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Pioneer habitat-adapted bermudagrass is prevalent in the water-level-fluctuating zone of the Three Gorges Reservoir area. This study was performed to explore the response characteristics of dissolved organic matter (DOM) qualities to bermudagrass decomposition and their regulation in the distribution and release of mercury (Hg) and methylmercury (MeHg) in the soil-water system. Compared to the control, the bermudagrass decomposition resulted in a great increase in the protein-like components in the water in the initial stages (p < 0.01), but it also greatly reduced the humification degree of water DOM (p < 0.01). However, it accelerated the consumption of protein-like components, the humification rate, and the synthesis of humic-like DOM in the water over time. This changing pattern of the DOM qualities resulted in an initial elevation and a subsequent great decrease in the dissolved Hg and MeHg concentrations in the pore water, which ultimately reduced their release levels into the overlying water by 26.50% and 54.42%, respectively, compared to the control. Our results indicate the potential inhibitory effects of short-term bermudagrass decomposition caused by flooding and how decomposition affects the release of total Hg and MeHg by shaping the DOM qualities, and they have implications for similar aquatic systems in which herbaceous plants are frequently decomposed after submergence. [ABSTRACT FROM AUTHOR]

To explore the effects of herbaceous plants on mercury (Hg) behaviors after flooding in the water-level fluctuation zone (WLFZ) of Jialing River, three typical local plants (D. pyramidalis, A. philoxeroides and C. dactylon) and their in-situ sediments were collected for flooding experiments to study the Hg dynamics of water and sediment in different treatments. The results showed that flooding increased sediment MeHg concentrations and flooded plants (especially for the D. pyramidalis) promoted this process. Similarly, the highest dissolved MeHg level and proportion of MeHg to total Hg (%MeHg) were observed in plant-water treatments in the presence of D. pyramidalis, indicating the potential for the methylation of Hg in the water body influenced by the decay process of herbaceous plants. These results suggest that the herbaceous plant D. pyramidalis contributes more to Hg methylation and release in the WLFZ of the Jialing River than other plants studied. [ABSTRACT FROM AUTHOR]

To develop high-performance biochar adsorbents, the adsorption ability and rate of untreated (BC-CK) and six modified biochars with amino (BC-NH), epoxy (BC-C2H2O), ethoxy (BC-C2H5O), hydrosulfuryl (BC-SH), selenium (BC-Se), and chitosan (BC-Chitosan) on Hg(II) and MeHg were investigated by simulated experiment. The results indicated that the some modified biochars (BC-NH, BC-C2H2O, BC-C2H5O and BC-Chitosan) showed lower adsorption capacity than the untreated, possibly due to the decreased specific surface area and pore volume. Whereas, BC-SH and BC-Se was improved immensely by forming stable –SH–Hg and Hg–Se with the adsorption capacity 1.26 and 1.51 times as much as BC-CK, respectively. In spite of that, Hg desorption capacities and rates of all biochars were extremely low, exhibiting great adsorption stability of biochars on Hg in another way. In addition, BC-Chitosan performed the highest adsorption speed. These provided insights on the adsorption effectiveness for Hg in the aqueous solution that was critical for evaluating the application of modified biochars. [ABSTRACT FROM AUTHOR]

Total mercury (THg) and methylmercury (MeHg) concentrations were measured in hair of 98 Chinese university students to study their levels of Hg exposure and influencing factors. The results showed that Hg exposure for university students was at a low level with concentrations lower than the USEPA recommended reference level (1 µg/g) across all hair samples. The percentage of MeHg to THg (%MeHg) in hair was about 50%, lower than the previously reported value of 70–100%, probably associated with the low %MeHg in the diet of university students. Fish and rice consumption were not a primary factor affecting hair Hg levels of university students, while smoking could be one main pathway of Hg exposure. In addition, the similarly dietary structure in the studied university narrowed the difference of Hg exposure levels among students. [ABSTRACT FROM AUTHOR]

Water and sediment samples were collected from a tributary (Ruxi River) of the Three Gorges Reservoir (TGR) to analyze the concentrations of seven heavy metals (HMs) and their fractions for better understanding the migration, bioavailability and potential environmental risk of HMs. The results indicated that the concentrations of HMs in water were lower than the Environmental Quality Standards for Surface Water Class I standards, except for Ni. Cd in sediment was found to be more sensitive to environmental changes, as the acid-soluble fraction of Cd accounted for about 40% of total Cd, and the sediment–water partition coefficient of Cd was the smallest among all the HMs. Meanwhile, multiple risk assessment methods of HMs indicated that sediment Cd in most sampling sites, significantly influenced by human activities, exhibited heavy pollution, suggesting that the Cd pollution should be attached great importance in the Ruxi River. [ABSTRACT FROM AUTHOR]

Mercury (Hg) methylation is mainly a microbial process mediated by anaerobes. The continued study of Pseudomonas putida (P. putida) strain TGRB4 genome was inspired by the fact that it can transform Hg into the highly toxic methylmercury (MeHg) under aerobic conditions. P. putida strain TGRB4 is a Gram-negative rod-shaped Gamma-proteobacterium (γ-proteobacterium), isolated from the soil in a typical water level fluctuation zone (WLFZ) of the Three Gorges Reservoir (TGR), which suffered from seasonally water level alternations every year. Draft genome assembly of P. putida strain TGRB4 is presented here, which was sequenced using Illumina Hiseq and PacBio single-molecule real-time (SMRT) platforms. Its genome harbors a total of 5504 genes and a G + C content of 62.6%. We further identified the enzymes related to Hg methylation, and found two well-known methyltransferase, including 5-methyl-tetrahydrofolate (5-methyl-THF) and S-adenosylmethionine (AdoMet), were annotated in the genome of P. putida strain TGRB4. This genome information could be treated as a research material to further study the Hg methylation mechanisms under aerobic environment. [ABSTRACT FROM AUTHOR]

Agricultural watersheds are a crucial contributor of terrestrial dissolved organic matter (DOM) for the adjacent aquatic environment. Recently, ecological engineering of the buffer zone such as a rice-paddy field was established to reduce the export of nutrients and contaminants from a small agricultural watershed. However, the potential of the rice-paddy field to reduce the terrestrial signature of DOM is unclear. Therefore, two small agricultural sub-catchments (i.e., sub-1 and sub-2) with different land uses and hill slope angles in the Three Gorges Reservoir (TGR) area of China were studied from 2014 to 2015. The results showed that the terrestrial DOM signals are indicated by optical indices (SUVA254, SR, fluorescence index) in the steeper and more forest covered, but rice-paddy field buffered sub-catchment (i.e., sub-2) decreased significantly, as compared to the reference sub-catchment (i.e., sub-1). Regardless of seasonal variations, the rice-paddy field retained a buffering role to reduce the terrestrial property of DOM and the highest capacity was observed during the rice-growth period. However, during storm events, the differences of DOM properties for two sub-catchments were not significant, because the buffer system was weakened. Finally, environmental implications of the role of such a buffer zone in the TGR areas are discussed. These results demonstrate that rice-paddy fields are successful in mitigating the terrestrial property of exported DOM, but the weaker performance during storm events still needs to be considered. [ABSTRACT FROM AUTHOR]

The objective of this study was to investigate the transport dynamics of total mercury (THg) and methylmercury (MeHg) in the first rainfall-runoff event after summer drought, to understand flushing effects (FFEs) and to quantificationally estimate contributions to the annual outputs of Hg. The results showed that both THg and MeHg in rainfall-runoff predominated by particulate fraction peaked at the beginning of the monitoring period. On average, more than 80% of THg and MeHg loadings were transported during the initial runoff (≤ 6 h). Simultaneously, significant FFEs were observed for both THg and MeHg, with a larger effect for MeHg. More importantly, the estimated output fluxes of THg and MeHg in runoff produced by this rainfall event contributed 3.0% (THg) and 7.8% (MeHg) to the annual output fluxes, respectively, suggesting the importance of the first-rainfall on the Hg loss (especially for MeHg). [ABSTRACT FROM AUTHOR]

Mercury (Hg) is one of the most toxic heavy metal pollutants, which can be easily transmitted and enriched through the food chain, posing severe threat to human beings. Forest ecosystems are one of the most active environments for biogeochemical cycles of Hg. It is essential to research on Hg cycling in the forest ecosystem, which contributes to a comprehensive understanding of global biogeochemical cycle of Hg. However, there is still a lack of consensus on whether the forest ecosystem is a "source" or "sink" of Hg in the global Hg cycle so far. Therefore, it is necessary to elucidate the current state of knowledge on Hg deposition, transformation and fate in the forest ecosystem, especially the existing puzzles or issues encountered by scientists worldwide. This review highlights the complexity and uncertainties of Hg cycling in forest ecosystems. It is proposed that a new perspective is required to further understand the role of forest ecosystems in global Hg cycle based on a sufficient understanding of Hg exchange fluxes at the interface of air–soil and air–plant, Hg deposition flux through litterfall, and accurate construction of Hg mass balance system. [ABSTRACT FROM AUTHOR]

The Three Gorges Reservoir (TGR) is a relatively large reservoir, and its water level management actions produce a widespread water level fluctuation zone (WLFZ), which has characteristics of both terrestrial and aquatic ecosystems. Here, an integrated overview of current knowledge on Hg behaviors in the TGR, especially the WLFZ, as well as exposure risk to local residents was presented. Hg levels in the TGR were comparable with other natural aquatic systems. WLFZ in the TGR was confirmed to be an environment favorable for Hg methylation by enhancing microbial activity, promoting sulfur cycling and increasing the level of low-molecular-weight organic matters. However, elevated fish Hg concentrations did not follow the impoundment of TGR, indicating no obvious reservoir effect, while it is still noteworthy that frequently consuming fish is likely to be a methylmercury (MeHg) exposure pathway for specific populations e.g. fishermen around the TGR. [ABSTRACT FROM AUTHOR]

Mercury (Hg) methylation and demethylation is supposed to simultaneously exist in the environment and form a cycle, which determines the net production of methylmercury (MeHg). Exploring the mechanisms of MeHg formation and degradation, and its final fate in the natural environment is essential to understanding the biogeochemical cycle of Hg. However, MeHg demethylation has been less studied in the past years comparing with Hg methylation, particularly in anaerobic microorganisms whose demethylation role has been under-evaluated. This review described the current state of knowledge on biotic (microorganisms) and abiotic demethylation (photodegradation, chemical degradation) of MeHg. The decomposition of MeHg performed by microorganisms has been identified as two different pathways, reductive demethylation (RD) and oxidative demethylation (OD). Anaerobic and aerobic microorganisms involved in the process of RD and OD, influencing factors as well as research background and histories are systematically described in this review. It is predicted that the photodegradation mechanism, as well as anaerobic microorganisms involved in MeHg formation and degradation cycle will be the focus of future research. [ABSTRACT FROM AUTHOR]

Purpose: Previous studies demonstrated that microorganisms had an important role in the mercury (Hg) methylation process in the water and sediments of Three Gorges Reservoir (TGR). The purpose of this research was to analyze the microbial methylation of Hg in the soils and sediments of the water-level-fluctuating zone (WLFZ) of TGR.Materials and methods: Different types of soils, sediment (≤ 155 m), semi-inundated soil (≥ 155 m), and non-inundated soil (≥ 175 m) of the WLFZ of Shibao (S), Zhenxi (Z), and Tujing (T) were investigated. Real-time PCR, terminal restriction fragment length polymorphism (T-RFLP), cloning, sequencing, and phylogenetic analysis were used to analyze the abundance and diversity of dsrB, hgcA, and mcrA genes, and their relationship with the levels of total Hg (THg), MeHg, and several biogeochemical factors that probably affected microbial methylation reaction.Results and discussion: THg concentrations in different soil types of the WLFZ of TGR did not show significant differences (p > 0.05) in site S, while there were significant differences (p < 0.05) of MeHg levels in different soil types of the three sites. Phylogenetic analyses found that the dominant groups of microorganisms with dsrB in the sediment and non-inundated soil in site S differed remarkably. Microorganisms that probably related with Hg methylation mainly distributed in the sediment, with δ-proteobacteria as the dominant class. Real-time PCR found that soil MeHg levels correlated positively with the resident quantities of microorganisms with dsrB. The abundance of dsrB was much higher than that of hgcA which may indicate that only a small part of sulfate-reducing bacteria (SRB) related with Hg methylation.Conclusions: Soil MeHg levels correlated positively with the resident quantities of microorganisms with the dsrB gene. The phylogenetic analysis indicated that SRB that probably related with Hg methylation distributed mainly in the sediment, rather than in the non-inundated soil. [ABSTRACT FROM AUTHOR]

Previous research found that the water-level fluctuating zone (WLFZ) of the Three Gorges Reservoir (TGR) was an Hg-sensitive area. However, little research has been conducted on the distribution of Hg-methylating microorganisms in this area. The goal of this research was to provide an initial description of the distribution of the dsrB (for sulfate-reducing bacteria) and hgcA (one gene confirmed for Hg methylation) genes. Different types of soil were selected to analyze the abundance of the dsrB and hgcA in different periods, in inundated soil (SI, ≤155 m, which becomes sediment during the wet period, SS) and in non-inundated soil (≥175 m, SN) from Shibao, a typical WLFZ of the TGR. A significant positive correlation was observed between dsrB and hgcA abundance and MeHg concentrations, suggesting that microorganisms with these genes contribute to Hg methylation. Principal component analysis (PCA) indicated that dsrB diversity was highest in SI, followed by SS; SS had the highest diversity of hcgA. Six phylogenetic trees were constructed and showed that more strains were present in SI than in SS. HgcA sequences in SS were confined to three evolutionarily distant clades, δ-Proteobacteria, a methanogen group, and a Clostridia group, which was relatively rare among most clades. [ABSTRACT FROM AUTHOR]

Purpose: The environmental safety of both nano-TiO particles and mercury (Hg) pollution has been of widespread concern. Soils and sediments were the main receiving environments of nano-TiO and Hg. There was a strong association between nano-TiO with Hg compounds. Very limited research has been carried out on the impact of nano-TiO on the environmental behavior of Hg in sediments. The objective of this study was to investigate the effects of nano-TiO on the release and transformation of Hg in sediments. Materials and methods: Two types of TiO nanoparticles were employed. Sediment samples were collected in the water level fluctuating zone of the Three Gorges Reservoir, China. Sediment samples spiked with HgCl solution were taken as Hg-contaminated sediments. The flooding experiments were conducted using capped borosilicate glass bottles containing 300 ml TiO suspensions (0.2 g L and 0.4 g L) and 30 g original or Hg-contaminated sediment samples outdoors. All experiments were conducted in triplicate. Water samples were collected at determined interval times over a 60-day period. Sediments were collected on the 60th day. Total Hg (THg) and methylmercury (MHg) in both water and sediment samples and Hg speciation just in sediment samples were determined. A series of control samples without TiO addition were also prepared. Results and discussion: The results showed that nano-TiO particles at high content (4 g kg) promoted the release of Hg in sediments, and the anatase particles showed a stronger effect. Methyl Hg concentrations in waters of nano-TiO treatments significantly decreased by the 10th day. The effect of nano-TiO greatly depended on anatase and rutile particles. After that, methyl Hg concentrations had no significant difference between nano-TiO treatments and the control, except 2 g kg rutile treatment by the 20th day. The changes of Hg speciation in sediments demonstrated that nano-TiO inhibited the transformation of Hg-bound organic matter into the oxidated state, especially upon 2 g kg rutile treatment. This was consistent with the lower MHg concentrations in the 2 g kg rutile treatment. Conclusions: Both anatase and rutile nano-TiO were found to affect the release of Hg in sediment. Nano-TiO promoted THg release in sediments and posed an increased risk of Hg contamination in waters, especially for anatase particles. Moreover, nano-TiO inhibited the methylation process of Hg in sediments at the initial stage of flooding and could affect the transformation of Hg speciation in sediments, especially for low-content rutile particles. [ABSTRACT FROM AUTHOR]

Atmospheric mercury deposition by wet and dry processes contributes to the transformation of mercury from atmosphere to terrestrial and aquatic systems. Factors influencing the amount of mercury deposited to subtropical forests were identified in this study. Throughfall and open field precipitation samples were collected in 2012 and 2013 using precipitation collectors from forest sites located across Mt. Jinyun in southwest China. Samples were collected approximately every 2 weeks and analyzed for total (THg) and methyl mercury (MeHg). Forest canopy was the primary factor on THg and MeHg deposition. Simultaneously, continuous measurements of atmospheric gaseous elemental mercury (GEM) were carried out from March 2012 to February 2013 at the summit of Mt. Jinyun. Atmospheric GEM concentrations averaged 3.8 ± 1.5 ng m, which was elevated compared with global background values. Sources identification indicated that both regional industrial emissions and long-range transport of Hg from central, northeast, and southwest China were corresponded to the elevated GEM levels. Precipitation deposition fluxes of THg and MeHg in Mt. Jinyun were slightly higher than those reported in Europe and North America, whereas total fluxes of MeHg and THg under forest canopy on Mt. Jiuyun were 3 and 2.9 times of the fluxes of THg in wet deposition in the open. Highly elevated litterfall deposition fluxes suggest that even in remote forest areas of China, deposition of atmospheric Hg via uptake by vegetation leaf may be a major pathway for the deposition of atmospheric Hg. The result illustrates that areas with greater atmospheric pollution can be expected to have greater fluxes of Hg to soils via throughfall and litterfall. [ABSTRACT FROM AUTHOR]

Sediment core samples were collected from the Weihe River in February and August 2013. Cores were sectioned and analyzed for total Hg (THg) and methyl mercury (MeHg). THg in sediment cores ranged from 156 to 282 ng g in February, and from 172 to 300 ng g in August. MeHg concentrations ranged from 0.80 to 3.11 ng g in both seasons. Results showed that the diffusive fluxes were up to two orders of magnitude lower than the in situ benthic fluxes. Fluxes of MeHg measured in in situ experiments in August were positively correlated with $$ {\text{SO}}_{4}^{2 - } $$ ( r = 0.930). THg and MeHg release were not strongly correlated with TOC in February. Patterns of MeHg flux differed greatly depending on oxidation-reduction potential ( Eh) ( r > 0.70) conditions in the two seasons. [ABSTRACT FROM AUTHOR]

Biogeochemical cycling of mercury in the young Three Gorges Reservoir (TGR), China, is strongly considered. Although methylmercury (MMHg) photodegradation (PD) is an important process involved in mercury cycling in this zone, little is known about this process. In situ incubation experiments were therefore performed to quantify the effect of different wavelength radiations and environmental factors on the PD process of MMHg in the water bodies of TGR. It was found that the effect of solar radiation on MMHg PD was highly dependent on wavelength and water depth. All PD-rate constants resulting from each wavelength range decreased rapidly with water depth. For surface water, UV-A radiation (320-400 nm) was the key driver, accounting for 49%-62% of MMHg PD. For the entire water column, both photosynthetically active radiation (PAR, 400-700 nm) and UV-A were responsible for MMHg PD. MMHg PD fluxes peaked in summer (7.5−18 ng m d), followed by spring (3.3-8.0 ng m d), autumn (1.0-2.7 ng m d), and winter (0.060-0.15 ng m d). The annual fluxes of MMHg PD were estimated to be 1.1-2.8 μg m a. Filtering the reservoir water and amending it with chemicals (i.e., Cl, NO, and dissolved organic matter (DOM)) showed significant effects on MMHg PD rate constants. Stepwise regression analysis showed that intensity of solar radiation, suspended particulate matter (SPM), DOM, Cl, and NO were involved in the PD process. Path analysis clarified the relationship between MMHg PD rate constants and environmental variables, as well as the comparative strength of direct and indirect relationships among variables. The results are of great importance for understanding MMHg cycling characteristics in TGR and also facilitate the understanding of the underlying process, MMHg PD, in natural waters. [ABSTRACT FROM AUTHOR]

In order to explore the contributions of wet deposition and runoff formed by rainfall events to the water body mercury burden in Three Gorges Reservoir (TGR), we conducted a 1-year successive study on the deposition fluxes and runoff output characteristics of total mercury (THg) and methylmercury (TMeHg) in a typical small agricultural watershed in TGR areas. The results showed that the annual volume-weighted concentration (VWC) of THg and TMeHg was 18 and 0.23 ng L, respectively. Particulate form was the main form of both THg and TMeHg, accounting for 61 % of THg and 59 % of TMeHg. The annual deposition fluxes of THg and TMeHg in rainfall were 13 ± 2.4 μg m year and 174 ± 52 ng m year, respectively. The VWCs of THg and TMeHg in runoff were 10 ± 6.5 and 0.15 ± 0.15 ng L. The annual output fluxes of THg and TMeHg to TGR from study area were 1.2 ± 0.73 μg m year and 17 ± 16 ng m year, respectively. [ABSTRACT FROM AUTHOR]

For a typical alpine forest reservoir that does not have other obvious mercury pollution sources, mercury levels in its downstream water can reflect the characteristics of mercury inputs and risks of a remote forest. To confirm this proposal, eight sampling campaigns were carried out in 2012 and 2013 to investigate the distribution patterns of Hg species in the water column and sediment profiles at four sampling stations in an alpine forest reservoir, southwestern China. The concentrations of total Hg (THg) and methylmercury (MeHg) in water samples of DaHong Reservoir varied from 2.8 to 8.2 ng L and 0.06 to 2.9 ng L, respectively. The concentrations of these Hg species in the wet seasons (summer and fall) were significantly higher than those in the dry season (winter and spring). Forest field runoff and diffusion of Hg from sediments could be the reasons for elevated concentrations of these Hg species in the wet season. Elevated MeHg concentrations in water samples from the bottom water and water-sediment interface demonstrated an active net Hg methylation in the downstream of DaHong (DH) Reservoir. Dissolved MeHg levels in the pore water of surface sediments and the bottom of downstream were apparently higher than those in the upstream, which indicated that MeHg sources of sediment pore water varied in space. MeHg diffusive fluxes from sediment to overlying water were higher in the wet season than those in the dry season, demonstrating that high temperatures favor Hg methylation processes in sediment. [ABSTRACT FROM AUTHOR]

Photo-reduction of divalent mercury (Hg(II)) in aquatic systems plays a key role in global biogeochemistry cycling of mercury (Hg) in the Earth's surface environment. The mechanisms of this process with various Cl concentrations ([Cl]) under different pH values and irradiation wavelength ranges are still unclear. In this work, photo-reduction and photo-oxidation experiments of Hg with different [Cl] and pH values under various light conditions were conducted. The results show that photo-reduction rate constants of Hg(II) decrease with the increasing of [Cl] in neutral solution under full light spectrum. Photo-reduction rate constants of Hg(II) with Cl is highly dependent on Hg(II) species, which is determined by [Cl] and pH value. Irradiation wavelength ranges have significant effects on reaction processes of photo-reduction of Hg(II) and photo-oxidation of Hg(0) in the presence of Cl. When cut off ultraviolet (UV) radiation (280-400 nm), the reduction rate constants decrease without Cl, and increase with higher [Cl], and the photo-oxidation rates of Hg(0) decrease with or without Cl. Except Cl complexation stabilize the reducible Hg ions in solutions, photo-oxidation is an important reason for Cl lowering photo-reduction rate of Hg(II). The results are of great importance for understanding the photo-redox characters of Hg(II) with Cl. [ABSTRACT FROM AUTHOR]

Field investigations were conducted to study the temporal and spatial distribution characteristics of total culturable bacteria (TCB) and its relationship with methylmercury (MeHg) in the soils of the water level fluctuation zone of the Three Gorges Reservoir. Different altitudes (170-180, 170-175, 165-170 and 160-165 m) in Zhenxi (Site 1), Shibaozhai (Site 2) and Tujing (Site 3), Chongqing, China were chosen as sampling sites. Results indicated that TCB did not have significant difference in the top (0-10 cm) and sub (10-20 cm) soil of the non-inundated area (175-180 m), but showing a significant difference in the water level fluctuation zone (<175 m, suggesting that water level fluctuation had an important effect on TCB. Moreover, TCB in soils of various altitudes of Site 1 and 2 had significant difference, while for Site 3, this difference was not significant. And the difference of TCB in Site 2 was much greater than that in Site 1. These results suggested that there were significant differences for TCB in soils of mainstream and tributaries. In addition, TCB in soils of 10-20 cm had significant or highly significant positive correlations with MeHg level ( r ≥ 0.762, P ≤ 0.048), thus we assumed that there may be some aerobic microorganisms playing dominant roles in mercury methylation. [ABSTRACT FROM AUTHOR]

The exchange of mercury (Hg) across the air-water interface is an important part of Hg biogeochemical cycle. Mercury fluxes across the air-water interface in paddy fields were measured by a Dynamic Flux Chamber (DFC) coupled with a Lumex® multifunctional mercury analyzer RA-915 at two sites (Chengjiang (CJ) and Caoshang (CS)) in Beibei, Chongqing, China in 2008. The results showed that mercury emission followed a power-law relationship with solar radiation and air temperature, and it increased exponentially with water temperature at both sites. Mercury emission was mainly influenced by the solubility of gaseous elemental Hg, photo-thermal effect, electron activity (Eh) and air Hg concentrations. Solar radiation made the greatest direct contribution to mercury emission during the daytime (0.80), with an 83.60% contribution, whereas at nighttime the water temperature (0.72) contributed to 71.65% of emissions. The temperature gradient between water and air might also influenced mercury emission across the air/water interface at nighttime. These findings suggest that paddy fields could act as a significant source of atmospheric mercury, and it can contribute significantly to the atmospheric mercury in a local region. [ABSTRACT FROM AUTHOR]

An investigation was conducted to identify the characteristics of heavy metals in orange ecosystem in three areas in the Three Gorge Reservoir Region by using the modified Tessier sequential extraction procedure. The contents of Cu and Pb in different speciation fractions of the soils can be ordered as the Residual (F6)>Reducible (F4)>Oxidable (F5)>Water soluble (F1)>Carbonate (F3)>Exchangeable (F2), and the contents of Zn and Ni follow the order of the Residual (F6)>Oxidable (F5)>Reducible (F4)>Water soluble (F1)>Carbonate (F3)> Exchangeable (F2), and those of Cd follow the order of the Reducible (F4)>Oxidable (F5)>Exchangeable (F2)>Carbonate (F3)>Residual (F6)>Water soluble (F1). The concentrations of Cu in the different organs of oranges follow the increasing sequence of pulp>leaf>pericarp, those of Zn and Ni following the increasing sequence of leaf>pulp>pericarp, and those of Pb and Cd follow the increasing sequence of leaf>pericarp>pulp. Correlation degrees of different forms of same heavy metals in soils are according to the order of Cu>Zn>Cd>Pb>Ni. Correlation degrees of different heavy metals in same forms are according to the order that the forms of Reducible (F4), Oxidable (F5) and Residual (F6) are higher than the forms of Water soluble (F1), Exchangeable (F2) and Carbonate (F3). There are either positive or negative correlations between heavy metals in leaves and in pulp, while there are all positive correlations between heavy mentals in leaves and in pericarp. There are significant correlations between the concentrations of some heavy metals in leaves, pericarp or pulp, and those in speciation fractions in the soils. [ABSTRACT FROM AUTHOR]

In order to investigate the spatial and temporal variability of atmospheric mercury (Hg) in Chongqing, China, gaseous elemental mercury (GEM) was measured from August 2006 to September 2007, using Lumex® multifunctional mercury analyzer RA-915+ (Lumex Ltd., Russia). The mean GEM concentration was 6.74 ± 0.37 ng m−3 in Chongqing, much higher than the accepted global background values (1.5–2 ng m−3). The GEM concentrations were different in different function areas. GEM in transport, industrial and commercial areas were 7.07 ± 1.04, 7.05 ± 0.96 and 6.71 ± 1.10 ng m−3, respectively, while GEM was 6.14 ± 1.30 and 4.32 ± 1.04 in the educational/recreational and nature conservation areas, suggesting that Hg emissions from mobile vehicles and industrial sources (specially coal combustion) were the most important contributors to atmospheric Hg in Chongqing. Mean Hg concentrations also had monthly variations with highest in November (8.24 ± 0.50 ng m−3) and lowest values in August (5.36 ± 0.70 ng m−3). Additionally, the diurnal variation of GEM concentrations was dependent on the local/regional atmospheric conditions. At Jinyun Mountain site (natural conservation area), hourly GEM concentrations had much higher values in daytime than at night. At Power Plant site, however, the hourly GEM concentrations were lower in daytime than at night. GEM concentrations in the air were correlated significantly with meteorological parameters except for barometric pressure. [ABSTRACT FROM AUTHOR]

As a result of intensifying human activities around the Changshou Reservoir, water environmental quality has declined over the years. Water quality had been monitored from 1999 to 2002. The result indicated that the concentrations of total nitrogen (TN) and total phosphorus (TP) are high. The concentrations of phosphorus range from 0. 037 mg/L to 0. 444 mg/L, exceeding the critical value (0.02 mg/ L) for eutrophication. The concentrations of total nitrogen and chlorophyll a range from 0.70 mg/L to 4.18 mg/L and from 1.10 mg/m³ to 61.2 mg/m³, respectively. The eutrophication status of the water body was assessed using the method of integrated nutrition state index, which revealed that all sampling sites were eutrophicated from the year of 2001. About 69.6%o of the annual total nitrogen input and 26% of the annual total phosphorus input originated from the upstreams. The contributions of nitrogen and phosphorus from precipitation to the water body are very small (0.9% and 0.3%0, respectively) owing to their low contents (1.21 mg/L and 0.029 mg/L, respectively). Runoff is the secondarily important input source, which accounts for 19.0% of the total N input and 47.0% of the total P input, respectively. Attention should be paid to the aquaculture inputs, whose contributions account for 10.5% of the total N and 26.6% of the total phosphorus to the water body, respectively. Nutrient loads are estimated to be 118 gNm-2 ⋅ a-1 and 8 gPm-2 ⋅ a-1. About 69.4% of nitrogen and 79.7% of phosphorus input into the reservoir were retained in 2002. [ABSTRACT FROM AUTHOR]