Anthropogenic pollution discharges, hotspot pollutants and targeted strategies for urban and rural areas in the context of population migration: Numerical modeling of the Minjiang River basin.

Abstract

Unprecedented urbanization-induced population migration in China severely affects the scale and geographic distribution of anthropogenic pollutant discharge. Understanding how pollutant discharge patterns respond to population migration can help guide future efforts to maintain water sustainability. Here, based on a new calculation framework with 18 dynamic parameters designed for anthropogenic discharges, we finely tracked and visualized the effects of population migration on the spatial and temporal changes in anthropogenic discharge from 1980 to 2019 in the Minjiang River basin. The results indicate that the increasing effect of population migration on anthropogenic discharges peaked in 2002 and started to contribute to pollutant reduction from 2010 onward. The direct impact of population migration only contributes to the shift of anthropogenic discharges from rural to urban areas, while the migration bonus is the key factor leading to the reduction in anthropogenic discharges. Population migration is highly beneficial for chemical oxygen demand (COD) reduction, which has contributed to a shift from COD to NH4+-N and total phosphorus (TP) as hotspot pollutants in the whole basin (NH4+-N in urban areas and TP in rural areas). Moreover, pollution reduction resulting from the demographic bonus phenomenon has remained limited only to urban areas. Since approximately 2010, the per capita amount and total amount of anthropogenic pollutant discharges in rural areas have exceeded those in urban areas; in particular, the per capita COD and TP discharges in rural areas reached four times those in urban areas. This suggests that future pollution control strategies should give more attention to rural areas and focus on the differentiation and targeting of urban and rural areas.