Phosphorus (P) is an essential nutrient for living systems with emerging sustainability challenges related to supply uncertainty and aquatic eutrophication. However, its long-term temporal dynamics and subsequent effects on freshwater ecosystems are still unclear. Here, we quantify the P pathways across China over the past four centuries with a life cycle process-balanced model and evaluate the concomitant potential for eutrophication with a spatial resolution of 5 arc-minutes in 2012. We find that P cycling in China has been artificially intensified during this period to sustain the increasing population and its demand for animal protein-based diets, with continuous accumulations in inland waters and lands. In the past decade, China's international trade of P involves net exports of P chemicals and net imports of downstream crops, specifically soybeans from the United States, Brazil, and Argentina. The contribution of crop products to per capita food P demand, namely, the P directly consumed by humans, declined from over 98% before the 1950s to 76% in 2012, even though there was little change in per capita food P demand. Anthropogenic P losses to freshwater and their eutrophication potential clustered in wealthy coastal regions with dense populations. We estimate that Chinese P reserve depletion could be postponed for over 20 y by more efficient life cycle P management. Our results highlight the importance of closing the P cycle to achieve the cobenefits of P resource conservation and eutrophication mitigation in the world's most rapidly developing economy.sustainability | phosphorus cycling | eutrophication | food production | industrial ecology T he cycling of phosphorus (P), an essential nutrient for living systems, has been massively altered by human activities, with emerging concerns about long-term supplies of affordable P for food production (1, 2). The one-way journey of P has also increased eutrophication, contributing to significant disruptions, such as water quality degradation and biodiversity losses in aquatic ecosystems (3, 4). Amplified production of phosphate rock, largely for fertilizer production, reached 225 million tons globally in 2013 (5), leading to the conclusion that anthropogenic P use is operating well beyond planetary boundaries (6, 7). Among all countries, China, with its rapid increase in population and affluence, faces perhaps the greatest sustainability challenges in its P sector. Although China is now the world's largest producer of phosphate rock, contributing 48% of total production in 2013 (5), concerns about scarcity of Chinese P reserves have begun to emerge. Although this possibility has not been as widely recognized for P as for other critical mineral resources (SI Appendix, Fig. S1), reliance of Chinese agriculture on imported P would have major ramifications for global fertilizer markets. Reflecting this amplified P use, most Chinese freshwaters have experienced excessive total P loading for years (8), triggering high-profile events, such as the cyanobacteria bloom in L...
