Does river restoration affect diurnal and seasonal changes to surface water quality? A study along the Thur River, Switzerland

Groundwater vulnerability to fluoride pollution and health risk assessment in the western part of Odisha, India

The fluoride dynamics of the Dharmagarh Block of Kalahandi District, Odisha, India, and associated health risk assessment have been studied. Complex data matrices were evaluated using groundwater quality index, fluoride pollution index, and principal component analysis to understand the geological evolution and identify potential sources for fluoride pollution. The study region comprises granite, granitic gneiss, and khondalite of hard and compact rock of Precambrian Eon, which supplies mostly the fluoride-bearing minerals. Altogether thirty-four (34) groundwater samples across the entire study area were collected and subjected to various physico-chemical analyses. The majority of the groundwater in the proposed region is hard to very hard type with Mg-HCO3 and Na-HCO3 being the two dominant facies. Groundwater contains fluoride in concentrations ranging from 0.21 to 2.26 mg/L. The statistical analysis of the quality parameters reveals the moderate positive correlation of fluoride with sodium (0.392) and pH (0.313) and week positive correlation with EC, TDS, TH, TA, Mg2+, and HCO3-, which directly depicts the initiation of fluoride problem within the study area. Based on the water quality index, 23.53% samples are good, 73.53% are poor, and 2.94% are very poor in nature. With respect to fluoride pollution index, 5.88% samples show high pollution, 55.88% samples show medium pollution, and 38.24% of samples show low pollution index. Human health risk assessment has also been carried out using the hazard quotient of fluoride. Altogether 70.59% of samples show Total Hazard Index (THI) values < 1 suggesting low risk of cancer and within the permissible range, whereas 29.41% of samples show THI > 1 suggesting the non-carcinogenic risk of pollutants, which exceeds the allowable limit for all the classes of male, female and children.

Spatio-temporal variations in water quality of a river-lake system during restoration treatments

To fill the knowledge gap about the functioning of the lake-river system subjected to restoration treatments, two tributaries, a shallow, restored lake and its outflow, were examined. The quality of water inflows, lake and outflow was compared before (BR), during sustainable (SR, deep water aeration, phosphorus inactivation and biomanipulation for 3 years) and limited lake restoration (LR, only aeration for 2 years). Physico-chemical parameters were analysed monthly at five stations. The nutrient concentrations at the inflows decreased over the years due to the improvement of water and sewage management in the catchment (in Mielcuch from 18.0 to 8.0 mgN L^-1 and 1.0 to 0.6 mgP L^-1). The decline at the outflow was the result of a better quality of water at the tributaries and SR in the lake. During LR, decrease of phosphorus concentration still occurred (0.11 mgP L^-1), but nitrogen concentration slightly increased (3.9 mgN L^-1). Although the outflowing waters still transported a high content of chlorophyll a and suspended solids during SR, their amount was lower (34.5 μg L^-1 and 17 mg L^-1, respectively) than that during BR and LR. During restoration, it is significant to monitor the water quality not only in the lake but also at the outflow. The slow deterioration of water quality at the outflow indicated that introducing changes in the applied restoration methods must be done carefully because the previously achieved effect may be lost. Hence, restoration of the upstream lake and good quality of its tributaries are of great importance for water bodies located downstream.

Analysing the change in water quality parameters along river Ganga at Varanasi, Mirzapur and Ghazipur using Sentinel-2 and Landsat-8 satellite data during pre-lockdown, lockdown and post-lockdown associated with COVID-19

Abstract

The proper functioning of the river ecosystem has been symbolised by healthy aquatic life. The river Ganga has shown signs of rejuvenation due to lockdown. In this study, an attempt has been made to analyse the change in river water quality using Sentinel-2 and Landsat-8 imageries. The quantitative analysis has been performed for temperature and normalised difference turbidity index (NDTI). The qualitative analysis has been performed for pH, dissolved oxygen (DO) and total suspended solids (TSSs). Ghazipur, Varanasi and Mirzapur stretches have been selected for this study. In the Ghazipur stretch, the river temperature decreased by 7.14% in May 2020 (lockdown period) as compared to May 2019 (1 year before lockdown). Similarly, in the Varanasi stretch, this decrease has been by 8.62%, and in the Mirzapur stretch, this decrease has been by 12.06% in May 2020 compared to May 2019. For the same period, NDTI in the Ghazipur, Varanasi and Mirzapur stretch has been decreased by 0.22, 0.26 and 0.24, respectively. The pH and DO of the river increased, and TSS decreased for the considered time period. The lockdown during the second wave of the coronavirus disease 2019 was not helpful for river rejuvenation. This study elicited how the behaviour of the parameters changed during the lockdown.

Research highlights

River Ganga becomes much cleaner in the lockdown period (May 2020) compared to the pre-lockdown time.

In the Mirzapur stretch, the temperature decreased most in May 2020 as compared to May 2019.

In the Varanasi stretch, there is a maximum variation in the NDTI value in May 2020 in comparison with that of May 2019.

The most significant task will be to maintain river conditions during post-lockdown similar to that prevailed during lockdown.

In the second wave COVID-19 lockdown the river again became polluted like the pre-COVID times.

Analysis of the Spatio-Temporal Variation of the Thermal Pattern of River Ganges in Proximity to Varanasi, India

The temperature of a river is a fundamental aspect of its water quality and has a bearing on its ecosystem to a greater extent. Therefore, in systematic planning for optimal stream monitoring programs involving the determination of location at monitoring stations, understanding this crucial thermal parameter is much desired. This would help to give an integrated scenario regarding physical, chemical, and biological processes occurring in the river ecosystem. Water quality parameters of the river such as dissolved oxygen, pH, salinity get affected due to change in river thermal patterns. In this study, the Landsat-8 TIR sensor was used to study spatial and temporal variations of river temperature. Thermal bands of 23 cloud-free Landsat-8 images from June 2013 to November 2020 were processed to prepare thermal maps of a stretch of river Ganges at Varanasi, India. The work has been validated by in-situ temperature measurement with a portable thermal sensor having high accuracy (± 0.1 °C). A good correlation (R² = 0.927 and RMSE = 0.956) was observed between the sensor's estimated temperature and the in-situ temperature. The results exemplify that water surface temperature at confluence points was relatively higher due to the incoming effluents than the mid-river temperature. The ‘confluence point 3’ has the least relative temperature variation. The relative temperature variation has been more prominent for the month of February in comparison to June and November. Owing to the time series data availability and worldwide coverage of the Landsat-8 satellite, the present work provides a promising strategy for studying the thermal patterns in other rivers.

Adaptive monitoring approach to assess dissolved organic matter dynamics during rainfall events

Rainfall events induce water quality transformation in river systems influenced by the watershed land use and hydrology dynamics. In this context, an adaptive monitoring approach (AMA) is used to assess non-point sources (NPS) of pollution events, through dissolved organic matter (DOM) contribution. The case study is a monitoring site in a semi-urban watershed characterized by NPS contribution. An integrated quali-quantitative method for DOM based on dissolved organic carbon (DOC) content, spectroscopic techniques of excitation-emission fluorescence (EEF), and UV-visible absorbance is proposed. The results indicate a mix of allochthonous and autochthonous DOM characteristics from NPS sources associated to vegetation area influence (A₂₈₅/DOC of 15.43 L (g cm)^-1 and SUVA₂₅₄ of 2.11 L (mg m)^-1). The EEF signals showed more humic-like than protein-like characteristics with peaks A and C (approximately 5.72 r.u.) more intense than peaks B, T₁, and T₂ (approximately 4.33 r.u.), indicating NPS from the soil leachate. The absorbance ratio values indicate a mix of organic compounds with greater proportion of refractory characteristics with high aromaticity and molecular weight (approximately A₃₀₀/A₄₀₀ of 4.15 and A₂₅₀/A₃₆₅ of 4.48), associated with the surface wash-off of accumulated residual and subsurface soil erosion, which contribute to complex organic matter structures. The fluorescence indexes, overall, indicated allochthonous sources with intermediate humic characteristics (FI ≈ 1.43, BIX ≈ 0.65, and HIX ≈ 7.98). The proposed integrated optical property strategy represents an opportunity for better understanding of DOM dynamic assessment for identifying potential mitigation techniques for organic pollution control and improving water quality conditions.

Diurnal Patterns in Solute Concentrations Measured with In Situ UV-Vis Sensors: Natural Fluctuations or Artefacts?

In situ spectrophotometers measuring in the UV-visible spectrum are increasingly used to collect high-resolution data on stream water quality. This provides the opportunity to investigate short-term solute dynamics, including diurnal cycling. This study reports unusual changes in diurnal patterns observed when such sensors were deployed in four tropical headwater streams in Kenya. The analysis of a 5-year dataset revealed sensor-specific diurnal patterns in nitrate and dissolved organic carbon concentrations and different patterns measured by different sensors when installed at the same site. To verify these patterns, a second mobile sensor was installed at three sites for more than 3 weeks. Agreement between the measurements performed by these sensors was higher for dissolved organic carbon (r > 0.98) than for nitrate (r = 0.43–0.81) at all sites. Higher concentrations and larger amplitudes generally led to higher agreement between patterns measured by the two sensors. However, changing the position or level of shading of the mobile sensor resulted in inconsistent changes in the patterns. The results of this study show that diurnal patterns measured with UV-Vis spectrophotometers should be interpreted with caution. Further work is required to understand how these measurements are influenced by environmental conditions and sensor-specific properties.

Hydraulic analysis of a meander on the Danube River using a 2D flow model

This paper presents the development, calibration and verification of a two-dimensional model for a Danube reach and its old cutoff meander. The considered meander was at one point separated from the main reach with a levee, which caused a series of unwanted environmental consequences. Aiming to stop the ongoing degradation of the meander, the validated model was engaged to investigate the effects different river works would have on its current state. The considered river works involved dredging in certain parts of the meander, while keeping in mind the negative effects these works can have on the environment, as well as possible widening of the existing opening in the levee. Numerical simulations showed that all the considered scenarios would result in a general increase of velocities, which is important from the aspect of sediment deposition. After a thorough evaluation of the results, it was found that by carefully selecting the locations where dredging should be conducted, no other interference is needed to put an end to the increasingly deteriorating situation in the meander. Computations confirmed that the suggested river works would increase the unit discharge in the entire meander, especially in its upstream part. The redistribution of flow around the island downstream of the levee (that formed during past years as a result of sediment deposition) was also predicted, where the flow would once again favor the left side of the island. This is a more natural path of flow that would aid the flushing of previously deposited sediment in this part of the meander.

Temporal and Spatial Study of Water Quality and Trophic Evaluation of a Large Tropical Reservoir

A water quality study was carried out at the Adolfo López Mateos (ALM) reservoir, one of the largest tropical reservoirs in Mexico, located within an intensive agricultural region. In this study, the seasonal and spatial variations of nine water quality parameters were evaluated at four different sites along the reservoir semiannually over a period of seven years (2012–2018), considering the spring (dry) and fall (rainy) seasons. An analysis of variance was performed to compare the mean values of the water quality parameters for the different sampling sites. Then, a multiparametric classification analysis was carried out to estimate the spatial density of the sampling points by using a probabilistic neural network (PNN) classifier. The observations (seasonal and spatial) of the water quality parameters at the ALM reservoir revealed no significant influence. The trophic status was evaluated using the Carlson Modified Trophic State Index, finding the trophic state of the reservoir at the mesotrophic level, with nitrogen being the limiting nutrient. The PNN revealed neural interactions between total suspended solids (TSS) and the other four parameters, indicating that the concentration ranges of five parameters are equally distributed and classified.

Water quality dynamic during rainfall episodes: integrated approach to assess diffuse pollution using automatic sampling

Diffuse pollution caused by rainfall events potentially affects water quality in rivers and, therefore, must be investigated in order to improve water quality planning and management recovery strategies. For these, a quali-quantitative approach was used to monitor the water quality parameters in a river located in a semi-urban watershed area based upon automatic sampling. Thirteen water quality parameters were measured during five rainfall events. Events ranged from 2.3 to 56.8 mm and water peak flows from 3.3 to 4.5 m³/s. The pollutographs measured showed a standard pattern for total suspended solids (TSS). However, for the other chemical parameters, as total phosphorous (TP) and dissolved organic carbon (DOC), the dilution effects were more evident. It was possible to observe the rainfall influence mainly for physical parameters indicating a mass transport pattern for diffuse pollutants, which increased, for example, the amount of TSS in the river. Furthermore, hydrological characteristics were relevant considering the pollutant behavior. Antecedent dry periods, ranging from 1.3 days to 21.4 days, and critical time, from 2.0 to 10.4 h, are determinants to evaluate non-traditional water quality impacts in the river. In general, each rainfall episode has its own characteristics, which produces distinct mass contribution and temporal behavior, being challenging in making generalization. Therefore, the results indicate that diffuse pollution has to be considered to establish future decision-making strategies to water resources management.

Study of the Water Quality of a Tropical Reservoir

A study of the water quality of the Adolfo López Mateos Reservoir (ALMD) was developed through different indicators from a spatial and seasonal perspective. Variables related to the general characteristics of water quality, trophic level, and ecological risk were assessed through the National Sanitation Foundation–Brown Water Quality Index (WQINSF–BROWN), the Carlson Trophic State Index (TSICARLSON) and the Håkanson Ecological Risk Index (RIHÅKANSON). Using data from physical, chemical, and biological parameters obtained from four sampling points in the ALMD, the water quality was assessed in each model used. The results indicated that the reservoir presents a water quality classified as “medium” (WQINSF–BROWN = 70), where significant variations in the concentrations of some parameters are observed. The reservoir showed a general trophic state (TSIGENERAL-AVERAGE = 43.04) classified as “mesotrophic”. The ecological risk analysis achieved the best classification of the methodology, discarding contamination by heavy metals in surface waters. This type of applied methodology will help in decision-making tools in the dam, and can be applied in other dams in the region.

Water Quality as an Indicator of Stream Restoration Effects—A Case Study of the Kwacza River Restoration Project

River restoration projects rely on environmental engineering solutions to improve the health of riparian ecosystems and restore their natural characteristics. The Kwacza River, the left tributary of the Słupia River in northern Poland, and the recipient of nutrients from an agriculturally used catchment area, was restored in 2007. The ecological status of the river’s biotope was improved with the use of various hydraulic structures, including palisades, groynes and stone islands, by protecting the banks with trunks, exposing a fragment of the river channel, and building a by-pass near a defunct culvert. The effects of restoration treatments were evaluated by comparing the physicochemical parameters of river water along the 2.5 km restored section between the source and the mouth to the Słupia, before restoration and 6 years after hydrotechnical treatments. A total of 18 physicochemical parameters were analyzed at 10 cross-sections along the river. The greatest changes were observed in the concentrations of NO3−-N and NH4+-N, which decreased by 70% and 50%, respectively. Dissolved oxygen concentration increased by 65%. Chloride values increased by 44%, and chlorophyll-a concentration increased by 30% after the project. The cut-off channel (by-pass), semi-palisades, and single groynes were the treatments that contributed most to water quality improvement. The results of this study indicate that river restoration projects can substantially reduce nitrogen pollution, which is particularly important in agricultural areas. Such measures can effectively reinstate natural conditions in river ecosystems. Hydrochemical monitoring is required to control the parameters of restored rivers.