Application of alkali-heated corncobs enhanced nitrogen removal and microbial diversity in constructed wetlands for treating low C/N ratio wastewater.

Lack of carbon source is the main limiting factor in the denitrification of low C/N ratio wastewater in the constructed wetlands (CWs). Agricultural waste has been considered as a supplementary carbon source but research is still limited. To solve this problem, ferric carbon (Fe-C) + zeolite, Fe-C + gravel, and gravel were used as substrates to build CWs in this experiment, aiming to investigate the effects of different carbon sources (rice straw, corncobs, alkali-heated corncobs) on nitrogen removal performance and microbial community structure in CWs for low C/N wastewater. The results demonstrated that the microbial community and effluent nitrogen concentration of CWs were mainly influenced by the carbon source rather than the substrate. Alkali-heated corncobs significantly enhanced the removal of NO2--N, NH4+-N, NO3-N, and TN. Carbon sources addition increased microbial diversity. Alkali-heated corncobs addition significantly increased the abundance of heterotrophic denitrifying bacteria (Proteobacteria and Bacteroidota). Furthermore, alkali-heated corncobs addition increased the copy number of nirS, nosZ, and nirK genes while greenhouse gas fluxes were lower than common corncobs. In summary, alkali-heated corncobs can be considered as an effective carbon source.

Biochar and hematite amendments suppress emission of CH4 and NO2 in constructed wetlands.

Constructed wetlands (CWs) are considered a widely used cost-effective technology for pollutant removal. However, greenhouse gas emissions are a non-negligible problem in CWs. In this study, four laboratory-scale CWs were established to evaluate the effects of gravel (CWB), hematite (CWFe), biochar (CWC), and hematite + biochar (CWFe-C) as substrates on pollutants removal, greenhouse gas emissions, and associated microbial characteristics. The results showed that the biochar-amended CWs (CWC and CWFe-C) enhanced the removal efficiency of pollutants, with 92.53 % and 93.66 % of COD and 65.73 % and 64.41 % of TN removal, respectively. Both single and combined inputs of biochar and hematite significantly reduced CH4 and N2O fluxes, with the lowest average of CH4 flux obtained in CWC (5.99 ± 0.78 mg CH4 m-2 h-1) and the least N2O flux in CWFe-C (287.57 ± 44.84 µg N2O m-2 h-1). The substantial reduction of global warming potentials (GWP) was obtained in the applications of CWC (80.25 %) and CWFe-C (79.5 %) in biochar-amended CWs. The presence of biochar and hematite mitigated CH4 and N2O emissions by modifying microbial communities with higher ratios of pmoA/mcrA and nosZ genes abundances, as well as increasing the abundance of denitrifying bacteria (Dechloromona, Thauera and Azospira). This study demonstrated that biochar and the combined use of biochar and hematite could be the potential candidates as functional substrates for the efficient removal of pollutants and simultaneously reducing GWP emissions in the constructed wetlands.

[Treatment Effect of Corncob and Rice Straw Enhanced Subsurface Flow Constructed Wetland on Low C/N Ratio Wastewater].

The lack of carbon sources severely inhibits denitrification in wastewater with a low C/N ratio. Corncob and rice straw were chosen as supplementary carbon sources to bring into the wetland system to supplement the carbon sources needed for denitrification, and the enhancing effects of the two carbon sources on nitrogen removal from the wetland were studied. The cumulative release of carbon was in the order of rice straw[(145.17±9.44) mg·g-1]>corncob[(57.41±5.04) mg·g-1] based on the 11-day pure water extraction and release experiment, whereas the cumulative release of nitrogen was in the order of rice straw[(2.31±0.09) mg·g-1]>corncob[(0.66±0.08) mg·g-1]. The average carbon/nitrogen ratios released and accumulated by corncob and rice straw during the observation period were 94.78 and 63.64, respectively. Corncob was more suited as an additional carbon source than rice straw. COD concentrations in the effluent from the corncob and straw constructed wetlands were found to be below 50 mg·L-1 for the 58-day pilot test of subsurface flow constructed wetlands, except on days 8 to 12. The NO3--N removal rates of the corncob-added built wetlands were 93%-99% over the observation period, with good denitrification performance. In comparison, the lowest NO3--N removal rate of the constructed wetland with the addition of rice straw was only 76.8% at the late stage of operation, and the denitrification rate dropped dramatically. The control group removal rates of NO3--N were only 76.2%-77.7%, indicating a clear lack of carbon sources. The accumulation of NO2--N was also induced by a lack of carbon supply. NO2--N effluent concentrations were 2.5-6 times and 6-26 times higher in the constructed wetlands with rice straw and the control groups, respectively, than those in the wetlands constructed with corncob. The addition of corncob resulted in a more substantial reduction in NO2--N content in the constructed wetland than the addition of rice straw (P<0.05). The TN removal rates of wetlands constructed with corncob and rice straw and the control group were 83.75%-93.49%, 76.59%-78.85%, and 67.85%-72.56%, respectively, with significant differences among the three (P<0.01). Finally, pretreatment with dilute alkali heating raised the cumulative carbon release of corncob to (93.73±17.49) mg·g-1 and the carbon/nitrogen ratio to 175.8, significantly improving the carbon release performance of corncob and demonstrating that it is a suitable source of extra carbon.

[Effects of Plastic Film Mulching and Biochar Application on N2O Emission from a Vegetable Field].

The aim of this research was to examine the effects of biochar addition (B0:0 t·hm-2, B20:20 t·hm-2, and B40:40 t·hm-2) and mulching (FM:film and NM:no film) on vegetables. The impact of N2O emissions in the field was based on the pepper-radish rotation vegetable field system on the farm of Southwest University, using static dark box/gas chromatography to conduct in-situ observations in the field for one year. In this experiment, a total of six treatments were set up, namely NMB0 (CK) and FMB0, NMB20 and FMB20, and NMB40 and FMB40. The results showed that FM significantly increased the content of ammonium and nitrate nitrogen in the pepper season soil (P<0.05) but had no significant effect on soil environmental factors in the radish season. Compared with that of NM, the pepper season FM increased the N2O emissions of the B0, B20, and B40 treatments by 52.87%, 52.97%, and 52.49% (P<0.05), respectively, but the radish season FM had no significant effect on N2O emissions. Biochar had no significant effect on soil environmental factors in the pepper and radish seasons. The addition of biochar in the radish season reduced N2O emissions by 28.76%-67.88% (P<0.01), and the addition of biochar in the pepper season had no significant effect on N2O emissions. Compared with that of NM, under different biochar levels, FM increased the yield of pepper by 15.85%-161.32% and increased the yield of radish by 43.97%-75.80%. Biochar significantly increased the yield of peppers and had no significant effect on the yield of radishes. Regardless of whether the film was covered or not, when the amount of biochar added was 20 t·hm-2, the yields of pepper and radish were the highest. The analysis of N2O emission intensity revealed that FM in the pepper season significantly reduced N2O emission intensity, whereas in the radish season FM and biochar significantly reduced N2O emission intensity, and both planting seasons reached the lowest N2O emission intensity under the FMB20 treatment. Therefore, mulching and applying 20 t·hm-2 biochar were the best farmland management measures for the pepper season and radish season, which could achieve high yields and the lowest N2O emissions, accomplishing a win-win for economic and environmental benefits.

[Effects of Hematite and Biochar Addition on Wastewater Treatment Efficiency, Greenhouse Gas Emission, and Microbial Community in Subsurface Flow Constructed Wetland].

The type and structure of the substrate in constructed wetland affects the diversity and abundance of microorganisms, thereby influencing the effect of sewage treatment. In this study, four groups of wetlands were constructed in the greenhouse:blank-constructed wetland (CW0), hematite-constructed wetland (CW1), biochar-constructed wetland (CW2), and hematite+biochar-constructed wetland (CW3), to study the differences in sewage treatment effects, greenhouse gas emissions, and microbial community structures of constructed wetland systems under different filler substrates. The results showed that the addition of hematite or biochar increased the COD removal rate of -0.12% to 1.7%. The addition of biochar increased the removal rate of NH4+-N by 22.48% and NO3--N by 6.82% and reduced the emission flux of CH4 by 83.91% and N2O by 30.81%. The addition of hematite reduced the removal rate of NH4+-N by 1.12%, increased the removal rate of NO3--N by 3.98%, and reduced the emission flux of CH4 by 33.29% and N2O by 25.2%. Adding biochar or hematite increased the relative abundances of Actinobacteria and Proteobacteria, which was beneficial to the removal of COD. The Ace, Chao, Sobs, and Shannon indexes in the substrate treated with biochar were the largest, and the Simpson index was the smallest. The treatment with hematite was the opposite, indicating that the richness and diversity of microbial communities in the treatment system with biochar was the largest. Adding hematite reduced the richness and diversity of the microbial community in the constructed wetland system. Adding biochar or hematite increased the relative abundances of Dechloromonas, Thaurea, Saccharimonadales, and other denitrifying bacteria, which was beneficial to wetland denitrification. The addition of biochar increased the abundances of nosZ, nirS, and nirK functional genes, which were conducive to the occurrence of denitrification. The addition of biochar increased the abundances of pmoA functional genes, reduced the abundance of mcrA functional genes, and inhibited the production of CH4. It also increased the abundance of methanotrophic bacteria and promoted the occurrence of the CH4 oxidation process. Although the addition of hematite increased the abundance of mcrA functional genes, Fe3+ competed with methanogens for electron donors and inhibited the production of CH4.

[Effect of Ferric-carbon Micro-electrolysis on Greenhouse Gas Emissions from Constructed Wetlands].

As the problem of global warming becomes increasingly serious, the greenhouse gas (GHG) emission reduction measures of constructed wetlands (CWs) have drawn significant attention. Ferric-carbon micro-electrolysis exhibits an excellent effect on wastewater purification as well as the potential to reduce GHG emissions. Therefore, to explore the impact of ferric-carbon micro-electrolysis on GHG emissions from intermittent aeration constructed wetlands, four kinds of different wetlands with different fillers were constructed. The four fillers were ferric-carbon micro-electrolysis filler+gravel (CW-Ⅰ), ferric-carbon micro-electrolysis filler+zeolite (CW-Ⅱ), zeolite (CW-Ⅲ), and gravel (CW-Ⅳ). Intermittent aeration technology was used to aerate the wetland systems. The results show that ferric-carbon micro-electrolysis significantly improved the nitrogen removal efficiency of the intermittent aeration constructed wetlands and reduced GHG emissions. Compared with CW-Ⅳ, the CH4 fluxes of CW-Ⅰ, CW-Ⅱ, and CW-Ⅲ decreased by 32.81% (P<0.05), 52.66% (P<0.05), and 54.50% (P<0.05), respectively. Among them, zeolite exhibited a stronger reduction effect on CH4 emissions in both the aeration and non-aeration sections. The ferric-carbon micro-electrolysis substantially reduced N2O emissions. In comparison with CW-Ⅳ, CW-, and CW-Ⅱ achieved N2O emission reduction by 30.29%-60.63% (P<0.05) and 43.10%-73.87% (P<0.05), respectively. During a typical hydraulic retention period, the comprehensive GWP caused by CH4 and N2O emitted by each group of wetland system are (85.21±6.48), (49.24±3.52), (127.97±11.44), and (137.13±11.45) g·m-2, respectively. The combined use of ferric-carbon micro-electrolysis and zeolite effectively reduces GHG emissions in constructed wetlands. Overall, ferric-carbon micro-electrolysis combined with zeolite (CW-Ⅱ) can be regarded as one of the valuable filler combination methods for constructed wetlands, which can ensure high removal efficiency of pollutants and effective GHG emission reduction in constructed wetlands.

[Wastewater Treatment Effects of Ferric-carbon Micro-electrolysis and Zeolite in Constructed Wetlands].

Ferric-carbon micro-electrolysis fillers and zeolite have been increasingly used as substrates in constructed wetlands due to their good wastewater pollution-removal efficiencies. To explore the effects of different fillers on wastewater treatment in constructed wetlands, four constructed wetlands were examined with vertical subsurface flow areas filled with ferric-carbon micro-electrolysis filler+gravel (CW-A), ferric-carbon micro-electrolysis filler+zeolite (CW-B), zeolite (CW-C), and gravel (CW-D). In addition, intermittent aeration was used to improve the dissolved oxygen (DO) environment. The results showed that, compared with CW-D, the ferric-carbon micro-electrolysis filler significantly increased the dissolved oxygen (DO, P<0.05) and pH (P<0.05) of the effluent from the wetlands. The mean removal efficiency of chemical oxygen demand (COD) in the four constructed wetlands were more than 95% (P>0.05). For TN, the mean removal efficiency of CW-A,-B, and-C was 7.94% (P<0.05), 9.29% (P<0.05), and 3.63% (P<0.05) higher than that of CW-D, respectively. The contribution of ferric-carbon micro-electrolysis filler and zeolite to improving the TN removal efficiency of the constructed wetlands was 73.55% and 26.45%, respectively. The mean removal efficiency of NH4+ in the four wetlands ranged from 67.93% to 76.90%, and compared with CW-D, the other treatments significantly improved the removal efficiency of NH4+ (P<0.05). The ferric-carbon micro-electrolysis filler had an excellent removal effect on NO3-, with a removal efficiency of more than 99%, which was significantly higher than the constructed wetlands without ferric-carbon micro-electrolysis (P<0.05). Considering the treatment effect of the organic pollutants and the nitrogen-containing pollutants, CW-B achieved the best removal efficiency in constructed wetlands with intermittent aeration.

[Effect of Plastic Film Mulching on Methane and Nitrous Oxide Emissions from the Ridges and Furrows of a Vegetable Field].

Investigate the effects of plastic film mulching on CH4 and N2O emissions from a vegetable field, a one-year in situ field observation was conducted using a static opaque chamber in a pepper-radish cropping system at the Key Field Station for Monitoring of Eco-Environment of Purple Soil of the Ministry of Agriculture of China at Southwest University, Chongqing. Two treatments (conventional and film mulching) were used to study the influence of film mulching on CH4 and N2O emissions. The results showed that mulching significantly increased the annual average soil pH (P<0.01), annual surface and subsurface (5 cm) temperature (P<0.05), and soil moisture content during the radish-growing season (P<0.05). The mulching also significantly reduced CH4 emissions in the field ridges (P<0.05); the average CH4 flux from ridges during the pepper-growing season was 0.110 mg·(m2·h)-1 and 0.028 mg·(m2·h)-1, and 0.011 mg·(m2·h)-1 and -0.019 mg·(m2·h)-1 during the radish-growing season, under the conventional and film mulching treatments, respectively. However, across the entire experiment, CH4 flux from field furrows was not significantly different between the two mulching treatments (P>0.05), with mean flux values during the pepper-growing season of 0.058 mg·(m2·h)-1 and 0.057 mg·(m2·h)-1, and 0.083 mg·(m2·h)-1 and 0.092 mg·(m2·h)-1 during the radish-growing season, for conventional and plastic film mulching, respectively. Except for the conventional treatment during the pepper-growing season, CH4 emissions from ridges were significantly higher than from furrows, but for other treatments, including conventional and film mulching treatments during radish-growing season and film mulching treatment during the pepper-growing season, the CH4 emissions from furrows were all significantly higher than those from ridges. This was related to the stable anoxic environment created in furrows under high rainfall conditions in Southwest China. The N2O emission flux from the ridges during the pepper-growing season was 65.41 µg·(m2·h)-1 and 68.39 µg·(m2·h)-1 under the conventional and film mulching treatments, respectively, and the N2O emission flux during the radish-growing season was 78.43 µg·(m2·h)-1 and 66.19 µg·(m2·h)-1, respectively. The N2O flux between conventional treatment and film mulching treatment in ridges or furrows were not significantly different (P>0.05), while the N2O emissions from the ridges were significantly higher than that from the furrows. CH4 emission flux was significantly positively correlated with surface and subsurface temperature, while N2O emission flux was only significantly positively correlated with alkaline nitrogen and ammonium nitrogen content.

[Characteristics of Aerosol Optical Depth in the Urban Area of Beibei and Its Correlation with Particle Concentration].

To understand the atmospheric quality of the Beibei District of Chongqing, using the simultaneous observation data of aerosol optical depth and particulate matter concentration in 2014, we analyzed the characteristics of aerosol optical depth (AOD) in the urban area of Beibei and its correlation with particle concentration. The results showed that the annual average of AOD500nm in Beibei District is 1.46±0.69, which varies significantly by month. The highest value in November was 2.90±1.85, and the lowest in September was 0.54±0.05. There is particulate matter pollution in Beibei District. The annual average values of PM2.5 and PM10 are (62±40)µg·m-3 and (94±51)µg·m-3, respectively, which exceed the secondary standard of GB 3095-2012 Ambient Air Quality Standard. The limit values, the daily average over-standard rates of PM2.5 and PM10, are 26% and 15%, respectively. There was significant correlation between fine particle PM2.5 and PM10 concentration of respirable particulate matter. The annual coefficient of determination R2 could reach 0.95 (P<0.01). The correlation between AOD and PM2.5 and PM10 was positive throughout the year. The coefficient of determination R2 was 0.48 and 0.46, respectively, and the coefficient of determination and correlation function were different in different seasons, among which the correlation in winter was the best and the correlation in summer was the worst. AOD and air quality index showed positive correlation characteristics throughout the year, and the coefficient of determination R2 was 0.15 (P<0.05). The AOD value was affected by the comprehensive effects of weather elements. The temperature, humidity, water vapor, and other factor data should also be collected synchronously during the observation period.

Distribution characteristics and comparison of chemical stabilization ways of heavy metals from MSW incineration fly ashes.

With the purpose of fully understanding the potential toxicity of heavy metals of various particle sizes in fly ash (FA) and finding an optimal chemical reagent stabilization scheme for fly ash with single or mixture reagents, basic physicochemical characteristics of FA was investigated using multiple chemical stabilization reagent schemes to stabilize heavy metals. The following compounds were used to develop single and mixed chemical stabilization schemes for heavy metals in waste incineration FA: sodium sulfide (Na2S), sodium dihydrogen phosphate (NaH2PO4), ammonium dibutyl dithiophosphate (DDTP), and 2,4,6-tri-mercapto-S-triazine trisodium salt (TMT-15). The results showed that the various particle sizes of FA were mainly distributed in the range of 48-1700 µm. FA was packed with heavy metals, and the smaller the particle size, the more toxic it was. The speciation distribution of Cu, Zn, Pb, Cd, and Cr in different particle sizes was identical to that of the mixed samples. In the experiments of single reagent stabilization scheme, 8% Na2S, 8% NaH2PO4, 4.2% DDTP or 4.2% TMT-15 could decrease the leaching concentration to meet the limits set by Chinese law, but 8% Na2S adding scheme had the lowest cost among them. However, in the mixture reagent scheme, 1.2% Na2S, 1.2% NaH2PO4 and 0.8% DDTP was more effective and even cheaper than other mixture or single schemes.

[Effect of Plastic Film Mulching on Greenhouse Gas Emissions from Rice-Rapeseed Rotation in Cropland].

A field experiment was conducted at the Key Field Station for Monitoring of Eco-Environment of Purple Soil of the Ministry of Agriculture of China at the farm of Southwest University in Chongqing. In the study, static chamber and gas chromatography methods were used to study the effects of plastic film mulching treatment on CO2, CH4, and N2O emissions from rice-rapeseed rotation in situ for one year. A control experiment was also conducted without using the film. The CO2, CH4, and N2O emission fluxes of the rotation showed obvious seasonal changes, and the seasonal variation patterns of these three greenhouse gases were similar under the two treatments. The CH4 emission of the rotation under the plastic film mulching treatment was (46.14±13.40) kg·hm-2, or 147.93% (P<0.05), compared with (18.61±2.05) kg·hm-2 for the control. However, the impact of plastic film mulching on CO2 and N2O emissions was not significant. The annual CO2 emissions under the plastic film treatment and the control were (-47.54±2.11) t·hm-2 and (-47.60±2.19) t·hm-2, respectively, and the annual emissions of N2O were (18.94±4.74) kg·hm-2 and (23.14±3.68) kg·hm-2, respectively. The rice-rapeseed rotation in the two experiments showed absorption and sinking of atmospheric greenhouse gases, although the difference was not significant. The global warming potential (GWP) values with the plastic film treatment and the control were -41.16 t·hm-2 and -40.95 t·hm-2, respectively.

[Effects of Plastic Film Mulching and Nitrogen Fertilizer Application on CH4 Emissions from a Vegetable Field].

To investigate the effects of plastic film mulching and nitrogen fertilizer application on CH4 emissions from a vegetable field, static opaque and gas chromatography methods were applied, and in situ field observations of a chili-radish rotation system, from May 2014 to April 2016, were carried out in the Key Field Station for Monitoring of Eco-Environment of Purple Soil of the Ministry of Agriculture of China in the farm of Southwest University in Chongqing. Eight treatments were set up in the field experiment:control routine (no N application and no plastic film mulching) (NN0), control mulching (FN0), low N routine (NN1), low N mulching (FN1), conventional N routine (NN2), conventional N mulching (FN2), high N routine (NN3), and high N mulching (FN3). The characteristics and influencing factors of CH4 emissions and the changes of soil carbon and nitrogen composition from all treatments were studied. The results showed that there was no significant difference in the CH4 emissions from the vegetable fields between the mulching methods. From May 2014 to April 2016, the annual average cumulative absorption of CH4 in nitrogen-free, low-nitrogen, medium-nitrogen, and high-nitrogen vegetable fields under film-mulching cultivation was 28.96, 51.90, 43.43, and 34.41 mg·m-2, respectively. The average annual cumulative uptake of CH4 under conventional planting was 40.76, 63.56, 62.77, and 21.92 mg·m-2, respectively. Different nitrogen application gradients had no significant effect on CH4 emissions from vegetable fields. There was a significant positive correlation between CH4 uptake and soil temperature, and a significant negative correlation between CH4 and soil water content. Plastic film coverage accelerated the mineralization of soil carbon in the pepper season, but there was no significant effect in the radish season.

[Effects of the Crop Rotation on Greenhouse Gases from Flooded Paddy Fields].

A field experiment was conducted at the Key Field Station for Monitoring Eco-environment of Purple Soil of the Ministry of Agriculture of China in the farm of Southwest University, Chongqing. The static chamber and gas chromatography method was used to study the effect of the cropping systems on greenhouse gases from rice-fallow (RF), rice-rapeseed rotation (RR), and rice-brussel mustard rotation (RV) cropland in situ for a year. An opaque chamber was used for CH4 and N2O observations and a transparent chamber was utilized for CO2 observations. The results show that the annual cumulative CH4 emissions from different crop rotations were (CH4, kg·hm-2) RF (422.87±27.1) > RR (132.05±23.11) > RV (50.91±3.83). The RV and RR were significantly lower than RF (P<0.05). The annual cumulative emissions of N2O[N2O, kg·hm-2] were RV (21.38±6.51) > RR (20.02±5.23) > RF (0.48±0.02). The RV and RR were significantly higher than RF (P<0.05). The annual net cumulative emissions of CO2 were (CO2, t·hm-2) RR (-55.43±5.04) > RV (-29.1±3.00) > RF (-14.08±1.81). The RV and RR were significantly higher than RF (P<0.05). At the time scale of 100 a, the integrated global warming potentials (GWP) of CH4, N2O, and CO2 were (CO2, t·hm-2)RR(-46.43) > RV(-22.01) > RF(-2.11), indicating that converting flooded paddy fields to paddy-upland crop rotation systems notably increases the potential increment of carbon sinks. Compared with RV, RR has a better effect, which suggests that rice-rapeseed rotation is the most effective measure for the escalation of carbon sinks of ecosystems in the southwestern area.

[Effects of Plastic Film Mulching and Nitrogen Fertilizer Application on N2O Emissions from a Vegetable Field].

To investigate the effects of plastic film mulching and nitrogen fertilizer application on N2O emissions from a chili-radish rotation system, field observations were conducted in situ from May 2014 to April 2016 in the Key Field Station for Monitoring of Eco-Environment of Purple Soil of the Ministry of Agriculture of China in the farm of Southwest University in Chongqing. Static opaque and gas chromatography was used to determine emissions. Eight treatments were set up in the field experiment:control routine (no N application and no plastic film mulching; NN0), control mulching (FN0), low N routine (NN1), low N mulching (FN1), conventional N routine (NN2), conventional N mulching (FN2), high N routine (NN3), and high N mulching (FN3). The characteristics and influencing factors of N2O emissions and the changes of soil carbon and nitrogen composition across all treatments were examined. The results demonstrated significant differences in N2O emissions from the vegetable fields between mulching and no mulching treatments. The mean N2O flux under no mulching was significantly greater than that of mulching during the chili growing season (P<0.05), but the opposite was true during the radish growing season (P<0.05). During the experimental period, the average annual cumulative N2O emissions from nitrogen-free, low-nitrogen, medium-nitrogen, and high-nitrogen vegetable plots under mulching treatment were 244.91, 730.49, 903.32, and 1865.45 mg·m-2, respectively; the average annual cumulative N2O emissions under no mulching treatment were 221.48, 840.33, 1256.50, and 1469.67 mg·m-2, respectively. The N2O emissions from vegetable plots with different N application gradients showed an increase in N2O emissions from vegetable plots as N application increased. By calculating the N2O emissions coefficient, it was determined that the N2O emissions coefficient was reduced to a certain extent under mulching treatment during the chili season, while there was no obvious trend in the radish season. From May 2014 to April 2015, the N2O emissions coefficients of low-nitrogen application under two mulching treatments were both the highest under the same mulching levels during the chili growing season, but they were both the highest in the high-nitrogen application under two mulching levels during the radish growing season. From May 2015 to April 2016, the highest N2O emissions coefficient was observed in the high-nitrogen application under two mulching treatments during the chili season; however, the lowest values were observed in the low-nitrogen application under two mulching treatments during the radish growing season. Such results may be related to the duration of plastic film mulching and the type of plant. The N2O fluxes were both significantly positively correlated to the content of soil N and soil temperature. Plastic film mulching can increase the soil N to a certain extent and can therefore can affect N2O emissions.

Methane and nitrous oxide emissions from the drawdown areas of the Three Gorges Reservoir.

To investigate the effect of dam impounding on CH4 and N2O emissions from the drawdown area of the Three Gorges Reservoir (TGR), CH4 and N2O fluxes were measured at the elevations of 180 m, 175 m, 165 m and 155 m (above the sea level) from September 2010 to August 2012 using the static chamber technique. The elevations of 175 m, 165 m and 155 m were located in the drawdown area and the non-flooded elevation of 180 m was taken as the control for the drawdown area. The drawdown area studied here acted as the sources of CH4 and N2O as a whole. Seasonal, inter-annual and spatial CH4, but not N2O, fluxes varied significantly between September 2010 and August 2012. The CH4 fluxes were highest in winter but lowest in summer, and significantly higher in the wet year than in the dry year. The annually cumulative CH4 emissions were 14.09 ±â€¯4.27, 12.61 ±â€¯3.59, 68.92 ±â€¯13.09 and 77.41 ±â€¯9.42 kg CH4 ha-1 from the elevations of 180 m, 175 m, 165 m and 155 m, respectively. Compared with 180 m elevation, the annual CH4 emission was insignificantly decreased by 11% at 175 m elevation (P > 0.05), and substantially increased by 389% and 449% at 165 m (P < 0.05) and 155 m elevations (P < 0.05), respectively. The annually cumulative N2O emissions were 4.74 ±â€¯1.78, 7.43 ±â€¯2.57, 3.39 ±â€¯1.05 and 8.83 ±â€¯1.95 kg N2O ha-1 from the above corresponding elevations, respectively, and there were no significant differences among the four elevations (P > 0.05). These results showed that CH4 emissions were increased but N2O emissions were not affected in the drawdown area after the dam impounding in the TGR, and CH4 emissions were increased with the decrease in the elevations while N2O emissions were not affected by the elevation in the drawdown area.

[Mass Concentrations and Size Distributions of Water-soluble Inorganic Ions in Atmospheric Aerosols in Beibei District, Chongqing].

In order to study the concentration and distribution characteristics of water-soluble inorganic ions in aerosol particles of the Beibei district of Chongqing, aerosol samples were collected with an Andersen cascade impactor between March 2014 and February 2015. Water-soluble inorganic ions, including Na+, NH4+, K+, Mg2+, Ca2+, F-, Cl-, NO3-, and SO42- were determined for different particle sizes (9.00, 5.80, 4.70, 3.30, 2.10, 1.10, 0.65, and 0.43 µm) using the ion chromatography method. Results showed that SO42-, NH4+, NO3-, Cl-, Na+, and K+ were mainly distributed in fine particles, while Mg2+, Ca2+, and F- were mainly present in coarse particles. SNA (SO42-, NH4+, and NO3-) exhibited clear unimodal distribution, with peaks in the droplet mode of 0.65-1.10 µm, mainly present in the form of (NH4)2SO4 and NH4NO3 in fine particles. The formation of SO42- is mainly attributed to in-cloud processes and partly to oxidation of SO2. Na+, Cl-, and Mg2+ exhibited bimodal distribution in coarse and fine particles; K+ was a single peak distribution in the range of 0.43-1.10 µm, while peaks of F- and Ca2+ concentrations were in coarse particles. Average annual concentrations of total water-soluble ions in PM2.1 and PM9.0 were (32.68±15.28) µg·m-3and (48.01±19.66) µg·m-3 over the observation period. Seasonal variations of PM2.1 and PM9.0concentrations decreased in the order of winter > spring > summer > autumn. This was the same for most ions, but a small number of ions (F-, Mg2+ and Ca2+) had a different pattern in the spring, summer, and winter. The SNA were the major components of water-soluble ions in PM2.1, and Ca2+ was the major component of water-soluble ions in PM9.0 besides SNA. The concentration of cations was significantly higher than that of anions' in PM2.1 and PM9.0, with a certain correlation between different ions. Emissions from motor vehicle exhaust, combustion processes, soil sources, and fugitive dust were the major sources of water-soluble ions in this area. The effect of air temperature on secondary ions is significant (P<0.05), but relative humidity and wind speed have no significant effect (P>0.05).

[Pollution Characteristics of Organic Carbon and Elemental Carbon in Atmospheric Aerosols in Beibei District, Chongqing].

To study the pollution characteristics of atmospheric carbon aerosols, aerosol samples were collected via a cascade impactor (Andersen) from March 2014 to February 2015 in Beibei District, Chongqing. Organic carbon (OC) and element carbon (EC) were detected using a DRI 2001A carbon analyzer. The results showed that the annual average concentrations of OC and EC in PM2.1 were (16.3±7.6) and (1.8±0.7), respectively, and (25.0±9.6), and (3.2±1.3) µg·m-3, respectively, in PM9.0. The concentrations of both OC and EC were higher in winter and spring than in summer and autumn for PM2.1, whereas, for PM9.0, the concentration of OC was higher in summer and spring than in winter and autumn and that of EC was higher in winter and spring than in summer and autumn. The particle size distributions of OC and EC for the study year were analyzed, and it was found that those of OC were bimodal, with peaks in the size ranges of 0.43-0.65 µm for fine particles and 4.7-5.8 µm for coarse particles, and those of EC were trimodal, with peaks in the size ranges of 0.43-0.65 µm for fine particles and 4.7-5.8 µm for coarse particles and a concurrent significant peak in the particle size range of 2.1-3.3 µm. In addition, the correlations between OC and EC were analyzed and the SOC in PM2.1 was estimated. It was found that the average concentration of SOC was (6.3±5.9) µg·m-3, which accounted for 33.5%±22.6% of the OC concentration in Beibei District. Furthermore, OC and EC were significantly correlated. Finally, the pollution sources of atmospheric aerosols in Beibei were analyzed, and it was found that the pollution in Beibei mainly came from the exhaust gas of gasoline vehicles, biomass combustion, and coal combustion.

[Effect of Plastic Film Mulching on Methane Emission from a Vegetable Field].

Using the static opaque chamber method and choosing a chili-radish cropping system, a field experiment, located in the Key Field Station for Monitoring of Eco-Environment of Purple Soil of the Ministry of Agriculture of China in the farm of Southwest University in Chongqing, was conducted in situ for one year. Mulching and non-mulching treatments were set in the field, and the seasonal variation of CH4 flux and CH4 concentrations in the soil profile and the seasonal changes in soil moisture and temperature were observed for different treatments to explore the effect of plastic film mulching on soil moisture and temperature. The results showed that plastic film mulching can significantly improve the surface soil temperature during the pepper growing season in spring and summer (P<0.01), but no significant difference was seen during the radish growing season in autumn and winter (P>0.05). The soil moisture of the plastic film mulching treatment was significantly higher than that of no mulching in the radish growing season (P<0.05), but no significant difference was observed for the pepper growing season (P>0.05). During the whole observation period and under the condition of plastic film mulching and conventional planting, the CH4 flux from soil had no significant seasonal variation under all treatments, and the mean CH4 fluxes were -7.64 µg·(m2·h)-1 and -9.00 µg·(m2·h)-1, respectively. The cumulative CH4 emissions for plastic film mulching and conventional planting were -0.54 kg·hm-2 and -0.64 kg·hm-2, respectively, in the whole observation period, and all the treatments showed a net absorption of CH4 for the whole observation period. The results showed that the plastic film mulching could weaken the ability of CH4 as a sink of the CH4 for the whole observation period. The CH4 concentrations in different soil profiles were in the order 10 cm>20 cm>30 cm, and the concentrations of CH4 change patterns in different soil layers were almost identical during the whole observation period. The CH4 concentrations at the depths of 20 cm and 30 cm under the plastic film mulching soil were significantly lower than those under no mulching soil (P<0.05), but no significant difference was observed for the depth of 10 cm (P>0.05). Correlation analysis showed that, under the plastic film mulching conditions, CH4 flux and the 5 cm geothermal showed significant positive correlation (P<0.05), but CH4 flux and soil moisture showed significant negative correlation (P<0.05). However, under the conventional cultivation conditions, there were no correlations between CH4 flux and the 5 cm geothermal or soil moisture. There was also significant positive correlation between CH4 concentration in the 10 cm and 20 cm depth soil layers with the CH4 concentration in surface soil (P<0.01), and the CH4 concentration in the 30 cm depth soil layer had significant positive correlation with the surface soil temperatures and the 5 cm geothermal. There was no significant correlation between soil CH4 concentration and soil water content.

[Change and Influencing Factors of Dissolved Carbon and Dissolved Nitrogen in Water of the Three Gorges Reservoir].

In order to understand the changes of dissolved carbon and dissolved nitrogen in the water of Three Gorges Reservoir,this research was carried out once a week by the bank of Yangtze River in Fuling beach from March 2011 to August 2012,and the variation characteristics of dissolved C,N composition and their source were analyzed.The results showed that the concentration of DOC ranged from 0.64 mg·L-1 to 9.07 mg·L-1,and had obvious seasonal change:summer >spring and autumn >winter.Annual total input of DOC was 1.78×109 kg,the seasonal change trend of the total input of DOC was similar to that of the concentration of DOC;The concentration of DTN ranged from 2.59 mg·L-1 to 4.35 mg·L-1:spring >winter >summer >autumn,annual total input was 1.32×109 kg,the seasonal input changed in the order of summer >autumn >spring >winter,among them DON,NO3--N accounted for 30.35%-63.45% and 35.87%-67.72%,respectively.DOC was affected by precipitation and air temperature,and mainly came from the exogenous input,in the spring and summer its exogenous input increased with the increase of rainfall runoff,but in the autumn and winter the endogenous contribution increased;DTN was relatively affected by human emissions and water dilution.Correlation analysis showed that there was a significant negative correlation between DOC and DON (P<0.05),DOC/DON ratio usually reflects the source of the DOM,the DOC/DON in the water of three gorges reservoir ranged from 0.35 to 7.28,the source of DOM had obvious seasonal characteristics.DOC/DON was the highest in summer,and the DOM mainly came from watershed erosion;DOC/DON was the lowest in winter,and the DOM mainly came from living sewage and endogenous field;the DOC/DON ratios in spring and autumn were higher than those in winter and lower than those in summer,and the DOM sources included watershed erosion,living sewage and endogenous field.

[Characteristics and Influencing Factors of CH4 Emissions from the Drawdown Area of the Three Gorges Reservoir].

Five levels (180 m, 175 m, 165 m, 155 m, and 140 m) in a typical drawdown area in Wangjiagou in the Three Gorges Reservoir were selected to study CH4 emissions from subtropical reservoirs. The experimental period lasted two years from September 2010 to August 2012. The methods of static opaque chambers during the drainage period and floating chambers during flooding period were used in this study. The elevations of 175 m, 165 m, and 155 m were all located in the drawdown area, whereas the 180 m elevation was located in the land and never flooded. The 140 m elevation was permanently flooded and used as a control area. The results showed that the CH4 fluxes showed no significant trends at 175 m and 165 m in the first year of the experiment, while the fluxes showed a single peak pattern with the climax in the summer at 155 m and 140 m. At 175 m, the CH4 emissions showed a single peak pattern with the climax during its flooding period, and then showed not regular CH4 emission sources or sinks alternately in the second year, whereas the CH4 fluxes at 165 m, 155 m, and 140 m presented a single-peak shape with winter climax. During the entire observation period, the CH4 emission fluxes at 180 m were stable and showed no obvious peaks. In addition, CH4 fluxes were higher during the flooding period than in the drainage period at 175 m, 165 m, and 155 m.The order of the annual CH4 cumulative emissions at the five elevations was 140 m (99.58 kg·hm-2) > 155 m (82.98 kg·hm-2) > 165 m (65.38 kg·hm-2) > 180 m (6.32 kg·hm-2) > 175 m (4.27kg·hm-2), suggesting that the soil was more conducive to CH4 production when the flooding period was longer. Correlation analysis indicated that there were no significant correlations between CH4 fluxes and the soil carbon component and pH on land and during the drainage period but CH4 fluxes increased with the increase in soil water content. There was a significant linear negative correlation between CH4 emissions from the gas-water interface at 140 m and in water. The soil moisture content was one of the key factors affecting the CH4 fluxes during the drainage period, while during flooding period, the CH4 fluxes were regulated by flooding depth.