Changing phosphorus metabolism of a global aquaculture city.

The anthropogenic phosphorus scarcity and phosphorus-induced pollution call for a substantial improvement of phosphorus use efficiency (PUE). Using substance flow analysis, phosphorus flow charts for an agriculture city with fast growing aquaculture, i.e. Zhangzhou in China for the period 1995–2014, were drawn to present phosphorus flow distribution through its food system and identify where PUE can be improved substantially. The results showed that the phosphorus input amount of the system increased 1.73 times, to 7.67 × 104 t P in 2014 since 1995, mainly attributed to the change of agricultural production structure, characterized as the rapidly expanding aquaculture. There was 325% (2.54 × 104 t P) increase of annual phosphorus input to aquaculture, compared with 20% (0.64 × 104 t P) increase for crop farming and 15% (679 t P) for feeding livestock. Accordingly, the amount of annual net phosphorus loss from aquaculture also increased much more than that from other subsystems. Thus, improving PUE in the aquaculture is more urgent than that in others. As for the food consumption subsystems, compared with rural residents, annual food phosphorus consumption of urban residents significantly increased (236%, 559 t P yr−1), resulting in rapid increase of its net environmental phosphorus load. Therefore, urbanization could be another driver on regional phosphorus loss by enhancing regional per capita food phosphorus footprint. However, most of the loss occurred during food production rather than food consumption, although the production loss was mainly driven by the change of food consumption amount and patterns. Reducing and recycling phosphorus loss in production is therefore much more important than recovering phosphorus from food consumption stage. Thus, improving PUE in an agricultural area should rely on optimizing and upgrading production structure and enhancing regional internal recycling/reusing of phosphorus. Image 1 • Phosphorus demand and loss from the city significantly increased since 1995. • Phosphorus demand and loss grew much faster from aquaculture than from others. • Great potential of improving phosphorus use efficiency lied in aquaculture. • Production is more important than consumption in reducing phosphorus loss. [ABSTRACT FROM AUTHOR]