摘要
可将临界负荷概念用于确定生态系统能够忍耐的无显著毒害作用的沉积水平。本文总结了瑞典研究课题"跨界大气污染的削减策略(ASTA)"中北方针叶林氮的临界负荷评估工作。不论是瑞典北方低水平氮背景沉降地区的野外实验,还是大尺度的监测研究,结果都表明:少量增加氮剂量会引发重大的植被变化;并且停止氮输入后,植被恢复非常缓慢。数据表明,即便氮输入的速率低于目前建议的临界负荷(北方针叶林下层植被的经验值为10～15kg N/hm^2·a),生态系统的关键成分也会发生变化。根据这些数据,我们认为临界负荷应降为6 kg N/hm^2·a。
The critical load concept is used to establish the deposition levels which ecosystems can tolerate without significant harmful effects.Here we summarize work within the Swedish research program Abatement Strategies for Transboundary Air Pollution (ASTA) assessing the critical load of N for boreal forests.Results from both field experiments in an area with low background N deposition in northern Sweden,and from a large-scale monitoring study, show that important vegetational changes start to take place when adding low N doses and that recovery of the vegetation after ceasing N input is a very slow process.The data presented indicate that changes in key ecosystem components occur even at a lower rate of N input than the present recommended empirical critical load for boreal forest understorey vegetation of 10-15 kg N ha^(-1) yr^(-1).Based on the data presented,we suggest that the critical load should be lowered to 6 kg N ha^(-1) yr^(-1).
