knowing the conditional density, the hydrological drought characteristics can be easily estimated for the given meteorological drought characteristics. This could provide users and researchers useful information about the probabilistic behavior of drought characteristics for optimal operation of surface water.

     

Evaluation of the Bankruptcy Approach for Water Resources Allocation Conflict Resolution at Basin Scale,Iran’s Lake Urmia Experience

Water conflicts appear when there are insufficient and less available water resources than water demands claimed by different agents. In this study, a new bankruptcy approach is investigated to resolve water conflicts in the Zarrinehroud River Basin, the largest and most important sub-basin of Lake Urmia’s Basin in the northwest of Iran. The new bankruptcy method is compared with the proportional rule (PRO) and another alternative based on the cessation of irrigated agriculture in the region proposed to supply and save environmentally in danger Lake Urmia. Four scenarios consisting of the current situation, optimistic, average and pessimistic scenarios regarding the future of water resources of the basin and agricultural developments were considered. According to the results, both bankruptcy rules helped Lake Urmia to receive more water, but neither could utterly overcome the water shortage of the Lake, so can be used as supplementary actions alongside other solutions. The cessation of irrigated agriculture throughout the basin overcame the average annual shortage of Lake Urmia in the first and second scenarios equal to 137 and 148 million cubic meters respectively. It showed disability to fully supply the lake in the third and fourth scenarios. These three methods must be combined with a social-economic policy like the purchase of decreased water allocations to farmers to be socially acceptable.     

Conjunctive Use of Surface and Groundwater with Inter-Basin Transfer Approach: Case Study Piranshahr

Disregarding water as a key sustainable development has led to the water crisis in Iran. This problem is the biggest factor for marginalizing the planning and long-term management of water. The sustainable development policies in water resources management of IRAN require consideration of the different aspects of management that each of them demands the scientific integrated programs. Optimal use of inter-basin surface and groundwater resources and transfer of surplus water to adjacent basins are important from different aspects. The purpose of this study is to develop an efficient optimization model based on inter-basin water resources and restoration of outer-basin water resources. In the proposed model the three different objectives are as follow supplying inter-basin water demand, reducing the amount of water output of the boundary of IRAN and increasing water transfer to adjacent basins (Urmia Lake basin) are considered. In this model, water allocation is done based on consumption and resources priorities and groundwater table level constraints. In this research, the non-dominate sorting genetic algorithm is used for performing the developed model regarding the complexity and nonlinearity of the objectives and the decision variables. The optimal allocation of each water resources and water transfer to adjacent basin can be determined by using of proposed model. Optimal allocation policy presented based on optimal value and planning horizon. The results show that we can transfer considerable volume of water resources within the basin for restoration the outside basin and prevent the great flow of water by the border rivers applying the optimal operation policy.     

Evaluation of dike-type causeway impacts on the flow and salinity regimes in Urmia Lake,Iran

Urmia Lake, located in a closed basin in north-west Iran, is the largest lake (5000–6000 km²) in the Middle East. It is very saline with total dissolved salts reaching 200 g/l compared with a normal seawater salinity of about 35 g/l. The construction of a causeway, which was initiated in 1979 but then abandoned until the early 2000s, is near completion and will provide road access between the western and eastern provinces. The causeway has an opening 1.25 km long and divides Urmia Lake into a northern and southern basin and restricts water exchange. The flow and salinity regimes are affected by the presence of this new causeway, and there are concerns over the well being of the Artemia population. This study investigates the effects of the construction of the causeway on flow and salinity regimes, considers remedial actions, and examines the effects of climatic variability on salinity and flow. Flow and salinity regimes were numerically simulated by using a commercially available two and three-dimensional (2D and 3D) MIKE model. The validity of the numerical model was assessed through sensitivity analysis of the model and comparing the simulated results against field measurements; the 3D model provided the higher correlation between simulated and actual data. Wind input was the main climatic and hydrologic factor influencing flow regime while river discharge, evaporation and rainfall were the key parameters affecting salinity distribution in the lake models. The 3D model was subsequently used to predict lake conditions in typical dry, wet and normal climates, to examine the environmental impacts from the new causeway, and to evaluate possible improvements that some remedial measures may provide.     

Assessment of lake–groundwater interactions and anthropogenic stresses,using numerical groundwater flow model,for a Rift lake catchment in central Ethiopia

A steady-state groundwater flow model (MODFLOW) was used to study lake and groundwater interactions in a complex rift volcanic catchment. It also was used to assess the effects of water pumping from wells, and of variable recharge rates associated with climate and lake level changes, on the dynamics of the volcanic aquifers surrounding Lake Awassa. The model simulations were made after first developing a reasonable conceptual model, on the basis of conventional hydrogeological mapping, pumping test and hydrometeorological data analyses, and from ancillary information obtained from hydrochemical and isotope techniques. The model results indicated that the lakes and Rift aquifers are fed by large groundwater inputs that originate in the highlands. The lakes and rivers have important roles in recharging the aquifers in some locations. Lake Awassa receives a major groundwater inflow from its southern and eastern shorelines, while substantial water leakage from the lake occurs along the northern shoreline. The annual groundwater outflow from the catchment is estimated to 52.5 × 10⁶ m³. Scenario analyses revealed that increasing the current pumping rate from wells by fourfold will substantially reduce the groundwater level substantially, although the regional flow pattern would remain the same. There appears to be no immediate danger to the Rift aquatic environment from the current water pumping rate. Drying the small Lake Shalo and associated swamps, however, will cause a large change in the water balance of the larger Lake Awassa. Slight changes in groundwater recharge can cause large differences in groundwater levels for most of the Rift caldera floor far from the lake shores. This study provides a reasonable foundation for developing detailed transient predictive models, which can then readily be used as a decision support tool for development and implementation of sustainable water resources practices.     

Groundwater as a source and pathway for road salt contamination of surface water in the Lake Ontario Basin: A review

In Ontario, there is limited comprehensive research regarding the contribution of chloride in groundwater to surface water systems. The delivery of chloride via groundwater can contribute to the degradation of the Great Lakes and their tributaries. Thus, this review intends to fill or identify knowledge gaps regarding assessing groundwater as a potential source of road salt, the single largest use of salt in urban cold region environments, contamination to surface water by synthesizing existing groundwater chloride research in the Lake Ontario Basin. Knowledge regarding source characterization, properties, pathways, and impacts of chloride in the environment is essential to evaluate the contribution of chloride via groundwater. Past groundwater chloride research in the basin is primarily concentrated in highly urbanized areas and has identified localized trends of increasing groundwater chloride concentrations in these regions; however, few investigations have been conducted in varying land uses (e.g., rural or less urbanized watersheds) or at sufficient temporal and/or spatial scales. Significant chloride accumulation is occurring in watersheds and aquifers within the basin. Concentrations are expected to increase until equilibrium is obtained, thus resulting in sustained yearlong elevated concentrations in tributaries. Recently, chloride loading to Lake Ontario has increased significantly, with groundwater inputs having the potential to support long-term increases in chloride concentrations in the lake. However, few studies have evaluated the explicit contribution via groundwater to Lake Ontario, and therefore a knowledge gap continues to exist. We provide a synthesis of additional research priorities to better understand the magnitude of groundwater chloride issues in the basin.