城市化对河流碳排放的影响研究进展

城市化造成的人类活动加剧,不仅打破了河流系统的碳循环平衡,还增加了河流系统的碳排放通量,对全球碳减排产生了消极影响。“双碳”(碳达峰与碳中和)背景下掌握城市河流碳排放特征及其影响因素,有助于合理制定流域生态治理(恢复)策略,保障城市生态系统可持续发展。探讨了城市化对河流碳排放的影响,总结了城市河流碳排放的关键影响因子,并提出该领域研究今后的发展方向。结果表明:城市河流碳排放通量明显高于人为干扰较少的自然河流,根据城市化对河流系统的干扰,将碳排放影响因素归纳为水环境因子、水文特征因子、气象因子和季节因子四大类型。水环境因子中,水温与碳排量呈正相关关系,DO和pH与之呈负相关关系,而营养盐因其营养负荷的不同使得河流系统中藻类物质主导的代谢方式不同,从而对河流系统中碳排放的影响不尽相同;水文特征因子中,高流速(一定范围内)会促进碳排放的增加,而流量和水位的变化大多会受水环境因子的间接影响而表现出对碳排放影响的不确定性;气象因子中,风速较大时会促进碳排放,气压则与之呈负相关关系;对季节因子的研究中,普遍认为碳排量在秋季较高,夏冬季适中,春季较低,但也有可能昼夜温差较大、表现为夏季碳排量较高。研究结果可为“双碳”背景下的城市河流生态治理(恢复)提供科学依据。

Soil carbon dioxide fluxes of a typical broad-leaved/Korean pine mixed forest in Changbai Mountain, China

The forest ecosystem plays an important role in the global carbon cycling. A study was conducted to evaluate soil CO2 flux and its seasonal and diurnal variation with the air and soil temperatures by using static closed chamber technique in a typical broad-leaved/Korean pine mixed forest area on the northern slope of Changbai Mountain, Jilin Province, China. The experiment was carried out through the day and night in the growing season (from June to September) in situ and sample gas was analyzed by a gas chromatograph. Results showed that the forest floor was a large net source of carbon, and soil CO2 fluxes had an obvi-ous law of seasonal and diel variation. The soil CO2 flux of broad-leaved/Korean pine mixed forest was in the range of 0.302.42 mmol穖-2穝-1 with the mean value of 0.98 mmol穖-2穝-1. An examination on the seasonal pattern of soil CO2 emission suggested that the variability in soil CO2 flux could be correlated with variations in soil temperature, and the maximum of mean CO2 flux occurred in July ((1.27±23%) mmol穖-2穝-1) and the minimum was in September ((0.50±28%) mmol穖-2穝-1). The fluctuations in diel soil CO2 flux were also correlated with changes in soil temperature; however, there existed a factor for a time lag. Soil CO2 flux from the forest floor was strongly related to soil temperature and had the highest correlation with temperature at 6-cm depth of soil. Q10 values based on air temperature and soil temperature of different soil depths were at the ranges of 2.09–3.40.

Advances in Greenhouse Gases Emission in Farmland Soils

[Objective] The aim was to overview the emission of greenhouse gases in farmland. [Method] Based on domestic and foreign references, production mechanism, discharging characters and major influential factors of CO2, CH4 and N2O in soils of farmland were overviewed. [Result] Production and discharge of CO2, CH. and N2O played an important role in circulation of carbon and nitrogen in terrestrial ecosystem and constituted a key method for carbon and nitrogen output. It is significant to conduct research on reduction of greenhouse gas and increase of absorption. [Conclusion] The research is beneficial for exploration on discharge rule and influential factors of greenhouse gases, providing theoretical references for reduction of greenhouse gases and study on climate change.

Methane Dynamics in Northern Peatlands: A Review

Northern peatlands store a large amount of carbon and play a significant role in the global carbon cycle. Owing to the presence of waterlogged and anaerobic conditions, peatlands are typically a source of methane (CH4), a very potent greenhouse gas. This paper reviews the key mechanisms of peatland CH4 production, consumption and transport and the major environmental and biotic controls on peatland CH4 emissions. The advantages and disadvantages of micrometeorological and chamber methods in measuring CH4 fluxes from northern peatlands are also discussed. The magnitude of CH4 flux varies considerably among peatland types (bogs and fens) and microtopographic locations (hummocks and hollows). Some anthropogenic activities including forestry, peat harvesting and industrial emission of sulphur dioxide can cause a reduction in CH4 release from northern peatlands. Further research should be conducted to investigate the in fluence of plant growth forms on CH4 flux from northern peatlands, determine the water table threshold at which plant production in peatlands enhances CH4 release, and quantify peatland CH4 exchange at plant community level with a higher temporal resolution using automatic chambers.

A comparison of the energy consumption and carbon emissions for different modes of transportation in open-cut coal mines

Transportation accounts for 80% of open-cut coal mine carbon emissions. With regard to the energy con- sumption and carbon emissions of transportation within an open-cut mine, this paper systematically compared the work and energy consumption of a truck and belt conveyor on a theoretical basis, and con- structed a model to calculate the energy consumption of open-cut mine transportation. Life cycle carbon emission factors and power consumption calculation model were established through a Process Analysis- Life Cycle Analysis （PA-LCA）. The following results were obtained： （1） the energy consumption of truck transportation was four to twelve times higher than that of the belt conveyor; （2） the C02 emissions from truck transportation were three to ten times higher than those of the belt conveyor; （3） with the increase in the slope angle for transportation, the ratio of truck to belt conveyor for both energy consumption and carbon emissions gradually decreased; （4） based on 2013 prices in China, the energy cost of transportation using a belt conveyor in open-cut coal mines could save 0.6-2.4 Yuan/（t kin） compared to truck transportation.

Soil Carbon Stock and Flux in Plantation Forest and Grassland Ecosystems in Loess Plateau, China

Carbon sequestration occurs when cultivated soils are re-vegetated. In the hilly area of the Loess Plateau, China, black locust （Robinia pseudoacacia） plantation forest and grassland were the two main vegetation types used to mitigate soil and water loss after cultivation abandonment. The purpose of this study was to compare the soil carbon stock and flux of these two types of vegetation which restored for 25 years. The experiment was conducted in Yangjuangou catchment in Yah＇an City, Shaanxi Province, China. Two adjacent slopes were chosen for this study. Six sample sites were spaced every 35-45 m from summit to toe slope along the hill slope, and each sample site contained three sampling plots. Soil organic carbon and related physicochemical properties in the surface soil layer （0-10 cm and 10-20 cm） were measured based on soil sampling and laboratory analysis, and the soil carbon dioxide （CO2） emissions and environmental factors were measured in the same sample sites simultaneously. Results indicated that in general, a higher soil carbon stock was found in the black locust plantation forest than that in grassland throughout the hill slope. Meanwhile, significant differences in the soil carbon stock were observed between these two vegetation types in the upper slope at soil depth 0-10 cm and lower slope at soil depth 10-20 cm. The average daily values of the soil CO2 emissions were 1.27 μmol/（m2·s） and 1.39 μmol/（m2·s） for forest and grassland, respectively. The soil carbon flux in forest covered areas was higher in spring and less variation was detected between different seasons, while the highest carbon flux was found in grassland in summer, which was about three times higher than that in autumn and spring. From the carbon sequestration point of view, black locust plantation forest on hill slopes might be better than grassland because of a higher soil carbon stock and lower carbon flux.

Embodied Energy and CO2 Associated with Buildings by Using Input and Output Table in Japan

In July 2009, the 2005 basic Japanese input/output table was publicized together with its physical transaction table. This research paper analyzed the 2005 IO （input/output） table to create building industry-related intensities and, at the same time, compared the building industry with industries at large for distribution margins and transportation. The analysis of distribution margins separately for middle and purchaser margins found that middle margins in the building industry are minor at 35% of the averages for all industries, while purchaser margins are sizable at 1.8 times, proving that it is an industry for which local production for local consumption is quite effective. CO2 emissions resulting from transportation in the building industry were calculated and concisely characterized. Although the ratio of transportation CO2 emissions to total CO2 emissions in each industry finds almost no difference between general industries and the building industry, transportation CO2 emissions per production value are two to three times heavier than those from general industries to be justified as a transportation-intensive industry.

Addressing Transportation Needs and Climate Change in Developing Nations

The analysis of data and information available on developing countries clearly suggests that the current systems and trends of urban transportation, with respect to both mobility and safety, are not sustainable. The cities of developing countries are typically characterized by high-density urban areas, absence of proper control on land use, lack of proper roads and parking facilities, poor public transport, lack of road user discipline etc. This results in the transportation problems, namely accident, congestion, and pollution, taking a very different and much severer shape in developing countries than those in cities of developed countries. Sustainable transport is also important for developing countries from the perspective of climate change, i.e., to improve carbon foot print/ecological foot print （E.F） etc. of transportation systems. From various researches, it has been established that worldwide the road transport has got a substantial share of carbon emissions （20-25% on an average）. This makes transportation an important sector for reducing carbon emissions and thus for addressing the climate change issue. These considerations therefore thrust the need for achieving sustainability in urban transport, particularly for developing countries, not just from mobility and safety perspective but also from the perspective of local and global environmental issues. This paper will critically analyze the above issues for developing countries and would suggest possible approaches to address both the transportation needs as well as climate change.

Carbon Dioxide Emissions by the Transportation Sector and Its Impact on Health in the Kathmandu Valley, Nepal

Air pollution is one of the leading cause of death for underdeveloped as well as developed countries. In 2011, the air pollution was the second leading cause of death in one of the main hospitals of the Kathmandu Valley, Nepal, and it was the third leading cause in the United States. Burning fossil fuels for transportation was one of the major causes. Among various impacts of the air pollution, COPD （chronic obstructive pulmonary disease） was one of the main consequences. In the 570 km2 Kathmandu Valley, vehicle registration was increased from 45,871 in 1990/1991 to 570,145 in 2010/2011, an increase of over 12-fold over 20 years. The vehicle registration and number of COPD patients＇ data were collected from various government divisions. In addition, the average daily travel distance and fuel mileage data were collected with a survey with residents of the Kathmandu Valley. This paper calculates the amount of carbon dioxide （CO2） emissions by transportation sector and determines correlation between CO2 emissions and COPD patients. Results show that there was a very high level of CO2 emissions, and it was positively correlated with the number of COPD patients in the valley.

Substrate availability regulates the suppressive effects of Canada goldenrod invasion on soil respiration

Invasive alien plants not only decrease riparian vegetation diversity but also alter wetland ecosystem carbon processes,especially when they displace the original vegetation.Invasive Canada goldenrod(Solidago canadensis L.)has colonized large areas of disturbed and undisturbed land in southeastern China,yet little is known regarding how it affects soil carbon cycling.To explore the response patterns of soil respiration following S.canadensis invasion and their driving mechanisms,an observational field study and a greenhouse experiment simulating invasion were performed.In the field study,soil respiration was measured weekly from 21th July 2018 to 15th December 2018.In the greenhouse experiment,soil,autotrophic and heterotrophic respiration were measured every 1st and 15th of the month from 15th July 2019 to 15th December 2019.Soil,autotrophic and heterotrophic respiration were measured using a closed-chamber system with the deep gauze collar root exclusion method.Solidago canadensis invasion appeared to decrease the total soil CO_(2) emissions in both the field study and the greenhouse experiment.The suppressive effects on soil respiration may be attributed to S.canadensis invasion-induced alterations in the quality and quantity of available soil substrate,suggesting that S.canadensis invasion may impact soil carbon cycling via plant-released substrates and by competing for the soil available substrate with native plant and/or soil microbes.These results have substantial implications for estimations of the effects of invasive plants on belowground carbon dynamics and their contribution to the warming world.

Greenhouse gas budget for terrestrial ecosystems in China

Terrestrial ecosystems may act as a source or a sink for the atmospheric greenhouse gases, carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O), depending on land use and management. This paper reviews the literature on carbon, CH4, and N2O fluxes from terrestrial ecosystems in China, and analyzes its national greenhouse gas budget. Carbon storage in biomass and soils in Chinese terrestrial ecosystems decreased in the past 300 years, due to deforestation and expansion of cultivated land, and reached a minimum in the late 1970s. Since then, carbon storage has increased at an estimated rate of 0.19 to 0.26 Pg C yr-1, mainly owing to reforestation and afforestation. CH4 emission from natural wetlands decreased from 6.65 Tg CH4 yr-1 in 1990 to 5.71 Tg CH4 yr-1 in 2000 owing to the decrease in wetland area. CH4 emission from flooded rice fields was 7.41 Tg CH4 yr-1. At the same time, aerobic soils took up atmospheric CH4 at a rate of 2.56 Tg CH4 yr-1. Nitrous oxide emission from forestlands, grasslands, and farmlands was positively correlated with precipitation at a national scale, and the emission rate was positively correlated with the CH4 uptake rate of forestlands and grasslands (P<0.01). Natural N2O sources were estimated to be 419 Gg N yr-1 and anthropogenic sources (from farmlands) to be 292 to 476.3 Gg N yr-1, with a mean of 372.6 Gg N yr-1. The integrated budget of greenhouse gasses indicates that Chinese terrestrial ecosystems act as a small net sink for global warming potential (GWP), ranging from 0.04 to 0.32 Pg CO2-eq yr-1, in a striking contrast to terrestrial ecosystems globally, which are a source of 2.75 to 6.78 Pg CO2-eq yr-1. The ratios of anthropogenic to natural sources of CH4 and N2O are much larger in Chinese terrestrial ecosystems than they are in global averages, reflecting greater human disturbance of terrestrial ecosystems in China.