The supreme people's procuratorate's south four lakes project hearing will announce the results of third-party monitoring

Source: Procuratorial Daily

The "eye" of the satellite is the ruler

The supreme people's procuratorate's south four lakes project hearing will announce the results of third-party monitoring

Yan Jingjing

Nansi Lake is the largest freshwater lake in the north of the mainland, with an area of 1266 square kilometers, which undertakes various functions such as flood diversion and storage, south-to-north water diversion, development of aquatic products, shipping and transportation. On April 8, 2021, the Supreme People's Procuratorate launched a public interest litigation prosecution procedure for the damage to the ecological environment in the NansiHu Lake Basin.

After 10 months, has the damage to the ecological environment in the South Fourth Lake Basin improved? Objectively existing images and data are precisely the yardstick for measuring the fairness of case handling. Recently, the reporter learned from the Chinese Academy of Sciences Aerospace Information Innovation Institute and the China Environmental Monitoring Station about some monitoring data since the case was handled, satellite remote sensing images faithfully recorded the nansi lake feature information far beyond the scope of human observation, the national environmental quality monitoring network data monitoring changes in water quality in different periods, through the comparison with the same period of previous years, you can clearly see the changes in the south four lakes.

The Institute of Aerospace Information Innovation of the Chinese Academy of Sciences, entrusted by the Supreme People's Procuratorate, conducted continuous remote sensing monitoring of the Nansi Lake and its surrounding ecological environment from a third-party objective position, and carried out the ecological and environmental clue mapping, typical on-site evidence collection, and follow-up of governance results for the Nansi lake project through technical means such as processing of obtained image data, model calculation and information extraction, comparative analysis and historical traceability, field investigation and investigation and evidence collection, results follow-up and dynamic display.

"Using satellite remote sensing data, in view of the different degrees of eutrophication, black odor, and suspended solids concentration changes in water bodies in the visible and near-infrared bands, the three typical water quality indicators of the black and odorous water body index, the degree of eutrophication of the water body, and the concentration of suspended solids in the south four lakes were observed and analyzed, reflecting the water quality of the south four lakes from different dimensions and comparing their annual changes." Liu Shuo, a researcher at the Institute of Aerospace Information Innovation of the Chinese Academy of Sciences, introduced.

The observation and calculation comparison shows that from late October 2020 to late October 2021, the water area of the south four lakes with high black odor index, high eutrophication degree of water body and high concentration of suspended solids in water bodies has been greatly reduced, while the water area of water bodies with low black odor index, low eutrophication degree of water body and low concentration of suspended solids in water bodies has increased significantly.

According to reports, in the entire process of satellite remote sensing monitoring and comparison, in order to ensure the objectivity of the comparison of satellite remote sensing data on water bodies in the Nansi Lake Basin, the satellite remote sensing monitoring technology has been strictly constrained in accordance with the "five same" methods of targeting the same region, using the same satellite data, the same time phase, the same processing algorithm, and the meteorological conditions when the same data is acquired. At the same time, considering that the water transfer of the South-to-North Water Diversion Project from 2020 to 2021 was completed before the flood, a large amount of external water entered the South Fourth Lake in the first half of the year; from June to September, a large amount of rainwater flowed into the South Fourth Lake, and the summer vegetation was lush and cloudy, and the observation from space to the water surface was more externally shaded; and the winter was a period of calm lake surface and impurity precipitation over the years, and the water quality was generally better than other seasons. Therefore, the time window of late October autumn is selected, with sunny days, water and grass gradually withering, and the water body is relatively stable, which is a more representative time window of water conditions, and the satellite observes the South Four Lakes. "Satellite remote sensing monitoring shows that under the impetus of the project, the overall water quality of the Water Body in the South Four Lakes Basin has improved significantly, and the risk of pollution involvement in key monitoring targets has been greatly reduced." Liu Shuo said.

The images reflect the objective changes in visual effects, and the water quality monitoring data confirms the treatment effect of Nansi Lake for a period of time from another side. The reporter learned that according to the surface water environmental quality standards, the quality of water is divided into several grades from class I to class V. The main indicators of water environment monitoring are total phosphorus, ammonia nitrogen, permanganate index, etc. The total phosphorus exceeding the standard mainly comes from non-point source pollution, the ammonia nitrogen exceeding the standard mainly comes from domestic sewage, and the permanganate index exceeding the standard indicates that the water body is likely to be contaminated by organic matter.

According to the data provided by the China Environmental Monitoring Station based on the National Environmental Quality Monitoring Network, there are 5 lake monitoring points in the Nansi Lake Basin and 28 monitoring sections of 19 rivers entering the lake. Monitoring data show that during the "13th Five-Year Plan" period, the water quality of the Nansi Lake was generally stable, but there were exceeding the standard in some areas and some periods, and problems such as urban and rural non-point source pollution, cyanobacterial blooms in lakes, and ecosystem imbalances were prominent. In August 2020, the water quality of Class IV to inferior Class V. appeared in many sections of the rivers entering the lake of Nansi Lake, and the permanganate index and total phosphorus exceeded the standard. The water pollution situation during the flood season is more serious, and the characteristics of non-point source pollution are obvious.

In August 2021, the South Four Lakes Project is in progress. Monitoring data show that the water quality of the secondary dam at the point of the lake has improved from class V. to class III. year-on-year, and the main improvement index is total phosphorus; 14 river stations into the lake have improved or improved significantly, and the main improvement indicators are total phosphorus and permanganate index. During the same period, the average daily concentration of total phosphorus during the flood season of the secondary dam of the Nansi Lake was significantly reduced year-on-year; the ammonia nitrogen and permanganate indexes showed a stable level, and there was no large fluctuation before the project. The daily average concentration of total phosphorus in the section of the river into the lake decreased significantly year-on-year; the concentration of permanganate index decreased year-on-year; and the overall concentration of ammonia nitrogen did not change significantly.

"After the case was filed, the quality of the water environment in the South Fourth Lake Basin has gradually improved, and the main pollution indicators have been reduced. The surrounding environment is cleaner and greener, and the effect of the project promotion is obvious. Li Wenpan, deputy director of the Water Ecological Environment Monitoring Office of the China Environmental Monitoring Station, said.