21. 题目: Distribution and drivers of antibiotic resistance genes in brackish water aquaculture sediment
Brackish water aquaculture has brought numerous economic benefits, whereas anthropogenic activities in aquaculture may cause the dissemination of antibiotic resistance genes (ARGs) in brackish water sediments. The intricate relationships between environmental factors and microbial communities as well as their role in ARGs dissemination in brackish water aquaculture remain unclear. This study applied PCR and 16S sequencing to identify the variations in ARGs, class 1 integron gene (intI1) and microbial communities in brackish water aquaculture sediment. The distribution of ARGs in brackish water aquaculture sediment was similar to that in freshwater aquaculture, and the sulfonamide resistance gene sul1 was the indicator of ARGs. Proteobacteria and Firmicutes were the dominant phyla, and Paenisporosarcina (p_ Firmicutes) was the dominant genus. The results of correlation, network and redundancy analysis indicated that the microbial community in the brackish water aquaculture sediment was function-driven. The neutral model and variation partitioning analysis were used to verify the ecological processes of the bacterial community. The normalized stochasticity ratio showed that pond bacteria community was dominated by determinacy, which was affected by aquaculture activities. The total nitrogen and organic matter influenced the abundance of ARGs, while Proteobacteria and Thiobacillus (p_Proteobacteria) were the key antibiotic-resistant hosts. Our study provides insight into the prevalence of ARGs in brackish water aquaculture sediments, and indicates that brackish water aquaculture is a reservoir of ARGs.
22. 题目: Aerobic denitrifying using actinobacterial consortium: Novel denitrifying microbe and its application
The aerobic denitrifying capacity of actinomycete strain has been investigated recently, while little is known about nitrogen and carbon substrate removal by mix-cultured aerobic denitrifying actinobacteria (Mix-CADA) community. Hence, three Mix-CADA consortiums, named Y23, X21, and Y27, were isolated from urban lakes to investigate their aerobic denitrification capacity, and their removal efficiency for nitrate and dissolved organic carbon were >97 % and 90 %, respectively. Illumina Miseq sequencing revealed that Streptomyces was the most dominant genus in the Mix-CADA consortium. Network analysis indicated that Streptomyces exfoliates, as the core species in the Mix-CADA consortium, majorly contributed to dissolved organic carbon and total nitrogen reduction. Moreover, the three Mix-CADA consortiums could remove 78 % of the total nitrogen and 61 % of the permanganate index from the micro-polluted l water. Meanwhile, humic-like was significantly utilized by three Mix-CADA consortiums, whereas Mix-CADA Y27 could also utilize aromatic protein and soluble microbial by-product-like in the micro-polluted raw water purification. In summary, this study will offer a novel perspective for the purification of micro-polluted raw water using the Mix-CADA consortium.
23. 题目: Exploring the carbon capture and sequestration performance of biochar-artificial aggregate using a new method
To achieve the ambitious goal of carbon neutrality, more carbon sequestration channels need to be developed. In this study, we tried to combine biochar with cold-bonded artificial lightweight coarse aggregate (ALCA) which is made from municipal solid household waste incineration bottom ash (MSWIBA).The strong carbon capture ability of biochar was used to attract external CO2 into the interior of ALCAs, which combined with CaO in MSWIBA to form CaCO3 to achieve the effect of chemical carbon sequestration. The total carbon sequestration and carbon sequestration rate of biochar-ALCAs were quantified by a self-designed CO2 concentration change test box, the physical and mechanical properties of biochar-ALCAs were investigated, as well as the changes before and after carbonization. The results showed that biochar and ALCAs had good synergistic carbon sequestration ability. The total carbon sequestration of biochar-ALCAs could reach 30.58–33.06 kg/ton. The carbon sequestration efficiency could reach 70.2 % and 84.9 % at 28 d/56 d in a low CO2 concentration environment (0.05 % VOL). In addition, the water absorption of biochar-ALCAs decreased by 4.3 %–13.9 %, the apparent density increased by 0.9 %–2.8 %, and the strength increased by 4.3 %–7.0 % after carbon sequestration, and the physical and mechanical properties were significantly improved. The purpose of this paper is to investigate the synergistic carbon sequestration of biochar in combination with ALCAs and to quantitatively assess its ability to solidify low concentrations of CO2 in the natural environment. A new test apparatus and test method were designed for this purpose. This paper may contribute for an important advance on the preparation of recyclable cement-type composites able to capture and solidify CO2 from the natural environment.
24. 题目: Enhanced nitrogen removal from low C/N municipal wastewater employing algal biochar supported nano zero-valent iron (ABC-nZVI) using A/A/O-MBR: Duration and rehabilitation
To bridge the organic-dependent barrier on nitrogen from low carbon/nitrogen (C/N) municipal wastewater, employing algal biochar supported nano zero-valent iron (ABC-nZVI) was investigated using A/A/O-MBR. Firstly, it can be seen that adequate carbon source is indispensable for the removal, since total nitrogen (TN) removal reached 77.89 % with the influent C/N of 7.8. Secondly, conducted in batch experiments with different doses of ABC-nZVI with/without active sludge, removal efficiency of total inorganic nitrogen (TIN) and the effective time achieved 84.94 % and 24 h with an ABC-nZVI dose of 300 mg/L, respectively. Thirdly, it was found that the duration of high-efficiency denitrification reached 9 h with the addition of 250 mg/L of ABC-nZVI to the anoxic tank of A/A/O-MBR, and the effluent NH4+-N also meet the national discharge standard. Besides, biodiversity of both anoxic and aerobic sludge was apparently promoted with the addition of ABC-nZVI, while the lab-scale A/A/O-MBR could also be fully rehabilitated within 12 h. Finally, predicted through PICRUSt2, relevant abundance of functional genes involved in nitrogen metabolism could be enriched by nZVI addition. As an alternative supporting electron donor and mediator, ABC-nZVI can also be participated in the enhanced nitrogen removal in A/A/O-MBR at low C/N.
25. 题目: Electron exchange capacities of colloidal biochar: Affected by spatial structure distribution instead of particle size
Electron exchange capacities (EEC) of biochar have a wide impact on the environmental electron transfer processes. However, during the application, the gradual disintegration and aging will lead to the structure of the residual biochar after producing micro/nanosized biochar being different from fine particles. It is questionable how the persistently produced micro/nanosized biochar and the residual biochar will perform especially in the EEC aspect. Herein, bulk biochar (<75 μm) was water-exfoliated repeatedly by ultrasonication of gradient intensity. The structure and functional groups as well as EEC of multi-exfoliated biochar (<1 μm) and the pristine/residual biochar were characterized. It turned out that the EEC of exfoliated biochar was influenced by spatial structure distribution instead of particle size. Colloidal starch-char expressed descending EEC while colloidal pine-char was reverse with increasing times of exfoliation, resulting from the different distribution of oxygenated functional groups in the bulk biochar particles. This distribution was ascribed to different pyrolysis mechanisms of starch (decomposition and condensation) and wood (unreacted-core-shrinking approximation). The findings can provide insights into long-term effects of EEC caused by biochar fragments physically degraded from bulk biochar during applications.
26. 题目: Meta-analysis of global soil data identifies robust indicators for short-term changes in soil organic carbon stock following land use change
The restoration of degraded lands and minimizing the degradation of productive lands are at the forefront of many environmental land management schemes around the world. A key indicator of soil productivity is soil organic carbon (SOC), which influences the provision of most soil ecosystem services. A major challenge in direct measurement of changes in SOC stock is that it is difficult to detect within a short timeframe relevant to land managers. In this study, we sought to identify suitable early indicators of changes in SOC stock and their drivers. A meta-analytical approach was used to synthesize global data on the impacts of arable land conversion to other uses on total SOC stock, 12 different SOC fractions and three soil structural properties. The conversion of arable lands to forests and grasslands accounted for 91 % of the available land use change datasets used for the meta-analysis and were mostly from Asia and Europe. Land use change from arable lands led to 50 % (32–68 %) mean increase in both labile (microbial biomass C and particulate organic C – POC) and passive (microaggregate, 53–250 μm diameter; and small macroaggregate, 250–2000 μm diameter) SOC fractions as well as soil structural stability. There was also 37 % (24–50 %) mean increase in total SOC stock in the experimental fields where the various SOC fractions were measured. Only the POC and the organic carbon stored in small macroaggregates had strong correlation with total SOC: our findings reveal these two SOC fractions were predominantly controlled by biomass input to the soil rather than climatic factors and are thus suitable candidate indicators of short-term changes in total SOC stock. Further field studies are recommended to validate the predictive power of the equations we developed in this study and the use of the SOC metrics under different land use change scenarios.
27. 题目: Novel Insights into the Temporal Molecular Fractionation of Dissolved Black Carbon at the Iron Oxyhydroxide - Water Interface
As the most reactive and mobile fraction of black carbon, dissolved black carbon (DBC) inexorably interacts with minerals in the biosphere. Nevertheless, the research on the mechanisms and compositions of DBC assembly at the mineral-water interface remains limited. In this study, we revealed the “kinetic architecture” of DBC on iron oxyhydroxide at novel insights based on the quantitative and qualitative approaches. The results indicated that high molecular weight, highly unsaturated, oxygen-rich (such as carboxyl-rich fraction, phenolics), aliphatics, and long C chains compounds were preferentially adsorbed on the iron oxyhydroxide. 2D-COS analyses directly disclosed the sequential fractionation: aromatic and phenolic groups > aliphatic groups, and few aromatics were continuously adsorbed after the rapid adsorption. Quantitative determinations identified that aromatic and phenolic components were adsorbed rapidly over the first 60 min, while aromatics achieved the dynamic equilibrium until ∼300 min, which was consistent with the 2D-COS observations. Our findings supported the hypothesis that “mineral-OM” and “OM-OM” interactions worked simultaneously, and the adsorption might be co-driven by ligand exchange, hydrophobic interactions, and other mechanisms. This work provided the theoretical basis for organic carbon storage and turnover, and it was valuable for predicting the behaviors and fates of contaminants at the soil-water interface and surface water.
28. 题目: Responses of N2O emissions to straw addition under different tillage soils: A 15N labelling study
Nitrous oxide (N2O) emissions contribute to global climate change and are regulated by the intensities of N mineralization, nitrification and denitrification processes. These processes depend on soil management, e.g., tillage and straw addition. Microbial mechanisms underlying the effects of straw addition on N2O emissions were investigated by 56-day incubation of soil from a long-term (27-year) no-tillage (NoTill) and conventional tillage (ConvTill) field experiment. The abundance of N functional genes (amoA, amoB, nirK, nirS and nosZ) in no-tillage and conventional tillage soils was analysed based on straw addition. The application of 15N-labelled straw allowed us to trace N2O sources. Conventional tillage with 15N-labelled straw (ConvTill+Straw) reduced N2O emissions derived from soil by 42 %, whereas no-tillage with 15N-labelled straw (NoTill+Straw) reduced N2O emissions by only 8 % compared with soil without straw addition. The N2O emissions derived from straw were higher under NoTill+Straw than under ConvTill+Straw, whereas they accounted for only ~4 % of the total N2O emissions under both conditions. The nirK and nirS gene abundances were higher than those in soil without straw addition. Compared to that under ConvTill, the nosZ gene abundance was higher and the N2O emissions were 40 % lower under ConvTill+Straw, indicating its strong capacity to reduce N2O to N2. Pathway analysis showed that gene (amoA and nirK) abundance combined with soil properties (particulate organic matter nitrogen (POMN) and NO3−) were the main factors affecting N2O emissions, with increased POMN and nirK abundance driving increased N2O production under NoTill+Straw. However, gene (amoA, amoB, nirS and nosZ) abundances affected N2O emissions, with the nosZ gene being the main factor decreasing N2O under ConvTill+Straw. These findings revealed that straw return suppressed N2O emissions in conventional tillage soil, which may mitigate greenhouse gas emissions.
29. 题目: Different feedstocks of biochar affected the bioavailability and uptake of heavy metals by wheat (Triticum aestivum L.) plants grown in metal contaminated soil
Heavy metals (HMs) contamination of agricultural soils is an emerging food safety challenge at world level. Therefore, as a possible treatment for the remediation of a HMs contaminated soil (sewage water irrigation for 20-years), the impact of biochar (BC) was investigated on the uptake of HMs by wheat (Triticum aestivum L.) plants. The BC was produced from seven different feedstocks (cotton stalks (CSBC), rice straw (RSBC), poultry manure (PMBC), lawn grass (LGBC), vegetable peels (VPBC), maize straw (MSBC), and rice husks (RHBC)). Each BC was applied at 1.25% (dry weight basis, w/w) in contaminated soil and a control was maintained without BC addition and wheat was grown in potted soil and harvested at maturity. Results revealed that the properties of different biochars regulated their effects on soil nutrient and HMs mobility and uptake by plants. The maximum plant phosphorous and potassium uptake and translocation to grain (173.4% and 341%, respectively) was found in RSBC treatment over control. The RHBC, PMBC, and MSBC treatments showed a maximum decrease in grain Cd concentration (32.9%, 33.8%, and 34.1%, respectively) compared to the control. The grain Pb (−41% to −51%, with no significant differences among different treatments) and Ni (−63%) concentrations were also reduced significantly following BC treatments compared to control. The daily intake and health risk index of Cd were significantly decreased due to PMBC (−28.1% and −33.8%, respectively), and MSBC (−28.3% and −34.1%, respectively) treatment over control. The BC treatments significantly increased the translocation factor of Cd in the order of VPBC (52.1%) > LGBC (25.4%) > CSBC (13.6%) > RSBC (12.1%) compared to control. The study demonstrated that the effects of BC on metal uptake in plants varied with feedstocks and suitable BC can be further exploited for the rehabilitation of contaminated soils and thereby ensuring food safety.
30. 题目: Insight into boron-doped biochar as efficient metal-free catalyst for peroxymonosulfate activation: important role of -O-B-O- moieties
In recent years, metal-free catalysts for persulfate-mediated oxidation processes have been widely applied to remove contaminants in the aquatic environment. Herein, a simple pyrolysis approach was used to synthesize the boron doped biochars (B@TBCs) derived from boric acid mixed with tea seed shells powders. The obtained B@TBCs exhibited fantastic capability to boost PMS (0.5 mM) activation for 90%~ removal of oxytetracycline (OTC) within 20 min. Through the correlation analysis and DFT calculations, it was concluded that the apparent rate constant of pollutants removal was greatly related to the -O-B-O- groups on the biochars, which could improve the electron-donating capacity of the biochar. In addition, the degradation process of OTC was pH-dependent because of the changed roles of ROSs under different pH. Finally, according to the DFT calculation, LC-MS and toxicological analysis, the degradation pathways of pollutants and the toxicity changes during the degradation process were obtained. These findings consolidated the theoretical basis for further boosting the catalytic activity of B-doped biochars and expanded the imagination for the modification of other metal-free biochar catalysts for PMS activation.
31. 题目: Synthesis of heated aluminum oxide particles impregnated with Prussian blue for cesium and natural organic matter adsorption: Experimental and machine learning modeling
Heated aluminum oxide particles impregnated with Prussian blue (HAOPs-PB) are synthesized for the first time using different molar ratios of aluminum sulfate and PB to improve the adsorption of cesium (133Cs+) and natural organic matter (NOM) from an aqueous solution. The Cs+ adsorption from various aqueous solutions, including surface, tap and deionized water by synthesized HAOPs-PB, is investigated. The influencing factors such as HAOPs-PB mixing ratio, pH and dosage are studied. In addition, pseudo 1st and 2nd order is tested for adsorption kinetics study. A machine learning model is developed using gene expression programming (GEP) to evaluate and optimize the adsorption process for Cs+ and NOM removal. Synthesized adsorbent showed maximum adsorption at a 1:1 M ratio of aluminum sulfate and PB in DI, tap, and surface water. The pseudo 2nd order kinetics model described the Cs + adsorption by HAOPs-PB more accurately that indicating physiochemical adsorption. Adsorption of Cs+ showed an increasing trend with higher HAOPs-PB concentration, while high pH also favored the adsorption. Maximum NOM adsorption is found at a higher HAOPs-PB dosage and a neutral pH value. Furthermore, the proposed GEP model shows outstanding performance for Cs+ adsorption modeling, whereas a modified-GEP model presents promising results for NOM adsorption prediction for testing dataset by learning the relationship between inputs and output with R2 values of 0.9348 and 0.889, respectively.
32. 题目: Early Diagenetic Processes in an Iron-Dominated Marine Depositional System
The early diagenetic interplay between reactive iron, sulfur, and organic matter in the bathymetrically isolated Santa Monica Basin (SMB) sediments are investigated in this study. We explore solid-phase and porewater profiles from the basin supplemented with a transect from 71 to 907 meters water depth that includes oxygenated (>60 μM O2) bottom waters near the coast and oxygen-deficient waters (∼4 µM O2) in the basin. The geochemical data of the basin sediments are further scrutinized by means of reactive transport modeling.
The results show that the basin sediments do not follow the traditional geochemical signatures of oxygen-deficient settings. A lack of dissolved sulfide accumulation and sulfurized iron persists despite the sediments being deposited under reducing conditions (without bioturbation/bioirrigation), strong organic carbon input (TOC up to 5.0 wt%), and active dissimilatory sulfate reduction. Not only did we find an exceptional enrichment in highly reactive Fe in the surface sediments (∼45% of total Fe), but the enrichment of reactive Fe, including ferrihydrite, persists downcore and coexists with high levels of dissolved Fe. The enhanced preservation of Fe oxides and lack of iron-sulfide precipitation is in part explained by detection via Mössbauer spectra of iron oxides bounded to organic matter (Fe[III]-OM coprecipitates).
The modeled Fe budget shows that most of the Fe oxides in the surface sediments are internally recycled by upward diffusion and subsequent oxidation of Fe2+. Sulfide oxidation coupled to Fe reduction effectively precludes sulfide accumulation while enhancing build-up of dissolved Fe, fueling the Fe cycle within the first 5 cm depth. Continuous reoxidation of Fe2+ enhances the formation of Fe(III)-OM coprecipitates, limiting the amount of reactive organic matter. In the unavailability of labile organic matter, other than within the uppermost layers, the organic-rich sediment profiles are dominated by iron cycling that limits the production and preservation of sulfides and enhances the preservation of Fe oxides and organic carbon. This study highlights key local controls on Fe availability in marginal basins and describes an intricate biogeochemical C-Fe-S cycling in modern and possibly ancient marine systems with important implications for Fe availability in the marine realm.
33. 题目: Inhibitors mitigate N2O emissions more effectively than biochar: A global perspective
Farmlands receive large amounts of nitrogen (N) from anthropogenic activities, which increase N2O emissions and promote crop productivity. Inhibitor or biochar applications have proven effective in reducing N2O emissions and promoting crop yields worldwide. However, a direct comparison of the response of N2O emissions and crop yields to inhibitor and biochar applications has not been performed. Here, we conducted a meta-analysis of 787 datasets from different locations worldwide to investigate the response of N2O emissions and crop yields to inhibitor or biochar applications for different climate factors and experimental conditions and determine the key influencing factors. We found that inhibitor applications (37.4 %) resulted in larger N2O emission reductions than biochar applications (20.2 %), but there was no difference in the crop yield improvement (5.8 % and 5.4 %, respectively). Nitrification inhibitor (NI) applications reduced N2O emissions by 40.8 %, a larger reduction than that of urease inhibitor (UI) applications (24.3 %) and the combination of NI and UI applications (36.4 %); 3,4-dimethylpyrazole succinic (DMPSA) was the most effective NI in reducing N2O emissions (50.7 %). We also found that NI applications were more effective in reducing N2O emissions than biochar applications in different climates and experimental conditions (N source, N rate, cropland type, and soil texture). In addition, the N rate was the most important factor impacting N2O emissions and crop yields when inhibitors were applied, whereas the experimental duration had the largest influence on N2O emissions under biochar applications. Moreover, soil factors were also related to N2O emissions under biochar applications or inhibitor applications. Our findings indicate that inhibitors are more effective in reducing N2O emissions than biochar worldwide.
34. 题目: Role of tobacco and bamboo biochar on food waste digestate co-composting: Nitrogen conservation, greenhouse gas emissions, and compost quality
Anaerobic digestion is considered an environmentally benign process for the recycling of food waste into biogas. However, unscientific disposal of ammonium-rich food waste digestate (FWD), a by-product of anaerobic digestion induces environmental issues such as odor nuisances, water pollution, phytotoxicity and pathogen transformations in soil, etc. In the present study, FWD produced from anaerobic digestion of source-separated food waste from markets and industries was used for converting FWD into biofertilizer using 20-L bench scale composters. The issues of nitrogen loss, NH3 volatilization, and greenhouse gas N2O emission were addressed using in-situ composting technologies with the aid of tobacco and bamboo biochar produced at pyrolytic temperatures of 450 °C and 600 °C, respectively. The results demonstrated that the phytotoxic nature of FWD could be reduced into a nutrient-rich compost by mitigating nitrogen loss by 29–53% using 10% tobacco and 10% bamboo biochar in comparison with the control treatment. Tobacco biochar mitigates NH3 emission by 63% but enhances the N2O emission by 65%, whereas bamboo biochar mitigates both NH3 and N2O emissions by 48% and 31%, respectively. Overall, 10% tobacco and 10% bamboo biochar amendment could reduce total nitrogen loss by 29% and 53%, respectively. Furthermore, the biochar addition significantly enhanced the biodegradation rate of FWD and the mature compost could be produced within 21 days of FWD composting as seen by an increased seed germination index (>50% on dry weight basis). The results of this study could be beneficial in developing a circular bioeconomy locally with the waste-derived substrates.
35. 题目: Transport of biochar colloids under unsaturated flow condition: Roles of chemical aging and cation type
Biochar colloids released from biochar materials are ubiquitous in the environment and undergo environmental transformation processes that may alter their properties. Natural subsurface environments are usually under unsaturated conditions, which could affect the transport of biochar colloids. This study investigated the transport of pristine and aged biochar colloids under unsaturated conditions by aggregation test, bubble column experiment, and sand column experiment. After aging, the biochar showed a more negative, hydrophilic, and rougher surface. Compared with pristine biochar colloids, aged biochar colloids in NaCl solution were not retained at the air-water interface (AWI) due to their more hydrophilic and rougher surface. In CaCl2 solution, more pristine and aged biochar colloids were retained at the AWI because Ca2+ weakened the electrostatic repulsion between biochar colloids and the AWI. With the decrease in saturation, the transport of pristine and aged biochar colloids decreased by 17 %‑67 % through the retention at AWI and air-water-solid (AWS) interface. The transport of biochar colloids in NaCl solution was increased by 10 %‑20 % after aging as the aged biochar was not retained at the AWI. The difference of transport between pristine and aged biochar colloids in CaCl2 solution (<8 %) was lower than that in NaCl solution due to the enhanced retention of aggregated biochar colloids at the AWI and AWS interfaces. These results highlight the importance of the surface structure of biochar on its behavior in the environment, which is essential for assessing the potential of biochar application for carbon sequestration and environmental protection.
36. 题目: Soil organic carbon sequestration in croplands can make remarkable contributions to China's carbon neutrality
The vast cropland in China is an important carbon pool with substantial carbon sequestration potential. Here, this study estimated the soil organic carbon stock in China's croplands based on a comprehensive investigation of 7.5 million soil samples from 2209 counties. We show that China's croplands (0–20 cm) store 4.53–4.98 Pg organic carbon in total. The soil organic carbon stock increased from 29.13 to 34.54 to 33.51–36.90 Mg C ha−1 during 1980–2010, with an annual average increase rate of 113.33 kg C ha−1 yr−1. The increase in soil organic carbon stock was mainly driven by the increasing inputs of crop residue and livestock manure. Furthermore, we designed four scenarios with different crop residue, livestock manure, and nitrogen fertilizer inputs to assess the soil organic carbon sequestration potential in China's croplands. The results show that the soil organic carbon storage is projected to reach 6.98–7.89 Pg by 2060, representing 6.1%–13.3% of the annual negative carbon emissions required by 2060 China's carbon neutrality target. We also proposed targeted strategies to further increase the soil organic carbon stock of cropland in different regions by considering characteristics such as soil properties and agricultural management practices.
37. 题目: Land use as a major factor of riverine nitrate in a semi-arid farming-pastoral ecotone: New insights from multiple environmental tracers and molecular signatures of DOM
The nitrogen contamination in rivers has become significant concern in arid and semiarid areas due to water resource shortage and extensive anthropogenic activities in relation to land-use changes in China. As a major nitrogen species, identifying driving factors, transformation and sources of nitrate is crucial for managing nitrogen pollution in rivers. In this study, nitrate sources and transformations were deciphered using physicochemical variables, molecular signature of dissolved organic matter and coupled isotopes of nitrate under different land use types in the Yang River, a typical farming-pastoral ecotone in the semi-arid area of North China. The results of river water showed a significant positive correlation between NO3− concentrations, δ15N-NO3− values and percentage of urban land and cropland, which confirmed the critical role of land use in the variations of riverine nitrate. The correlation between dissolved organic matter composition (aliphatic and lignin-like compounds) and NO3−/Cl− ratios as well as Cl− concentrations verified the effect of agricultural activities on nitrate source and transport. The variation in water chemical variables and dual isotopes of nitrate in river and soil extracts (δ15N-NO3− and δ18O-NO3−) was indicative of the concurrence of in-soil nitrification process and assimilation, whereas denitrification was inhibited under aerobic conditions in the semiarid area. The Bayesian model revealed that about 60% of nitrate was derived from non-point sources (manure, soil organic nitrogen and chemical fertilizer) and 36% from sewage. Although urban is not the major land-use type in the farming-pastoral ecotone, sewage contributed to about 36% of nitrate. The source identification of nitrate stresses the importance of the management of non-point pollution and demand for sewage treatment facilities in the farming-pastoral ecotone. This multiple-tracer approach will help gain deeper insights into nitrogen management in semi-arid areas with extensive human disturbance.
38. 题目: Hydrothermal synthesis of sewage sludge biochar for activation of persulfate for antibiotic removal: Efficiency, stability and mechanism
The use of biochar materials as catalysts to activate persulfate (PS) for the degradation of antibiotics has attracted much attention. In this study, a carbonaceous material (Cu/Zn-SBC) was prepared from sewage sludge by hydrothermal modification. The efficiency of PS activation by Cu/Zn-SBC was investigated using tetracycline (TC) as the model antibiotic. In the Cu/Zn-SBC + PS system, the TC removal rate reached 90.13% at 10 min and exceeded 99% within 4 h. This not only met the requirement of removing large amounts of pollutants in a short time but also achieved the complete removal of pollutants in the subsequent time. Additionally, the Cu/Zn-SBC + PS system was found to be dominated by radical and nonradical pathways. Cu, hydroxyl and carboxyl groups on the surface of Cu/Zn-SBC promoted the production of free radicals and non-free radicals. Under several changes in reaction conditions and water environment factors, the TC removal rate remained above 85% within 10 min. Furthermore, the removal rate of TC was still 85.79% when Cu/Zn-SBC combined with PS was reused twice and 77.14% when reused four times. This study provides an ideal solution for the treatment of sewage sludge, and offers a stable and efficient material for removing antibiotics from wastewater.
39. 题目: Changes in soil fungal community composition and functional groups during the succession of Alpine grassland
Background and aims
This study explores trends in soil fungal patterns, potential functions and their responses to carbon and nitrogen applications over alpine grassland succession in the Qilian Mountain area of China.
The soil fungal community was characterized via Illumina sequencing of ITS genes. The FUNGuild database was used to predict functional groups in alpine grassland succession from swamp meadow to alpine meadow and steppe meadow. The levels of soil carbon and nitrogen, vegetation carbon and nitrogen, and soil enzyme activity were also assessed.
Soil fungal operational taxonomic units increased from swamp meadow to alpine meadow stage and then reached a relatively stable state in steppe meadow successional stage. This result is consistent with the changing trend of sobs and Chao1 index. Moreover, the soil fungal community differed significantly between different succession stages. During succession, while most phyla of soil fungi followed linear decreasing trends, Ascomycota was the dominant fungal phylum. Its abundance increased significantly, from 60.00% in swamp meadow to 72.26% in steppe meadow. The relative abundances of Pathotroph and Saprotroph fungal functions increased with successional stages, while Symbiotroph did not change significantly. Soil ammonium nitrogen and organic carbon levels dominated the effect on the soil fungal microbial community and functional groups.
These findings indicate that the fungal community shifted dramatically in the first stage(swamp to alpine meadow) of succession but then reached a relatively stable state in the second(alpine to steppe meadow) successional stage. The soil fungal function group did not follow the same successional trajectory. Soil ammonium nitrogen and soil organic carbon levels imposed the strongest influence on the fungal community and its function, respectively.
40. 题目: Soil aggregate disintegration effects on soil erodibility in the water level fluctuation zone of the Three Gorges Reservoir, China
Spatial hydrological alterations can affect soil structural stability. Over time, forces induced by water weaken soil aggregates and this has a negative implication to soil health. The Three Gorges Reservoir (TGR) in particular, experienced a long-term hydrological condition and repetitive seasonal water level fluctuations that could affect soil health. The present study was conducted to investigate the effects of different water levels on soil aggregate disintegration rate over time and its relation to soil erosion susceptibility in water reservoirs. Samples from different elevations (155 m, 160 m, 163 m, 166 m, 172 m, and 180 m) in the water level fluctuation zone (WLFZ) were exposed to continuous wet-shaking for 3, 9, 27, 54, and 81 min resulted to different WLF intensity accordingly. The results showed a comparative difference between aggregates size before and after the experiment where micro-aggregates (<0.25 mm) increased with respect to elevations increase. The exponential prediction proved that aggregate stability decreased with the increase of WLF intensity, insisting the effects of continuous hydrological stress to aggregate break-down. A couple of factors definitely confirmed that soil erodibility (k) is primarily determined by disintegration of soil aggregates for the surface soil of the TGR. Despite the fact that Disintegration rate (Dr) and k showed a positive relationship, R2 = 0.73 (p < 0.05), the results showed that the soil properties decreasing Dr also decreases soil erodibility in the study area. Non-effective role of soil organic matter (SOM) for stabilizing soil aggregates was primarily related to water level fluctuations inhibiting decomposition. Relying on the present findings, environmental problems mostly soil erosion in the TGR could be therefore linked to excessive destabilization of soil aggregates. Therefore, the results of this study should play a major role in determining the factors primarily inducing soil erosion in river reservoirs.