Effects of urbanization on phosphorus metabolism in a typical agricultural area

Phosphorus loss during food production and consumption and the effect of urbanization on cropland loss have been widely studied. However, the effect of urbanization on phosphorus metabolism in agricultural areas has received little attention. Using substance flow analysis, this paper reveals the effect of urbanization on food phosphorus metabolism. By developing comprehensive mass balance models, we quantify P flows in a typical agricultural area after summarizing the critical pathways for the effect of urbanization on P metabolism. Then, based on indicators such as per capita food P demand or loss, we discuss the effect of urbanization on food consumption, food production, food export and food waste management. Urbanization resulted in the growth of urban population, the increase of animal-derived food proportion in diet, the increase of food export and its animal-derived food proportion, more emission and declined recycling rate of urban excreta and food waste. Quantitative analysis of urbanization and P metabolism reveals that the increase of P loss driven by urbanization was mainly due to the expansion of animal-derived food production and the increase of food export. The sum of their contribution reached 99.2% of the cumulative urbanization-related P loss over the 20 years. These factors led to more P demand and losses in the regional food consumption-production system. Opportunities for sustainable phosphorus use in food production and consumption system rely on the improvement of P use efficiency in agricultural production, especially animal-derived foods. In this case, the increase of P loss from animal production accounted for 84.5% of total increase of cumulative urbanization-related P loss during the period, due to much lower P use efficiency in livestock feeding and aquaculture than grain planting. Moreover, it was more useful to recycle food waste P and excreta P (as crop fertilizer) than to enhance P removal in wastewater treatment plants.