Application of two-dimension, high-resolution evidences to reveal the biogeochemical process patterns of trace metals in reservoir sediments

Pollutions of trace metals (TMs) in reservoirs are blooming due to TMs were trapped efficiently in reservoir sediments by dams. Despite the mobilization of TMs in sediments have been well-documented, the patterns of biogeochemical processes occurred in sediments remain poorly understanding. Herein, a deep reservoir was selected to investigate the patterns of TMs biogeochemical processes in sediments by using high-resolution ZrO-Chelex-AgI diffusive gradient in thin films technique (HR-ZCA DGT) and the laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). 2-dimension high-resolution (2D-HR) images showed significant differential spatial enrichment of TMs (V, Mn, Fe, Co, Zn and Sb) in sediments, indicating strong heterogeneity in sediments. Correlations of TMs within microniches (diameter < 1 mm) in horizontal were usually different even contrast with that in vertical profile, suggesting distinct biogeochemical process patterns occurred in vertical vs. in horizontal. Further analyses from 2D-HR images showed the distributions of TMs in microniches reflected their mobilization that was driven by microenvironmental conditions. In contrast, distributions in sediment vertical profile recorded the diagenesis in different deposition depth. The diagenesis in sediment vertical is continuously accumulated by the discrete, microniches mobilization of TMs in horizontal. Collectively, our findings evidenced that 2D-HR data is an update complement to 1-dimension data for better interpret the biogeochemical process patterns of TMs in sediments, that have implication for water management to metals pollution in reservoir ecosystems.

Source apportionment of heavy metal(loid)s in sediments of a typical karst mountain drinking-water reservoir and the associated risk assessment based on chemical speciations

As important place for water storage and supply, drinking-water reservoirs in karst mountain areas play a key role in ensuring human well-being, and its water quality safety has attracted much attention. Source apportionment and ecological risks of heavy metal(loid)s in sediments of drinking-water reservoir are important for water security, public health, and regional water resources management, especially in karst mountain areas where water resources are scarce. To expound the accumulation, potential ecological risks, and sources of heavy metal(loid)s in a drinking-water reservoir in Northwest Guizhou, China, the surface sediments were collected and analyzed based on the combined use of the geo-accumulation index (Igeo), sequential extraction (BCR), ratios of secondary phase and primary phase (RSP), risk assessment code (RAC), modified potential ecological risk index (MRI), as well as the positive matrix factorization methods. The results indicated that the accumulation of Cd in sediments was obvious, with approximately 61.9% of the samples showing moderate to high accumulation levels, followed by Pb, Cu, Ni, and Zn, whereas the As and Cr were at low levels. A large proportion of BCR-extracted acid extractable and reducible fraction were found in Cd (72.5%) and Pb (40.3%), suggesting high bioavailability. The combined results of RSP, RAC, and MRI showed that Cd was the major pollutant in sediments with high potential ecological risk, while the risk of other elements was low. Source apportionment results of heavy metal(loid)s indicated that Cd (75.76%) and Zn (23.1%) mainly originated from agricultural activities; As (69.82%), Cr (50.05%), Cu (33.47%), and Ni (31.87%) were associated with domestic sources related to residents' lives; Cu (52.36%), Ni (44.57%), Cr (34.33%), As (26.51%), Pb (24.77%), and Zn (23.80%) primarily came from natural geological sources; and Pb (47.56%), Zn (22.46%) and Cr (13.92%) might be introduced by mixed sources of traffic and domestic. The contribution ratios of the four sources were 18.41%, 36.67%, 29.48%, and 15.44%, respectively. Overall, priority control factors for pollution in relation to agricultural sources included Cd, while domestic sources are primarily associated with As. It is crucial to place special emphasis on the impacts of human activities when formulating pollution prevention and control measures. The results of this study can provide valuable reference and insights for water resources management and pollution prevention and control strategies in karst mountainous areas.

Sediment quality of the Ridracoli fresh water reservoir in Italy: Insights from aqua regia digestion and sequential extractions

The inter-element relationships and the forms in which metals exist strongly influence their mobility and, in turn, have a signature on the environment and human health. Located in the northern Apennines within the Emilia-Romagna region, the Ridracoli artificial lake is one of Italy's most important reservoirs that provides drinking water for about one million people. This work characterized the reservoir sediments by ICP-MS after aqua regia digestion (ARD), comparing the limits by law to assess environmental compliance and XRF data from the same sample-set taken as total concentrations. The Degree of Extraction (DE) from pseudo-total concentrations of ARD analysis allows assessing elements mobility and the associated environmental risk. Principal Component Analysis (PCA) on the obtained data helped to investigate inter-element relationships better; for example, we observed carbonate-sourced sediments, many trace elements (e.g., Ni, Zn) linked to FeMn oxyhydroxides, the importance of the grain size in elements distribution, and the central role of the organic matter in element partitioning. In addition, a Sequential Extraction Procedure (SEP) was applied to the sediment samples to understand the partitioning of many analytes, including Potentially Harmful Elements (PHE) such as Fe, Mn, Cu, Cr, Ni, Pb, and Zn. The results indicated that the most easily mobilized forms were predominant in the area near the dam, in correspondence to sediments affected by the formation of a seasonal anoxic layer.

Antibiotic resistomes in water supply reservoirs sediments of central China: main biotic drivers and distribution pattern

Water supply reservoirs form one of the critical drinking water resources. Their water quality directly affects human health. However, reservoir sediments have not received adequate attention in antibiotic resistance genes (ARGs) dissemination, though they reflect long-term ARGs contamination of water supply reservoirs. Moreover, the physicochemical parameters in water supply reservoir sediments are generally better than those in the other media. Thus, the main ARGs biotic drivers of the media would demonstrate their unique characteristics. In this study, sediment samples were collected from 10 water supply reservoirs in central China, and the antibiotic resistomes were determined with the metagenomic method. As revealed from the results, 174 ARGs (18 ARG types) were detected in the reservoir sediment. Besides, multidrug-, sulfonamide-, and vancomycin-ARGs were the dominant ARGs in the sediment samples. The macrolide-resistant Microcystis was prevalent (100% detection frequency with 0.35% average percentage) in reservoir sediments and posed potential risks to human health. Furthermore, the results of the Mantel test and VPA demonstrated that mobile genetic elements (MGEs) were the more essential biotic drivers in ARG contents of reservoir sediments rather than the bacteria community.

Geochemical and U-Th isotopic insights on uranium enrichment in reservoir sediments

Uranium (U) geochemistry and its isotopic compositions of reservoir sediments in U mine area were poorly understood. Herein, U and Th isotopic compositions were employed to investigate source apportionment and geochemical behavior of U in 41 reservoir sediments from a U mining area, Guangdong, China. The remarkably high contents of both total U (207.3-1117.7 mg/kg) and acid-leachable U (90.3-638.5 mg/kg) in the sediments exhibit a severe U contamination and mobilization-release risk. The U/Th activity ratios (ARs) indicate that all sediments have been contaminated apparently by U as a result of discharge of U containing wastewater, especially uranium mill tailings (UMT) leachate, while the variations of U/Th ARs are dominated by U geochemical behaviors (mainly redox process and adsorption). The U isotopic compositions (δ²³⁸U) showed a large variance through the sediment profile, varying from - 0.62 to - 0.04‰. The relation between δ²³⁸U and acid-leachable U fraction demonstrates that the U isotopic fractionation in sediments can be controlled by bedrock weathering (natural activity), UMT leachate (anthropogenic activity) and subsequent biogeochemical processes. The findings suggest that U-Th isotopes are a powerful tool to better understand U geochemical processes and enrichment mechanism in sediments that were affected by combined sources and driving forces.

Magnetic parameters as proxies for anthropogenic pollution in water reservoir sediments from Mexico: An interdisciplinary approach

We assess the element pollution level of water reservoir sediments using environmental magnetism techniques as a novel approach. Although "La Purísima" Water Reservoir is an important source for multiple activities (e.g. recreational, fishing and agricultural) in Guanajuato state, it has been receiving for the last centuries a high load of pollutants by mining extraction, urbanization and land-use change from the Guanajuato Hydrological Basin. The analyses of environmental magnetism, geochemistry, X-ray energy dispersive spectroscopy, scanning electron microscopy and multivariate methods were applied to study sediments from the reservoir and basin. Accordingly, they indicate the presence of iron oxides (magnetite and hematite) and iron sulfides (pyrite and greigite), which evidences relevant differences in particle size and concentration within the water reservoir (median mass-specific magnetic susceptibility χ = 23.2 × 10^-8 m³/kg), as well as with respect to the river basin sediments (median χ = 88.8 × 10^-8 m³/kg). The highest enrichment factor EF values (median values of EF = 2-10 for As, Co, Ba, Cu, Cd, Ni and EF > 20 for S) are mainly associated with historical mining activities that have led to an enrichment of potentially toxic elements on these water reservoir sediments. We propose the use of concentration and grain size dependent magnetic parameters, i.e. χ, remanent magnetizations and anhysteretic ratios ARM/SIRM and χ_ARM/χ, as proxies for Ba, Co, Cr, Ni, P and Pb pollution in these river and water reservoir sediments. Such parameters allow to evaluate this sedimentary environment, and similar ones, through useful and convenient proxies.

Dataset for the assessment of metallic pollution in the Saint-Charles River sediments (Québec City, QC, Canada)

This Data in Brief article presents sedimentological and geochemical parameters from a set of sedimentary samples collected in the Saint-Charles River, a tributary of the Saint-Lawrence River flowing in Québec City (QC, Canada). It details the experimental design, methods, materials and results of destructive analyses related to a multi-proxy study of polymetallic contamination in sediments collected within an urban reservoir (Spatial and temporal patterns of metallic pollution in Québec City, Canada: Sources and hazard assessment from reservoir sediment records, https://doi.org/10.1016/j.scitotenv.2019.04.021, (Chassiot et al., 2019)). The present article summarizes the results of relevant parameters on a set of 68 samples: total organic carbon (TOC), sulfur content, grain-size, and concentrations of heavy and trace metals. It also presents the calculation of enrichment factors, geoaccumulation indexes, and metallic pollution index.

Environmental Risk of Metal Contamination in Sediments of Tropical Reservoirs

Reservoir sediment can work as both sink and source for contaminants. Once released into the water column, contaminants can be toxic to biota and humans. We investigate potential ecological risk to benthic organisms by metals contamination in six reservoirs in Southeast Brazil. Results of the bioavailable fraction of copper (Cu), chromium (Cr), cadmium (Cd), lead (Pb), zinc (Zn), and iron (Fe) in sediment samples are presented. Considering Cu, Cd, and Zn concentrations, about 6% of the samples exceeded the threshold effect levels of sediment quality guidelines. The comparison to sediment quality guidelines is conservative because we used a moderate metal extraction. Control of contaminant sources in these reservoirs is key because they are sources of water and food. The mixture toxicity assessment showed an increased incidence of toxicity to aquatic organisms showing that mixture toxicity should be taken into account in sediment assessment criteria.

Long-term variations in sediment heavy metals of a reservoir with changing trophic states: Implications for the impact of climate change

Two dated sediment cores from the Miyun Reservoir of Beijing in China were analyzed to reconstruct the pollution history of heavy metals including cadmium (Cd), chromium (Cr), iron (Fe), nickel (Ni), and zinc (Zn) as well as phosphorus (P). Enrichment factor (EF) and geoaccumulation index (I_geo) were applied to assess the enrichment status of heavy metals. Average EF and I_geo values indicated that the studied heavy metals in the sediments mainly originated from non-point source pollution and soil-water erosion, showing low ecological risks. In addition, correlation analysis and principal component analysis (PCA) identified that Cd, Zn, and P were mainly from agricultural diffusion pollution caused by utilization of the phosphate fertilizer; Zn, Ni, and Cr originated from soil erosion. PCA analysis was further conducted to investigate the relationships among meteorological factors, algae-dominant total organic carbon (TOC), and heavy metals. Results showed that algae-dominant TOC had strong positive correlation with temperature, which can be explained by that increased temperature accelerated the growth of algae. Meanwhile the opposite loadings between algae-dominant TOC and heavy metal suggested that primary production played an important role in migration and transformation of metals. Moreover, stepwise multiple regression models showed that Fe was sensitive to temperature, which accounted for approximately 39.0% and 40.1% of the variations in Fe of two sediment cores, respectively. Fe showed significant decreasing trends during the past 50years. Reductive environment of water-sediment interface caused by increasing temperature probably contributed to the restoration of ferric iron, resulting in the release of soluble Fe to overlying waters. Future climate change with elevated temperature and extreme weather events will aggravate the ecological risk of heavy metals in water environment due to the enhanced leaching effect and non-point source pollution as well as the release of heavy metals from sediments to water environment.

Behaviour of glyphosate in a reservoir and the surrounding agricultural soils

Glyphosate (GPS) is an herbicide currently used on olive crops in Spain, and can be transported to the nearby reservoirs currently used for human consumption. The purpose of this work was to study the behaviour and environmental fate of GPS in water and sediments of the Vibora Reservoir, its tributary river, and the surrounding agricultural soils to assess the risk of water pollution of this reservoir. The adsorption of GPS by different matrices was as follows: heading of the reservoir sediment (Cabecera)>tail sediment (Cola)>soils>Vibora sediment. The highest amount of oxides (especially Fe oxides) was observed in sediments from Cabecera and Cola whereas the lowest values were recorded on Vibora sediment. Results indicate that the highest GPS adsorption is due to the amorphous oxides and the edge sites of the clay minerals. Glyphosate adsorption increased with decreasing pH from 8 to 7. The desorption percentage of GPS from the four soils studied ranged only from 0.40 to 1.22%. Desorption was almost irreversible for Cabecera and Cola sediments, with values between 0 and 1.1%. Conversely, Vibora sediment presented about 20% desorption, probably due to its coarse texture and lower levels of amorphous oxides. Hockey-stick first-order kinetics was the best descriptor for water glyphosate dissipation at the Cabecera and Cola locations, and simple first-order kinetic for the water from the tributary Vibora River. The half-lives (DT50) were between 6.3 and 11.0days. The rapid degradation of GPS in surface waters and its practically irreversible sorption on these soils and sediments implies that GPS use in similar agricultural areas is of very low environmental risk. This manuscript also outlines the importance of the presence of photo-sensitizers in waters in the degradation routes of GPS in reservoirs.

Historical Trends of Polycyclic Aromatic Hydrocarbons in the Reservoir Sediment of the Dianchi Watershed, Southwest China

Using gas-chromatography/mass spectrometry (GC-MS) method dating data (²¹⁰Pb and ¹³⁷Cs) and OCPs signatures, the temporal distribution of polycyclic aromatic hydrocarbons (PAHs) was investigated in dated sediment core from Baoxianghe reservoir in Dianchi watershed, Southwest China. The concentrations of total PAHs were in the range of 162.3-762.2 ng g^-1 from 1945 to 2013. There showed an obvious increase from 1960s to 2000s. The distributions of PAHs were influenced by local population and Gross Domestic Product (GDP) during the period between1962 and 2004. PAHs sources changed from biomass or domestic coal combustion (before 1980) to liquid fossil fuel combustion (after 1980). Total toxic toxicity equivalents (TEQs) of the carcinogenic PAHs were very low (3.03-28.08 ng g^-1).

Atmospheric pollution history at Linfen (China) uncovered by magnetic and chemical parameters of sediments from a water reservoir

We studied magnetic and chemical parameters of sediments from sediments of a water reservoir at Linfen (China) in order to quantitatively reconstruct the atmospheric pollution history in this region. The results show that the main magnetic phases are magnetite and maghemite originating from the surrounding catchment and from anthropogenic activities, and there is a significant positive relationship between magnetic concentration parameters and heavy metals concentrations, indicating that magnetic proxies can be used to monitor the anthropogenic pollution. In order to uncover the atmospheric pollution history, we combined the known events of environmental improvement with variations of magnetic susceptibility (χ) and heavy metals along the cores to obtain a detailed chronological framework. In addition, air comprehensive pollution index (ACPI) was reconstructed from regression equation among magnetic and chemical parameters as well as atmospheric monitoring data. Based on these results, the atmospheric pollution history was successfully reconstructed.

Heavy metal partitioning in sediments and bioaccumulation in commercial fish species of three major reservoirs of river Cauvery delta region, India

Chemical partitioning of heavy metals (Fe, Mn, Cu, Cr, Pb, Zn, Ni) were determined in surface sediments of three reservoirs at the Delta region of Cauvery River, India. The abundance of metals in sediments varied in the following descending order: Fe, Mn, Cr, Zn, Cu, Ni, and Pb. Higher concentrations of Zn, Pb, Fe, Mn and Cu in exchangeable and carbonate fraction indicated toxicity risk to the biota. Therefore, to understand the extent of bioaccumulation, six commercial fish species were collected from the same sites and analyzed for heavy metals distribution in different organs. Among the metals found in fish samples, iron was observed in the highest concentration, followed by Zn, Pb, Cr, Mn, Cu, and Ni. Concentrations of Pb, Cr and Zn in many fish samples exceeded the permissible limits of Food and Agriculture Organization. The concentrations of Pb (17.7-31.7%), Cr (6.2-15.1%), Cu (15.2-30.5%) and Zn (30-40%) associated with exchangeable and carbonate fractions had significant positive correlation with the respective metal concentrations in fish. Among the fish species, Catla catla and Etroplus suratensis showed the highest accumulation of metals suggesting risk for human consumption.