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Water in arid and semi-arid environments is characterized by the presentation of complex interactions, where dissolved chemical species in high concentrations have negative effects on the water quality. Radon is present in areas with a high uranium and radium content, and it is the main contributor of the annual effective dose received by humans. The objective of this study was to evaluate concentrations of 222Rn and the water quality of spring waters. Water was classified as calcium sulfated and sodium sulfated. Most of the water samples with high radon concentrations presented higher concentrations of sulfates, fluorides, and total dissolved solids. 222Rn concentrations may be attributed to possible enhancement of 226Ra due to temperature and salinity of water, as well as evaporation rate. In 100% of the sampled spring waters the 222Rn levels exceeded the maximum acceptable limit which is proposed by international institutions. Aridity increases radiological risk related to 222Rn dose because spring waters are the main supply source for local populations. The implementation of environmental education, strategies, and technologies to remove the contaminants from the water are essential in order to reduce the health risk for local inhabitants.

We investigate the occurrence of anomalous (non‐Fickian) transport in an hydrological catchment system at kilometer scales and over a 36‐year period. Using spectral analysis, we examine the fluctuation scaling of long‐term time series measurements of a natural passive tracer (chloride), for rainfall and runoff. The scaling behavior can be described by a continuous time random walk (CTRW) based on a power‐law distribution of transition times, which indicates two distinct power‐law regimes in the distribution of overall travel times in the catchment. The CTRW provides a framework for assessing anomalous transport in catchments and its implications for water quality fluctuations. Plain Language Summary Rain falling on an hydrological catchment, and chemicals dissolved in the rain, can follow circuitous pathways below the ground surface until they reach a stream outlet that drains the catchment. Dissolved chemicals can diffuse into lower conductivity regions within the subsurface, and chemicals can also be transported in relatively fast pathways. We investigate a unique data set that monitors chemical transport over kilometer scales, and over a long, 36‐year duration. We develop a mathematical framework to describe the transport and retention of chemical tracers in a catchment, and their arrival times to a draining outlet. Solutions of the equations exhibit characteristic features of tracer concentration variations, and offer a means to characterize and quantity catchment response to chemical inputs. Key Points An hydrological catchment system at kilometer scales is shown to exhibit anomalous (non‐Fickian) transport over a 36‐year period A continuous time random walk suggests two distinct power‐law regimes in the distribution of overall catchment travel times In the catchments considered here, preferential flow appears to occur at all length and time scales

Denitrifying woodchip bioreactors are passive, low-tech systems primarily designed to remove nitrate from shallow ground waters as well as point source discharges. Despite their capacity to achieve constant nitrate removal over several years, natural aquatic environments may be affected by the leaching of dissolved organic matter (DOM) from fresh woodchips during start-up. Simple on-site measures might reduce the woodchip leachate during start-up and thus add to the overall environmental sustainability of woodchip bioreactor installations. The aim of the study was to investigate whether foam fractionators could provide an effective solution. Water was flowed through fresh laboratory-scale woodchip bioreactors and recirculated through foam fractionators for 11 days. The bioreactors removed nitrate but increased phosphate and ammonia, which were not effectively removed via foam fractionation. However, foam fractionation did remove 37.8 ± 4.7% of the dissolved chemical oxygen demand (CODdiss) leached during the first 11 days of operation. Fluorescence spectroscopy revealed that the DOM composition differed between the foam and water, where the foam fraction contained higher amounts of DOM associated with the highest bioavailability and hence the greatest potential environmental impact. Optimised foam fractionators could therefore help to reduce the environmental impact of DOM leachate from woodchip bioreactors during start-up.

The evaluation of irrigation suitability plays a crucial role for the socio-economic development of the society, especially in the region of Sundarban. For sustainable agricultural practices, groundwater quality must be suitable for irrigation; otherwise, it can degrade soil and diminish crop yield. The entropy information theory, several irrigational indices, multivariate statistics, GIS, and geostatistics are used in this work to evaluate the geographical distribution and quality of groundwater in the Indian Sundarban region. In total, 33 groundwater samples were collected in 2018 (April and May), and they were evaluated for major cations, anions, as well as other parameters like electrical conductivity (EC), soluble sodium percentage (SSP), potential salinity (PS), total dissolved solids (TDS), Kelly ratio (KR), sodium absorption ratio (SAR), permeability index (PI), residual sodium carbonate (RSC), magnesium hazard (MH), and residual sodium bicarbonate (RSBC). The overall trend of the principal cations and anions is in the sequence of Na +  ≥ Mg 2+  ≥ Ca 2+  ≥ K 2+ and HCO 3 −  ≥ Cl −  ≥ NO 3 −  ≥ SO 4 2−  ≥ F − , respectively, whereas the spatial variation of %Na, SAR, RSBC, and MH demonstrate very poor irrigation water quality, and spatial variation of KR, RSC, SSP, PI, and PS signifies that the irrigation water quality is excellent to good. In order to identify the specific association and potential source of the dissolved chemical in the groundwater, statistical techniques like correlation and principal component analysis were also employed. The hydrochemical facies indicates that mixed type makes up the bulk (51.51%) of the water samples. Following the Wilcox plot, more than 75% of the water samples are good to doubtful; however, by the US salinity hazard map, roughly 60.60% of the samples had high salinity (C3-S1 zone). The EWQII reports that no samples fall into the very good (no restriction) category, whereas 30.30%, 30.30%, and 39.40% of the sample wells record good (low restriction), average (moderate restriction), and poor (severe restriction) irrigation water quality, respectively. Based on this study, the bulk of the groundwater samples taken from the study area are unsuitable for cultivation. The findings of this study will also help decision-makers develop adequate future plans for irrigation and groundwater resource management.

In mountainous watersheds, floodplain sediments are typically characterized by gravel bed layers capped by an overlying soil unit that serves as a hotspot for biogeochemical reactivity. However, the influence of soil biogeochemistry on gravel bed underflow composition remains unclear, especially during hydrological transitions that alter the vertical connectivity between overlaying soils and the underlying gravel bed. This study investigates these dynamics by measuring hydraulic gradients and water compositions over three hydrological years in a typical mountainous, low‐order stream floodplain in the Upper Colorado River Basin. Results indicate that the timing of hydrological conditions strongly influences the vertical exchanges that control water quality. Specifically, during flooding events such as beaver ponding, that induce downward flushing of the soil, anoxic conditions prevalent in the biogeochemically active soil are transferred downstream via gravel bed underflow. Conversely, snowmelt and drought conditions increase oxic conditions in the gravel bed due to diminished hydrological connectivity with the overlying soil. To compare water quality response to hydrological transitions across similar floodplain environments, we propose a conceptual model that quantifies the inundation‐induced flushing of soil porewater to measure solute exchange efficiency with the gravel bed solute convergence efficiency (SCE). This model provides a framework for quantifying biogeochemical processes in hydrological underflow systems, which is critical for water and elemental budgets in these globally important mountainous ecosystems. Plain Language Summary Mountains are important sources of freshwater for humans and ecosystems. They are however increasingly impacted by climate change. In this paper, we investigate how changes in water availability (droughts, snowmelt, inundations) can cascade into changes in water quality (concentrations of dissolved chemical elements). We show that in mountain valleys, the zone of contact between the soil and the underlying gravel bed aquifer is important for water quality. Chemical elements from the soil can be flushed down into the gravel bed aquifer, then transported by groundwater to the stream. Chemical elements from the soil can also react with chemical elements present in the aquifer. Our research can be used to better predict the water and elemental budgets in these important mountainous systems. Key Points Soil / gravel bed connectivity in floodplains is important for water quality Snowmelt and drought both reduce soil / gravel bed connectivity Beaver ponding increases downward flushing to gravel bed unit

The geochemistry of rivers draining into the Arabian Sea has received lesser attention than their eastern counterparts draining into the Bay of Bengal. The major ion concentrations in the third-major river (Mahi) draining into the Arabian Sea have been reported. Hydrochemistry of seasonally collected samples ( n =  67) during two consecutive years reveals that the average solute export and the cationic charges are ~ 1.2 and ~ 4 times their corresponding global average values. Generally, lower solute levels (except Ca) in the rainy season reflect the dilution effect. In contrast, the higher intensity of carbonate weathering out-weighing the dilution effect, aided by CaCO 3 precipitation in summer, dominates the Ca dynamics. Chemical weathering in the catchment is mediated predominantly by carbonic acid, as evident from the alkalinity/(Ca + Mg) and SO 4 /(Ca + Mg) molar ratios. Using a forward model, the estimated average contributions from various sources to the cationic composition are atmospheric (5 ± 1%), evaporites and soil salts (27 ± 9%), silicates (39 ± 12%), and carbonates (29 ± 13%). Runoff exerts the dominant control on the weathering rates, with the best estimated average silicate (11 t km −2 yr −1 ), carbonate (22 t km −2 yr −1 ), and evaporite and soil-salt (8 t km −2 yr −1 ) weathering rates, which sums up to a dissolved chemical flux of ~ 41 t km −2 yr −1 . The lower-bound estimate of CO 2 consumption by silicate weathering of the Mahi basin is ~ 2.8 × 10 5  mol km −2 yr −1 , translating into CO 2 consumption of ~ 9.7 × 10 9  mol yr −1 . This is ~ 0.08% of the global average value (by silicate weathering) and is disproportionately higher than its fractional continental drainage area (~ 0.03%). Integrating the data of Mahi with those available for the other two major rivers (Narmada & Tapti), this study underscores the prominent role of these rivers in supplying solutes to the Arabian Sea and controlling the biogeochemistry of the Arabian Sea.

The multinational Paraná River (drainage basin ~ 2.6 × 106 km2; current discharge ~ 540 km3 y−1) has in its middle and lower stretches a long (~ 1200 km) and wide (~ 30 – 50 km) flood valley mantled with riparian vegetation and fully carved with lentic and lotic water bodies. Most of the wetland (~ 50000 Km2) holds myriad water bodies which, following the seasonal variation of the prevailing discharge regime, exchange water, dissolved chemical species, sediment, and biological materials with the Paraná’s main stem. Exceptional hydrological events (e.g., strong El Niño-triggered floods) sporadically inundate almost totally the flood valley’s expanse. The examination of chemical data collected in the main channel during the 1982–1983 event showed: (a) TDS was diluted to almost ¼ of the original concentration during the high flood; (b) water pH decreased to ~ 6.5, and CO2 partial pressure increased up to ~ 16000 ppmv during the overbank stage and afterwards; (c) throughout the event water remained within the medium dilute/dilute water types (375 > TZ+ > 1500 µeq L−1); and (d) dissolved inorganic carbon (DIC)—along with other variables—reached the highest concentrations in the descending limb, when the floodplain was drained. Dissolved organic carbon (DOC) showed an uneven variability pattern, seemingly unrelated to DIC, but definitely influenced by the significant lentic–lotic exchange. A 10-year long (1965–1975), uninterrupted series of alkalinity measurements allowed probing into the mechanisms that contributed to determine the observed alkalinity variability. Such variation appeared controlled by several biogeochemical processes occurring in the wetland (e.g., photosynthesis/respiration), sporadically impacted by changing hydrological stages.

To determine the hydrochemical characteristics and health risks associated with their use as drinking water, 54 river water and 44 groundwater samples were collected and analyzed in a rural area of Jiangjin District, Chongqing City. The concentration of solutes in river water and groundwater showed significant spatial variability in the region. A number of dissolved chemical constituents including nitrate (NO3−), nitrite (NO2−), aluminum (Al), arsenic (As), boron (B), barium (Ba), iron (Fe), manganese (Mn), nickel (Ni), lead (Pb) and selenium (Se) exceeded their respective recommended drinking water limits at some locations. Ternary plots of cations, anions and silica indicated that carbonate weathering was the primary source of major ions in water, followed by silicate weathering. Elevated concentrations of some chemical constituents including NO3− and chloride (Cl−) were found in water samples in areas with the most intensive agricultural land use activities. A health risk assessment indicated that Cl− and NO3− were the most important chemical constituents that were a non-carcinogenic health concern. A carcinogenic health risk assessment indicated that chromium (Cr) and As were the chemical constituents of most concern in water from the area that might be used as a drinking water source. The average annual carcinogenic risks for Cr in drinking water were determined to be in the range of 3.14E−05 and 7.90E−05 for adults and children, respectively. Similarly, the average annual carcinogenic risks for As in drinking water for adults and children were calculated to be in the range of 4.43E−07 and 1.11E−06, respectively. These values are within the risk values of 10−6 to 10−4, which generally indicate that there are health concerns that need to be addressed in more detail. The highest values of carcinogenic risk for drinking water were mainly located in the northern part of the study area where there are industrial activities that are potential sources of arsenic and chromium in surface water and groundwater.

The production of oil and natural gas has recently played a significant role in boosting the economy. In this process, the discharge of industrial waste through activities like exploration and extraction operations cause elevated levels of dissolved chemicals, which severely degrade water sources and render them unsafe for human consumption. The aim of the present study was to evaluate the distribution of nineteen physicochemical parameters including heavy metals (pH, EC, TDS, TH, As, Cr, Cu, Ni, Pb, Zn, Ca 2+ , Mg 2+ , Na + , K + , Cl − , F − , SO 4 2− , NO 3 − and HCO 3 − ) in groundwater samples collected around oil and natural gas drilling sites and assess the knowledge gap for a sustainable and safe environment. Groundwater quality was assessed using various hydrogeochemical parameters and pollution indices such as the geoaccumulation index ( I geo ), enrichment factor (EF), contamination factor (CF), degree of contamination ( C deg ) with principal component (PCA) and regression coefficient analysis to identify the collective contamination source. The potential ecological risk indices (PERI) and health risk assessments were made using exposure factors references from USEPA’s database. The major findings indicated the Piper diagram is predominantly characterised by the Ca–Cl type whereas, Gibb’s plot showed evaporation and rock–water interaction influencing groundwater chemistry. Water quality index (WQI) results indicated 2% of samples were excellent, 22% were good, 20% were poor, 8% were extremely poor, and 48% were unsuitable for drinking. The pollution index of groundwater (PIG) showed that 50% of samples from the study area were unsafe to drink. The human health risk assessment revealed significant noncarcinogenic and carcinogenic effects to both adults and children. The study area's geology indicates that the presence of elements in groundwater is primarily due to drilling activities, as no geological formations show high concentrations. The implications of this study highlighted the current status of groundwater quality by identifying the main pollutants arising due to drilling extraction methods and developing a strategy aimed at mitigating both point and non-point sources of contamination.

This study investigated the effectiveness of palygorskite (Pal) as an adsorbent for removing total phenolic content (TPC), dissolved chemical oxygen demand (d-COD), and color from treated olive wastewater (TOW). Experiments were conducted to evaluate the impact of varying Pal dosages (2.5–20 g/L), initial TPC concentrations (80–400 mg/L), and pH (2–9). The results showed that increasing the Pal dosage improved the removal efficiency of TPC and d-COD, though there were diminishing returns beyond 10 g L−1, which indicates equilibrium adsorption behavior. The maximum TPC and d-COD removal reached 68% and 55%, respectively, while color removal exceeded 95% regardless of dosage. Adsorption was most efficient at lower TPC concentrations and an acidic pH (2–3), with up to 85% TPC removal. This suggests that pH-dependent phenolic ionization enhances Pal adsorption. Color removal remained consistently high across all conditions, highlighting palygorskite’s mesoporosity and affinity for chromophoric compounds. These findings affirm the potential of Pal as a cost-effective and versatile adsorbent for TOW treatment.