1961-2010年中国区域氮沉降时空格局模拟研究

由于人类活动的干扰,近年来,通过沉降和施肥形式进入陆地生态系统的氮素持续增加,众多研究表明,中国已经成为继欧洲和北美之后的第三大氮沉降区。氮与陆地生态系统生物地球化学循环的一系列过程都相互联系,碳循环及其格局也受到氮的影响,因此大气氮沉降的变化受到广泛关注,探明区域大气氮沉降的时空格局对评估氮沉降对陆地生态系统碳循环的影响具有重要意义。构建了一个基于降水、能源消费和施肥数据的氮沉降时空格局模拟方法,通过与观测数据的比较说明该模拟方法能够较好地模拟氮沉降的时空变化,在此基础上,利用该方法模拟了1961-2010年中国区域氮沉降的时空格局。结果表明:(1)1961-2010年中国区域年平均氮沉降速率为0.81 g N m^-2 a^-1,由20世纪60年代的0.31 g N m^-2 a^-1增加到21世纪初的1.71 g N m^-2 a^-1,年增长率为0.04 g N m^-2 a^-1。总氮沉降量由20世纪60年代的2.85 TgN/a增加至15.68 TgN/a。(2)NH_x-N的沉降速率大约是NO_y-N的4倍,是主要的氮沉降形式。1961-2010年我国湿沉降平均速率为0.63 g N m^-2 a^-1,是干沉降速率(0.17 g N m^-2 a^-1)的3.63倍,是氮素进入陆地生态系统的重要途径。(3)在空间上,我国的大气氮沉降速率呈现出由东南向西北梯度递减的格局,华北、华中和东北的农田是氮沉降速率最大的区域,同时也是氮沉降速率增长最快的区域。

Modeling the temporal-spatial patterns of atmospheric nitrogen deposition in China during 1961-2010

Anthropogenic activities have altered the global nitrogen cycle, which has led to increases of nitrogen input into ecosystems through N deposition. China has become the third largest N deposition region. Excess N input can have negative impacts on ecosystem health via processes such as soil acidification, losses of biodiversity, and changes in the carbon cycle. Meanwhile, nitrogen input is an important factor linked to terrestrial carbon sinks. Specifically, such input is connected with a number of biogeochemical cycles that can influence the carbon cycle and its spatial pattern. Because of these wide-ranging effects, atmospheric N deposition rates have attracted much concern, and several studies have attempted to reveal the spatial and temporal patterns of N deposition with the purpose of evaluating N deposition effects on the carbon cycle of terrestrial ecosystems. We have established a new mathematical model that can be used to estimate regional N deposition over long time periods based on data related to precipitation, energy consumption, and fertilizer use. Comparisons between simulations and observations showed that the model can simulate the spatial and temporal variations of N deposition reasonably well. Then, we estimated the N deposition in China during 1961-2010 based on this model. The results were as follows. (1) During 1961-2010, the average total nitrogen deposition in China was 0.81 g N m^-2 a^-1, and the deposition values increased from 0.31 g N m^-2 a^-1 in the 1961-1970 to 1.71 g N m^-2 a^-1 in the 2001-2010; the total N deposition increased from 2.85 Tg N/a to 15.68 Tg N/a. (2) The NH_x-N deposition rate was about 4 times that of NO_y-N, and NH_x-N was the main deposition type. The wet deposition rate was 3.63 times that of the dry deposition during 1961-2010; thus, wet deposition represents a main pathway for N input into ecosystems in the region. (3) In terms of spatial distribution patterns, the N deposition decreased from southeastern to northwestern China. The north, central, and cropland areas of the northeast had the largest overall N deposition rates and the largest increases in the N deposition rates over time.