Yindong Tong; Wei Zhang; XuejunWang; et al

Domestic wastewater and agricultural activities are important sources of nutrient pollutants such as phosphorus and nitrogen.Upon reaching freshwater, these nutrients can lead to extensive growth of harmful algae, which results in eutrophication. Many Chinese lakes are subject to such eutrophication, especially in highly polluted areas, and as such, understanding nutrient fluxes to these lakes offers insights into the varying processes governing pollutant fluxes as well as lake water quality. Here we analyse water quality data, recorded between 2006 and 2014 in 862 freshwater lakes in four geographical regions of China, to assess the input of phosphorus from human activity. We find that improvements in sanitation of both rural and urban domestic wastewater have resulted in large-scale declines in lake phosphorus concentrations in the most populated parts of China. In more sparsely populated regions, diuse sources such as aquaculture and livestock farming offset this decline. Anthropogenic deforestation and soil erosion may also oset decreases in point sources of pollution. In the light of these regional differences, we suggest that a spatially flexible set of policies for water quality control would be beneficial for the future health of Chinese lakes.

水华是淡水水体中藻类大量繁殖的一种自然生态现象，是水体富营养化（可用养分增加导致藻类过度生长）的显著特征。富营养化可能会在湖泊中自然发生，但其主要原因仍是生活及工农业生产中含有大量氮、磷的污水进入水体后，造成蓝藻、绿藻、硅藻等大量繁殖，其中蓝藻水华的发生范围最广，且危害最大，对人类健康威胁不容忽视。目前，人为向水体排放营养物已经使全球范围内的富营养化现象明显加重，导致水质下降、鱼类灭绝和生物多样性减少。

　　（来源：Nature Geoscience, 2017, DOI: 10.1038/NGEO2967）