Significance: The biogeochemical cycle of phosphorus (P) has been massively altered in China, challenging its food security and causing eutrophication of freshwaters. This study shows, for the first time to our knowledge, how P cycling in China was intensified in the past four centuries to sustain the increasing population and its demand for animal protein. Our analysis also reveals the spatial disparity of its concomitant eutrophication impact. The findings advance the knowledge base needed for closing the P cycle to sustain future food production and maintain healthy rivers, lakes, and oceans.

Understanding historical patterns of phosphorus (P) cycling is critical for sustainable P management and eutrophication mitigation in watersheds. This study built a bottom-up model using the substance flow analysis approach to quantify P cycling in the Chaohu watershed during 1978–2012. We found that P flows have been intensified, with a 5-fold increase of annual P inputs to sustain the expanding intensive agriculture. Annually, most P inputs (75%) were stored within the watershed, which caused accelerating buildup of legacy P in cultivated land (from 4.9 Gg to 6.5 × 102 Gg), uncultivated land (from 2.1 Gg to 1.3 × 102 Gg) and surface water (from 3.7 Gg to 2.6 × 102 Gg) during 1978–2012. The main legacy P sources include fertilizer application for cultivated land, phosphogypsum abandonment for uncultivated land, respectively. The animal husbandry contributed about 63–66% of total P inputs to surface water. The contribution of animal food-P increased greatly during 1978–2012, from 7% to 24% and from 1% to ...