Spatio-seasonal patterns and sources of major ions in the Longjiang River catchment, Southern China

River water quality is closely related to the major ion sources and hydrological conditions. However, there is a limited cognition about the geochemical sources and the seasonal variations of major ions. Thus, in this study, a total of 90 water samples were collected from the Longjiang River and its three tributaries in the dry and wet seasons. The samples were analyzed, including major ion concentrations and physicochemical parameters. Statistical analysis, such as correlation analysis and principal component analysis (PCA), was employed to investigate the spatial and seasonal variations in major ion composition and their respective sources. Our study revealed that the predominant major ions in the studied samples are Ca2+, Mg2+, HCO - 3, and SO2 - 4. Most of ions exhibited notable spatial disparities attributable to variations in geological settings and human activities. Regions characterized by igneous rock outcrops tend to exhibit higher levels of K+ and Na+, while areas with higher population densities in the middle and downstream segments show elevated concentrations of Cl-, NO - 3, SO2 - 4, Na+, and K+. The observed peak SO2 - 4 levels may be attributed to active mining operations. Most parameters displayed higher values in flood season than those in dry season due to dilution effects. Stoichiometric analysis indicated that carbonate weathering inputs contribute to over 85% of the mean total cation concentrations in the water, followed by contributions from silicates, atmospheric deposition, and anthropogenic inputs. On the whole, although the water quality remains non-polluted and is suitable for drinking and irrigation purposes, the enrichment of SO2 - 4 and NO - 3 may contribute to water eutrophication. Caution is warranted during the dry season due to reduced water flow resulting from dam interceptions and limited dilution capacity, potentially leading to elevated pollutant concentrations. Taken together, our results provided a scientific basis for water quality managements of monsoon rivers.

Machine learning coupled with causal inference to identify COVID-19 related chemicals that pose a high concern to drinking water

Various synthetic substances were utilized in large quantities during the recent coronavirus pandemic, COVID-19. Some of these chemicals could potentially enter drinking water sources. Persistent, mobile, and toxic (PMT) substances have been recognized as a threat to drinking water resources. It has not yet been assessed how many COVID-19 related substances could be considered PMT substances. One reason is the lack of high-quality experimental data for the identification of PMT substances. To solve this problem, we applied a machine learning model to identify the PMT substances among COVID-19 related chemicals. The optimal model achieved an accuracy of 90.6% based on external test data. The model interpretation and causal inference indicated that our approach understood causation between PMT properties and molecular descriptors. Notably, the screening results showed that over 60% of the COVID-19 chemicals considered are candidate PMT substances, which should be prioritized to prevent undue pollution of water resources.

Linking multivariate statistical methods and water quality indices to evaluate the natural and anthropogenic geochemical processes controlling the water quality of a tropical watershed

The improvement of water management requires monitoring techniques that accurately evaluate water quality status and detect the effects of land use changes on water chemistry. This study aimed to evaluate how multivariate statistical methods and water quality indices can be applied together to evaluate the processes controlling water chemical composition and the overall water quality status of a tropical watershed. Thirty-four water samples were collected in the Formoso River basin, located on the border of the Amazon Forest. Water parameters were measured in situ using a multiparameter and in the lab using spectroscopic and volumetric techniques. The water quality dataset was interpreted through principal component analysis, multivariate linear regression, and water quality indices. Statistical methods allowed us to identify the sources and geochemical processes controlling water quality chemistry, which were carbonate dissolution, runoff/erosion, nutrient input due to anthropogenic activities, and redox reactions in flooded zones. They were also used to create linear functions to evaluate the effects of land use changes on the geochemical processes controlling water chemistry. Conversely, the water quality indices provide information about the overall condition of the water. The Weight-Arithmetic Quality Index correctly evaluates water suitability for its multiple uses, according to the Brazilian guidelines. Conversely, the Ontario Water Quality Index is not suitable to evaluate the water quality of tropical rivers, since the usual higher water temperature and the low oxygen contents associated with tropical environments result in biased water quality evaluations by this index.

Synergistic effects of prokaryotes and oxidants in rapid sand filters treatment of groundwater versus surface water: Purification efficacy, stability and associated mechanisms

Effective elimination of manganese (Mn) and ammonium (NH₄⁺-N) from drinking water is still challenging. Utilizing oxidants to improve the simultaneous removals of Mn and NH₄⁺-N from rapid sand filter (RSF) systems has been extensively studied. However, the prokaryotes containing in the water geochemical properties greatly affected the RSF performance. In this study, groundwater and micro-polluted surface water were used to compare with/without potassium permanganate (KMnO₄) assistant on the contaminants removals and system stability. Results showed that KMnO₄ reduced the start-up period of RSF for treating groundwater and surface water to 20 and 41 days, respectively, with excellent Mn removal rates (>97%). The relative abundance of efficient ammonia-oxidizing bacteria (Nitrospira) in RSF treated groundwater without KMnO₄ was higher than that in RSFs treated micro-polluted surface water or with KMnO₄, resulting in a higher NH₄⁺-N removal rate of the former (∼57%). Notably, KMnO₄ and prokaryotes synergistically contributed to the amorphous structure, mixed phases (buserite, MnO₂ and birnessite) and mixed-valence Mn system of active manganese oxides (MnOx), whose abundant oxygen vacancies and highly reactive Mn(III) favored the autocatalytic oxidation of Mn, while NH₄⁺-N removal relied more on bacteria actions. Additionally, prokaryotes enriched the bacterial community diversity, leading to a more stable RSF system when facing hydraulic loading shock. This paper provided new insight into the synergistic effect of KMnO₄ and prokaryotes on Mn and NH₄⁺-N eliminations in RSFs and was helpful for practical applications.

Dominance of Arcobacter in the white filaments from the thermal sulfidic spring of Fetida Cave (Apulia, southern Italy)

The thermal spring of Fetida Cave, a still active sulfuric acid cave opening at sea level and located in Santa Cesarea Terme, southeastern Salento (Apulia region, Southern Italy) hosts abundant floating white filaments. The white filaments were mainly composed of sulfur crystals surrounded by microbial mass of the phyla Epsilonbacteraeota, Proteobacteria, Bacteroidetes, and Patescibacteria. The most abundant genus in the white filaments collected from the waters in the innermost part of the cave dominated by sulfidic exhalations was Arcobacter. This abundance can be related to the higher concentration of sulfide dissolved in water, and low oxygen and pH values. Conversely, lower Arcobacter abundances were obtained in the filaments collected in the entrance and middle part of the cave, where sulfidic water mixes with seawater, as the cave is subjected to tides and the mixing of fresh (continental) with marine water. The geochemical analysis of water and atmospheric gases confirmed these environmental constraints. In fact, the highest concentrations of H₂S in the air and water were recorded closest to the spring upwelling in the innermost part of the cave, and the lowest ones near the cave entrance. The metabolic versatility of Arcobacter might provide a competitive advantage in the colonization of water bodies characterized by high sulfide, low oxygen, and dynamic fluid movement.

Nitrate dynamics in groundwater under sugarcane in a wet-tropics catchment

The transport of nitrogen (N) to groundwater and surface water in the form of nitrate (NO₃^-), as a by-product of the application of N-rich fertilisers, has been studied extensively. Yet, in the catchments adjacent to the Great Barrier Reef (GBR) in tropical north Queensland, Australia, NO₃^- transport in groundwater is not regularly monitored. An assessment of groundwater chemistry in the Liverpool Creek catchment of Queensland's wet-tropics region was conducted by regular sampling and analysis of groundwater over 12 months, through wet and dry seasons. A distinct spatial variability in groundwater chemistry was observed; groundwater aquifers with very low dissolved oxygen (DO) and NO₃^- consistently displayed relatively higher concentrations of sulphate (SO₄^2-), sulphur (S^2-) and ferrous iron (Fe²⁺) and low concentrations of dissolved organic carbon (DOC) (<2 ppm). Combined with averaged measured redox potential (Eh) of <250 mV, this indicates certain regions of the catchment have conditions favourable for removal of NO₃^- via autotrophic denitrification (DN), while other groundwater aquifers retained NO₃^– concentrations just above the acceptable trigger limits defined in regional water quality guidelines. Observations indicate that the naturally heterogeneous structure of the coastal alluvium contributes to the distinct variability in groundwater chemistry over small distances, with NO₃^- concentrations influenced by a combination of DN, lateral shallow drainage and potential adsorption to clay surfaces within the alluvial sediments.

Flow and transport of Phenol in groundwater using PGWT equation

With the increasing population, one has to depend on the groundwater for domestic, agricultural and industrial requirements. Hence conservation of groundwater in its pure form requires attention. Mismanagement of groundwater along with its deteriorating quality are major concerns in developing countries. The objective of this investigation is to understand the occurrence and degree of dissolved contaminants, as well as the rate and direction of contaminant's movement within the groundwater flow system. In this study, a Phenol Groundwater Transport (PGWT) equation is developed with Lagrangian interpolation function using a nine noded rectangular element. PGWT equation is used to determine the unknown concentration of a Phenol in the porous media for the range of concentrations and permeabilities. The equation is validated with the results of developed Physical Aquifer Model (PAM). It is observed that the transport equation of degree ten delivers the accurate concurrence with the physical model when contrasted with lower degrees of polynomial function.

Water quality and solute sources in the Marsyangdi River system of Higher Himalayan range (West-Central Nepal)

Surface waters, cold and hot springs were collected in different catchments along the Marsyangdi basin, in the Himalayan Range of West-Central Nepal, during the post-monsoon season in 2017 and analyzed for major ions and trace elements, with the aim of assessing the sources of dissolved species and to contribute in watershed planning. The major element data indicate that surface waters coming from the Tethyan Himalayan Sequence (THS) range from the Ca-Mg-HCO₃ to the Ca-Mg-HCO₃-SO₄ water-types and reflect a two-component mixing of waters from carbonate- and sulfate-bearing sources. The latter component is attributable to sulfide oxidation with minor silicate weathering. In the Greater Himalaya Sequence (GHS), alteration of pedogenetic carbonates formed in response to silicate weathering under a variable CO₂ gas pressure dominates, yielding a Ca-HCO₃ signature. The stability diagram in the K₂O-Al₂O₃-SiO₂-H₂O system and the paired increases in Ca²⁺, Na⁺, K⁺ and silica indicate that degradation of silicate minerals through kaolinization and possibly plagioclase albitization reactions is the main process for hot groundwater. Cold and hot springs define a trend of increasing Li, SiO₂ and Cl^-, suggesting that lithium was leached from silica-rich sources, such as pegmatite dykes and sills occurring in host rocks, and concentrated into halite-bearing salt aquifers. In hot waters Sb, As and Tl exceed the EU and USEPA thresholds. Tl is usually incorporated into pyrite and correlates with Li indicating the occurrence of an ore-bearing zone possibly related to hydrothermal activity at the transition zone between THS and GHS, as suggested by the relatively high Ba, Ni, Cu, Sb, As and Mn contents. The obtained data on water quality have significant implications for people living along the Upper Marsyangdi River in the management of water resources, especially in terms of the enhancement of cold water aquaculture and hot water uses for recreation purposes and tourism.

Geochemistry and microbial diversity of cave waters in the gypsum karst aquifers of Emilia Romagna region, Italy

Fifty-seven control points of waters (sinking streams, rivers in caves, and resurgences) hosted in gypsum karst areas in Emilia Romagna region (N-Italy) were sampled in the framework of a Project LIFE+08NAT/IT/000369 "Gypsum" in the period 2010-2014. The microbiology and chemistry of these waters have been analyzed to evaluate the impact of human activities or natural factors, in the gypsum karst systems. Waters have been analyzed for major chemistry (Ca, Mg, Na, K, SO₄, HCO₃, Cl, NO₃) and some minor constituents (F, Br, NH₄ and PO₄), measuring pH, electric conductivity (EC), total dissolved solids (TDS) and temperature (T) in situ. The same samples have been analyzed with traditional microbiology techniques focused on total microbial count and on fecal microbiota, as index of human and/or animal contamination, and molecular biology techniques (sequencing of 16S rRNA segment and PCR-DGGE), focused on the characterization of microbial populations in the different sampling sites and determination of their variations and/or changes during the five years of the project. As expected, waters tend to be increasingly mineralized from sinking streams to resurgences, with only local and temporarily high contents in nitrates and ammonium, often related to the presence of bat colonies. PCR-DGGE revealed ecological changes, in terms of microbial populations present in the bulk water samples, in different sampling sites within the same cave. Although the impact of fecal microorganisms only rarely exceeded 2 log UFC/ml, the results evidenced fluctuations of these microorganisms mainly correlated to the season and to the biological activity of bats.

Geochemistry of the Adige River water from the Eastern Alps to the Adriatic Sea (Italy): evidences for distinct hydrological components and water-rock interactions

The Adige River flows from the Eastern Alps to the Adriatic Sea and the understanding of its fluvial dynamics can be improved by geochemical and O-H isotopic investigation. The most negative isotopic compositions are recorded close to the source (δ(18)O between -14.1 and -13.8 ‰, δD between -100.3 and -97.0 ‰), and δD and δ(18)O values generally increase downstream through the upper part (UP, the mountainous sector), stabilizing along the lower part (LP, the alluvial plain) of the river with δ(18)O between -12.4 and -11.8 ‰, δD between -86.9 and -83.7 ‰. The isotopic variations along the stream path (δ(18)O-δD vs distance from the source) depict subparallel distributions for all the investigated periods, with less negative values recorded in winter. Total dissolved solids (TDS) concentration shows the lowest value (<100 mg/l) at the river source, jumping to 310 mg/l at the Rio Ram inflow, then decreasing down to the Isarco River confluence; from here, we observed an increase toward the river mouth, with different values in the distinct sampling periods. The lowest values (140-170 mg/l) were recorded during high discharge in spring, whereas higher TDS values (up to 250 mg/l) were recorded during winter low flow conditions. Extreme TDS values were observed in the estuarine samples (up to 450 mg/l), as result of mixing with seawater. The results allow for the identification of distinct water end-members: glacio-nival component(s) characterized by the most negative isotopic composition and extremely low TDS, a rainfall component characterized by intermediate isotopic and elemental composition and groundwater characterized by the less negative isotopic composition and comparatively higher TDS. An additional component is represented by seawater, which is recorded at the lowest reach of the river during drought periods. These contributions variously mix along the stream path in the distinct hydrological periods, and the presented data are a snapshot of the current hydroclimatic conditions. Future investigations will evaluate possible hydrological variations related to meteo-climatic changes. Monitoring is fundamental for future water management to overcome the vanishing of a significant water end-member of the basin, i.e., the glacio-nival reservoir that is severely affected by the ongoing climatic changes.