Are nitrogen-to-phosphorus ratios of Chinese lakes actually increasing?

Tong et al. (1) demonstrate an increased mass ratio of total nitrogen to total phosphorus (TN:TP) and decreased TP concentration in many Chinese lakes in association with widespread construction of sewage collection and treatment plants during 2008 to 2017. We argue this conclusion is not true and likely leads to reduced pressure for nutrient loading reduction. We examined the difference of TP and TN:TP between 2008 and 2018 in 30 lakes (15 lakes were included in ref. 1) and found that TP increased in 47% of lakes and decreased in 23% of lakes, and TN:TP increased in 13% of lakes and decreased in 20% of lakes ( P < 0.05). We collected monthly monitored TP and TN:TP of 12 representative large lakes (nine lakes were included in ref. 1) during 2007 to 2018. TP increased in seven lakes and decreased in five lakes (Fig. 1 A ), and TN:TP mass ratios increased in two lakes and decreased in … [↵][1]1To whom correspondence may be addressed. Email: qinbq{at}niglas.ac.cn. [1]: #xref-corresp-1-1