作为生命系统的必需元素之一，磷的生物地球化学循环与人类社会的可持续发展休戚相关。然而，自然状态下单向流动的磷循环在人类活动的影响下，其流动速度被快速地提高。这一方面造成人们对磷这种战略性自然资源枯竭的担忧，另一方面，大量的磷流失进入水体造成了一系列危害生态系统乃至人类社会的富营养化事件。因此，有必要全面分析社会经济部门的磷流动过程以作为缓解由磷引起的资源环境问题的“抓手”。

本研究基于元素流分析，建立了涵盖中国7个社会经济部门和4个自然部门的磷核算框架，核算了中国31个省（自治区、直辖市）的磷流量，以2000年、2005年、2010年、2015年和2020年为研究的时间点。基于元素流核算结果，对中国区域尺度磷流量时间变化特征进行分析，明晰两个尺度上的关键流动部门；分析磷流量空间分布格局，探究中国内部磷活动热点区域；基于生命周期影响评价对磷排放进入水体造成的淡水富营养化进行评估，从末端指出应重点施策控制的区域，同时使用情景分析方法，设定不同政策情景，对2020-2050年的磷排放总量变化趋势进行预测，指明应重点控制的产业环节。

结果表明，2000-2020年中国的磷输入输出总量经历了先增后减的变化趋势，并于2015年达到峰值（51.6 Mt）。输入输出总量自始至终受到社会经济部门的主导，其中输出总量的关键部门从2000-2005年的工业生产转变为后期的采掘业，其占比峰值出现在2015年（31.2%）。在农业部门、地表水和海洋等部门中，磷表现除显著的累积现象（均超过17%）。将路径标量化，发现工业流类型是对总量贡献最大的流量类型，历年占比均在53%以上。区域尺度考察磷流量时间变化，输入输出总量变化趋势除华北地区和西北地区外，与国家尺度一致。两个尺度下的结合研究发现其关键部门存在一定差异。国家层面2005-2020年期间影响磷流动的主要部门是采掘业。但在区域尺度上，2005-2015年关键部门为工业生产，2020年关键部门发生转变，即有45%地区的主导节点为食品加工业。国家层面表现出主导地位采掘业部门则仅仅是内部四个产磷省份的关键部门。

中国磷流输出总量空间分布总体呈现出“中部多，南北少”的格局，以长江流域分布最为显著，且2000-2020年期间并未发生明显变化。这是因为长江流域集中了中国所有的磷矿石主产区（输出占比40%左右）。输入总量分布与输出总量类似。区域层面关键部门食品加工业的分布主要集中在东部地区，而西北地区体量较小。中国贸易产业链格局表现为“前端输出、后端输入”，净出口主要分布在长江中上游地区，而净进口地区则主要分布在东部沿海经济发达区。磷产业密度表现出“东南高，西北低”，但GDP强度和人均磷输出量的分布则表现出“西高东低”的现象。磷流失进入水体环境的量主要分布在长江流域和西部地区，前者被以采掘为代表的人类活动主导，而后者则更多可归因于自然过程，尤其在西藏和青海。综合分布格局来看，这两个区域的磷产业活动均值得注意。

对历年来淡水富营养化影响评估的结果表明，水生生物物种永久性消失影响大的地区集中分布在南部边境和沿海地区，表现出“南高北低”格局，且历年未发生明显变化。而水生生物物种暂时性消失影响大的地区则集中分布在长江中下游地区和西部地区，尤其是前者，对中国整体贡献最大的五个地区均位于此，占比超过53%。在情景分析中，考察单因素影响时，发现提高农村生活污水治理率对磷排放量的控制作用最大，其次为提高秸秆循环率和减小磷矿石生产规模。综合控制情景下磷排放量下降了16.6%。除该情景外，单一情境中，废物循环优化的控制力最强。在综合控制情景下，位于产业链相对上游的采掘业、工业生产、农业和社会消费部门的磷排放量有明显的减少，但与此同时，由于下游的废水处理和固废处理部门的处理量变大，其部门本身的磷排放量有12%左右的增加。因此，在具体控制措施上，废物循环措施应该被首要考虑，同时对生产投入的控制以及平衡生产消费的措施也不可轻视。

通过以上结果，本研究指出了国家和区域两个尺度上的关键流动部门和重点活动区域，指明了应重点控制的地理区域和优先施策的流动环节。可以促进磷行业可持续发展，协助区域达成绿色发展目标，为科学施政提供参考。

As one of the essential elements in the biosphere, the biogeochemical cycling of phosphorus is closely intertwined with the sustainable development of human society. However, the unidirectional flow of phosphorus in its natural state has been accelerated under the influence of human activities. On one hand, this acceleration has prompted concerns about the depletion of phosphorus as a strategic natural resource. On the other hand, the substantial loss of phosphorus entering water bodies has led to a series of eutrophication events, posing risks to ecosystems and human societies. Hence, it is imperative to comprehensively analyze the phosphorus flow within the socio-economic systems as a lever for mitigating resource and environmental issues stemming from phosphorus.

This study establishes a phosphorus bookkeeping framework based on material flow analysis, encompassing seven socio-economic systems and four natural systems in China. The phosphorus flow within the 31 provinces (autonomous regions, municipalities) of China is accounted for, focusing on the years 2000, 2005, 2010, 2015, and 2020. Based on the results of material flow analysis, the temporal variations in phosphorus flow at the regional scale in China are analyzed to elucidate key flow sectors at both national and regional levels. Additionally, the spatial distribution pattern of phosphorus flow is examined to identify hotspots of phosphorus activities within China. Furthermore, using a life cycle impact assessment, the eutrophication caused by phosphorus emissions into water bodies is evaluated. Key regions requiring targeted interventions are identified, and scenario analysis is conducted to forecast trends in phosphorus emissions from 2020 to 2050, indicating priority industrial sectors for control measures.

The results indicate that the total phosphorus input and output in China experienced an initial increase followed by a decrease from 2000 to 2020, peaking in 2015 at 51.6 Mt. Throughout this period, the total input and output were predominantly influenced by the socio-economic system, with the mining sector emerging as the key sector for output from 2000 to 2005, reaching its peak in 2015 at 31.2%. The agricultural system, surface water, and marine systems exhibited significant accumulation trends, each exceeding 17%. Industrial flow emerged as the largest contributor to total phosphorus output, consistently accounting for over 53% annually. At the regional scale, the temporal trends in phosphorus flow were consistent with the national scale, except for the North China and Northwest regions. Key sectors influencing phosphorus flow varied between the national and regional scales, with the mining sector dominating at the national level from 2005 to 2020, whereas at the regional level, the key sectors shifted from industrial production to food processing, with 45% of regions being led by the latter in 2020.

The spatial distribution of phosphorus output in China generally follows a pattern of "more in the central region, less in the north and south," with the Yangtze River Basin exhibiting the most significant distribution, which remained relatively unchanged from 2000 to 2020 due to its concentration of phosphorus ore-producing areas, accounting for approximately 40% of output. The distribution of input is similar to that of output. The key sector of food processing is mainly concentrated in the eastern region at the regional level, with a smaller presence in the Northwest. The trade pattern of phosphorus industries exhibits a "front-end output, back-end input" pattern, with net exports primarily concentrated in the upper and middle reaches of the Yangtze River, and net imports mainly in the economically developed coastal areas in the east. The density of phosphorus industries shows a pattern of "high in the southeast, low in the northwest," while the distribution of GDP intensity and per capita phosphorus output exhibits a "high in the west, low in the east" pattern. Phosphorus loss entering water environments is primarily distributed in the Yangtze River Basin and western regions, the former being dominated by human activities such as mining, while the latter is largely attributable to natural processes, especially in Tibet and Qinghai. Overall, the phosphorus industry activities in these two regions deserve attention.

The results of the assessment of eutrophication impacts from 2000 to 2020 indicate that areas with significant permanent loss of aquatic species are concentrated in the southern border and coastal regions, showing a "higher in the south, lower in the north" pattern, with no significant changes over the years. Areas with significant temporary loss of aquatic species are concentrated in the middle and lower reaches of the Yangtze River and western regions, especially the former, with the top five regions contributing most to China's total located there, accounting for over 53%. In scenario analysis, when examining single-factor impacts, it was found that increasing the rate of rural sewage treatment had the greatest control effect on phosphorus emissions, followed by increasing the recycling rate of straw and reducing the scale of phosphorus ore production. In the comprehensive control scenario, phosphorus emissions decreased by 16.6%. Apart from this scenario, waste recycling optimization had the strongest control effect in single scenarios. In the comprehensive control scenario, phosphorus emissions from upstream sectors such as mining, industrial production, agriculture, and social consumption systems decreased significantly, but at the same time, due to increased processing volumes in downstream wastewater treatment and solid waste treatment systems, the phosphorus emissions of the systems themselves increased by about 12%. Therefore, waste recycling measures should be given priority in specific control measures, while control of production inputs and measures to balance production and consumption should not be overlooked.

Based on these results, this study identifies key flow sectors and priority activity areas at both national and regional scales, indicating geographic regions requiring targeted control measures and flow sectors warranting prioritized actions. This can promote the sustainable development of the phosphorus industry, assist regions in achieving green development goals, and provide references for scientifically sound governance.