Climate Effect Of Gaseous Reactive Nitrogen And Critical Loads Of Nitrogen Deposition In China

Anthropogenic reactive nitrogen (N) emissions have increased significantly in China due to industrial, agricultural and rapid urban development in the past three decades, and progress has been made with regard to research into climate effect of gaseous reactive nitrogen(N2O、NO、and NH3) in China. However, the studies in the past had many deficiencies in the aspects of data assimilation and precision characterization and so on, and still lacking of the comprehensive evaluation of the climate effect of gaseous reactive nitrogen and its derivatives in China. At the same time, since the 1980s, the increases of nitrogen deposition driven by anthropogenic reactive nitrogen emissions, has led to changes in the structure and function of terrestrial ecosystems in China. As an important method for quantifying nitrogen pollution of ecosystems and scientific basis of nitrogen emission control in the future,there are many studies of critical loads of nitrogen deposition, but in the area of China, still lacking of full assessment of critical loads of nitrogen deposition and risk assessment. Therefore, evaluating comprehensively the comprehensive climate effects of gaseous reactive nitrogen and its derivatives in China, quantifying the critical loads of nitrogen deposition in China and evaluating its potential risks,not only conducive to understand comprehensively the impacts of Chinese gaseous reactive nitrogen emissions on global climate change,but also has a great significance for the formulation of relevant government policy and reducing atmospheric reactive nitrogen pollution, nitrogen deposition and its negative ecological effect.In this paper, we obtained a series of data sets such as reactive nitrogen emission in China, land cover, spatial and reference parameters and so on through various approaches and methods. Based on the integration, processing and assimilation of these data sets, 2010 as the benchmark year, studying the impacts of atmosphere reactive nitrogen deposition on carbon sequestration, nitrous oxide and methane emissions of terrestrial ecosystems in our country, evaluating the climate effects of gaseous reactive nitrogen and its derivatives in our country based on multiple metrics, and have been studied the critical loads of nitrogen deposition of terrestrial ecosystems and risk assessment in our country. The main results are as follows.1. The climate effects of the terrestrial ecosystems carbon sequestration, nitrous oxide and methane emissions induced by nitrogen deposition in 2010 were -221.75±25.49,27.43±23.24 and 8.29±22.45 Tg CO2e, respectively, and the total greenhouse gas balance effect was -185.98±41.22 Tg CO2e, which was net uptake effect. The high-value regions of carbon sequestration and nitrous oxide emissions in cropland ecosystem were concentrated in the north China, central China and east China, but methane emissons were concentrated in southern paddy field area. The high-value regions of carbon sequestration in forest ecosystem was concentrated in the north China, central China and southern region, but nitrous oxide and methane emissions were scattered in eastern and southern China. The high-value regions of carbon sequestration, nitrous oxide and methane emissions in grassland ecosystem were scattered in parts of northeast China and north China. The net carbon exchange volume of China’s terrestrial ecosystems in 2010 was 154.61±26.57 Tg,moreover generally showed a spatial pattern characteristic of net carbon uptake, and the high-value regions of net carbon uptake were concentrated in north China, central China, east China and south China.2. On a 20-a and 100-a basis, CO2eGTP (emission load of equivalent carbon dioxide based on GTP(Global temperature potential)) driven by gaseous reactive nitrogen emissions in 2010 were-344±317 and 224±137 Tg CO2e, presenting the cooling and warming effect, respectively. On a 20-a and 100-a basis, the warming effects were mainly derived from nitrous oxide emissions,methane emissions induced by nitrogen deposition and fertilization and the processes of reduction in carbon sequestration due to plants destructed by ozone and so on, other manifestations were the cooling effects. The comprehensive climate effects of the reactive nitrogen in industrial source were-416±145 and 104±98 Tg CO2e on a 20-a and 100-a basis,presenting the cooling and warming effect, respectively. The comprehensive climate effect of the reactive nitrogen in agricultural source was mainly derived from the long-lived nitrous oxide emissions, agricultural source showed a net warming effect on a 20-a and 100-a basis,the CO2eGTP20 and CO2eGTP100 were 85±278 and 122＋89 Tg CO2e, respectively.3. The total direct radiative forcing driven by gaseous reactive nitrogen emissions in 2010 was-9.30±4.87 mW/m2,the warming effects were mainly derived from nitrous oxide emissions(0.77±0.06 mW/m2), reduction of the amount of carbon sequestration due to increased surface ozone(0.22±0.19 mW/m2), the methane emissions promoted by nitrogen deposition and fertilization(0.20±0.83 mW/m2); But the cooling effects were mainly derived from NOx and NH3 emissions which led to the increases of the inorganic aerosols(-3.84±2.83 mW/m2), NOx impacts on ozone-methane(-5.51±3.89 mW/m2) and carbon sequestration promoted by nitrogen deposition and fertilization(-1.16±0.10 mW/m2).4. For the forest ecosystem, nitrogen critical loads of cold temperate deciduous coniferous forest,temperate coniferous broad-leaved forest and subtropical evergreen broad-leaved forest area were 30-50, 10-60 and 20-90 kg N ha-1 a-1, security levels of nitrogen critical roads of forest ecosystem in different vegetation areas were at a higher level or above,there is not a potential threat of the intake of nitrogen deposition on forest ecosystem; And for the grassland ecosystem, nitrogen critical loads of temperate grassland, temperate desert and high-cold vegetation area of Qinghai-Tibet Plateau were 10-60,10-70 and 10-80 kg N ha-1 a-1, security levels of nitrogen critical roads of grassland ecosystem in different vegetation areas were at a higher level or above,there is not a potential threat of the intake of nitrogen deposition on grassland ecosystem.According to the results of this fhesis research, there are all cooling effects induced by China’s gaseous reactive nitrogen emissions either in the present or a short period in future, but over time,we will face enormous pressure because of warming climate effect derived from anthropogenic reactive nitrogen emissions. Although the cooling effect produced by terrestrial ecosystems carbon sequestration induced by nitrogen, which could partly offset the warming effect of gaseous reactive nitrogen, and agricultural N2O and industrial NOx emissions have great mitigation potential for climate change, due to the carbon sequestration potential induced by nitrogen is limited even may disappear gradually in the future. Therefore, the more positive goals and more powerful measures need to be called for and strictly implemented, implementing scientific management for reactive nitrogen, climate and other related problems in order to maintain at a specific level of radiative forcing. At the same time, it is of great significance for preventing the ecological problems may caused by high nitrogen deposition.