In this paper we have pointed out the hydrogeological condition in the catchment area of the Jablanica river in the south Serbia (Yugoslavia). The two units are separately presented here. The first one is mountainous part of the catchment area upstream of the gaging station of Lebane and the second one is the part of the terrain in the plain down stream to the river mounth near Pecenjevac. The hydrogeological characteristics of the two mentioned regions are given to explain the reasons of existing the constant flow of the Jablanica to Lebane and its disappearing course in the period of recession in the plain downstream. The quality of water in the Jablanica river at Lebane is good. Down stream of this gaging station the waste water collector flows into the river. In the part of recession period the ratio between them is unfavourable. We have also discussed the quality of water at the gaging station of Pecenjevac and pointed out the function of sandy-gravel deposits in the process of natural purification of the Jablanica flow.

Estuarine environments faced with contaminations from coastal zones and the inland are vital sinks of antibiotic resistance genes (ARGs). However, little is known about the temporal-spatial pattern of ARGs and its predominant constraints in estuarine environments. Here, we leveraged metagenomics to investigate ARG profiles from 16 China's estuaries across 6 climate zones in dry and wet seasons, and disentangled their relationships with environmental constraints. Our results revealed that ARG abundance, richness, and diversity in dry season were higher than those in wet season, and ARG abundance exhibited an increasing trend with latitude. The prevalence of ARGs was significantly driven by human activities, mobile gene elements, microbial communities, antibiotic residuals, physicochemical properties, and climatic variables. Among which, climatic variables and human activities ranked the most important factors, contributing 44% and 36% of the total variance of observed ARGs, respectively. The most important climatic variable shaping ARGs is temperature, where increasing temperature is associated with decreased ARGs. Our results highlight that the prevalence of ARGs in estuarine environments would be co-driven by anthropogenic activities and climate, and suggest the dynamics of ARGs under future changing climate and socioeconomic development.

Emission of antibiotics into riverine environments affects aquatic ecosystem functions and leads to the development of antibiotic resistance. Here, the profiles of forty-four antibiotics and eighteen antibiotic resistance genes (ARGs) were analyzed in two large rivers of the Pearl River System. In addition, the risks of ecotoxicity and resistance selection posed by the antibiotics were estimated. As compared to the reservoirs, the river sections close to the urban and livestock areas contained more antibiotics and ARGs. Seasonal variations of antibiotics (higher in the dry season) and relative ARGs (normalized by 16S rRNA gene, higher in the wet season) were found in the water, but not in the sediment. Sulfonamide resistance genes were the most prevalent ARGs in both river water and sediment. Antibiotic concentration was correlated with ARG abundance in the water, indicating that antibiotics play a critical role in ARG spread. In addition, oxytetracycline was the most abundant antibiotic with concentrations up to 2030 ng/L in the water and 2100 ng/g in the sediment respectively, and posed the highest risks for resistance selection. Oxytetracycline, tetracycline and sulfamethoxazole were expected to be more ecotoxicologically harmful to aquatic organisms, while ofloxacin, enrofloxacin, norfloxacin, chlortetracycline, oxytetracycline and tetracycline posed ecotoxicological risks in the sediment. The Nanliujiang river with intensive livestock activities was contaminated by antibiotics and ARGs and faced high ecotoxicological and resistance selection risks. Collectively, these findings reflect the impacts of anthropogenic activities on the spread of antibiotic resistance in large river basins.

This study investigates the behavior of Tl in the Ría de Huelva (SW Spain), one of the most metal polluted estuaries in the world. Dissolved Tl concentration displayed a general decrease across the estuary during the dry season (DS); from 5.0 to 0.34 μg/L in the Tinto and Odiel estuaries, respectively, to 0.02 μg/L in the channel where the rivers join. A slighter decrease was observed during the wet season (WS) (from 0.72 to 0.14 μg/L to 0.02 μg/L) due to the dilution effect of rainfalls in the watersheds. These values are 3 orders of magnitude higher than those reported in other estuaries worldwide. Different increases in Tl concentrations with salinity were observed in the upper reaches of the Tinto and Odiel estuaries, attributed to desorption processes from particulate matter. Chemical and mineralogical evidences of particulate matter, point at Fe minerals (i.e., jarosite) as main drivers of Tl particulate transport in the estuary. Unlike other estuaries worldwide, where a fast sorption process onto particulate matter commonly takes place, Tl is mainly desorbed from particulate matter in the Tinto and Odiel estuaries. Thus, Tl may be released back from jarositic particulate matter across the salinity gradient due to the increasing proportion of unreactive TlCl⁰ and K⁺ ions, which compete for adsorption sites with Tl⁺ at increasing salinities. A mixing model based on conservative elements revealed a 6-fold increase in Tl concentrations related to desorption processes. However, mining spills like that occurred in May 2017 may contribute to enhance dissolved and particulate Tl concentrations in the estuary as well as to magnify these desorption processes (up to around 1100% of Tl release), highlighting the impact of the mine spill on the remobilization of Tl from the suspended matter to the water column.

Understanding wetland water quality dynamics and associated influencing factors is important to assess the numerous ecosystem services they provide. We present a combined self-organizing map (SOM) and linear mixed-effects model (LMEM) to relate water quality variation of multipond systems (MPSs, a common type of non-floodplain wetlands in agricultural regions of southern China) to their extrinsic and intrinsic influences for the first time. Across the 6 test MPSs with environmental gradients, ammonium nitrogen (NH₄⁺-N), total nitrogen (TN), and total phosphate (TP) almost always exceeded the surface water quality standard (2.0, 2.0, and 0.4 mg/L, respectively) in the up- and midstream ponds, while chlorophyll-a (Chl-a) exhibited hypertrophic state (≥28 μg/L) in the midstream ponds during the wet season. Synergistic influences explained 69±12% and 73±10% of the water quality variations in the wet and dry season, respectively. The adverse, extrinsic influences were generally 1.4, 6.9, 3.2, and 4.3 times of the beneficial, intrinsic influences for NH₄⁺-N, nitrate nitrogen (NO₃⁻-N), TP, and potassium permanganate index (CODMₙ), respectively, although the influencing direction and degree of forest and water area proportion were spatiotemporally unstable. While CODMₙ was primarily linked with rural residential areas in the midstream, higher TN and TP concentrations in the up- and midstream were associated with agricultural land, and NH₄⁺-N reflected a small but non-negligible source of free-range poultry feeding. Pond surface sediments exhibited consistent, adverse effects with amplifications during rainfall, while macrophyte biomass can reflect the biological uptake of CODMₙ and Chl-a, especially in the mid- and downstream during the wet season. Our study advances nonpoint source pollution (NPSP) research for small water bodies, explores nutrient “source-sink” dynamics, and provides a timely guide for rural planning and pond management. The modelling procedures and analytical results can inform refined assessment of similar NFWs elsewhere, where restoration efforts are required.

Bacteria and archaea (prokaryotes) are vital components for maintaining healthy function of groundwater ecosystems. The prokaryotic community composition and associated putative functional processes were examined in a shallow sandy aquifer in a wet-dry tropical environment. The aquifer had a contaminated gradient of saline mine-water, which primarily consisted of elevated magnesium (Mg²⁺) and sulfate (SO₄²⁻), although other major ions and trace metals were also present. Groundwaters were sampled from piezometers, approximately 2 m in depth, located in the creek channel upstream and downstream of the mine-water influence. Sampling occurred during the dry-season when only subsurface water flow was present. Next generation sequencing was used to analyse the prokaryote assemblages using 16S rDNA and metabolic functions were predicted with FAPROTAX. Significant changes in community composition and functional processes were observed with exposure to mine-waters. Communities in the exposed sites had significantly lower relative abundance of methanotrophs such as Methylococcaceae and methanogens (Methanobacteriaceae), but higher abundance in Nitrososphaeraceae, associated with nitrification, indicating potentially important changes in the biogeochemistry of the exposed sites. The changes were most strongly correlated with concentrations of SO₄²⁻, Mg²⁺ and Na⁺. This knowledge allows an assessment of the risk of mine-water contamination to groundwater ecosystem function and aids mine-water management.

Atmospheric size-classified particles in sizes ranging from small to nanoparticles (PM₀.₁) are reported for Rangsit City in the Bangkok Metropolitan Region (BMR) of Thailand, for October 2019 (wet season) and January–February 2020 (dry season). The sampling involved the use of a PM₀.₁ cascade air sampler to determine the mass concentration. The PMs consisted of six stages including TSP–PM₁₀, PM₂.₅₋₁₀, PM₁.₀₋₂.₅, PM₀.₅₋₁.₀, PM₀.₅₋₁.₀ and PM₀.₁. Elemental carbon (EC) and organic carbon (OC) were evaluated by a carbon analyzer following the IMPROVE_TOR protocol. The average PM₀.₁ mass concentrations were found to be 13.47 ± 0.79 (wet season) and 18.88 ± 3.99 (dry season) μg/m³, respectively. The average OC/EC ratio for the rainy season was lower than that in the dry season. The char-EC/soot-EC ratios were consistently below 1 for the PM₀.₁ fraction in both seasons indicating that vehicular traffic appeared to be the main emission source. However, the influence of open biomass burning on fine and coarse PM particles on local air pollution was found to be an important issue during the wet season. In addition, long-range transport from other countries may also contribute to the carbon content in the Bangkok Metropolitan Region (BMR) atmosphere during the dry season. The higher secondary organic carbon to organic carbon (SOC/OC) ratio in the dry season is indicative of the contribution of secondary sources to the formation of PM, especially finer particles. A strong correlation between OC and EC in nanoparticles was found, indicating that they are derived from sources of constant emission, likely the diesel engines. Conversely, the OC and EC correlation for other size-specific PMs decreased during the dry season, indicating that these emission sources were more varied.

Natural background levels (NBLs) and threshold values (TVs) are crucial parameters for identification and the quantification of groundwater pollution, and the evaluation of pollution control measures. The cumulative probability distribution technique was used for the evaluation of NBLs for 36 samples collected during two climate conditions in the part of the desert area from Rajasthan, India. The NBLs for Na⁺, Cl⁻, SO₄²⁻, HCO₃⁻, NO₃⁻ and F⁻ ions were assessed and compared with the natural and anthropogenic processes. The TVs were also calculated for Na⁺, Cl⁻, SO₄²⁻, HCO₃⁻, NO₃⁻ and F⁻ ions, and compared with the drinking limits of the Bureau of Indian Standards. Additionally, the pollution percentage (%) at the individual well was estimated and identified the polluted zones. Results indicate that most of the polluted areas were situated in the southern part, which was influenced by the natural and anthropogenic factors. The sodium concentrations above the TVs, in indicating the saline nature of water. Chloride threshold value above the drinking water limit was mainly observed in the dry season, related to intensive evaporation and industrial waste, which leads to groundwater quality degradation. The NO₃⁻ concentration (∼56% samples) above the TVs indicates extensive use of nitrate fertilizers and sewage effluent. The values of total dissolved solids (TDS) shows the suspicious scenario as about 84% of the samples in the dry period and about 89% in the wet season exceeding the drinking limit. Assessment of background concentrations and threshold values on regional and local scale assigns the basis for the identification of groundwater pollution, and helpful for better water quality guidelines to protecting of water resources.

The current study was conducted to (1) examine seasonal and spatial distribution of heavy metals and metalloid in sediment from the Saigon River and (2) apportion and quantify their pollution sources. Ninety-six sediment samples were taken in the rainy and dry season on 13 sampling sites, distributed over the lower reaches of the River, to analyze for exchangeable concentration of 11 heavy metals and metalloid (Al, B, Cd, Co, Fe, In, Mn, Ni, Pb, Sr, and Zn), pH, EC, organic carbon content, and particle-size distribution. Generally, the concentration of 11 elements was ranked in the order Mn > Al > Fe > Zn > Sr > In > B > Ni > Co > Pb > Cd. Hierarchical cluster analysis grouped 13 sampling sites into two parts based on the similar concentration of the 11 elements. Three-way analysis of variance showed that the total exchangeable concentration of 11 elements was significantly higher in the rainy season than in the dry season and in the upper part than in the lower part of the river. Principal component analysis/factor analysis and correlation analysis revealed that three pollution sources (PS) may contribute to enriching the 11 examined elements in the sediment. These sources included (PS1) from catchment through water erosion over natural areas, explaining 83%, (PS2) mixed sources from catchment through water erosion over agricultural fields and inside Ho Chi Minh City, accounting for 6%, and (PS3) mixed sources from lowland areas, explaining 7.8% of the total variance of the elements. In brief, the sediment concentration of 11 metals and metalloid varied with season and space and three major pollution sources from river catchment, inside Ho Chi Minh City, and lowland contributively enriched the elements in the sediment of the River.

In order to investigate the impacts of dam-related water impoundment on the spatial-temporal variations and transport of anthropogenic organic pollutants, 15 priority polycyclic aromatic hydrocarbons (PAHs) were analyzed in water samples from the Shuikou Reservoir (SKR) of the Minjiang River. The SKR was formed after the construction of the Shuikou Dam, which is the largest hydropower station in Southeast China. The water samples were collected from the backwater zone of the SKR, in both the wet and dry seasons, corresponding to the drainage and impoundment periods of water flow, respectively. The concentrations of the dissolved PAHs in surface water from the wet season (average of 161 ± 97 ng L⁻¹) were significantly higher (ANOVA, p < 0.01) than those from the dry season (average of 43 ± 21 ng L⁻¹). PAH concentrations in the SKR decreased from upstream (industrialized cities) to downstream (rural towns or counties), indicating high PAH loads caused by intensive urbanization effects. The high proportions of 3-ring PAHs in the wet season were from local sources via surface runoff; while the elevated proportions of 4- to 6- ring PAHs in the dry season reflected atmospheric deposition emerged of these PAHs and/or volatilization of 3-ring PAHs enhanced. Molecular diagnostic ratios of PAH isomers in multimedium and principal component analysis indicated that PAH presence in the SKR was mainly attributed to pyrogenic origin. The isomeric ratios of fluoranthene to fluoranthene plus pyrene in the wet season were homogeneous, implying that there were continuous new inputs along the riverine runoff. However, these ratios showed spatial downward trend in the dry season, indicating continued degradation of PAHs occurred along the transport path during the impoundment period. The input and output fluxes of PAHs in the SKR were 5330 kg yr⁻¹ and 2991 kg yr⁻¹, revealing that the reservoir retained contaminants after impoundment of the hydropower dam.