1952—2016年长江经济带天然与人为氮输入时空演变趋势

Spatiotemporal evolution of natural and anthropogenic nitrogen inputs to Yangtze River Economic Belt from 1952 to 2016

过量氮输入是水体氮污染的关键驱动因子,解析氮输入的结构和时空变化模式成为氮素环境管理的重要基础和难点.基于1952-2016年长江经济带各地区氮活动数据,分别构建了天然氮输入和人为氮输入模型,评估了氮输入负荷的时空变化特征.结果表明:①长江经济带氮输入负荷总体越过EKC曲线拐点进入由增长向下降的发展阶段,拐点出现在人均GDP为35777~36299元·人-1时,发生时间为"十二五"时期,主要原因是化肥和食物输入下降;②氮输入负荷存在显著的时空差异,东部地区表现为倒U型,中部为S型,西部为J型,表明氮负荷存在从东向西的空间转移,西部地区成为氮输入负荷增长的热点地区,这与东部地区化肥施用量下降有关;③人为输入是长江经济带氮输入的主要来源,输入量及其占总输入的比例均呈现显著的增长趋势,空间上表现为从西到东部逐步递增的变化规律,与氮驱动力分布一致;④植被的多年平均固氮量为1771 kg·km^-2·a^-1,其中,非农作物的固氮速率为763 kg·km^-2·a^-1,植被固氮量的年际波动较小,天然输入对长江经济带总体氮输入影响较小.

Excessive nitrogen(N)inputs from anthropogenic and natural sources are key drivers of increasing nitrogen loads in waters,and it is of great importance to identify nitrogen sources to establish effective environmental policy.Based on nitrogen activity data from 1952 to 2016 in Yangtze River Economic Belt,anthropogenic and natural N inputs models were built to estimate spatiotemporal evolution of N in the region.Results show that①N inputs to the Yangtze River Economic Belt have overall crossed the turning point of EKC curve,reversing from increasing trend to decreasing trend due to the decrease of fertilizer and food inputs.The turning point lies in the 12th Five-year Plan period(2011-2015)with the GDP per capita between 35777~36299 RMB.②There are huge variations of N inputs among different regions of Yangtze River Economic Belt.N inputs in the east,middle and west regions follow inversed U shape,S shape and J shape,respectively.The decrease of fertilizer use in east region is responsible for the change.③Human activiety induced dominate N inputs in Yangtze River Economic Belt.Both human-induced loads and contribution to the total N inputs of the region have increased over the period.④Nitrogen fixation of vegetation is 1771 kg·km^-2·a^-1 based on multi-year average and non-crop sources accounts for 763 kg·km^-2·a^-1 with little inter-annual variability,indicating a relative small contribution of vegetation N fixation to total N inputs in Yangtze River Economic Belt.