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1.
Different land uses in subtropics play an important role in regulating the global environmental changes. To reduce uncertainties of greenhouse gas (GHG) emissions of agricultural soils in subtropical ecosystem, a four years campaign was started to determine the temporal GHG (CO 2 and CH 4) fluxes from seven sites of four land use types (1 vegetable field, 3 uplands, 2 orchards, 1 pine forest). The mean annual budgets of CO 2, and CH 4 were 6.5~10.5 Mg CO 2 ha ?1 yr ?1, and +0.47 ~ ?2.37 kg CH 4 ha ?1 yr ?1, respectively. Pine forest had significantly lower CO 2 emission and higher CH 4 uptake than agriculture land uses. Tilled orchard emitted more CO 2 and oxidized less CH 4 than non-tilled orchard. Upland crops had higher CO 2 emissions than orchards, while abrupt differences of CH 4 uptake were observed between upland crops and orchards. Every year, the climate was warm and wet from April to September (the hot–humid season) and became cool and dry from October to March (the cool–dry season). Driven by seasonality of temperature and WFPS, CO 2 fluxes were significantly higher in the hot–humid season than in cool–dry season. Soil temperature, WFPS, NO 3?–N and NH 4+–N contents interactively explained CH 4 uptake which was significantly higher in cool–dry season than in hot–humid season. We conclude that soil C fluxes from different land uses are strongly under control of different climatic predictors along with soil nutrient status, which interact in conjunction with each other to supply the readily available substrates. 相似文献
2.
人工湿地处理的生活污水含氮量或者有机物含量很高时,可能会造成人工湿地在处理污水的过程中排放大量温室气体。研究了垂直潜流式人工湿地在人工合成的生活污水不同污染物进水C/N负荷条件下污水处理效果和温室气体(CO2和CH4)的排放量,利用现场测量和碳平衡模型估算分析了可以达到最佳污水净化效果和最少温室气体排放量的污染物进水C/N负荷条件。结果显示,在进水C/N负荷为C/N=6∶1~9∶1时可以得到最佳的污染物去除率。温室气体CH4排放量较CO2排放量可以忽略不计,而在进水C/N负荷为C/N=3∶1~6∶1时可以实现最少的温室气体排放。综上所述,最优的进水C/N负荷确定为C/N=6∶1,此时人工湿地可以得到较高的污染物去除率而排放较少的温室气体。 相似文献
3.
Manure-based soil amendments (herein “amendments”) are important fertility sources, but differences among amendment types and management can significantly affect their nutrient value and environmental impacts. A 6-month in situ decomposition experiment was conducted to determine how protection from wintertime rainfall affected nutrient losses and greenhouse gas (GHG) emissions in poultry (broiler chicken and turkey) and horse amendments. Changes in total nutrient concentration were measured every 3 months, changes in ammonium (NH 4+) and nitrate (NO 3?) concentrations every month, and GHG emissions of carbon dioxide (CO 2), methane (CH 4), and nitrous oxide (N 2O) every 7–14 days. Poultry amendments maintained higher nutrient concentrations (except for K), higher emissions of CO 2 and N 2O, and lower CH 4 emissions than horse amendments. Exposing amendments to rainfall increased total N and NH 4+ losses in poultry amendments, P losses in turkey and horse amendments, and K losses and cumulative N 2O emissions for all amendments. However, it did not affect CO 2 or CH 4 emissions. Overall, rainfall exposure would decrease total N inputs by 37% (horse), 59% (broiler chicken), or 74% (turkey) for a given application rate (wet weight basis) after 6 months of decomposition, with similar losses for NH 4+ (69–96%), P (41–73%), and K (91–97%). This study confirms the benefits of facilities protected from rainfall to reduce nutrient losses and GHG emissions during amendment decomposition. Implications: The impact of rainfall protection on nutrient losses and GHG emissions was monitored during the decomposition of broiler chicken, turkey, and horse manure-based soil amendments. Amendments exposed to rainfall had large ammonium and potassium losses, resulting in a 37–74% decrease in N inputs when compared with amendments protected from rainfall. Nitrous oxide emissions were also higher with rainfall exposure, although it had no effect on carbon dioxide and methane emissions. Overall, this work highlights the benefits of rainfall protection during amendment decomposition to reduce nutrient losses and GHG emissions. 相似文献
4.
Biochar has been recently proposed as a management strategy to improve crop productivity and global warming mitigation. However, the effect of such approach on soil greenhouse gas fluxes is highly uncertain and few data from field experiments are available. In a field trial, cultivated with wheat, biochar was added to the soil (3 or 6 kg m −2) in two growing seasons (2008/2009 and 2009/2010) so to monitor the effect of treatments on microbial parameters 3 months and 14 months after char addition. N 2O, CH 4 and CO 2 fluxes were measured in the field during the first year after char addition. Biochar incorporation into the soil increased soil pH (from 5.2 to 6.7) and the rates of net N mineralization, soil microbial respiration and denitrification activity in the first 3 months, but after 14 months treated and control plots did not differ significantly. No changes in total microbial biomass and net nitrification rate were observed. In char treated plots, soil N 2O fluxes were from 26% to 79% lower than N 2O fluxes in control plots, excluding four sampling dates after the last fertilization with urea, when N 2O emissions were higher in char treated plots. However, due to the high spatial variability, the observed differences were rarely significant. No significant differences of CH 4 fluxes and field soil respiration were observed among different treatments, with just few exceptions. Overall the char treatments showed a minimal impact on microbial parameters and GHG fluxes over the first 14 months after biochar incorporation. 相似文献
5.
The open lots and manure stockpiles of dairy farm are major sources of greenhouse gas (GHG) emissions in typical dairy cow housing and manure management system in China. GHG (CO 2, CH 4 and N 2O) emissions from the ground level of brick-paved open lots and uncovered manure stockpiles were estimated according to the field measurements of a typical dairy farm in Beijing by closed chambers in four consecutive seasons. Location variation and manure removal strategy impacts were assessed on GHG emissions from the open lots. Estimated CO 2, CH 4 and N 2O emissions from the ground level of the open lots were 137.5±64.7 kg hd -1 yr -1, 0.45±0.21 kg hd -1 yr -1 and 0.13±0.08 kg hd -1 yr -1, respectively. There were remarkable location variations of GHG emissions from different zones (cubicle zone vs. aisle zone) of the open lot. However, the emissions from the whole open lot were less affected by the locations. After manure removal, lower CH 4 but higher N 2O emitted from the open lot. Estimated CO 2, CH 4 and N 2O emissions from stockpile with a stacking height of 55±12 cm were 858.9±375.8 kg hd -1 yr -1, 8.5±5.4 kg hd -1 yr -1 and 2.3±1.1 kg hd -1 yr -1, respectively. In situ storage duration, which estimated by manure volatile solid contents (VS), would affect GHG emissions from stockpiles. Much higher N 2O was emitted from stockpiles in summer due to longer manure storage. Implications: This study deals with greenhouse gas (GHG) emissions from open lots and stockpiles. It’s an increasing area of concern in some livestock producing countries. The Intergovernmental Panel on Climate Change (IPCC) methodology is commonly used for estimation of national GHG emission inventories. There is a shortage of on-farm information to evaluate the accuracy of these equations and default emission factors. This work provides valuable information for improving accounting practices within China or for similar manure management practice in other countries. 相似文献
6.
High-density polyethylene (HDPE) membranes are commonly used as a cover component in sanitary landfills, although only limited evaluations of its effect on greenhouse gas (GHG) emissions have been completed. In this study, field GHG emission were investigated at the Dongbu landfill, using three different cover systems: HDPE covering; no covering, on the working face; and a novel material-Oreezyme Waste Cover (OWC) material as a trial material. Results showed that the HDPE membrane achieved a high CH 4 retention, 99.8% (CH 4 mean flux of 12 mg C m -2 h -1) compared with the air-permeable OWC surface (CH4 mean flux of 5933 mg C m -2 h -1) of the same landfill age. Fresh waste at the working face emitted a large fraction of N 2O, with average fluxes of 10 mg N m -2 h -2, while N 2O emissions were small at both the HDPE and the OWC sections. At the OWC section, CH 4 emissions were elevated under high air temperatures but decreased as landfill age increased. N 2O emissions from the working face had a significant negative correlation with air temperature, with peak values in winter. A massive presence of CO 2 was observed at both the working face and the OWC sections. Most importantly, the annual GHG emissions were 4.9 Gg yr -1 in CO 2 equivalents for the landfill site, of which the OWC-covered section contributed the most CH 4 (41.9%), while the working face contributed the most N 2O (97.2%). HDPE membrane is therefore, a recommended cover material for GHG control. Implications: Monitoring of GHG emissions at three different cover types in a municipal solid waste landfill during a 1-year period showed that the working face was a hotspot of N2O, which should draw attention. High CH4 fluxes occurred on the permeable surface covering a 1- to 2-year-old landfill. In contrast, the high-density polyethylene (HDPE) membrane achieved high CH4 retention, and therefore is a recommended cover material for GHG control. 相似文献
7.
To assess the effects of nitrogen (N) deposition on greenhouse gas (GHG) fluxes in alpine grassland of the Tianshan Mountains in central Asia, CH 4, CO 2 and N 2O fluxes were measured from June 2010 to May 2011. Nitrogen deposition tended to significantly increase CH 4 uptake, CO 2 and N 2O emissions at sites receiving N addition compared with those at site without N addition during the growing season, but no significant differences were found for all sites outside the growing season. Air temperature, soil temperature and water content were the important factors that influence CO 2 and N 2O emissions at year-round scale, indicating that increased temperature and precipitation in the future will exert greater impacts on CO 2 and N 2O emissions in the alpine grassland. In addition, plant coverage in July was also positively correlated with CO 2 and N 2O emissions under elevated N deposition rates. The present study will deepen our understanding of N deposition impacts on GHG balance in the alpine grassland ecosystem, and help us assess the global N effects, parameterize Earth System models and inform decision makers. 相似文献
8.
In coastal Antarctica, freezing and thawing influence many physical, chemical and biological processes for ice-free tundra ecosystems, including the production of greenhouse gases (GHGs). In this study, penguin guanos and ornithogenic soil cores were collected from four penguin colonies and one seal colony in coastal Antarctica, and experimentally subjected to three freezing–thawing cycles (FTCs) under ambient air and under N 2. We investigated the effects of FTCs on the emissions of three GHGs including nitrous oxide (N 2O), carbon dioxide (CO 2) and methane (CH 4). The GHG emission rates were extremely low in frozen penguin guanos or ornithogenic soils. However, there was a fast increase in the emission rates of three GHGs following thawing. During FTCs, cumulative N 2O emissions from ornithogenic soils were greatly higher than those from penguin guanos under ambient air or under N 2. The highest N 2O cumulative emission of 138.24 μg N 2O–N kg ?1 was observed from seal colony soils. Cumulative CO 2 and CH 4 emissions from penguin guanos were one to three orders of magnitude higher than those from ornithogenic soils. The highest cumulative CO 2 (433.0 mgCO 2–C kg ?1) and CH 4 (2.9 mgCH 4–C kg ?1) emissions occurred in emperor penguin guanos. Penguin guano was a stronger emitter for CH 4 and CO 2 while ornithogenic soil was a stronger emitter for N 2O during FTCs. CO 2 and CH 4 fluxes had a correlation with total organic carbon (TOC) and soil/guano moisture (M c) in penguin guanos and ornithogenic soils. The specific CO 2–C production rate (CO 2–C/TOC) indicated that the bioavailability of TOC was markedly larger in penguin guanos than in ornithogenic soils during FTCs. This study showed that FTC-released organic C and N from sea animal excreta may play a significant role in FTC-related GHG emissions, which may account for a large proportion of annual fluxes from tundra ecosystems in coastal Antarctica. 相似文献
9.
Wastewater treatment plants (WWTPs) have been recognized as important sources for anthropogenic greenhouse gas (GHG) emission. The objective of the study was to thoroughly investigate a typical industrial WWTP in southern Taiwan in winter and summer which possesses the emission factors close to those reported values, with the analyses of emission factors, mass fluxes, fugacity, lab-scale in situ experiments, and impact assessment. The activated sludge was the important source in winter and summer, and nitrous oxide (N2O) was the main contributor (e.g., 57 to 91 % of total GHG emission in a unit of kg carbon dioxide-equivalent/kg chemical oxygen demand). Albeit important for the GHGs in the atmosphere, the fractional contribution of the GHG emission to the carbon or nitrogen removal in wastewater treatment was negligible (e.g., less than 1.5 %). In comparison with the sludge concentration or retention time, adjusting the aeration rate was more effective to diminish the GHG emission in the activated sludge without significantly affecting the treated water quality. When the aeration rate in the activated sludge simulation was reduced by 75 %, the mass flux of N2O could be diminished by up to 53 % (from 9.6 to 4.5 mg/m2-day). The total emission in the WWTP (including carbon dioxide, methane, and N2O) would decrease by 46 % (from 0.67 to 0.36 kg CO2-equiv/kg COD). However, the more important benefit of changing the aeration rate was lowering the energy consumption in operation of the WWTP, as the fractional contribution of pumping to the total emission from the WWTP ranged from 46 to 93 % within the range of the aeration rate tested. Under the circumstance in which reducing the burden of climate change is a global campaign, the findings provide insight regarding the GHG emission from treatment of industrial wastewater and the associated impact on the treatment performance and possible mitigation strategies by operational modifications. 相似文献
10.
Energy supply utilities release significant amounts of greenhouse gases (GHGs) into the atmosphere. It is essential to accurately estimate GHG emissions with their uncertainties, for reducing GHG emissions and mitigating climate change. GHG emissions can be calculated by an activity-based method (i.e., fuel consumption) and continuous emission measurement (CEM). In this study, GHG emissions such as CO 2, CH 4, and N 2O are estimated for a heat generation utility, which uses bituminous coal as fuel, by applying both the activity-based method and CEM. CO 2 emissions by the activity-based method are 12–19% less than that by the CEM, while N 2O and CH 4 emissions by the activity-based method are two orders of magnitude and 60% less than those by the CEM, respectively. Comparing GHG emissions (as CO 2 equivalent) from both methods, total GHG emissions by the activity-based methods are 12–27% lower than that by the CEM, as CO 2 and N 2O emissions are lower than those by the CEM. Results from uncertainty estimation show that uncertainties in the GHG emissions by the activity-based methods range from 3.4% to about 20%, from 67% to 900%, and from about 70% to about 200% for CO 2, N 2O, and CH 4, respectively, while uncertainties in the GHG emissions by the CEM range from 4% to 4.5%. For the activity-based methods, an uncertainty in the Intergovernmental Panel on Climate Change (IPCC) default net calorific value (NCV) is the major uncertainty contributor to CO 2 emissions, while an uncertainty in the IPCC default emission factor is the major uncertainty contributor to CH 4 and N 2O emissions. For the CEM, an uncertainty in volumetric flow measurement, especially for the distribution of the volumetric flow rate in a stack, is the major uncertainty contributor to all GHG emissions, while uncertainties in concentration measurements contribute a little to uncertainties in the GHG emissions. Implications:Energy supply utilities contribute a significant portion of the global greenhouse gas (GHG) emissions. It is important to accurately estimate GHG emissions with their uncertainties for reducing GHG emissions and mitigating climate change. GHG emissions can be estimated by an activity-based method and by continuous emission measurement (CEM), yet little study has been done to calculate GHG emissions with uncertainty analysis. This study estimates GHG emissions and their uncertainties, and also identifies major uncertainty contributors for each method. 相似文献
11.
An increasing nitrogen deposition experiment (2 g N m ?2 year ?1) was initiated in an alpine meadow on the Qinghai-Tibetan Plateau in May 2007. The greenhouse gases (GHGs), including CO 2, CH 4 and N 2O, was observed in the growing season (from May to September) of 2008 using static chamber and gas chromatography techniques. The CO 2 emission and CH 4 uptake rate showed a seasonal fluctuation, reaching the maximum in the middle of July. We found soil temperature and water-filled pore space (WFPS) were the dominant factors that controlled seasonal variation of CO 2 and CH 4 respectively and lacks of correlation between N 2O fluxes and environmental variables. The temperature sensitivity ( Q10) of CO 2 emission and CH 4 uptake were relatively higher (3.79 for CO 2, 3.29 for CH 4) than that of warmer region ecosystems, indicating the increase of temperature in the future will exert great impacts on CO 2 emission and CH 4 uptake in the alpine meadow. In the entire growing season, nitrogen deposition tended to increase N 2O emission, to reduce CH 4 uptake and to decrease CO 2 emission, and the differences caused by nitrogen deposition were all not significant ( p < 0.05). However, we still found significant difference ( p < 0.05) between the control and nitrogen deposition treatment at some observation dates for CH 4 rather than for CO 2 and N 2O, implying CH 4 is most susceptible in response to increased nitrogen availability among the three greenhouse gases. In addition, we found short-term nitrogen deposition treatment had very limited impacts on net global warming potential (GWP) of the three GHGs together in term of CO 2-equivalents. Overall, the research suggests that longer study periods are needed to verify the cumulative effects of increasing nitrogen deposition on GHG fluxes in the alpine meadow. 相似文献
12.
Up to now, carbon gas fluxes from urban lakes in the boreal zone have seldom been studied. In summer 2005 we investigated fluxes from an urban boreal lake basin in southern Finland with long history of eutrophication and anoxia. Hypolimnetic CO 2 and CH 4 concentrations were high compared to other boreal lakes. During the open-water period, the lake basin acted as a source of CO 2 and CH 4 with fluxes of 2.10 mol m −2 and 0.04 mol m −2, respectively. Despite the high oxidation rate (83%), CH 4 flux was higher than in other lakes and CH 4 contributed 60% to Global Warming Potential. The ratio of carbon emission to accumulation was 4, i.e. emissions were an important route for carbon departure but less so than in rural lakes. Since the lake oxygen conditions affected nutrient availability, there was a positive feedback from hypolimnion to carbon uptake, which was reflected in gas concentrations. 相似文献
13.
Methane (CH 4) is an important greenhouse gas that is predominantly emitted to the atmosphere from anoxic wetland ecosystems. Understanding the sources and emissions of CH 4 is crucially important for climate change predictions; however, there are significant discrepancies between CH 4 source estimates derived via so-called bottom-up and top-down methods. Here we report CH 4 emission from the stems of mature wetland alder ( Alnus glutinosa) trees in the UK, a common tree of northern hemisphere floodplains and wetlands. The alder stems most likely behave as conduits for soil-produced CH 4 either in the gaseous or aqueous phase, and may, therefore, help to reconcile methodological differences in the way the wetland CH 4 source is estimated.Alder tree stems emitted average peak CH 4 fluxes of 101 μg CH 4 m ?2 h ?1 (on a stem area basis) in early October, a rate that is similar to that obtained from mature Japanese ash ( Fraxinus mandshurica var. japonica) in Japan and amounting to approximately 20% of the measured CH 4 flux from the soil surface. The finding suggests that trees, which occupy 60% of Earth's wetlands and are normally excluded from the measurement programmes that form the basis for bottom-up estimates of the global wetland source, could be important contributors to overall terrestrial ecosystem CH 4 flux. 相似文献
14.
The spatial variability of carbon dioxide (CO 2), methane (CH 4), and nitrous oxide (N 2O) fluxes from forest soil with high nitrogen (N) deposition was investigated at a rolling hill region in Japan. Gas fluxes were measured on July 25th and December 5th, 2008 at 100 points within a 100 × 100 m grid. Slope direction and position influenced soil characteristics and site-specific emissions were found. The CO 2 flux showed no topological difference in July, but was significantly lower in December for north-slope with coniferous trees. Spatial dependency of CH 4 fluxes was stronger than that of CO 2 or N 2O and showed a significantly higher uptake in hill top, and emissions in the valley indicating strong influence of water status. N 2O fluxes showed no spatial dependency and exhibited high hot spots at different topology in July and December. The high N deposition led to high N 2O fluxes and emphasized the spatial variability. 相似文献
15.
Measuring greenhouse gas (GHG) source emissions provides data for validation of GHG inventories, which provide the foundation for climate change mitigation. Two Toyota RAV4 electric vehicles were outfitted with high-precision instrumentation to determine spatial and temporal resolution of GHGs (e.g., nitrous oxide, methane [CH 4], and carbon dioxide [CO 2]), and other gaseous species and particulate metrics found near emission sources. Mobile measurement platform (MMP) analytical performance was determined over relevant measurement time scales. Pollutant residence times through the sampling configuration were measured, ranging from 3 to 11 sec, enabling proper time alignment for spatial measurement of each respective analyte. Linear response range for GHG analytes was assessed across expected mixing ratio ranges, showing minimal regression and standard error differences between 5, 10, 30, and 60 sec sampling intervals and negligible differences between the two MMPs. GHG instrument drift shows deviation of less than 0.8% over a 24-hr measurement period. These MMPs were utilized in tracer-dilution experiments at a California landfill and natural gas compressor station (NGCS) to quantify CH 4 emissions. Replicate landfill measurements during October 2009 yielded annual CH 4 emissions estimates of 0.10 ± 0.01, 0.11 ± 0.01, and 0.12 ± 0.02 million tonnes of CO 2 equivalent (MTCO 2E). These values compare favorably to California GHG Emissions Inventory figures for 2007, 2008, and 2009 of 0.123, 0.125, and 0.126 MTCO 2E/yr, respectively, for this facility. Measurements to quantify NGCS boosting facility-wide emissions, during June 2010 yielded an equivalent of 5400 ± 100 TCO 2E/yr under steady-state operation. However, measurements during condensate transfer without operational vapor recovery yield an instantaneous emission rate of 2–4 times greater, but was estimated to only add 12 TCO 2E/yr overall. This work displays the utility for mobile GHG measurements to validate existing measurement and modeling approaches, so emission inventory values can be confirmed and associated uncertainties reduced.Implications:? Measuring greenhouse gas (GHG) source emissions provides data and validation for GHG inventories, the foundation for climate change mitigation. Mobile measurement platforms with robust analytical instrumentation completed tracer-dilution experiments in California at a landfill and natural gas compressor station (NGCS) to quantify CH4 emissions. Data collected for landfill CH4 agree with the current California emissions inventory, while NGCS data show the possible variability from this type of facility. This work displays the utility of mobile GHG measurements to validate existing measurement and modeling approaches, such that emission inventory values can be confirmed, associated uncertainties reduced, and mitigation efforts quantified. 相似文献
16.
The polyfluorinated carboxylic acids 5:3 acid (C 5F 11CH 2CH 2CO 2H) and 7:3 acid (C 7F 15CH 2CH 2CO 2H) are major products from 6:2 FTOH (C 6F 13CH 2CH 2OH) and 8:2 FTOH (C 8F 17CH 2CH 2OH) aerobic biotransformation, respectively. The 5:3 and 7:3 acids were dosed into domestic WWTP activated sludge for 90 d to determine their biodegradability. The 7:3 acid aerobic biodegradability was low, only 1.7 mol% conversion to perfluoroheptanoic acid (PFHpA), whereas no transformation was observed previously in soil. In stark contrast, 5:3 acid aerobic biodegradability was enhanced 10 times in activated sludge compared to soil. The 5:3 acid was not activated by acyl CoEnzyme A (CoA) synthetase, a key step required for further α- or ß-oxidation. Instead, 5:3 acid was directly converted to 4:3 acid (C 4F 9CH 2CH 2CO 2H, 14.2 mol%) and 3:3 acid (C 3F 7CH 2CH 2CO 2H, 0.9 mol%) via “one-carbon removal pathways”. The 5:3 acid biotransformation also yielded perfluoropentanoic acid (PFPeA, 5.9 mol%) and perfluorobutanoic acid (PFBA, 0.8 mol%). This is the first report to identify key biotransformation intermediates which demonstrate novel one-carbon removal pathways with sequential removal of CF 2 groups. Identified biotransformation intermediates (10.2 mol% in sum) were 5:3 Uacid, α-OH 5:3 acid, 5:2 acid, and 5:2 Uacid. The 5:2 Uacid and 5:2 acid are novel intermediates identified for the first time which confirm the proposed pathways. In the biodegradation pathways, the genesis of the one carbon removal is CO 2 elimination from α-OH 5:3 acid. These results suggest that there are enzymatic mechanisms available in the environment that can lead to 6:2 FTOH and 5:3 acid mineralization. The dehydrogenation from 5:3 acid to 5:3 Uacid was the rate-limiting enzymatic step for 5:3 acid conversion to 4:3 acid. 相似文献
17.
通过构建曝气及未曝气潜流人工湿地小试实验系统,研究曝气对人工湿地床体中污染物沿程变化规律的影响。实验结果表明,曝气对污染物沿程降解规律的影响与污染物种类有关,在净化COD和氨氮时,曝气人工湿地污染物主要以水平推流式降解为主,未曝气系统床体中则出现分层现象,深度为40 cm以上的床体区域中污染物以水平推流式降解为主,40 cm以下区域则以垂直梯度降解方式为主。对于磷来说,两对比系统均以水平推流降解方式为主,但不同深度上的降解速率有所差异,曝气系统30~50 cm的床体中间层降解速率较快,而未曝气系统50 cm以下的床体底层降解速率较快。将对比系统总体净化效果进一步比较发现,对于COD的去除来说,温度的影响大些,而对于氨氮和TP的去除来说,曝气的影响则更为显著。 相似文献
18.
During the summertime of 2007/2008, carbon dioxide (CO 2) and methane (CH 4) fluxes across air–water interface were investigated in the littoral zones of Lake Mochou and Lake Tuanjie, east Antarctica, using a static chamber technique. The mean fluxes of CO 2 and CH 4 were ?70.8 mgCO 2 m ?2 h ?1 and 144.6 μgCH 4 m ?2 h ?1, respectively, in the littoral zone of Lake Mochou; The mean fluxes were ?36.9 mgCO 2 m ?2 h ?1 and 109.8 μgCH 4 m ?2 h ?1, respectively, in the littoral zone of Lake Tuanjie. Their fluxes showed large temporal and spatial dynamics. The CO 2 fluxes showed a significantly negative correlation with daily total radiation (DTR) and a weakly negative correlation with air temperature and water temperature, indicating that sunlight intensity controlled the magnitude of CO 2 fluxes from the open lakes. The CH 4 fluxes significantly correlated with local air temperature, water table and total dissolved solids (TDS), indicating that they were the predominant factors influencing CH 4 fluxes. Summertime CO 2 budgets in the littoral zones of Lake Mochou and Lake Tuanjie were estimated to be ?152.9 gCO 2 m ?2 and ?79.7 gCO 2 m ?2, respectively, and net CH 4 emissions were estimated to be 312.3 mgCH 4 m ?2 and 237.2 mgCH 4 m ?2, respectively. Our results show that shallow, open, alga-rich lakes might be strong summertime CO 2 absorbers and small CH 4 emitters during the open water in coastal Antarctica. 相似文献
19.
This study was conducted to estimate annual CH 4 efflux from wetlands and watercourses in Europe and some adjacent areas. Wet ecosystems were divided into seven categories: ombrotrophic mires, minerotrophic mires, freshwater marshes, saltwater marshes, small lakes, large lakes and rivers. The geographical distribution and total area coverage for each of these respective ecosystems were taken from CORINE 2000, Global Land Cover 2000 [JRC, 2003. Harmonisation, mosaicing and production of the Global Land Cover 2000 database (Beta Version). EUR 20849 EN, Joint Research Center, Ispra, Italy] and ESRI 2003 databases. CH 4 release factors were obtained from an extensive overview of published literature. Less than 3% of the study area of 22,560,000 km 2 consisted of wetlands and watercourses. Large lakes (40%), minerotrophic mires (24%) and ombrotrophic mires (20%) covered almost 85% of the total area of wetlands and watercourses. The total CH 4 release from European wetlands and watercourses was estimated to be 5.2 Tg a ?1. CH 4 release from minerotrophic mires (48%), large lakes (24%), and ombrotrophic mires (12%) composed most of the total CH 4 efflux. High variation in the rate of CH 4 release within the main ecosystem types, small number of studies in some ecosystems and ecologically inadequate land-cover classification are the main reasons for the uncertainties of the estimate. A better estimation of European CH 4 effluxes from natural sources, now and future, would require: a much more detailed and ecologically relevant mapping of the area of different types of wetlands and watercourses, and long-term measurements of CH 4 fluxes and their controlling environmental factors in poorly studied types of wetlands and watercourses. Finally, the data could be used for dynamic modelling of CH 4 fluxes in the current and changing environmental conditions. 相似文献
20.
Substantial greenhouse gas (GHG) emissions from hydropower reservoirs have been of great concerns recently, yet the significant carbon emitters of drawdown area and reservoir downstream (including spillways and turbines as well as river reaches below dams) have not been included in global carbon budget. Here, we revisit GHG emission from hydropower reservoirs by considering reservoir surface area, drawdown zone and reservoir downstream. Our estimates demonstrate around 301.3 Tg carbon dioxide (CO 2)/year and 18.7 Tg methane (CH 4)/year from global hydroelectric reservoirs, which are much higher than recent observations. The sum of drawdown and downstream emission, which is generally overlooked, represents 42 % CO 2 and 67 % CH 4 of the total emissions from hydropower reservoirs. Accordingly, the global average emissions from hydropower are estimated to be 92 g CO 2/kWh and 5.7 g CH 4/kWh. Nonetheless, global hydroelectricity could currently reduce approximate 2,351 Tg CO 2eq/year with respect to fuel fossil plant alternative. The new findings show a substantial revision of carbon emission from the global hydropower reservoirs. 相似文献
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