Recently, a study, Decline in Chinese lake phosphorus concentration accompanied by shift in sources since 2006 was published in Nature Geoscience. This research, with the first author Yindong Tong, from Tianjin University’s School of Environmental Science and Engineering, was the first to study total phosphorus concentration in 862 lakes across the country since 2006. The study showed that the susceptibility of eutrophication potential decreased significantly in Chinese lakes, the total phosphorus concentration levels declined by a third, and the number of lakes with heavy phosphorus pollutants was cut largely.

As lakes are sensitive to human activities, they are often referred to as the “sentinels” of the terrestrial ecosystem. “Nothing else is more appropriate than lakes to reflect the impacts of human activities,” Tong explained. Unlike flowing rivers, lakes are relatively static.

Phosphorous is vital to life, but high concentrations can trigger excessive phytoplankton blooms in aquatic ecosystems that choke aquatic life and threaten human and livestock’s health. Anthropogenic sources of phosphorous include wastewater, livestock farming, aquaculture and chemicals.

The results showed that median TP concentrations went from 80 μg l-1 (range of 3–247 μg l-1) in 2006 to 51 μg l-1 (range of 3–128 μg l-1) in 2014. In 2006, ~22% of sampling sites had TP concentrations higher than 200 μg l-1 (the lower limit of Grade V by China’s water quality standards), while in 2014 only 7% exceeded this level. Overall, TP decreased in 60% of the monitoring sites between 2006 and 2014, with larger declines for sites with TP>100 μg l-1 in 2006.

This decline brings improvements in the living environment of residents, Yindong Tong said, “For example, in summer, the number and frequency of phytoplankton blooms in water bodies have dropped significantly.”

In terms of regional distribution, total phosphorus concentrations in the lakes of Eastern, Mid and Western China have declined significantly and this trend is also affirmed in China’s five largest freshwater lakes (known as Chaohu, Dongtinghu, Hongzehu, Poyanghu, and Taihu Lake).

“The decrease in phosphorus concentrations in water bodies indicates that the risk of eutrophication is reducing, as phosphorus is the key indicator of lake’s quality,” said Tong.

Although the reasons for the improvement of lake water quality in different areas of China were not totally the same, there is no doubt that urban development and sanitation facilities made significant contributions.

With the regulation, Assessment of Reduction of the total Emission of Major Pollutants entered into force in 2006, pollution control and emission reduction have been incorporated into environmental performance appraisal in China. According to the data, from 2006 to 2014, China invested about 792.3 billion RMB to deal with domestic and industrial wastewater. By the third quarter of 2016, almost 5,000 wastewater treatment plants had been built and put into use in China.

However, there are still issues causing concerns. While the phosphorus concentration of lakes in China has decreased by almost one third, the median level of 51 μg l-1 still remains high. According to European water quality standards, less than 25 μg l-1 phosphorus concentration can be considered as high-quality water.

Generally, in Eastern and Mid China, there exists diffuse sources, such as domestic wastewater and cage aquaculture in rural areas. As the use rate of baits exceeds 30%, superfluous baits and fish faeces increase phosphorus concentrations in water bodies.

In the West, most of the variance in lake total phosphorus concentrations is explained by crop farming and the phosphate chemical industry. Dianchi Lake in Yunnan Province has an annual phosphorus loading of 30 tons from the mining and related industries. In Northeast China, other potentially important factors should be considered, such as increased phosphorus loading from soil erosions induced by intensified heavy rainfall.

“At present, the widely buildings of wastewater treatment plants in our country have achieved a significant reduction of nutrients. With a higher rate of wastewater treatment, the plants can attempt to adopt flexible effluent targets as the next step and turn the plants from ‘reducers’ of nutrients into ‘regulators’ of nitrogen and phosphorus concentrations in the lakes.” Tong said.　

Tong is concerned about environmental issues for all human beings. “For developing countries, the priority should be the improvement of water quality through urban wastewater treatment. It can bring about changes in the water environment in a short period of time. Considering the difference of driving forces, it is necessary that the flexibility in water pollution control policy reflects the level of economic development and natural conditions.”

In regard to environmental protection, Tong suggested that: “It is best not to develop remote clean lakes for the tourism industry. Once the environment of these clean lakes is damaged, it will be very difficult to restore it. In addition, tourism and catering businesses need better control and planning, in case the pursuit of economic benefit comes at the cost of the environment.”

“It is expected to be long time before Chinese lakes reach an acceptable ecological status. At least, we have made a good start.” Tong added.