Focus interview

Original title: From "Ecological Tragedy" to the Splendid Water and Great Technology Empowering South Lake

It can be seen from the two photos of South Lake in Jiaxing, Zhejiang Province, taken from the same perspective in 2016 and 2021, that the change of water quality has been clearly visible five years apart. The water of the South Lake today is rippling and crystal clear. In the past seven years, the water quality of the South Lake has risen from the former Class V to the current Class III water in the lake and reservoir. How did this change happen?

In early summer, many rivers and marshes in Jiaxing are still planting water plants.

Jiang Xia, director and researcher of the Lake Ecological Environment Research Institute of the Chinese Academy of Environmental Sciences: For the seeds with high mobility, we may use cutting. For better water bodies, we can also use some seed throwing methods.

Today's Jiaxing South Lake is green and clear, and the change of water quality is related to the aquatic plants planted to the bottom. Seeing here, don't think that the water quality of the South Lake has become the Class III water of the lake and reservoir today, and it is only by planting water plants. It has been nearly 7 years to provide a safe water environment for these plants.

Jiaxing is located in the lower reaches of Taihu Lake basin, the hinterland of Hangjiahu Plain; It faces the sea to the east and the Qiantang River to the south; The Beijing Hangzhou Grand Canal also has more than 110 kilometers passing through Jiaxing. There are more than 200 rivers in the city. The water system is crisscross and there are many lakes. The water area accounts for 12% of the whole city. Nine radial water systems connect the central South Lake.

Of Jiaxing's water sources, 80% are transit water, entering from Wujiang, Huzhou and Hangzhou respectively. For a long time in the past, the quality of water from the upstream has seriously affected the water environment of Jiaxing. As a granary in northern Zhejiang and a gathering place of textile printing and manufacturing industries, Jiaxing's water was once regarded as an "ecological disaster" due to the complex causes of pollution.

In 2016, the country began a major science and technology project for water pollution control and governance during the "13th Five Year Plan", of which Jiaxing's water environment governance is one. Scientists from more than ten scientific research institutions, including the National Academy of Environmental Sciences, entered Jiaxing together. Jiaxing has become a pilot city for national water ecological restoration on the basis of "five water treatment" in Zhejiang. The time is pushed forward to 2020. Jiaxing encountered a bottleneck from pollution control to ecological restoration.

Shi Xiaosong, Director of Jiaxing Municipal Bureau of Ecological Environment: There is a provincial control section in the South Lake Center that has always failed to meet the Class III standard for lakes and reservoirs, and there are several other monitoring sections. We see hope in the treatment process, but there has always been no hope for the South Lake, because it is a lake and reservoir standard with higher requirements.

The standard of Class III water in lakes and reservoirs means that the South Lake should not only meet the water quality standards, but also have good ecological functions. The South Lake is connected by nine rivers, and its ecological restoration is a whole body. The Ecological Environment Research Institute of Zhejiang Tsinghua Yangtze River Delta Research Institute is also one of the research teams of Jiaxing Water Ecological Restoration Project.

Liu Rui, Director of the Ecological Environment Research Institute of the Yangtze River Delta Research Institute, Tsinghua University, Zhejiang Province: From an ecological perspective, if you want to move forward to the third stage, it is ecological restoration. To better achieve the improvement of biodiversity, you must first have a good background before you can do ecological restoration. Therefore, source control is the most basic guarantee and the most important guarantee. Otherwise, the effect of ecological restoration is difficult to maintain.

For the problem of how to quickly judge and control potential and more complex pollution sources, Liu Rui's team has two innovations. First, they collected the data of the main rivers in Jiaxing in the past ten years, and formed a database after detailed sorting and analysis to summarize the water quality change rules and possible pollution characteristics of different rivers under different climatic conditions and external environments. Once a monitoring section has problems, the real-time monitoring data will be compared with the large database, and they can quickly and efficiently lock the rivers and regions that need to be investigated.

In the next laboratory, they are making another new attempt: they are sorting out a fingerprint database for comparison of possible pollution sources in Jiaxing. They not only need to know the temper and character of the water in the river, but also have a set of means to collect fingerprints for the river.

Liu Rui, Director of the Ecological Environment Research Institute of the Yangtze River Delta Research Institute, Tsinghua University, Zhejiang Province: Fingerprint information is that there are many substances in the water that can emit fluorescence. Given an excitation wavelength, the substance will emit another wavelength, forming a specific fingerprint like spectrum.

By comparing the problematic water sample fingerprint with the fingerprint database, all possible pollution source information can be quickly locked. Whether it is online monitoring, or the collation and analysis of large databases, or even the use of fluorescence spectrum to collect fingerprints, as well as the sonar technology of unmanned ships and the means of surveying underwater sewage pipe networks. None of these technologies alone can be said to be absolutely innovative, but the comprehensive use of this series of means by scientists in the traceability and precise prevention and control of water pollution is a new attempt to build a beautiful China enabled by science and technology. This will bring about changes in management philosophy and methods.

Yu Junjie, Head of the Science and Technology Division of the Science and Technology and Finance Department of the Ministry of Ecological Environment: With the upgrading of scientific and technological means, the upgrading of instruments and equipment, and the updating of governance concepts, now we are more from the original end to the process, to the front, to the early warning, and more advanced research and judgment of some unknown events, which will bring many disruptive changes, There will be many disruptive changes to our future management model.

In the process of ecological restoration of Jiaxing South Lake, the problem of precise source tracing and control has been solved. But how to make these aquatic plants survive, the scientific research team still faces another challenge.

Jiang Xia, director and researcher of the Lake Ecological Environment Research Institute of the Chinese Academy of Environmental Sciences: We were also considering how to drain the heavily polluted passenger water directly and quickly through the city or through the surrounding area. We used the water in some relatively good areas as early water to provide a good environment for the growth of aquatic vegetation, But its hydrodynamic conditions are really poor.

Jiaxing is located in a plain river network. The whole urban water area spans more than 100 kilometers from upstream to downstream, but the water level drop is less than one meter. In addition, the tide of the Shanghai Ocean acts as a support to the urban water body, and Jiaxing's water flow is extremely poor.

Wang Rongchang, associate professor of the School of Environmental Science and Engineering of Tongji University: This is a difficult point for us and also a place of wisdom. The water level control in plain river network areas depends on the limited water level difference. The river network water system that is somewhat tide catching sometimes has high water level and sometimes low water level. When the water level is high, the gate will be opened and led here. When the water level is low, it will fall down and the water level will be saved.

Jiaxing, as a waterlogged city, has a relatively complete flood control system. 54 gates and dams and 5 hubs just enclose the main urban area in the middle. The scientific research team from Tongji University skillfully used the existing flood control works to create some water level differences through artificial means, which improved the water mobility and created conditions for selectively supplementing the high-quality water flowing through Jiaxing's passenger water to the urban water network. In short, it is to leave good water and drain bad water.

Professor Wang Rongchang used their hydrodynamic model based on big data to show the water transfer and replacement scenarios of Jiaxing's entire urban water network in corresponding time under different schemes. As the central point of the water network, South Lake also realized the regulation and transformation of water body in this way.

Wang Rongchang, associate professor of the School of Environmental Science and Engineering of Tongji University: Our real challenge is not hydrodynamic simulation, which is relatively mature. Our simulation is to add water quality indicators to make the South Lake gradually become a transparent system. This transparency refers to the monitoring and support of data on the characteristics of the whole water quality, biological characteristics and ecological characteristics.

Digital intelligence is one of the typical characteristics of South Lake water ecological restoration technology empowerment. When the water quality conditions are met, the Institute of Lake Ecology of the Chinese Academy of Environmental Sciences has to solve the final problem.

Jiang Xia, director and researcher of the Institute of Lake Ecological Environment of the Chinese Academy of Environmental Sciences: Its sediment is like flowing, very thin. After sailing, it was disturbed, and plants could not take root. In the case of flowing mud, the organic matter is relatively high. How can I carry out phytoremediation.

They used a seemingly simple but very intelligent approach. In the specific area of South Lake, priority should be given to the water body that can be used for water ecological restoration, and some underwater and surface projects should be used as auxiliary measures to reduce disturbance, so as to improve the transparency of water body while reducing human intervention.

Jiang Xia, director and researcher of the Institute of Lake Ecological Environment of the Chinese Academy of Environmental Sciences: This can quickly take root and expand vegetation.

The South Lake is like this. From the edge to the center of the lake, it becomes clearer and clearer. Now, the aquatic plants in the South Lake have recovered from three artificially planted species to more than ten, and the species of benthos have also reached more than ten. The underwater forest here is already a colorful ecosystem. The successful experience of South Lake is also radiating the ecological integration process of the whole Yangtze River Delta. In Jiashan County, Xiangfudang after ecological restoration has become a science and innovation green valley in the Yangtze River Delta; In Pinghu, water ecological restoration is helping the construction and industrial development of beautiful villages here.

The beautiful water is grand, and the red boat is still there. This is the process of ecological transformation of the whole South Lake.

With a healthy ecological environment, the water quality of the South Lake has been stable and maintained at the level of Class III water in the lake and reservoir. Strengthening scientific and technological support is an important part of improving the security system for building a beautiful China. Science and technology enable the construction of beautiful China, and the South Lake is just a microcosm. We can see that monitoring is a means, model is a means, and ecological measures are a means. Scientific researchers have organically integrated these means into a technical system, which also provides a useful reference for cross regional and cross domain ecological environment governance. High level protection and high-quality development are the significance of science and technology enabling the construction of a beautiful China.