81. 题目: Role of extracellular polymeric substances in sludge dewatering under modified corn-core powder and sludge-based biochar pretreatments
Extracellular polymeric substances (EPS) which wrapped on sludge particles were deemed to hinder the outflowing of combined water in sludge system. The complex composition of EPS was the bottleneck for revealing its relationship with sludge dewaterability. In this study, a combined modified corn-core powder (MCCP) and sludge-based biochar (SBB) condition was executed to treat sludge for enhancing dehydration performance, and the concentration and the form distribution of organics in EPS, the variances of protein secondary structures were investigated. Correlation between the sludge dewaterability and EPS components were performed, found strong correlations among the net sludge solids yield (YN) and the specific resistance of filtration (SRF) (R = −0.923), Zeta potential (R = −0.971). Furthermore, the relationship between the secondary structures of protein and dehydration performance were strong related. With the optimal dosage of SBB and MCCP, aggregated strands and -helix were released, indicated that the unfolding and despiralization in soluble EPS (S-EPS) were improved, disordered the sludge network, reduced the flowing resistance of bound water, finally enhancing sludge dewaterability.
82. 题目: Facet-Dependent Adsorption and Fractionation of Natural Organic Matter on Crystalline Metal Oxide Nanoparticles
83. 题目: Stable Carbon Isotopes δ 13 C as a Proxy for Characterizing Carbon Sources and Processes in a Small Tropical Headwater Catchment: Nsimi, Cameroon
84. 题目: Soil survey reveals a positive relationship between aggregate stability and anaerobically mineralizable nitrogen
Soil health status should be monitored to allow planning sustainable management, but indicators available do not encourage frequent soil health evaluation because of the complexity, time-consumption, and expensiveness of the methodologies. Aggregate stability (AS) is a good soil physical health indicator associated with soil (SOC) and particulate (POC) organic carbon but is difficult to monitor. Anaerobically mineralizable nitrogen (AN) has been proposed as soil health indicator because is cheap, simple, and safe to measure, is sensitive to soil-use changes, is also related to soil (SOC) and particulate (POC) organic carbon, and is frequently determined by farmers in Mollisols of the Southeastern Argentinean Pampas to support soil fertility diagnosis. We hypothesize that AN is positively related to and can be used as indicator of AS. Soil samples were taken at 0–5 and 5–20 cm depths from 46 sites throughout the southeastern Buenos Aires province, Argentinean Pampas. In each site, we sampled Mollisols under continuous cropping (CC) and others that had not been disturbed for many years (pseudo-pristine, PRIS). We determined texture, SOC, mineral-associated organic C, POC, AS and AN. We also calculated variable values for 0–20 cm. Soil organic carbon, POC, AN and AS were reduced by continuous cropping. Anaerobically mineralizable N was positively related to SOC (R2 = 0.74, 0.46, and 0.62 at 0–5, 5–20, and 0–20 cm) and POC (R2 = 0.73, 0.33, and 0.60, respectively). An important proportion of the total variability in AS was explained by SOC (R2 = 0.77, 0.65, and 0.73 at 0–5, 5–20, and 0–20 cm, respectively), POC (R2 = 0.75, 0.63, and 0.73, respectively), and AN (R2 = 0.78, 0.69, and 0.81, respectively). The AS increased with the increase of SOC, POC, and AN at all three depths, with slopes that did not differ between CC and PRIS, but with intercepts that differed. Neither sand nor clay contents significantly contributed to explain the variations in AS as a function of SOC, POC, and AN. An independent validation of the regression model relating AS and AN at 0–20 cm was done and the output was very good (RPIQ (ratio of performance to interquartile distance) = 2.20). Results support our hypothesis because AN was positively related to AS. Consequently, AN would be a good indicator of AS, SOC, and POC. Based on our results, we consider that a simple and cheap soil analysis as AN can not only be used to diagnose soil fertility, but to monitor soil physical and biochemical health status.
85. 题目: Main factors dominating the development, formation and dissipation of hypoxia off the Changjiang Estuary (CE) and its adjacent waters, China
Hypoxia off the Changjiang Estuary (CE) and its adjacent waters is purported to be the most severe in China, attracting considerable concern from both the scientific community and the general public. Currently, continuous observations of dissolved oxygen (DO) levels covering hypoxia from its appearance to disappearance are lacking. In this study, twelve consecutive monthly cruises (from February 2015 to January 2016) were conducted. The consecutive spatiotemporal variations in hypoxia throughout the annual cycle were elucidated in detail, and the responses of annual variations in hypoxia to the different influential factors were explored. Overall, hypoxia experienced a consecutive process of expanding from south to north, then disappearing from north to south. The annual variations in hypoxia were mainly contingent on stratification variations. Among different stages, there was significant heterogeneity in the dominant factors. Specifically, low-DO waters initially appeared from the intrusion of nearshore Kuroshio branch current (NKBC), as NKBC intrusion provided a low-DO background and triggered stratification. Thereafter, stratification was enhanced and gradually expanded northward, which promoted the extension of low-DO areas. The formation of hypoxia was regionally selective, and more intense organic matter decomposition at local regions facilitated the occurrence and discontinuous distribution of hypoxia. Hypoxic zones were observed at the Changjiang bank and Zhejiang coastal region from August (most extensively at 14,800 km2) to October. Thereafter, increased vertical mixing facilitated the dissipation of hypoxia from north to south.
86. 题目: Investigating sources and transformations of nitrogen using dual stable isotopes for Lake Okeechobee restoration in Florida
An analysis of nitrate concentrations and isotopic compositions was undertaken on Florida's large (1730 km2) and shallow (mean depth 2.7 m) Lake Okeechobee to determine possible connectivity between the lake's many inflows and outflows and to illustrate how stable isotopes can assist in the restoration of a very large subtropical lake. The Kissimmee River, as expected, dominated inflows to Lake Okeechobee (58.4 ± 2.11 m3/s) much higher than the second most important inflow, Fisheating Creek, (9.2 ± 0.27 m3/s).The primary outflows (which are sometimes inflows) are the Caloosahatchee (27.7 ± 0.63 m3/s), which flows westward to the Gulf of Mexico and the St. Lucie River (6.98 ± 0.30 m3/s) that flows eastward to the Atlantic Ocean. Water samples of inflows and outflows were collected at 14 locations around the lake in both the dry and wet seasons in 2018. Total nitrogen and total phosphorus averaged 1.56 ± 0.42 mg L−1 and 0.11 ± 0.06 mg L−1 respectively with no significant seasonal variations. Dissolved organic nitrogen (DON = TKN-NH4+) was the dominant form of nitrogen at all sampling sites, with an average value of 1.18 ± 0.32 mg L−1. The TN:TP ratios were mostly less than 22:1.
Isotope δ15N-NO3− ranged from −8.75 to 9.14‰, and δ18O-NO3− from −0.26 to 11.97‰. Inflow δ15N-NO3− and δ18O-NO3− measurements ranged from −3.92 to 9.14‰ and 0.50 to 11.97‰. A Bayesian mixing model output revealed that non-point sources from NH4+ fertilizers and soil nitrogen were the main nitrate sources in Lake Okeechobee. NH4+ fertilizer contributes 36.7% of nitrate in the dry season and 54.9% in the wet season, while soil N contributes 31.4% in the dry season and 25.1% in the wet season. Although pasture is the dominant land use in the watershed of Lake Okeechobee, manure was not the dominant source of nitrate; it contributes only 12.0% of the nitrate in the wet season and 25.4% in the dry season. Isotopes of NO3− suggested that denitrification was strong, and nitrification was weak in both the dry and wet seasons. High levels of NH4+ during the wet season, partly caused by weakness of nitrification, promoted uptake of NH4+ that affects microbial food web recycling processes in the lake. These results indicate that monitoring and regulatory strategies for the lake restoration should consider the control of nitrogen pollution sources from agriculture to complement the control of phosphorus inflows that are thought to be the main drivers for harmful algal blooms in the lake and downstream of the lake.
87. 题目: Effects of micro-topography on N2O emission from sediments in temperate streams
Denitrification is a major biological source or sink of N2O, an important greenhouse gas, which is a multi-step respiratory process that converts nitrate (NO3−) to gaseous forms of nitrogen (N2 or N2O). In aquatic ecosystems, the residence time and flow length within the streambed can modulate denitrification, which is highly affected by micro-topography of streambed. For the reason, various restoration projects targeting streams and rivers incorporate the installment of dune-shaped streambed, but its role in ecosystem functions and key controlling variables are still elusive. In this study, N2O fluxes according to streambed micro-topography were measured at four locations in two streams with dune-shaped streambeds in Korea. We found that micro-topographical variations influenced N2O fluxes, chemical properties, and denitrifier abundances, but that this effect was highly constrained by carbon availability. In sites with relatively higher DOC, N2O fluxes increased along the flow direction, and the highest flux of each site (19.1 ± 5.67 μg N2O-N m−2 h−1 and 16.2 ± 0.896 μg N2O-N m−2 h−1, respectively) was observed in the slope on the back side of the dune, followed by decreases afterward. In contrast, streams with low DOC concentration did not exhibit micro-topographical variations. This study suggests that the presence of small dunes in streams can substantially enhance N2O fluxes when carbon availability was appropriate. The variations of N2O flux highlight the importance of micro-topography and DOC concentration of sediment for the accurate estimation of uncertainty of N2O flux. This has further implication for stream restoration where installment or management of dune-shaped streambed is of importance in the removal of inorganic N in water.
88. 题目: Evolution properties and dechlorination capacities of particulate organic matter from a landfill
Particulate organic matter (POM) includes humin and non-degradable residues, and the knowledge about its composition, evolution and environmental behavior is limited. The composition, evolution and its influence on dechlorination of the POM in landfill was studied. The results show that POM accounts for 27 %–57 % of the organic matter in landfill cell, which is mainly composed of protein-, fulvic- and humic-like components. Firmicutes and Proteobacteria were the main microorganisms driving the compositional evolution of POM during the landfilling process. The electron acceptance capacities (EAC) and electron donating capacities (EDC) of POM were in the range of 0.05–0.51 μmol/gC−1 and 0.13–0.66 μmol/gC−1, respectively, and the average EAC and EDC of POM in the intermediate and old stage of landfill were higher than those in the initial stage. The combined action of MR-1 and POM increased the degradation rate of PCP by 20 %–40 %, which was ascribed to the reduction capacities and electron transfer process of POM. POM derived from the intermediate and old stages promoted PCP dechlorination more effectively when compared with the initial stage due to its high electron transfer capacities (ETC), which are of great significance for soil in-situ bioremediation.
89. 题目: Temporal trends of organic carbon accumulation in seagrass meadows from the northern Mexican Caribbean
Carbon sequestration in seagrass meadows mitigates the currently rising CO2 atmospheric levels, as these ecosystems are highly productive and preserve sediment organic carbon over long periods. Five 210Pb dated sediment cores, collected from seagrass meadows dominated by Thalassia testudinum in the northern Mexican Caribbean touristic corridor Cancun-Riviera Maya, were used to establish temporal trends of organic carbon (Corg) content, burial rates and stock variation over the past 100 years. Corg contents (0.17–1.94%) and burial rates (2.0–252 g m−2 yr−1) were generally within the lower end range reported for seagrass meadow sediments worldwide. Corg stock gradually increased over the past decades, associated with increasing sediment accumulation, possibly caused by inland erosion promoted by agricultural and forestry activities and, in the recent decades, by a rapid increase of urban development due to a fast growth of the tourist industry and population, likely causing fertilization of coastal waters. Seagrass meadow sediments in the northern Mexican Caribbean coastline showed long-term Corg storage and preservation, since ~ 40 to ~ 100 years depending on the core, which emphasizes the need to protect these ecosystems against impacts of global change, and their incorporation into climate change mitigation strategies should be considered.
90. 题目: The effect of climatic and edaphic factors on soil organic carbon turnover in hummocks based on δ13C on the Qinghai-Tibet Plateau
Hummocks (thúfur, pounus) are peculiar landforms usually formed by repeated freeze–thaw processes and differential frost heave, and are common in frost soil regions, especially in the Qinghai-Tibet Plateau. However, little is known about the response of δ13C in soil organic carbon (δ13CSOC) to soil and climate properties in hummocks. The β value indicates the decomposition rate of soil organic carbon (SOC) in soil, and was obtained from the slope of the regression between the log10-transformed SOC concentration and δ13CSOC in soil depth profiles. In this study, we investigated δ13CSOC and SOC contents along a soil profile (0–60 cm), together with edaphic and climatic properties, both in hummocks and control plots (alpine grasslands) on the northeastern Qinghai-Tibet Plateau. Then, the variations in δ13CSOC and β values, and the main factors affecting them, were analyzed. The results show that δ13CSOC increases with soil depth, while SOC decreases both in the hummocks and control plots. However, β values in the hummocks were significantly (P < 0.05) higher than in the control plots while δ13CSOC showed no difference between hummock and control. Redundancy analysis showed that altitude is the main control factor for δ13CSOC and β in the hummocks. Climate type was the main factor affecting δ13CSOC in the control plots, while mean annual precipitation and soil fractal dimension were the main factors controlling β. Overall, climate, rather than soil, is the key factor that affects the carbon turnover rate in the hummock in the northeastern QTP. The findings of this study will expand our understanding of the soil carbon cycle and δ13CSOC changes, especially in the case of hummocks.
91. 题目: Effects of dam construction on arsenic mobility and transport in two large rivers in Tibet, China
Construction of dams on the Singe Tsangpo (ST) and the Yarlung Tsangpo (YT) Rivers, the upper stretch of the Indus and the Brahmaputra Rivers, respectively, are expected to affect material transport. To evaluate the effects of dam construction on arsenic (As) mobility and transport in the ST River and the YT River in Tibet and the downstream river basins, water column and sediment core samples in the Shiquan Reservoir of the ST River and in the Zam Reservoir of the YT River were obtained in August 2017, and January and May 2018, and additionally, at the inflows and outfalls of the reservoirs. The seasonal variation of dissolved As contents in the inflow water of the Zam Reservoir and the Shiquan Reservoir was regulated by the mixing between the low-As river runoff and the high-As hot spring input. Water residence time (WRT) is a key variable regulating the variation of dissolved As contents in reservoirs and outflow waters with time. The absence of the oxic layer at the sediment-water interface reduced the accumulation of As in surface sediments under high-flow conditions. Arsenic mobility in sediment of the two reservoirs was mainly controlled by Mn oxides and organic matter. Reservoirs with long water residence time are more favorable for As retention. Sedimentation was the main mechanism of As retention. The Shiquan Reservoir with a longer WRT of 385 days can effectively retain 55% of the total arsenic load from upstream, while the Zam Reservoir has no effective retention of arsenic due to the very short WRT of 1.1 days. These have important implications on the geochemical and ecological environments of the downstream river basins.
92. 题目: Vermiremediation of cotton textile sludge by Eudrilus eugeniae: Insight into metal budgeting, chromium speciation, and humic substance interactions
Information on prospective metal remediation by Eudrilus eugeniae during vermicomposting of cotton textile sludge (CTS) is rather scarce. This investigation, therefore, evaluates the sanitization efficiency of this species in CTS and CTS + cow-dung (CD) based feedstocks against aerobic composting. Accordingly, reduction in Pb, Cd, Cr, and Zn concentrations was between 50 and 70% under vermicomposting. Budget equations substantiated that humic compound mediated chelation was the dominant route of metal removal, against nominal bioaccumulation by earthworms. Correlation statistics revealed that formation of humic compounds (humic acid, fulvic acid, and humin) greatly influenced the transition of toxic Cr6+ to benign Cr3+ during vermicomposting. Moreover, increase in total N content and P availability was significantly greater under vermicomposting than composting. Thus, E. eugeniae efficiently stabilized the feedstocks by reducing pH, Ca, S, and organic C and CTS + CD(2:1) was the most favorable feedstock for E. eugeniae vermicomposting in respect of metal detoxification and nutrient stabilization.
93. 题目: Water management impact on denitrifier community and denitrification activity in a paddy soil at different growth stages of rice
Rice is one of the largest water-consuming crops. Alternate wetting and drying (AWD) is now an effective water-saving practice for rice cultivation that has been widely applied across the world. AWD may increase denitrification loss. However, the underlying mechanism remains unclear. This study investigated denitrifier activity, abundance and community structure in the rice rhizosphere and bulk soil in response to water management at the internode elongation (IE) and flowering (F) stages. The results revealed that at the IE stage, AWD significantly increased denitrification capacity (DC) in the rhizosphere compared with continuously flooded practice (CF). DC was significantly and positively related to electrical conductivity (EC) and the abundance of nirS-harboring denitrifiers. AWD led to higher EC in the 0–20 cm soil layer than CF. Although AWD lowered nirS abundance by 15 % compared with CF, the activity of nirS-harboring denitrifiers was enhanced by 1.89-folds of CF. At the F stage, AWD significantly decreased DC relative to CF. AWD had lower dissolved organic carbon (DOC) than CF, and DOC was significantly correlated with DC. Compared with CF, AWD also markedly changed the structure and network stability of nirS and nirK communities, resulting in sharp decreases in the total number of links in nirK and nirS networks of rhizosphere. The soil pH and EC were the key factors shaping the structure of nirS and nirK communities. Overall, the increase in denitrification losses due to AWD occurred primarily at the IE rather than F stage, and this increase was attributed to a rise in EC and changes in the activity and structure of nirS community. These findings provide a new insight into the mechanism of impact of the water-saving practice on denitrification loss for rice cultivation.
94. 题目: Molecular composition and source apportionment of fine organic aerosols in Northeast China
We examined the characteristics and source apportionment of organic aerosols in ambient PM2.5 samples collected during the late autumn in Changchun, Northeast China. 8 compound classes (>90 individual species) were detected in the aerosol samples, including biomass burning tracers, aliphatic lipids (fatty acids and fatty alcohols), secondary oxidation products, polycyclic aromatic hydrocarbons (PAHs), sugar compounds, hopanes and biogenic secondary organic aerosol (SOA) tracers. The concentrations of total quantified organic species ranged from 138.2 to 6.8 × 103 ng m−3, among which levoglucosan was the most abundant compound. Biomass burning tracers (anhydrosugars, lignin and resin acids) were the most abundant compounds, followed by fatty acids, secondary oxidation products, PAHs, sugar compounds and fatty alcohols. Biogenic SOA tracers and hopanes were less abundant. The homohopane index [defined as 31abS/(31abS + 31abR)] was 0.5, indicating a potential contribution of traffic emission. PAHs showed a dominance of benzo(b)fluoranthene (BbF), and the diagnostic ratios implicated a substantial contribution of petroleum combustion as well as coal combustion. 2-methylglyceric acid to 2-methyltetrols ratio (2.2) indicated that NOx influence isoprene oxidation products formation. Furthermore, the average ratio of cis-pinonic acid plus pinic acid to 3-hydroxyglutaric acid (31.4) revealed the much fresher α/β-pinene oxidation products to some extent. A good correlation was found between β-caryophyllinic acid and levoglucosan (r = 0.61), suggesting that β-caryophyllene can mainly be generated by biomass burning. The biogenic secondary organic carbon (SOC) was underestimated by the tracer-based method, which only occupied 0.4% of the organic carbon (OC). In contrast, PMF model indicated that emissions from fossil fuel combustion and biomass burning were most important, accounting for 42.4% and 33.6%, respectively, followed by biogenic SOA emission (17.0%) and fungal spore derived source (7.0%), suggesting biogenic aerosol is a nonnegative contributor.
Fossil fuel combustion (42.4%) as well as biomass burning (33.6%) were most important contributors of organic aerosols in a typical city in Northeast China.
95. 题目: Revisiting afro-alpine Lake Garba Guracha in the Bale Mountains of Ethiopia: rationale, chronology, geochemistry, and paleoenvironmental implications
96. 题目: Molecular Characterization of Water‐soluble Brown Carbon Chromophores in Beijing, China
High abundance and strong light absorption of atmospheric brown carbon (BrC) have been reported in East Asia, especially in northern China. However, the molecular‐level understanding of BrC chromophores in this area are still limited and quite challenging. In this study, elemental composition of individual BrC chromophores were first investigated in the megacity of Beijing, China, using a powerful platform for the characterization of BrC chromophores, with combination of high‐performance liquid chromatography coupled to a UV/Vis absorbance detector and a time‐of‐flight mass spectrometer with an electrospray ionization source (LC/DAD‐ESI‐HR‐TOFMS). The results from this study showed that S‐containing compounds (e.g., CHOS and CHONS) significantly increased in highly polluted days compared to lightly polluted days, probably due to increased emissions from sources such as coal combustion and favorable conditions for organosulfates formation. It was found that CHON and CHO compounds were the most abundant water‐soluble organic compounds in Beijing especially during the wintertime. Nitro‐aromatic compounds were the major water‐soluble BrC chromophores, with three major BrC chromophores (e.g., C6H5NO3, C7H7NO4, and C6H5NO4) found under all conditions, while other specific BrC chromophores with CHON‐ and CHO‐containing elemental formulas identified and varied in different seasons and pollution conditions. Overall, the water‐soluble BrC chromophores identified in this study explained about 2‐18% of the bulk BrC absorbance over the wavelength range of 300‐400 nm. In‐depth studies on exploring more BrC chromophores as well as their chemical structures, related sources and formation mechanisms should be conducted in the future.
97. 题目: A new in-field indicator to assess the impact of land management on soil carbon dynamics
The assessment of the impacts of land-use and management on soil organic carbon (SOC) dynamics is a major environmental concern, as the soil carbon cycle underpins key ecosystem services. However, assessments based on short-term SOC dynamics face methodological and experimental difficulties. Hurisso et al. (2016) proposed a method to assess SOC dynamics by coupling two methods: Permanganate Oxidizable Carbon (POXC) and Basal Soil Respiration (BSR). This method has been used in laboratory on dried and re-wetted soil samples from temperate regions mainly. In our study, we adapted this method to the field and proposed a cost-effective in-field indicator combining the POXC and in situ Basal Soil Respiration (SituResp® method).
We tested the indicator at four study sites (n = 169 points) within various tropical land-use and management contexts based on rubber, soybean and oil palm cropping systems respectively in Thailand, Cambodia and Indonesia. The results demonstrated the relevance, sensitivity and robustness of the POXC-SituResp® indicator to characterize the impact of a gradient of disturbance on SOC dynamics. The results also highlighted the potential of conservation agriculture (no-tillage and crops residues) and compost amendments to accumulate SOC. Rock-Eval® analysis showed that POXC-SituResp® indicator is negatively linked to excess of potentially mineralizable labile carbon. Carbon pools targeted by the POXC were specified by Rock-Eval® pyrolysis measurements to be a rather thermal resistant pool of SOC.
Our study confirms that the integrated indicator based on POXC and BSR assess a relative carbon stabilization of SOC pools. This indicator can be measured in the field by a rapid and cost-effective method.
98. 题目: Chemical and physical characterization of spent coffee ground biochar treated by a wet oxidation method for the production of a coke substitute
Coke production relies on the availability, cost and quality of coking coal. Depleting coking coal resources and environmental pressure force the metallurgical industry to search for alternative methods to produce coke. Waste spent coffee grounds (biomass) treated via hydrothermal liquefaction (HTL) is an energy-efficient method to produce biochar. In this study the use of HTL biochar as feedstock for the production of a coke substitute was investigated. Wet oxidation treatment of the prepared biochar samples was done with different wet oxidant hydrogen peroxide concentrations (5, 15, 30%). The biochar was treated for different time durations (0.5, 1, 2, 6 and 24 h) and at different temperatures (room temperature and 80 °C). Thereafter, the various samples were characterized and pyrolysed to obtain a coke substitute. Characterization of the various samples before and after thermal treatment was done using Fourier-transform infrared spectroscopy (FTIR), free swelling index, ultimate and proximate analysis, gross calorific value and compressive strength determination. The investigated characteristics of the produced coke substitute obtained from the pyrolysed biochar treated for 24 h with 30 vol% H2O2 at room temperature, showed the most promising results when compared to blast furnace coke.
99. 题目: The remediation of urban freshwater sediment by humic-reducing activated sludge
Organic pollution of urban rivers caused by stormwater discharge is a global problem. Traditional bioremediation of organic matters (OM) by aerobes could be restrained in anaerobic environments, which usually occurr in polluted river sediments. In this study, an anaerobic remediation technology has been developed to enhance the in-situ removal of organic matters in river sediments, humic-reducing sludge (HRS) was adapted from traditional activated sludge; it exhibited a strong humic-reducing ability. Nitrate and biostimulants were used to stimulate HRS. The change of microbial community between AQDS-adapted and non-AQDS-adapted was analyzed, and the effect of HRS augmentation and Nitrate/biostimulant addition on TOM removal were discussed from the perspective of light and heavy fraction organic matters (LFOM and HFOM). The results have indicated that, after adaptation, HRS had increased the bacterial population of Anaerolineales and Desulfuromonadales, which was related to the carbon metabolism and electron-transfer ability. On the other hand, the adaptation decreased the population of bacteria related to the sulfur/sulfate circulation. This characteristic of the HRS was potentially benificial to reducing the occurrence of black-odor phenomenon. Also, the removal efficiency of TOM in sediment was significantly improved by using HRS because HRS could facilitate the removal of HFOM. Fourier Transform Infrared Spectroscopy (FTIR) analysis indicated that the advantage of decomposing HFOM using HRS resulted from the fact that the HFOM contained redox mediators to facilitate humic-reducing respiration. In addition, nitrate appeared to be crucial for the enhancement of HRS in sediments. These findings have allowed for the development of a technology for in-situ anaerobic remediation of urban river sediments. They could also help to understand humic-reducing mechanism in the sediment during anaerobic bioremediation.
100. 题目: The driving factors of mercury storage in the Tibetan grassland soils underlain by permafrost
Soils, especially permafrost in the Arctic and the Tibetan Plateau, are one of the largest reservoirs of mercury (Hg) in the global environment. The Hg concentration in the grassland soils over the Tibetan Plateau and its driving factors have been less studied. This study analyzes soil total mercury (STHg) concentrations and its vertical distribution in grassland soil samples collected from the Tibetan Plateau. We adopt a nested-grid high-resolution GEOS-Chem model to simulate atmospheric Hg deposition. The relationship between STHg and soil organic carbon (SOC), as well as atmospheric deposition, are explored. Our results show that the STHg concentrations in the Tibetan Plateau are 19.8 ± 12.2 ng/g. The concentrations are higher in the south and lower in the north in the Tibetan Plateau, consistent with the previous results. Our model shows that the average deposition flux of Hg is 3.3 μg m−2 yr−1, with 57% contributed by dry deposition of elemental mercury (Hg0), followed by dry (19%) and wet (24%) deposition of divalent mercury. We calculate the Hg to carbon ratio (RHg:C) as 5.6 ± 6.5 μg Hg/g C, and the estimated STHg is 86.6 ± 101.2 Gg in alpine grasslands in the Tibetan Plateau. We find a positive relationship between STHg and SOC in the Tibetan Plateau (r2 = 0.36) and a similar positive relationship between STHg and atmospheric total Hg deposition (r2 = 0.24). A multiple linear regression involving both variables better model the observed STHg (r2 = 0.42). We conclude that SOC and atmospheric deposition influence STHg simultaneously in this region. The data provides information to quantify the size of the soil Hg pool in the Tibetan Plateau further, which has important implications for the Hg cycles in the permafrost regions as well as on the global scale.