Hydrochemical Variations Research Articles

Analysis of Groundwater Hydrochemical Variation and Its Source During the Low Water Level Period in the Southern Oasis Area of Gaochang District, Turpan City

To explore the changes in groundwater hydrochemistry and its source influence in the low water level period of the southern oasis area of Gaochang District, Turpan City before and after the management of groundwater overexploitation, based on 12 groups of water samples in 2016 （three groups of unconfined water, nine groups of confined water） and 18 groups of water samples in 2023 （five groups of unconfined water, thirteen groups of confined water）, mathematical statistics, hydrochemical diagraph, hydrogen and oxygen isotope means, and an absolute principle component-multiple linear regression （APCS-MLR） model were used to analyze the changes and sources of groundwater hydrochemistry. The results showed that due to the dynamic conditions of groundwater, the dominant cation changed from Na+ to Ca2+, and the anion changed from HCO3- to SO42-. The dominant cation of confined water changed from Ca2+ to Na+, and the dominant anion remained unchanged as SO42-. The main supply source of both unconfined water and confined water was atmospheric precipitation, which was affected by evaporation, and the effect of evaporation of unconfined water was greater than that of confined water. The chemical composition of groundwater was mainly controlled by rock weathering and cation exchange. Na+, Ca2+, and Mg2+ were mainly derived from the dissolution of evaporative salt rock and silicate salt rock. NO3- was mainly derived from agricultural fertilizers, human and animal manure, and domestic sewage. Leaching and enrichment （F1）, agricultural activity and primary geological activity （F2）, and industrial activity （F3） were the main factors affecting groundwater chemistry in the study area, and the contribution rates were 58.41%, 18.12%, and 9.12%, respectively.

Patterns of spatiotemporal variations in the hydrochemistry and controlling factors of bedrock aquifers in the northern region of the Linhuan mining area

Systematically studying the hydrochemical evolution of bedrock groundwater in mining areas during mining process is crucial for effective groundwater resource management and coal mine production. The spatiotemporal characteristics and hydrochemical evolution patterns of the Permian fractured sandstone aquifer (PA) and the Carboniferous Taiyuan Formation limestone aquifer (CTA), both of which are directly associated with coal mining in the northern Linhuan mining area, China, were investigated using multivariate statistical analyses, hydrochemical graphical methods, ion ratio analysis, and a conceptual model. 72 groundwater samples, collected before and after mining, were classified into four groups by hierarchical cluster analysis (HCA). Principal component analysis (PCA) and ion ratio analysis indicated that water-rock interactions involve mineral dissolution (carbonates, gypsum, dolomite, silicates), cation exchange, and common ion effects. Hydrochemical evolution is influenced by bedrock paleotopography, aquifer hydraulic conductivity, and mining drainage. Paletopographic differences significantly influence water-rock interactions and spatial variability in hydrochemistry, with ion concentrations in groundwater increasing as paleotopographic elevation decreases. The pattern of hydraulic conductivity reflects the control exerted by variations in aquifer characteristics on mineral dissolution, leading to minor changes in hydrochemical characteristics. Mining activities disrupt the aquifer's reducing environment, resulting in a significant increase in groundwater SO42− concentration. These findings provide insights and a solid theoretical foundation for studying the hydrochemical variations patterns of groundwater and these control mechanisms in the hidden coal fields of North China.

Hydrochemical variation characteristics and driving factors of surface water in arid Areas—a case study of Beichuan River in Northwest China

Examining the chemical properties of river water and the controlling factors is crucial for devising efficacious strategies in water resources management and ecological conservation. This study investigates the hydrochemical characteristics and driving factors of the Beichuan River in the arid region of Northwest China. Surface water samples were collected during wet and dry seasons, and analyzed using hydrochemical diagrams, mathematical statistics, and principal component analysis (PCA). The results show that the pH value of Beichuan River is generally weakly alkaline, the main hydrochemical types are HCO3-Ca, and the average TDS are 224 mg/L and 236 mg/L respectively, which are higher than the world average level (115 mg/L). The seasonal variation of hydrochemical components is mainly controlled by rainfall, showing that the concentrations of Na+, Cl− and NO3− in the wet season are higher than those in the dry season, while the concentrations of other chemical components show an opposite trend, while the spatial variation is mainly controlled by human activities, and the concentrations of hydrochemical components show a gradual increasing trend from upstream to downstream, especially Na+, Mg2+, Cl− and NO3−. Rock weathering is the key natural factor controlling the Hydrochemical Composition of Beichuan River. Na+ and Cl− are mainly from the dissolution of silicate, Ca2+ and Mg2+ are mainly from the weathering of carbonate rocks and silicate, and SO42- is mainly from the dissolution of evaporite. It is noted that human activities, especially domestic sewage and agricultural runoff, contribute significantly to NO3− in the water body. PCA identified rock weathering and agricultural runoff as major wet-season factors, while domestic sewage predominantly affects the dry season. This study can provide a scientific basis for the rational development of water resources and ecological environment protection in arid areas.

Geological influence on groundwater quality in volcanic aquifers of Eastern Mount Cameroon, West of the Penda Mboko River

This study explores the utility of silica concentration in deciphering geological controls and hydrogeochemical processes affecting groundwater quality in Mount Cameroon’s volcanic terrain. Fifty water samples from wells, boreholes, springs, and rivers were analysed for hydrochemical properties (EC, pH, temperature, TDS) and major ion concentrations (Ca2+ > Mg2+ > K +> Na+ and HCO3− > Cl −> NO3− > SO42−). The groundwater exhibits low mineralization, with a dominance of Ca2+, Mg2+, HCO3−, and SiO2, reflecting minimal water–rock interaction and short residence times. Spatial variations in hydrochemistry suggest diverse water–rock interactions and potential mixing processes (76% of samples in rock dominance zone). Silica concentrations (5.8–58.7 mg/L) and estimated chalcedony temperatures (> 60 ℃ at five sites) indicated depths exceeding 1000 m. This research highlights silica’s effectiveness in tracking water–rock interactions across diverse geological settings, regardless of flow depth or interaction time variations. Mineral saturation indices pointed towards supersaturation with silicate minerals (quartz) but undersaturation with carbonates, sulphates, and halides. These findings contribute to a better understanding of groundwater evolution in Mount Cameroon, valuable insights into the hydrogeochemical processes shaping groundwater quality, aiding sustainable water resource management practices that can benefit local communities by ensuring a reliable source of freshwater. However, opportunities exist to improve future studies and water resource management. For a more comprehensive understanding, future analyses should include a broader range of geochemical tracers, such as nitrate (NO3−) and phosphate (PO43−), to assess potential agricultural or anthropogenic contamination. The study also found elevated levels of chloride and sodium, suggesting potential anthropogenic influences on groundwater quality, such as agricultural practices and waste disposal.

Linking recharge water sources to groundwater composition in the Hindon subbasin of the Ganges River, India

Groundwater resources of the densely populated Indo-Gangetic Basin are under increasing pressure, not only from extensive groundwater abstraction, but also from contamination. In this study we aim to better understand how different recharge sources affect the hydrochemical and isotope composition of groundwater. We used the Hindon subbasin in Northern India as a case study. Recharge water sources and groundwater were analysed for hydrochemical variables and stable isotopes along a 50 km transect between the Yamuna and Ganges rivers. Groundwater samples were statistically clustered based on hydrochemical variables, and the spatial variation of the groundwater clusters was compared with recharge sources.Groundwater quality could be linked to both recharge from irrigation canal water as well as recharge from polluted river water of the Hindon and its tributaries. We could not directly link groundwater outside these related zones to their recharge source. However, we suspect that shallow polluted groundwater (< 40 m depth) is affected by recharge from agricultural areas and infiltration of municipal wastewater, whereas deeper unpolluted groundwater (40–80 m depth) originates from recharge by rain and river water under more pristine conditions. Our findings show that human activities significantly impact the quality of groundwater, as we found vertical recharge of clean irrigation canal water and polluted municipal, agricultural and river surface water (up to 40 m depth). At one location, groundwater at 75 m depth shows increased Cl, NO3 and SO4 concentrations, suggesting accelerated downward displacement of polluted shallow groundwater by pumping. Limited horizontal displacement was found. We present a conceptual model demonstrating the evolution from a previously unpolluted groundwater system discharging to the river, to a contemporary system with infiltration dominance of polluted river, municipal and agricultural water and local clean irrigation canal water. This model may be relevant for large parts of the Indo-Gangetic Basin.

Carbon emission from the Lower Ob River floodplain during spring flood

Carbon emission from Arctic rivers constitutes a positive feedback between the climate warming and C cycle. However, in case of rivers with extensive floodplains, the impacts of temporary water bodies and secondary channels on CO2 exchange with atmosphere, compared to the main stem and tributaries, remain strongly understudied. In order to quantify the relative role of various water bodies of the Arctic river basin in the C cycle, the hydrochemical variables and greenhouse gases GHG concentrations and fluxes were measured within the floodplain of the largest Arctic River, Ob, in its low reaches located in the permafrost zone. These included the main stem, secondary channels, tributaries and floodplain lakes sampled over a 900 km north-south transect (25,736 km2 of the main stem and adjacent floodplain area; 7893 km2 water surface) during peak of spring flood (May 2023). In addition to main stem and tributaries, providing less than a half of overall C flux, floodplain lakes and secondary channels acted as important factor of C emission from the floodplain water surfaces. Multi-parametric statistical treatment of the data suggested two main processes of C emission from the Ob River floodplain waters: terrestrial organic matter-rich flooded wetlands (fens) provided elevated pCO2, whereas the sites of possible groundwater discharge in the secondary channels decreased the CO2 fluxes due to more alkaline environments, rich in labile metals and anionic elements.Based on available high-resolution Landsat-8 images, which matched the period of field work, it was found that the total water coverage of the floodplain during spring 2023 was 30 % of overall territory, compared to 18 % during the baseflow. Based on chamber-measured CO2 fluxes (1.56 ± 0.47 g C-CO2 m−2 d−1), overall CO2 emissions during 2 months of the spring flood from the entire Lower Ob River floodplain water surfaces including the main stem amounted to 0.73 ± 0.25 Tg C. Diffuse CH4 flux represented <1 % of total C flux. The main stem of the Ob River accounted for 34 % and 18 % of CO2 and CH4 emissions, respectively, whereas the floodplain lakes provided 59 % and 50 % of CO2 and CH4 emission, respectively. Considering that the low reaches of the Ob River represent >70 % of total river basin floodplain, and that during some years, the entire floodplain can be covered by water, emissions from the river – if assessed solely from summer (July–August) measurements – can be at least 3 times underestimated. It is therefore important to account for extended water surface during high water levels on Arctic rivers when assessing global riverine C emissions.

Hydrogeochemistry of aquifers in the northern portion of the Lagoa Santa Karst Environmental Protection Area and surroundings, state of Minas Gerais, Brazil

The studied region, located in the central part of Minas Gerais state, Brazil, encompasses the northern portion of the Lagoa Santa Karst Environmental Protection Area (APA) and adjacent areas to the west. It is notable for harboring important karstic aquifers and archaeological and paleontological sites of global significance. The research aims to define the key parameters that characterize the waters of the aquifers, quantifying their most frequent maximum and minimum concentrations. For this purpose, water sampling and hydrochemical analyses were conducted at 51 water points. Hierarchical clustering analysis facilitated the association of samples with aquifer units. Utilizing Piper and Stiff diagrams, boxplot graphs, and proportional symbol maps enabled the classification of water and the determination of its hydrochemical signatures. All sampled waters are bicarbonated, with 87% being calcic. Waters associated with metacalcareous rocks exhibit higher concentrations of calcium (Ca2⁺), bicarbonate (HCO₃⁻), electrical conductivity (EC), total dissolved solids (TDS), and hydrogenionic potential (pH) compared to waters associated with non-carbonate rocks. Waters from the Lagoa Santa Member differ from those of the Pedro Leopoldo Member by higher concentrations of Ca2⁺ and HCO₃⁻ and slightly lower concentrations of sodium (Na⁺), magnesium (Mg2⁺), and silica (SiO₄2⁻). Non-carbonate waters related to granite-gneisses differ from those associated with metapelites by slightly higher concentrations of potassium (K⁺), sodium (Na⁺), silica (SiO₄2⁻), and barium (Ba2⁺). Additionally, hydrochemical variations have been linked to the regional groundwater flow (from west to east). The results obtained have enabled advancements in the hydrogeochemical understanding of the study area and can be valuable for comparative studies in other karst regions, contributing to more effective water resource management aimed at environmental conservation and water sustainability, a growing global concern.

The Limited Effect of Reduced Typhoon Frequency on Stream Hydrochemistry in a Subtropical Forest Watershed

AbstractTropical cyclones are often accompanied by large amount of precipitation potentially impacting stream hydrochemistry. Global warming is altering typhoon disturbance regime. Little is known about how cyclone changes, especially cyclone‐frequency reduction may affect stream hydrochemistry. In this study, we compared water and nutrient input via precipitation and output via streamflow between a frequent‐typhoon period (2013–2017), with 1.2 typhoon yr−1, and a no‐typhoon period (2018–2022) at a long‐term monitoring site, the Fushan Experimental Forest of Taiwan. Precipitation and streamflow quantities were not different between the two periods because typhoons increased the fluctuation but not the mean of monthly precipitation in the major typhoon months (July–September). Inputs of Mg2+, NO3−, and SO42− via precipitation were greater in the frequent‐typhoon period than the no‐typhoon period while inputs of other ions were not different between the two periods. Only the output of Mg2+ was different between the two periods, greater in the frequent‐typhoon period. Output/input ratio of NO3− was greater in the no‐typhoon period than the frequent‐typhoon period despite the greater input in the frequent‐typhoon period, while no differences were found for others. Increases in mineralization rates due to warming is suggested to be the cause of the greater NO3− output/input ratio during the no‐typhoon period. Relationships between stream discharge and ion export were similar between the two periods both with and without removing typhoon events. The limited variation in hydrochemistry between periods of contrasting cyclone activities suggests high resilience of the undisturbed subtropical forests to changes in cyclone frequency at the decadal scale.

Evolution origin analysis and health risk assessment of groundwater environment in a typical mining area: Insights from water-rock interaction and anthropogenic activities

Coal mining changes groundwater environment, results in deterioration of water quality and endangering human health in the mining area. However, the comprehensive study of groundwater evolution and its potential impact in mining area is still insufficient. In this study, 95 groundwater samples were collected from 2019 to 2020 in a typical mining area of China. Ion ratio coefficients, isotopic tracing technology, Entropy-weighted water quality index (EWQI) and human health risk assessment model (HHRA) were applicated to investigate the hydrochemical variation reasons, groundwater quality and its potential health risk in the study area. Results showed that the groundwater hydrochemical types changed from HCO3∙SO4–Ca∙Mg type to SO4–Ca∙Mg and SO4∙Cl–Ca∙Mg type. Water-rock interaction, agricultural activities, manure and sewage input, precipitation and evaporation controlled the groundwater hydrochemical composition. Groundwater quality showed a trend of fluctuation with an average EWQI of 59.23, 68.92, 63.75, 58.02 and 64.92, respectively. 91.6% of the water samples was fair and acceptable for drinking. The groundwater health risk of nitrate in the study area ranged from 0.03 to 17.80. Infants had the highest health risk and nitrate concentration was the most sensitive parameter. The results will present a comprehensive research of groundwater evolution and potential impacts through a typical mining area example. Thereby offering valuable insights into the influencing factors identification, hydrochemical processes evolution, protection and utilization of groundwater in global mining areas.

Comparative assessment of hydrochemical characterization and groundwater quality for irrigation in an autochthonous karst aquifer with the support of GIS: case study of Altinova, Turkey

This study aims to present a comparative assessment of hydrochemical characterization and groundwater quality in karst aquifers with the support of GIS which is essential to correlate the source of water with climate and geology, and to evaluate suitability of water for various uses. The study area is the Altinova region in Turkey where intensive agricultural activities prevail and travertine covers 85% of the study area. A total of 25 groundwater wells were monitored by seasonal field measurements and extensive water quality analyses for a period of one year to establish correlation between groundwater quality, its source, regional climate, and geology. A comprehensive analysis was conducted to assess the groundwater's suitability for irrigation based on electrical conductivity, sodium adsorption ratio, sodium percentage, magnesium hazard, permeability index, residual sodium bicarbonate, Kelly’s ratio, and an irrigation water quality (IWQ) index. This multi-parameter evaluation was further integrated with geospatial analysis using ArcGIS, providing a detailed spatial understanding of hydrochemical variations across the area. Major cations and anions dominance were identified as Ca2+ > Na+ > Mg2+ > K+ and HCO3− > Cl− > SO42−, respectively. Spatial mapping identified high concentrations of Ca2+, TDS, TH, and SO42− in non-karstic areas, occasionally exceeding WHO guidelines. Nitrate concentrations displayed varied spatial distribution. The SAR values generally matched C2-S1 and C3-S1 classes, suggesting medium to high salinity risks and low sodium presence. Based on the IWQ index and observed correlations with total dissolved solids, the groundwater in Altinova’s karstic aquifer is considered suitable for irrigation, with salinization largely due to ionic interactions and geology. The presented comparative assessment provides a holistic approach for understanding hydrochemical characteristics of karst aquifers, and analyzing the impacts of natural factors and anthropogenic pollution sources on groundwater quality.

Estimating groundwater geogenic arsenic contamination and the affected population of river basins underlain mostly with crystalline rocks in Ghana

Arsenic is a human carcinogen and contributes to the incidences of cancer, diabetes, and skin diseases in the exposed populations. Therefore, its occurrence in drinking water is of public health concern worldwide, especially in the Tano, Pra, and Ankobra River Basins in Ghana. The metasediments and metavolcanic formations which underlie these basins (42,092.5 km2) host arsenic sulphide minerals that are a source of arsenic contamination of the weathered and fractured aquifers that serve as drinking water supply to most of the population (∼9.8 million), especially in the rural areas. A random forest machine learning method and partial dependence plots were applied to maps of spatially continuous environmental factors (fault density, surface bulk density, coarse fragment and soil pH; and sub-surface silt and soil pH) and hydrochemical variables, respectively, and arsenic measurements from wells (n = 229) which included 57 new datasets of which 7.86 % exceeded the 10 µg/L to develop arsenic prediction models for the basins at thresholds of 1 µg/L, 5 µg/L, and 10 µg/L. Fault density and coarse fragments were more reliable contributors to the models. A partial dependence plot and Spearman's rank correlation analysis showed a significant positive correlation (p < 0.01) between arsenic enrichment and HCO3−, pH, Fe, and Mn, except NO3− in groundwater. Arsenic hotspots occurred in urban districts in the Ashanti Region and known gold-mining areas in Nzema, Obuasi, Prestea, and Tarkwa. Spatially, arsenic contamination in groundwater covered 49.44 % of the land area of the basins. By cross-referencing population density estimates and the arsenic hazard map,15.8 % of the population is exposed to arsenic-contaminated groundwater in the basins. The hazard model will facilitate efforts to reduce rural poverty and protect public health by delivering potable water in Ghana. The hazard models apply to crystalline terrain in other sub-Saharan African countries.

Evaluating arsenic contamination in northwestern Bangladesh: A GIS-Based assessment of groundwater vulnerability and human health impacts

One of the biggest environmental worries in the world today is the risk of arsenic (As) contamination in groundwater. The Atomic Absorption Spectrometer (AAS) was used in this work to assess the As content in groundwater samples from 38 shallow (27 m) tubewells in northwest Bangladesh to determine the existing situation, potential source(s), and likely health risk of As and other important water quality parameters. The range of arsenic concentrations (μgL−1) was troublesome and greater than the WHO recommended level for drinking water, ranging from 0.50 to 164 (mean ± SD: 20.22 ± 36.46). In groundwater, the concentrations of Fe, and Mn vary from 0.04 to 52.75 mgL−1 (mean ± SD: 4.23 ± 9.68), and 0.23 to 3.27 mgL−1 (mean ± SD: 1.10 ± 0.67). The obtained groundwater samples have pH values ranging from 5.9 to 7.1, which indicates a somewhat acidic to neutral character. Major cations have an average abundance that is as follows: Ca2+ > Mg2+ > Na+ > K+, while major anions have an average abundance that is as follows: HCO3− > Cl− > SO42− > NO3−; Ca2+ and HCO3− are the main cation and anion, respectively. The groundwater in the Rajarampur village was deemed unfit for drinking or irrigation based on analyses of water quality performed using the entropy water quality index. The Ca–HCO3 type of water, in which Ca2+ and HCO3− are the main positive ions and negative ions, is suggested by the Piper tri-linear diagram. It was discovered that silicate weathering regulates the hydro-geochemical activities in groundwater using a bi-variate examination of several hydro-chemical variables. Four major clusters were observed for the water sample. According to reductive dissolution processes and principal component analysis, the arsenic in groundwater is geogenic in origin. Arsenic is discharged from sediment to groundwater by reductive dissolution of FeOOH and MnOOH, as shown by the modest connection between As, Fe, and Mn. The United Nations Environmental Protection Agency's (USEPA) suggested value for probable cancer risk assessment was 10−6, however the probable cancer risk assessment found a higher value, indicating that the population in the study region was at high risk for cancer. Remedial measures for arsenic mitigation include removing arsenic from groundwater after it is extracted, searching for alternative aquifers, and implementing various water-supply technologies such as dugwells, deep tubewells, pond-sand filters, and rainwater harvesting systems.

Hydrotectonics of Grand Canyon Groundwater

The Grand Canyon provides a deeply dissected view of the aquifers of the Colorado Plateau and its public and tribal lands. Stacked sandstone and karst aquifers are vertically connected by a network of faults and breccia pipes creating a complex groundwater network. Hydrochemical variations define structurally controlled groundwater sub-basins, each with main discharging springs. North Rim (N-Rim), South Rim (S-Rim), and far-west springs have different stable isotope fingerprints, reflecting different mean recharge elevations. Variation within each region reflects proportions of fast/slow aquifer pathways. Often considered perched, the upper Coconino (C) aquifer has a similar compositional range as the regional Redwall-Muav (R-M) karst aquifer, indicating connectivity. Natural and anthropogenic tracers show that recharge can travel 2 km vertically and tens of kilometers laterally in days to months via fracture conduits to mix with older karst baseflow. Six decades of piping N-Rim water to S-Rim Village and infiltration of effluent along the Bright Angel fault have sustained S-Rim groundwaters and likely induced S-Rim microseismicity. Sustainable groundwater management and uranium mining threats require better monitoring and application of hydrotectonic concepts. ▪Hydrotectonic concepts include distinct structural sub-basins, fault fast conduits, confined aquifers, karst aquifers, upwelling geothermal fluids, and induced seismicity.▪N-Rim, S-Rim, and far-west springs have different stable isotope fingerprints reflecting different mean recharge elevations and residence times.▪The upper C and lower R-M aquifers have overlapping stable isotope fingerprints in a given region, indicating vertical connectivity between aquifers.▪S-Rim springs and groundwater wells are being sustained by ∼60 years of piping of N-Rim water to S-Rim, possibly inducing seismicity.

MULTIVARIATE DATA ANALYSIS TO ASSESS GROUNDWATER HYDROCHEMICAL CHARACTERIZATION IN RAWADANAU BASIN, BANTEN INDONESIA

A multivariate statistical technique of principal component analysis (PCA) and hierarchical cluster analysis (HCA) has been applied to identify and classify the various water sources that comprise the Rawadanau Basin. The data collection includes 60 samples taken during the dry (29 samples) and the rainy season (31 samples) in tropical regions. Sources of sampled water include dug wells, rivers, cold springs, and hot springs. Water chemistry measurable variables include field data (T, pH, EC), major ions (Na+, K+, Ca2+, Mg2+, Cl-, HCO3 -, SO4 2-), SiO2 , Fetotal, Mn, and stable isotopes of water (δ2H, and δ18O). The correlation of the concentration of water chemistry shows changes in the rainy season to Fetotal and Mn. Interpretation based on HCA using the dendrogram based on the chemical elements of water produces two clusters. Cluster A reflects an unconfined aquifer and bicarbonate type. Meanwhile, cluster B is a chloride type from the confined aquifer and does not change in different seasons. The PCA results show that the three-component matrix accounts for 86.12% of the data structure describing the Rawadanau Basin water sources that volcanic rocks affect and strongly correlate with Na+, K+, Ca2+, and Mg2+. PC1 has a high positive value for hydrochemical composition, indicating that lithology influences the kind of water. PC2 has a positive value for the stable isotope (δ18O and δ2H), meaning it is the main water source in Rawadanau. PC3 has a positive value for elevation and a negative for longitude, indicating a recharge area influenced by geological factors and is correlated with geothermal influences and volcanic rocks. This multivariate analysis can identify components and clusters of hydrochemical variables that have not been determined in previous studies.

Metabolic processes control carbon dioxide dynamics in a boreal forest ditch affected by clear-cut forestry

Boreal watercourses are large emitters of carbon dioxide (CO2) to the atmosphere. For forestry intensive areas of the Nordic and Baltic countries, a high share of these watercourses are man-made ditches, created to improve drainage and increase forest productivity. Previous studies have suggested that terrestrial sources sustain the CO2 in these ditches and variability in hydrology is the main temporal control. However, few studies have explored ditch CO2 dynamics and its associated controls in catchments being exposed to forest harvest. An altered hydrology, increased nutrient export and light availability following forest harvest are all factors that potentially can change both levels, dynamics, and source controls of ditch CO2. Here, high-frequency (30 min) CO2 concentration dynamics together with other hydrochemical variables were studied in a forest ditch draining a fully harvested catchment in the Trollberget Experimental Area, northern Sweden. We collected data during the snow-free season from May to October. Ditch CO2 concentrations displayed a clear seasonal pattern with higher CO2 concentrations during summer than in spring and autumn. Concentrations ranged from 1.8 to 3.5 mg C L−1 (median: 2.4 mg C L−1, IQR = 0.5 mg C L−1). Strong diel cycles in CO2 developed during early summer, with daily amplitudes in CO2 reaching up to 1.1 mg C L−1. These pronounced daily cycles in CO2 were closely related to the daily sum of shortwave radiation and water temperature. Variations in hydrology had generally a low impact on the CO2 dynamics but did vary among seasons and between individual hydrological events. It was evident from our study that growing season CO2 concentrations in a forest ditch affected by clear-cut harvest were highly variable and mainly controlled by light and temperature induced metabolism. These high dynamics and the associated controls need to be considered when scaling up ditch CO2 emissions across boreal landscapes affected by intensive forestry.

Water quality and health risk assessment in the Gandaki river basin, central Himalaya, Nepal

Public health is at threat due to chemical contaminants in drinking water which may have direct health concerns. The suitability of water for health is primarily governed by the mineral constituents present in the water. The present study was carried out to evaluate the water quality and associated health risks in the Gandaki River Basin (GRB) in Central Himalaya, Nepal considering hydrochemical variables such as total dissolved solids (TDS); major cations (Ca2+, Mg2+, K+, and Na+); major anions (Cl-, NO3-, SO42-, and HCO3-) and trace metals (As, Cu, Mn, Ni, Pb, Zn, Ba, Cr, Li and Sr) in spatiotemporal levels. Water Quality Index (WQI), Health Risk Assessment (HRA), and Cancer Index (CI) were analyzed to evaluate the overall quality of water in the GRB. The results revealed that all the examined variables were within the National Guidelines recommended for domestic uses. Moreover, the results revealed that concentrations of TDS, major ions, and trace metals showed significant seasonality and the WQI values were found to be 36.38, 23.77, and 30.36 in pre-monsoon, monsoon, and post-monsoon, respectively indicating better water quality in the monsoon season. Additionally, CI analysis of the selected trace metals such as As, Cr and Pb indicated relatively low cancer risk in the river water during all the seasons. The hazard quotient (HQ) dermal values of all the elements were &lt; 1, signifying the little or no adverse effects via a dermal path, while HQ ingestion values of Ba, Li, Sr, and Zn were found to be &gt;1 during all the seasons indicating their possible threat via ingestion path. This study provides a useful database and suggests regular assessment and, also appropriate policy formulations for safeguarding the water bodies in the Himalayas.

Comparison on distribution and sources of typical major and toxic trace elements in various glacial watersheds of the northeast Tibetan Plateau

Toxic and major elements, such as As and Fe, in watersheds can significantly impact the surrounding water environment and ecosystem. Thus, in this study, we conducted an investigation into the origins and spatial distribution of typical toxic trace elements (As and Mn) and crustal major elements (Al, Fe, and Ti) in suspended particulate matter (SPM) across various glacial watersheds located at different elevations in the northeastern Tibetan Plateau (NETP) from June to July in 2017. The results revealed that the mean value of each element followed the order of abundance in the samples, with Al having the highest mean value at 21307 µg/L, followed by Fe at 13366 µg/L, Ti at 1520 µg/L, Mn at 245 µg/L, and As at 66.6 µg/L. Moreover, our study identified high content of these elements from the Dabanshan Snowpack, Laohugou Glacier No.12, and Yuzhufeng Glacier in the upper reaches of the basin, which were found to be 9.9, 10.2, and 19.4 times higher, respectively, than that of the upper reaches of the Heihe River. We found that As and Mn exhibited clear indications of anthropogenic influence on a local and regional scale. The calculated enrichment factor (EF) demonstrated a significant As enrichment (EF>100) in the Qiyi and Lenglongling Glaciers, possibly resulting in the release of upstream glacier melt and anthropogenic-derived As deposition. Our findings suggested that the upstream region was primarily linked to glacier meltwater discharge. In contrast, the middle and lower reaches of the basin exhibited a more pronounced influence from local human activities. Based on the findings, the water environment of the glacier watershed appears to be in good condition overall. However, the presence of elevated levels of As element in the water system can be traced back to both anthropogenic and natural factors. As a result, ensuring the safety of the water supply for nearby residents is a matter of utmost concern. This study provides a comprehensive examination of hydrochemical variations and the overall water environment of high-altitude glacier basins in the NETP, offering valuable insights into the topic.

Hydrochemistry of Kupinde Lake at the Lesser Himalaya in Karnali Province, Nepal

Hydrochemical assessment of the freshwater lakes provides important insights into the sources of dissolved ions, geochemical processes, and anthropogenic activities taking place in the environment. This study focuses on the assessment of hydrochemistry and water quality of Kupinde Lake, Karnali Province, Nepal. Surface water samples were collected from 24 different locations of the lake in October 2021 and analyzed for 18 different physico-chemical parameters. The pH, temperature, electrical conductivity and total dissolved solids were measured on-site, and concentration of major ions (Ca2+, Mg2+, Na+, K+, NH4+, HCO3-, Cl-, SO42-, PO43-, NO3-), including hardness and free CO2 were measured in the laboratory. The results revealed that lake water was alkaline with abundance of the major ions in the following order: Ca2+ &gt; Mg2+ &gt; Na+&gt; K+ &gt; NH4+ and HCO3- &gt; Cl- &gt; SO42- &gt; PO43- &gt; NO3- for the cations and anions, respectively. The lake water was dominated by Ca-HCO3, indicating calcium carbonate dominated lithology in the area. Gibb’s plot and Piper diagram illustrated rock weathering as the most dominant process in controlling the hydrochemistry of the lake basin. The suitability of water for drinking and irrigation was determined using geochemical indices and WHO standards. The results indicated that the Kupinde Lake water could be used for drinking and irrigation purposes in terms of measured hydrochemical variables.

Evaluating the relationship between groundwater quality and land use in an urbanized watershed.

Understanding the impact of urbanization on groundwater quality is critical. Effective water management requires understanding the relationship between land use and water quality. The study's goals were to compare the effects of land use, identify the types of land that impact hydrochemistry, and define how different land use affects water quality. For this purpose, the comparative relationship between groundwater quality, land use classes and landscape metrics were established for the years 2016 and 2021. Water samples were collected from 42 wells, and different hydro-chemical variables were considered to calculate the water quality index (WQI). The WQI value in 2016 ranged from 26.49 to 151.03 and 29.65 to 155.62 in 2021. The results indicate that the water quality in most parts of the study area is moderate for drinking and domestic purpose use. The google earth engine platform wasused and radiometrically corrected and orthorectified Sentinel-2 satellite images were processedto classify land use classes for selected years. Five buffer zones were established within a 2-km watershed along each well site, and the effects of land use types and landscape metrics on water quality in the buffer zones were analyzed. Results revealed that the effects of land use types on water quality were mainly reflected in buffer 1 (B1), buffer 4 (B4), buffer 5 (B5) in 2016 and B1, buffer 3 (B3), and B5 in 2021. The impacts of landscape-level metrics on water quality are mainly reflected in buffer 2 (B2) and B3 in 2021, while at the class-level, they are mainly reflected in B1 and B4 in 2021. The redundancy analysis revealed that different hydro-chemical variables behaved differently with the land use classes and landscape metrics in the various buffer zones.

Assessing Sustainable Development of Deep Aquifers

AbstractDeep groundwater aquifers are exploited for a variety of purposes. In general, impermeable rock layers protect these aquifers from anthropogenic influences. As such, they are a last resort for groundwater in a pre-industrial state, and a crucial resource in cases of emergency, such as floods contaminating shallow groundwater. The EU Water Framework Directive (WFD) provides the regulatory framework to protect its quality and quantity. Recent monitoring of the hydrochemical state of Upper Jurassic wells in Bavaria and Austria has shown fluctuations that were connected to new exploitation activities and might indicate an unsustainable development of the aquifer. We propose a new workflow in accordance with the WFD which uses clustering algorithms to assess these fluctuations. Our data consists of 5 to 42 hydrochemical analyses per well with yearly sampling intervals spanning up to 30 years. From the cluster analysis we derived thresholds for two corridors: Natural Range Corridor (NC) and Action Corridor (AC). While the NC represents a well-specific natural variation range, the AC hints towards unsustainable development and should trigger a detailed (re)assessment. To show the potential of the new method, the workflow was applied to two wells with different geological characteristics. Distinct fluctuation events were clearly recognized and can be used in the context of an early warning system, such that malign hydrochemical variations can be detected before they become legally problematic to well operators. Our workflow thus provides a novel, robust, and reproducible method to assess the grade of sustainability at which a well is exploited and ensures a good status of a unique and important resource.