The properties and metal-binding abilities of dissolved organic matter (DOM) rely on its molecular weight (MW) structure. In this study, the spatial differences of DOM in compositions, MW structures, and binding mechanisms with copper (Cu²⁺) in Dongping Lake were investigated by applying excitation-emission matrix combining parallel factor analysis (EEM-PARAFAC), synchronous fluorescence (SF) spectra, two-dimensional correlation spectra (2D-COS), and Fourier transform infrared (FTIR) spectra. The EDOM for the entrance of the Dawen River and PDOM for the macrophyte-dominated region were divided from DOM of Dongping Lake based on hierarchical clustering analysis (HCA) and principal component analysis (PCA) and were size-fractioned into MW < 500 kDa and <100 kDa fractions. According to EEM-PARAFAC, Dongping Lake was dominated by tryptophan-like substances with MW < 500 kDa. The concentration of PDOM was higher than that of EDOM (p < 0.05). 2D-COS showed that protein-like components preceded humic-like components binding to Cu²⁺ regardless of sample type (215 nm > 285 nm > 310–360 nm). The Cu²⁺ binding capacity of DOM exhibited specific differences in space, components, and molecular weights. The humic-like component 1 (C1) and tryptophan-like component 4 (C4) of PDOM showed stronger binding abilities than those of EDOM. Endogenous tryptophan-like component 4 (C4) had a higher binding affinity for Cu²⁺ than humic-like components (logKₐ: C4 > C1 > C2) in PDOM irrespective of MW. Humic-like components with MW < 500 kDa displayed higher binding potentials for Cu²⁺. FTIR spectra showed that the main participants of DOM-Cu complexation included aromatic hydrocarbons, aliphatic groups, amide Ⅰ bands, and carboxyl functional groups. This study provides spatial-scale insights into the molecular weight structure of DOM in influencing the behavior, fate, and bioavailability of heavy metals in lakes.

Dissolved organic matter (DOM) has important impacts on the transportation of antibiotics through chemical and biological processes in composting. The interaction between DOM and antibiotics is reciprocal. The interaction between DOM ligands and antibiotics could be characterized based on a technique combining parallel factor analysis (PARAFAC) and microbial community structure analysis. However, PARAFAC cannot reveal the dynamic changes in each DOM peak in one PARAFAC component under antibiotic stress. In this study, two-dimensional correlation spectroscopy (2DCOS) combined with PARAFAC and bacterial community diversity analyses were employed to reveal the effects of oxytetracycline (OTC) stress and the key microorganisms on the transformation of different fluorescent peaks from DOM PARAFAC components during chicken manure composting. The results showed that OTC inhibits the transformation between DOM PARAFAC components by inhibiting the core microbial activities involved in the transformation of DOM components. Protein-like components (C1 and C2) were more sensitive to OTC residue, and components with a high humification degree promoted the degradation of OTC. The interaction between special DOM PARAFAC components and certain bacteria affects the degradation of OTC. The DOM PARAFAC components A2(C1), B1(C2), B2(C2) and Z1(C4) enhanced OTC degradation by stimulating the genera Pseudomonas, Glycomyces and Hyphomicrobium. With these promising results, the true effect of DOM PARAFAC components on the degradation of OTC can be revealed, which is helpful for addressing antibiotic contamination to improve the bioavailability of compost products.

The occurrence of excessive ammonium in groundwater threatens human and aquatic ecosystem health across many places worldwide. As the fate of ammonium in groundwater systems is often affected by a complex mixture of transport and biogeochemical transformation processes, identifying the sources of groundwater ammonium is an important prerequisite for planning effective mitigation strategies. Elevated ammonium was found in both a shallow and an underlying deep groundwater system in an alluvial aquifer system beneath an agricultural area in the central Yangtze River Basin, China. In this study we develop and apply a novel, indirect approach, which couples the random forest classification (RFC) of machine learning method and fluorescence excitation-emission matrices with parallel factor analysis (EEM-PARAFAC), to distinguish multiple sources of ammonium in a multi-layer aquifer. EEM-PARAFAC was applied to provide insights into potential ammonium sources as well as the carbon and nitrogen cycling processes affecting ammonium fate. Specifically, RFC was used to unravel the different key factors controlling the high levels of ammonium prevailing in the shallow and deep aquifer sections, respectively. Our results reveal that high concentrations of ammonium in the shallow groundwater system primarily originate from anthropogenic sources, before being modulated by intensive microbially mediated nitrogen transformation processes such as nitrification, denitrification and dissimilatory nitrate reduction to ammonium (DNRA). By contrast, the linkage between high concentrations of ammonium and decomposition of soil organic matter, which ubiquitously contained nitrogen, suggested that mineralization of soil organic nitrogen compounds is the primary mechanism for the enrichment of ammonium in deeper groundwaters.

The results of studying the content and composition of aliphatic hydrocarbons and polycyclic aromatic hydrocarbons in the suspended particulate matter of surface waters and in the surface layer of bottom sediments in 2019–2021 in the Kerch Strait in comparison with earlier studies in other areas of the Black Sea (Theodosia Gulf, Tuapse area, Coastal waters of the Crimean Peninsula, Big Sochi, Central part of the Sea) are presented. Despite the high concentrations of aliphatic hydrocarbons (especially in the waters of the strait itself: 28–254 on average 87 μg/L. The highest content of aliphatic hydrocarbons was confined to the cross-section through the Kerch Strait. Accumulation of aliphatic hydrocarbons, as well as the suspended particulate matter, occurs in the western part of the Strait, which is associated with the predominant wind direction and coastal orography. The composition of alkanes did not correspond to the smooth distribution of homologues characteristic of oil. Their distribution was bimodal in most samples, which may indicate a mixed genesis of alkanes. Among the low-molecular-weight alkanes either even numbered autochthonous alkanes n-C₁₆, C₁₈, C₂₂, arising during the microbial transformation of aliphatic hydrocarbons, or n-C₁₇, indicating the inclusion of phyto- and zooplankton alkanes, prevailed. Despite the different sources of hydrocarbons input, the distribution of the total concentrations of aliphatic hydrocarbons and polycyclic aromatic hydrocarbons basically coincided. Polycyclic aromatic hydrocarbons composition was dominated by fluoranthene and pyrene, which are formed in high-temperature combustion processes Low values of the Σnaphthalenes/Phen ratio (0.05–0.11) may indicate an insignificant inclusion of petroleum polyarenes. In contrast to suspension of surface waters, the highest content of hydrocarbons in the surface sediments was found not in the strait, but at stations in areas with aleurite-pelitic sediments, which is due to the pattern of currents in these areas and the higher sorption capacity of finely dispersed sediments. The average Cₒᵣg content in July 2020, was 1.8 times lower (0.34%) than in September 2019 (0.63%), and aliphatic hydrocarbons, on the contrary, was 2.2 times higher (47 μg/g) than in April 2019 (21 μg/g). In surface sediments the maximum concentration of aliphatic hydrocarbons was established in July 2020 (233 μg/g), and the highest average content in July 2021 (58 μg/g). This area is also associated with higher concentrations of aliphatic hydrocarbons in the composition of Cₒᵣg –≥1%. The composition of alkanes in surface sediments differed from their composition in suspension. The ratio of low-to-high molecular weight homologues (L/H = 0.08–0.54) was lower and the odd-to-even ratio (CPI = 1.19–4.58) was higher than in particulate matter. Due to the coarse composition of sediments, the content of polycyclic aromatic hydrocarbons in their surface layer was lower (0–631 ng/g) compared to other areas of the Black Sea. In their composition, along with fluoranthene and pyrene, methylated naphthalene homologues also belonged to the dominant compounds. Correlation analysis of individual polyarenes, as well as factor analysis, indicates their mixed genesis oil + pyrogenic, with the preference of the latter in most samples. The entry of pollutants into the marine environment increases the hydrocarbons content in water and bottom sediments, creating a modern hydrocarbon background.

The present study attempts to decipher the seasonal variations in hydro-geochemistry of groundwater in the Terekhol River Basin, western coastal region, Maharashtra, India. A total of 65 groundwater samples of post-monsoon (POMS) and pre-monsoon (PRMS) seasons were collected and analyzed for major ion composition using standard analytical procedures of APHA. Piper and Gibbs plots is used to elucidate the controlling factors which altering the groundwater composition. Scatter plots of ions indicate that major ions from lithologies exposed in the study area and anthropogenic activities are altering the groundwater chemistry. Statistical analysis includes correlation, factor analysis and cluster analysis used to interpret the hydrochemical data. As compared to the WHO drinking standards, all the groundwater samples are fit for drinking. Irrigation water suitability was ascertained based on SAR, %Na and KR indices. Overall, the groundwater chemistry in study area is reflects changes in natural processes rather than anthropogenic inputs.

In coastal aquifers, seawater intrusion is a significant groundwater issue. The research paper contributes to the understanding of the consequences of seawater intrusion in the Chennai coastal aquifer from Foreshore Estate to Thirunilai along the coastline. 110 groundwater samples were collected and analyzed for physicochemical parameters such as pH, (EC), (TDS), (TH), major anions (Cl⁻, NO₃⁻, HCO₃²⁻, and SO₄²⁻), and cations (Ca²⁺, Mg²⁺, Na⁺, and K⁺) during the pre-monsoon (June 2014) and post-monsoon (January 2015) seasons. Stable isotopic analyses of ¹⁸O were performed on 24 groundwater samples collected from various locations throughout the research region based on EC, TDS, Na, and Cl⁻ concentrations for both seasons. The stable isotopic composition of ¹⁸O and Deuterium in groundwater samples was determined for the study region. According to the Correlation matrix and Factor analysis, the main contributors to groundwater salinity as a result of seawater intrusion into the coastal aquifer are EC, TDS, Na⁺, and Cl⁻. GMWL exhibits a similar pattern, and the samples have been classified into various molar ratio diagrams to identify seawater intrusions for better evaluation. The result revealed that seasonal, geogenic, and anthropogenic factors always make a significant contribution to the heterogeneous chemistry of groundwater.

In the current research, the impact of the COVID-19 lockdown period on groundwater quality of Lower Meriç Plain (Thrace Region of Türkiye) was evaluated. Some significant nutrient characteristics (NO₃⁻, NO₂⁻, and PO₄³⁻), salinity characteristics (EC, TDS, and salinity), and physical characteristics (temperature, DO, pH, and turbidity) were investigated in groundwater samples collected from 45 sampling points in pre-lockdown and lockdown periods. Water quality index (WQI) and nutrient pollution index (NPI), Pearson correlation index (PCI), cluster analysis (CA), one-way ANOVA test (OWAT), and factor analysis (FA) were applied to assess ecological risk. Excluding recorded statistical differences in temperature and DO due to climatic conditions (p < 0.05), levels of all the investigated water quality parameters show no statistically significant differences and no significant reduction in pollutants measured in the lockdown period. On the contrary, the WQI and NPI scores have increased between the rates of 4.76–27.10% during the lockdown period. In the lockdown period, although the reduction of industry or limited production of many industrial facilities reduced the inorganic contaminant releases to the environment, ongoing agricultural activities and domestic wastes caused to prevent the reduction of organic pollutants in groundwater of the region during the lockdown period.

Guar fracturing technology has been considered as a kind of popular EOR technology, but the weak static suspension capacity becomes a challenge due to the poor temperature resistance and stability of guar fracturing fluid. The main goal of this investigation is to explore the effect of different factors on the high-pressure static sand suspension of guar gum fracturing fluid by a synthetic efficient nano-ZrO₂ cross-linker. In particular, a mechanism of static suspended sand of nano-ZrO₂ cross-linker is analyzed by microscopic simulation. The adsorption performance of guar fracturing fluid on the shale surface is also studied for analyzing the environmental pollution and damage of guar gum fracturing fluid to shale reservoirs after cross-linking in this investigation. The results obtained that the inclusion of a small content of nano-ZrO₂ cross-linker (0.4%) leads to an apparent increase of fracturing fluid viscosity and decrease in the falling quality of gravel (104 mPa·s and 0.3 g) compared to the classical cross-linker (63 mPa·s and 3.5 g). The lower adsorption capacity of guar fracturing fluid containing nano-ZrO₂ cross-linker on the shale surface means that it has a weaker pollution ability to the shale reservoir than the commercially available cross-linker. Meanwhile, the grid structure density formed by nano-cross-linker and guar gum is considered to be the key factor to significantly change the suspended sand capacity. The investigation of nano-cross-linker cannot only provide necessary theoretical technology and data support for the stability of water-based fracturing fluid, efficient sand carrying, and the development of water-based fracturing technology, but also effectively protect the underground shale reservoir.

Trophic transfer and bioaccumulation of trace metals have a profound impact on the structure and function of coastal areas; however, the metal accumulation patterns in detritus-based food webs and the influence of climatic variability have not been thoroughly investigated. The Tampamachoco Lagoon (Gulf of Mexico) is a coastal system impacted by emissions from a thermoelectric plant. We evaluated the spatial–temporal distribution patterns of Al, Cd, Hg, Cr, Cu, and Pb in water, sediments, and in organisms categorized by trophic levels (TLs), trophic guilds, and habitat preferences. The sediments had the highest concentrations of metals with no significant differences between seasons. The indices of geo-accumulation and potential ecological risk classified sediments as “moderately contaminated”, evidencing a threat to human health through consumption of detritivores and filter-feeders. The lowest TLs (filter-feeders and detritivorous) reached the maximum Metal Pollution Index in the rainy season. According to discriminant analyses of metals and species, omnivorous and zoobentivorous organisms were associated with Hg during the rainy and dry seasons; while Al, Cd, and Cu were related to low TLs, and seston was associated with Pb. Food web magnification factor analysis showed that: (a) Pb, Cu, and Cr were biodiluted as trophic levels increased; (b) Cd and Hg showed temporal biomagnification trends; (c) Al, Pb, Cu, and Cd showed significant biodilution from the lowest TL to intermediate TLs; and (d) Hg was transferred from the lowest to intermediate TLs with clear biomagnification effects.

This study aims to investigate the ecological risk level of potentially toxic elements (PTEs) in İzmir Inner Gulf. Samples were taken from 16 stations selected in the southern littoral zone of the gulf for four seasons (winter, spring, summer, and autumn). Multi-element, total organic carbon, chlorophyll-a, biogenic silica and carbonate analyses were carried out. To determine contamination level and ecological risks, some indices (enrichment factor, modified hazard quotient and potential risk analysis, toxic risk index, etc.) were calculated. Mo and Pb show significant anthropogenic enrichment in the inner gulf. These are followed by Cu, Cd, and Zn with moderate accumulation. Risk assessment indices point out that Ni, Cr, and Cd have a serious potential to create risk for ecosystem, and these are followed by As, Hg, Pb, Zn, and Cu. According to the spatial distribution, land use maps, and factor analysis, the Cd, Zn, and Cr increases are localized at the mouth of the Poligon Stream. Pb and Cu accumulate at the mouth of four large streams feeding the eastern part of the gulf. Pb and Cu enrichment is associated with traffic and industrial discharges. While one of the sources of Hg is anthropogenic, another source is eutrophication resulting from benthic and planktonic diatom blooms. While Fe and Mn are added to the gulf via rivers as a result of rock and soil erosion, another source is sediment. Cr, As, and Ni come from anthropogenic and lithogenic sources and immobilized in sediment. CO₃⁻² source is marine (biogenic) and dilutes other immobilized PTEs. It is understood that the peripheral stations rich in allochthonous organic carbon and the stations close to the central area rich in autochthonous organic carbon contribute to the carbon source in question.