Chen X Y, Mulder J, Wang Y H, Zhao D W, Xiang R J
Department of Plant and Environmental Sciences, Agricultural University of Norway, 1432-Aas, Norway.
Environ Geochem Health. 2004 Jun-Sep;26(2-3):179-86. doi: 10.1023/b:egah.0000039580.79321.1a.
In recent years, China has conducted considerable research focusing on the emission and effects of sulphur (S) on human health and ecosystems. By contrast, there has been little emphasis on anthropogenic nitrogen (N) so far, even though studies conducted abroad indicate that long-range atmospheric transport of N and ecological effects (e.g. acidification of soil and water) may be significant. The Sino-Norwegian project IMPACTS, launched in 1999, has established monitoring sites at five forest ecosystems in the southern part of PR China to collect comprehensive data on air quality, acidification status and ecological effects. Here we present initial results about N dynamics at two of the IMPACTS sites located near Chongqing and Changsha, including estimation of atmospheric deposition fluxes of NOx and NHx and soil N transformations. Nitrogen deposition is high at both sites when compared with values from Europe and North America (25-38 kg ha(-1) yr(-1)). About 70% of the deposited N comes as NH4, probably derived from agriculture. Leaching of N from soils is high and nearly all as NO3-. Transformation of N to NO3- in soils results in acidification rates that are high compared to rates found elsewhere. Despite considerable leaching of NO3- from the root zone of the soils, little NO3- appears in streamwater. This indicates that N retention or denitrification, both causing acid neutralization, may be important and probably occur in the groundwater and groundwater discharge zones. The soil flux density of mineral N, which is the sum of N deposition and N mineralization, and which is dominated by the N mineralization flux, may be a good indicator for leaching of NO3- in soils. However, this indicator seems site specific probably due to differences in land-use history and current N requirement.
近年来，中国开展了大量关于硫（S）排放及其对人类健康和生态系统影响的研究。相比之下，尽管国外研究表明氮（N）的长距离大气传输及其生态效应（如土壤和水体酸化）可能很显著，但迄今为止对人为源氮的关注较少。1999年启动的中挪合作项目“大气污染对中国南方森林生态系统的影响及适应对策研究”（IMPACTS），在中国南方的五个森林生态系统建立了监测站点，以收集空气质量、酸化状况和生态效应的综合数据。在此，我们展示了位于重庆和长沙附近的两个IMPACTS站点氮动态的初步结果，包括氮氧化物（NOx）和铵态氮（NHx）的大气沉降通量估算以及土壤氮转化情况。与欧洲和北美的数值相比，两个站点的氮沉降都很高（25 - 38千克·公顷⁻¹·年⁻¹）。大约70%的沉降氮以铵态氮形式出现，可能来自农业。土壤中氮的淋溶量很高，几乎全部以硝酸根（NO₃⁻）形式存在。土壤中氮向硝酸根的转化导致的酸化速率，与其他地方相比很高。尽管土壤根区有大量硝酸根淋溶，但溪水中硝酸根含量很少。这表明氮的保留或反硝化作用（两者都会导致酸碱中和）可能很重要，并且可能发生在地下水和地下水排放区。矿质氮的土壤通量密度（即氮沉降和氮矿化的总和，且以氮矿化通量为主），可能是土壤中硝酸根淋溶的一个良好指标。然而，这个指标似乎因地点而异，可能是由于土地利用历史和当前氮需求的差异。
