Reservoir Water Quality Research Articles

A new optimized model to control eutrophication in multi-purpose reservoirs

The entry of excess nutrients into the reservoir causes problems such as eutrophication, and as a result, we see a decline in the quality of water in the reservoirs and changes in the downstream ecosystem. In this study, a simulation–optimization model has been developed in the framework of selective withdrawal methods to achieve optimal operation policies that can meet the different objectives of the reservoir. A two-dimensional model called CE-QUAL-W2 was used to simulate the reservoir water quality processes. Also, the non-dominated sorting genetic algorithm (NSGA-II) was used as an optimization algorithm in the developed simulation–optimization model. The results show that the dissolved oxygen concentration of the outlet from the lower gate Seimare reservoir for the optimal operation policy is about 30% better than the current operating conditions. In addition, hydropower energy has increased by about 50%. The eutrophication status in the reservoir improved in relation to the existing condition, in most months of the year; the reservoir is in low eutrophication state for optimal operation policy. The results showed the high efficiency of this method and the considerable improvement of the various objectives of the reservoir.

State-transition matrices as an analysis and forecasting tool applied to water quality in reservoirs

ABSTRACT Water reservoirs have the function to control the temporal variability of the water availability, thus bringing greater security over these resources. The water quality of these systems must be adequate for their multiple uses, and one of the main tools to understand it, is mathematical modelling. Given the importance of the water quality, the goal of this paper is to develop an analysis that takes into account the randomness of the variables that affect the thermal and/or biochemical regimes of a reservoir. For this, it is proposed a combination of deterministic and statistical analysis, where the probabilities of occurrence of a given event are considered. Difficult factors, such as the lack of data on the water quality and other variables, were considered, which increases the replicability of the method. The research method is divided into three groups: Modelling, Scenarios and Compilation of these scenarios. Through modelling, a base layout is created, enabling the use of scenarios, which are statistically analysed, and compiled into a state-transition matrix. With this, a more robust tool to understand the dynamics of water quality in a system is obtained, since it is not heavily dependent on field measurements and is easily adaptable and replicable.

Spatiotemporal variations in water dissolved organic carbon and dissolved inorganic carbon concentrations in Wenwusha Reservoir in subtropical estuary, Southeast China

沿海水库汇聚并埋藏着大量的碳，是全球碳循环的重要区域.水体溶解有机碳（DOC）和溶解无机碳（DIC）的生物地球化学行为是水库碳循环研究的重要组成部分，对其系统生物过程和生态环境变化具有重要的影响.为了解亚热带河口区文武砂水库表层水体DOC和DIC的时空分布特征，本研究于2018年11月、2019年3月和6月分别对库区表层水进行多空间点位采样分析.结果表明，研究期间，文武砂水库表层水体DOC和DIC浓度变化范围分别介于0.10～21.13和0.38～34.94 mg/L，其均值分别为（4.09±0.18）和（15.83±0.24） mg/L，最大值分别出现在夏季和秋季；空间分布趋势，整体表现为北库区>南库区，且由库区周边的浅水区向库区中心的深水区域呈现出递减的趋势；浮游植物光合作用强度是影响库区DOC和DIC浓度的季节变化的重要因素，而外源污染输入强度是引起库区DOC和DIC浓度空间变化的重要因素.本文结果扩展对水库碳循环的认知，对提高水库水质也提供了有益参考.;Coastal reservoirs receive and accumulate a large amount of carbon; therefore, they are important areas for global carbon cycling. The biogeochemical cycles of dissolved organic carbon (DOC) and dissolved inorganic carbon (DIC) are important components of coastal reservior carbon cycle, with significant effects on biological process and environmental change. This study was conducted to analyze the spatiotemporal variation in DOC and DIC concentrations at Wenwusha Reservoir, a subtropical coastal reservoir in Southeast China, based on the high spatial resolution filed sampling in November 2018 (autumn), March 2019 (spring), and June 2019 (summer). The results showed that the DOC and DIC concentrations of the surface water in Wenwusha Reservoir during the research period changed in the ranges of 0.10-21.13 mg/L, 0.38-34.94 mg/L, with mean values of 4.09±0.18 mg/L and 15.83±0.24 mg/L, respectively. Temporally, concentrations of DOC and DIC in the reservoir showed the highest values in summer and autumn, respectively. Spatially, DOC and DIC concentrations in the northern part of the reservoir were higher than those in the southern part. Furthermore, the DOC and DIC concentrations decreased along a gradient from shallow water (<1 m) to deeper water (>3 m) in the reservoir. The seasonal variations in DOC and DIC concentrations were mainly influenced by phytoplankton photosynthesis, while the spatial changes of DOC and DIC concentrations were primarily affected by exogenous input (e.g., sewage discharge and river flow). The results improve the understanding of carbon cycling in aquatic ecosystem and also be helpful for improving water quality in reservoirs.

Research on Reservoir Water Quality Prediction Based on Grey Model

Combining the gray model to predict the water quality of Qingshan Reservoir, the analysis results show that the grey model has good applicability for the prediction of reservoir water quality. The prediction errors of total nitrogen, total phosphorus, COD5, and ammonia nitrogen are all within 30%, meeting the accuracy requirements of water quality prediction. The research results have important method reference value for reservoir water quality prediction.

Soil and water characteristics of Nanak Sagar reservoir, Tarai region of Uttarakhand, India

The present study was directed to assess the Nanak Sagar reservoir's soil and water characteristics, located in the Tarai region of Uttarakhand. Monthly samplings were conducted at three selected sites during August 2016 to March 2017. The catchment area of Nanak Sagar reservoir is mainly silty and loamy. During the study period, the range of variation in water temperature, transparency, electrical conductivity and TDS was recorded as 16.9 to 340 C, 67.9 to 155.5 cm, 118 to 336 µScm-1 and 91.7 to 156 mg L-1, respectively. The highest values of temperature, transparency, electrical conductivity and TDS were found in the months of September, November, August and August, while the lowest values were recorded in January, August, September and October respectively. Chemical parameters like pH, dissolved oxygen, free CO2, Alkalinity, Phosphate and Nitrate were found to vary from 7 to 8.7, 3.2 to 9.6 mg L-1, 0 to 6 mg L- 1, 60 to 140 mg L-1, 0.043 to 0.2 mg L-1 and 0.224 to 0.64 mg L-1 respectively. The highest and lowest values of pH, dissolved oxygen, free CO2, total Alkalinity, Phosphate and Nitrate were recorded in the month of January, February, August, February, September while lowest values were recorded in the month of August, September, March, August and March respectively. The reservoir's water quality is within normal condition so fish production from the reservoir could be increased.

An Open-source Wireless Platform for Real-time Water Quality Monitoring with Precise Global Positioning

Sustainable development associated with the agri-cultural field of Arequipa, a region in economic growth, is vul-nerable to contamination of water resources, putting production systems and food security at risk. Therefore, it is necessary to implement an automated system to control, management, and monitor this vital resource. The proposed work proposed a system to measure water quality monitoring in reservoirs and lakes with high accurate related to global positioning. It includes an embedded computer, multiparameter sonde, and an additional dual GNSS/INS in hardware architecture. The software architecture is fully open-source with compatibility, modularity, and interoperability features between Python and MySQL, al-lowing data management for real-time data in visual interface on a platform that stores unlimited data logging, monitors and analyzes. The proposed system is validated in an experimental test that measures the water quality of a huge agricultural reservoir, where certified instrumentation is mandatory, as compared to other methods used locally for this action.

Remote Sensing of Turbidity for Lakes in Northeast China Using Sentinel-2 Images With Machine Learning Algorithms

Monitoring water quality of inland lakes and reservoirs is a great concern for the public and government in China. Water turbidity is a reliable and direct indicator that can reflect the water quality. Remote sensing has become an efficient technology for monitoring large-scale water turbidity. This study aims to search an optimal regression model to accurately predict water turbidity using remote sensing data. To achieve this goal, 187 water samples were collected from field campaigns across Northeast China in 2018, of which the samples were gathered within 6 days of Sentinel-2 overpasses. The spectral reflectance data was used as independent variables for modeling. The simple regression (SR), partial least squares regression (PLSR), support vector regression (SVR), extreme learning machine (ELM), back-propagation neural network (BP), classification and regression tree (CART), gradient boosting decision tree (GBDT), random forest (RF), and K-nearest neighbor (KNN) were used to compare. From model validation, we identified GBDT as the best regression model (R2=0.88, RMSE=9.90 NTU, MAE=6.71 NTU). We applied GBDT to retrieve the water turbidity and obtained a satisfactory result. Feature selection technique from tree-based ensemble method was also tested. We selected B2, B3, B4 and B5 as the important variables because of their high ability to explain the variation of turbidity. These results demonstrated the significance of using a promising method to retrieve water turbidity using Sentinel-2 imagery at the regional scale. It is beneficial to monitor the spatial-temporal distribution of water turbidity; support water quality management and inland water environment protection.

Spatial and seasonal variations in the physicochemical parameters of water quality of a tropical reservoir, Nigeria

Abstract. In this study, the physicochemical properties of a water supply reservoir in the Esa- Odo community, Obokun Local Government Area of Osun State, Nigeria, were determined. Thirteen selected sampling stations over the three reaches of Esa-Odo reservoir along its main axis were monitored between February 2017 to December 2018 with a view to determining the seasonal and spatial variations in the general physicochemical water quality parameters of the reservoir water. From each sampling station, surface water samples were collected bi-monthly for two annual cycles (rainy and dry seasons). The collected water samples were treated and analyzed for physicochemical water quality parameters using standard instrumental and non-instrumental methods. The data obtained were analyzed using appropriate descriptive and inferential statistics. The result of the analyses of the reservoir water showed an increasing clarity from the upstream to the downstream stations with regard to water temperature, depth, transparency, turbidity, and colour. The water was generally near neutral (pH: 7.01 0.04 - 7.07 0.50) but slightly more near neutral in the rainy season than during the dry season. The water in the reservoir can be classified as a dilute salt bicarbonate freshwater with mean conductivity at the three reaches ranging from 113.39 1.67 Scm-1 to 115.24 2.46 Scm-1. Ca2+ and HCO3- were the dominant cation and anion, respectively, at all stations investigated irrespective of seasons of sampling. The mean values of most parameters determined were within permissible limits, making the river water suitable for most probable domestic and industrial uses and livestock support.

Study on the Influence of Reservoir Dispatch of the Upper Yangtze River on the Runoff Control

The reservoir group focusing on the Three Georges reservoir has been established in the upper Yangtze River, with a total regulation capacity of 51.5 billion m3. The reservoir group dispatch plays an important role in regulating the runoff. Economic activity in the Yangtze River estuary poses high requirements for water resources security. The water quality of main water supply reservoirs is influenced by the saltwater intrusion. The upstream reservoir group dispatch can enhance sea inlet runoff and mitigate saltwater intrusion hazard. In order to clarify the upstream reservoir group’s influence on the sea inlet water quantity in the Yangtze River estuary, the author designed three typical reservoir group dispatch scenarios to analyze flow rate change and different dispatch scenarios of Datong section. According to the findings, the upstream reservoir group dispatch is important to secure water quantity in the dry season. Through normal dispatch, the Three Georges reservoir can cut the days with a flow rate less than 100 million m3/s from 50.6 days to 8.8 days. In the special dry year, the sole emergency water supplement by the Yangtze River reservoir to the estuary will exert influence on the reservoir power generation. The joint operation of upstream reservoir group can basically eliminate such influence.

Water Quality Index variations in a Mediterranean reservoir: a multivariate statistical analysis relating it to different variables over 8 years

Evaluating the status of the water quality of freshwater bodies is crucial for safe use. In this work, the water quality of an understudied Mediterranean reservoir was investigated, using Water Quality Index (WQI) and principle component analysis (PCA) during an 8-year study period, between 2009 and 2016. The WQI was analyzed based on weighted sum aggregation function, considering the following variables: temperature, salinity, pH, conductivity, dissolved oxygen, nitrate, nitrite, ammonia, phosphate, sulfate, and total dissolved solids. After describing the evolution of these variables, WQI was evaluated. It was mostly moderate and showed a deteriorating trend between 2009 and 2016. This deterioration was due to the previously weakened water infrastructure that was furthermore impacted by the sudden increase in the habitants of the basin following Syrian refugees influx after 2011 Syrian crisis. In a new approach, WQI results were also compared to river inflow, reservoir water depth and precipitation. WQI increased with the increased water depth and water volume of the reservoir showing better water quality. Monthly precipitation above 250 mm showed better water quality and increased WQI. No clear relation was found between the WQI and the river flow. PCA analysis indicated that water quality in the reservoir was affected by erosion and fertilizers. WQI results agreed with Carlson Trophic State Index previously applied to the reservoir. These innovative results linking WQI to hydrological variables, urbanization, and trophic index together with the incorporation of PCA with WQI provide a multidimensional nature of water quality evaluation concept.

Evaluation of Phytoremediation Potential of Vetiver Grass (Chrysopogon zizanioides (L.) Roberty) for Wastewater Treatment

Water pollution is one of the most critical global issues. Meanwhile, the problem of water pollution of rivers especially in Iran is rising due to expansion of agricultural and industrial applications. Due to a large number of sewer catchments, there are some dam reservoirs like ZHAVE in Iranian state of Kurdistan that have not been able to collect significant amount of water since last 10 years. Removal of heavy metals as contaminants from runoffs and recycling of water is a necessity and a vital issue in the world. Various methods and standards are invented and used to isolate and remove all types of pollutants. This study focuses on the purification and removal of contaminants in water sources using the phytoremediation method by introducing Vetiver grass species in the case of floating treatment wetland (FTW). This study’s preliminary purpose is to investigate a practical remedial solution and improvement methodology for the water quality of reservoirs and rivers by growing the floating Vetiver island method. The results show that following parameters such as COD by 97%, TN by 90%, phosphorus by 66%, TDS by 26%, and evapotranspiration by 40% were reduced. Therefore, we concluded that for a wastewater with varying neutrient concentrations such as in ZHAVE dam, concentration of nutrients N and P was controlled and consequently inhibition and prevention of the eutrophication of water resources in the medium and long term became possible due to reduction in the rate of evaporation from reservoirs.

Солевой состав вод Бурейского водохранилища

Significance. Significance of the work lies in the need to study the salt composition of the Bureya reservoir water from the beginning of filling, which is important for predicting the water quality of reservoirs in the Amur basin that are to be designed. The objective is to evaluate content of main ions in the water of the Bureya reservoir, and to identify factors determining their spatial and temporal variability. Methods. Hydro/chemical observations in the Bureya reservoir were made from 2003 to 2008 at five plots covering the major part of the water area. Water samples were taken from the surface, middle, and near-bottom horizons in winter, summer, and fall. Water samples were taken from the surface in January, July 2019 in the landslide area and in July 2020 at eight sites in the water body between the landslide and the hydropower dam. Analytical work was carried out according to the methods accepted in hydrochemistry. Materials of the Amur Basin Water Administration for 2005-2019 were used in the work. Results. The content of the main ions in the water of the reservoir during the filling period and the following years was assessed. The dominance of calcium ion among cations and hydrocarbonate ion among anions in the salt composition of water was shown. It is established that the emergence of oxygen deficit in water due to the increased area of flooded forests and reduced water inflow caused the absence of sulfate ion in the reservoir water in autumn and winter 2005. It is shown that staged filling of the reservoir contributed to gradual smoothing of differences in the content of major ions and stabilization of the salt composition of water in the sixth year of filling. In current conditions the content of sodium and potassium ions and chloride ions in the water area of the reservoir is relatively evenly distributed, the highest values of concentrations of calcium and magnesium hydrogen carbonates are observed near the mouth of the Tyrma River. The effect of a large landslide on the content of major ions in the water in 2019-2020 is considered.

Reservoir water-quality simulation using simplified mathematical models (case study: Seymareh Reservoir)

In this research, the performance of simple mathematical models was evaluated for predicting total dissolved solids (TDS), biochemical oxygen demand (BOD) and nitrate (NO3–) in a case study, the Seymareh Reservoir located in the south-west of Iran. The accuracy of the mathematical models was compared with a two-dimensional model, called CE-Qual-W2, and real observations. The models were considered as two different input-data scenarios and one scenario for applied mathematical equations (completely mixed reactor). The modelling period was from October 2012 to September 2013. The results of the simple mathematical models show an acceptable performance with the mean relative error (MRE) of 10.8–73.8 compared with the complex CE-Qual-W2 model, whereas they require fewer input data and take less time to execute. To verify the accuracy of the equations, the results were also compared with the sampling data from the reservoir. The best performance of the proposed mathematical models showed a MRE of ~10.8%, 31.5% and 16.5% for TDS, BOD and NO3– respectively. These findings suggest using such simple models for screening/feasibility studies and also to model water quality in several dams across the basin to save time and cost.

Qualidade das águas em resposta aos efeitos do uso da terra na área de influência direta de reservatório pelo emprego da análise multivariada

The process of water degradation in a reservoir is directly related to the exchange of organic and inorganic matter between the river, the plain and its basin, whose effects are the alteration of the abiotic and biotic patterns and processes of aquatic ecosystems. The present work aimed to apply the “PCA - Principal Components Analysis” for analise the interrelationship between the types of land use and land cover related with the water quality of “Barra dos Coqueiros Reservoir”. The samples of water were collected in July 2016, dry season, at 39 different points of the reservoir. The Principal Component Analysis Model was defined using only 18 of the 36 variables on physical, chemical and biological characteristics of water. The results obtained by the “PCA” demonstrated that the first axes explain 42,60% of the total variation of the physical-chemical characteristics of the water in the reservoir. The plot of PCA show a separation between the points that are influenced by the urbanized area and agriculture / pastures. The first axis of the “PCA” is under the influence of organic pollution and ions dissolved in water. The second axis of the “PCA” indicates a component associated with the distribution of solids inside the reservoir. The method employed using “PCA” demonstrate a great value for the explanation of the influence of land use and cover on the water quality of reservoir. Keywords: PCA, multivariate statistical, reservoir, physical-chemical variables of water.

Water quality index and spatio-temporal perspective of a large Brazilian water reservoir

Abstract The water spatio-temporal variability of the Irapé Hydroelectric Power Plant reservoir and its main tributaries was evaluated by analysing the temporal trend of the main parameters and applying the Canadian Council of Ministers of the Environment Water Quality Index (CCME WQI), using data from 2008 to 2018. This reservoir is in Minas Gerais, Brazil, and covers an area of approximately 143 km2 across seven municipalities. The dissolved iron (DFe) presented the highest percentage of standards violations (31.7% to 80.5%), most frequently in the reservoir tributaries. The Mann–Kendall tests indicated that the monitoring stations showed an increasing trend of 78.5% N–NH4+ and 64.1% DFe. During the evaluated period, the reservoir waters were classified as excellent (1.2%), good (61.3%), acceptable (29.5%), and poor (8.0%) according to the WQI for the proposed use. The poorest quality classes were more frequent in the tributaries, especially in the year 2009. The WQI seasonal assessment indicated a worsening during the rainy season in 57% of the stations, as a result of external material transport to the water bodies. The CCME WQI, in conjunction with temporal statistical analysis, contributed to the interpretation of the monitoring data, generating important information for reservoir water quality management.

Thermal stratification responses of a monomictic reservoir under different seasons and operation schemes

This study investigates the thermal stratification responses of a monomictic reservoir operated under different facilities. The analysis of 60-year long data showed that the reservoir's thermal regime varies with season and withdrawal scheme and is affected by upstream reach control through the vertical curtain. Isothermal conditions exist during winter (December–March) while stratification onsets in spring (starting April), intensifies in summer (August) and weakens during fall (October–November). Considering summer stratification, deep hypolimnetic withdrawals through the penstock intake promoted thicker epilimnion, with low values of thermal stability (Schmidt Stability Index, SSI) and thermocline strength index (TSI). Meanwhile, shallow withdrawals using selective outflow system resulted in narrower epilimnion, with larger TSI for no curtain scenario and larger SSI for with curtain scenario. Strongest thermoclines do not necessarily translate to largest magnitudes of thermal stability. Longer duration of stratification is associated with shallow withdrawals. Depending on the outflow depth and the occurrence of prolonged hot or cold atmospheric conditions, the onset of stratification could be likely shifted early or late. The 3D numerical simulation determined the individual effects of each operation, which strongly supported the results of the long term analysis. Since thermal stratification directly influences the reservoir's water quality regime, this study can be a helpful reference in optimizing the water quality management of the reservoir.

Modelling the variability of hydrological parameters of the Sasyk reservoir impoundment under various options of its operation

This paper highlights the results of adaptation and verification of the Delft3D Flexible Mesh numerical model under the conditions of the Sasyk reservoir. The objective of this work is to evaluate the expected spatio-temporal variability of water salinity in the Sasyk reservoir after completion of the Sasyk renaturalization project by means of establishing a constant water exchange with the sea through the artificial channel.&#x0D; The Sasyk Lagoon was separated from the sea and transformed into a freshwater reservoir in the late 1970s. However, due to the poor water quality in the Sasyk reservoir in the modern period, the solution of the problem of transforming the reservoir to its original coastal conditions, i.e. the renaturalization, has acquired particular importance.&#x0D; Model results, obtained under conditions of 2019, indicate the possibility of using a hydrodynamic model to evaluate the effectiveness and possible consequences of various scenario-based decisions to be implemented for the management of the hydrological regime of the reservoir under various options of its operation.&#x0D; The model runs were used to evaluate the flushing time of the Sasyk Lagoon and the pattern of the salinity fluctuations in the reservoir after the restoration of the artificial channel in the sand bar with a width of 100 m and a depth of 1.5 m and the establishment of the constant “sea-lagoon” interconnection. Applying the hydrometeorological conditions of 2019, a scenario-based modelling for two consecutive years was performed. For the first year of the simulation, a variant of water management under the absence of freshwater inflow from the Danube and the presence of sea water inflow throughout the year was considered. The model results at the end of the first year of the simulation were set as the initial conditions for the second year, and the rest of the external forcing remained unchanged. Additionally, the variant considering the Danube discharge into the lagoon during May-July for the second year of simulation was investigated.&#x0D; Based on the simulation results, it was found that in the case of a constant water exchange with the sea through the connecting “sea-lagoon” channel (with the abovementioned morphometric characteristics) and under the absence of the Danube freshwater inflow throughout the year: 1) the flushing time of the lagoon will be 1 year and 5 months; 2) stabilization of water salinity in the lagoon will not occur, i.e. the salinization of the lagoon water takes place in the long-term perspective; 3) the time period from the moment of initiating the water exchange with the sea, during which the lagoon reaches the water salinity limit of 7-8 ‰, that is critical for the existence of freshwater species of flora and fauna, is expected to amount to 4 months for the southern part and to 5.5 months for the northern part of the lagoon; after which the formation of the marine ecosystem of the reservoir will begin.&#x0D; It is shown that the stabilization of water salinity in the lagoon in the second year of the simulation can be achieved under conditions of ensuring the Danubian freshwater discharge in the period of significantly higher water level in the Danube River, compared to the lagoon water level (May-July 2019).

A new approach for designing a hypolimnetic oxygenation system to improve the water quality in tropical reservoirs

A new approach for designing a hypolimnetic oxygenation system to improve the water quality in tropical reservoirs

A case study of factors controlling water quality in two warm monomictic tropical reservoirs located in contrasting agricultural watersheds

The integration of internal (e.g., stratification) and external (e.g., pollution) factors on a comprehensive assessment of reservoir water quality determines the success of ecosystem restoration initiatives and aids watershed management. However, integrated analyses are scarcer than studies addressing factors separately. Integration is likely more efficient in studies of small well-characterized (experimental) reservoir watersheds, because the isolation of factor contributions is presumably clearer. But those studies are uncommon. This work describes the water quality of two small 5.5 m-deep reservoirs (MD-Main and VD-Voçoroca dams) located in Pindorama Experimental Center, state of São Paulo, Brazil, considering the interplay between reservoir dimension, seasonal thermal stratification, chemical gradients, erosive rainfall events, presence of natural biofilters, and land uses and landscape patterns around the reservoirs and within the contributing watersheds. The monitoring of agricultural activities and water quality parameters occurred in October 2018–July 2019. A 4 °C thermal stratification occurred in October (difference between surface and bottom water temperature), which decreased until disappearance in January (VD) or April (MD). The longer stratification period of MD was justified by its larger area relative to VD (≈10×). Thermal stratification triggered hypoxia at the bottom of both reservoirs (DO ≈ 1 mg/L), more prolonged and severe in MD. Hypoxia activated Ec and TDS peaks in January likely explained by bottom-sediment nutrient releases, presumably phosphorus. The Ec peak reached 560 μS/cm in MD and 290 μS/cm in VD. The smaller VD peak was probably explained by the action of macrophytes. In March, a 240 NTU turbidity peak occurred in MD, caused by precedent erosive rainfall and the lack of vegetation protection alongside the south border. As expected, the study accomplished clear isolation of factor contributions, verified by Factor and Cluster analyses. Our results can subsidize studies on larger reservoir watersheds requiring restoration, where the isolation of factors is more challenging.

Climate change effects on the thermal stratification of Lake Diefenbaker, a large multi-purpose reservoir

Large multi-purpose reservoirs serve not only to generate hydropower but to supply water for agricultural irrigation, animal and human consumption and to provide flood control. One of the key factors affecting physical functioning and deteriorating aquatic ecosystems in reservoirs is climate change. For instance, increases in water temperature accelerate chemical reaction rates, decomposition rates and oxygen demand at the water-sediment interface. Earlier thermal stratification onset, and longer and more intense reservoir thermal stratification are all consequences of global warming. Such disruptions in thermal stratification have been associated with reductions in hypolimnion dissolved oxygen, increasing anoxia events and enhancing reservoir eutrophication. In this research paper, we implement the 2 D hydrodynamics and water quality model, CE-QUAL-W2, to investigate the effects of climate change and streamflow scenarios on the thermal structure of Lake Diefenbaker, a large, multipurpose reservoir, located in Saskatchewan, Canada. Model results indicate that meteorological variability will dictate a nonlinear increase in reservoir water temperature in the coming decades, where larger increases in water temperature will occur during summer and fall in the upper layers. Also, decreases in reservoir streamflows will reduce water temperature at intermediate layers during summer and fall. Our model can be used as a tool to mitigate and manage the effects of climate change on the reservoir water quality.