Located in a key section of the Yellow River in North China's Inner Mongolia Autonomous Region, the Ulansuhai Nur in Bayannur plays an important role in the northern sand prevention and in the water ecological security of the Yellow River.
The Ulansuhai Nur region features one of the eight large freshwater lakes in China and the largest functional grassland and wetland in the Yellow River basin. It maintains water regulation, ice prevention, flood control and water purification.
Owing to the development of irrigation areas, waste water from farmlands, urban domestic and industrial sewage, and mountain torrent flew into the Ulansuhai Nur Lake, which severely polluted the lake water and led to rapid formation of bog, reduction of lake area, and degradation of ecological function. Prompt restoration of the local ecological environment was extremely urgent.
In response to the call for ecological environment restoration, companies such as the CCCC Third Highway Engineering Co., Ltd and CCCC Highway Consultants Co., Ltd. — both subsidiaries of China Communications Construction Company Ltd (CCCC) — participated in the pilot restoration project in April 2019.
The project included overall protection, system restoration, and comprehensive treatment of the mine, lake, grass and forest and the farmland.
Over the past two years, CCCC subsidiaries completed restoration of the pilot area and promoted implementation of local rural revitalization, regaining the area's previous condition.
Birds are seen flying over the Ulansuhai Nur Lake in Inner Mongolia Autonomous Region. [Photo/sasac.gov.cn]
Re-building ecosystem
"We can't move any farther, it's all water plants ahead."
That's what it was when Lin Guanhao, a technical designer at CCCC, and his colleagues arrived at the Ulansuhai Nur region for the first survey in July 2019.
Via an unmanned aerial vehicle, they found that the water surface was fully covered with the green water plants.
The water plants formed a lush "underwater forest". As the main producers and regulators in a water ecosystem, they were supposed to improve diversity and stability of the lake. Given a large lake surface area, it became hard to handle the massive dead water plants, which led to continuous accumulation under the lake and made it a polluted area.
Considering local conditions, the survey team selected two relatively independent and heavily polluted open water areas as pilots to conduct experiments using different technologies.
On a sunny day, the team was investigating the water surface when they saw a bird holding a fish fly over. This enlightened the team to use a biological way to control the growth of the water plants.
According to Yang Bo, chief engineer of the project, the pollution source was controlled by using the fully automatic mower boat, and treatment of the water plants mainly relied on the herbivorous fish released in the areas.
"With the power of the food chain, water grass is expected to be effectively reduced," Yang said.
Meanwhile, the team also adopted the taming and cultivation of local microorganisms. This led to improved self-cleaning and restoration capacity of the water ecosystem.
A view of the Ulansuhai Nur Lake [Photo/sasac.gov.cn]
Improving connection of water systems
"From a distance, the reeds blowing in the breeze looked like a wave of wheat," Yang said, recalling the first time he and his team saw the scenery. "It was beautiful, but the reeds turned out to be a big trouble for the treatment project."
Nearly a half of the Ulansuhai Nur lake area was covered with reeds. The dense plants divided the lake area into several parts unconnected, which lowered mobility of the water and hindered dilution of pollutants in the area.
Therefore, the team decided to dredge the area densely covered with reeds to remove the endogenous pollutants silted at the bottom of the lake for years.
However, the team later found that the dredging work with land excavators and barges was costly but had low efficiency. So they came up with the idea of using suction dredgers.
In May 2020, several suction dredgers were shipped to the region. They worked efficiently, and the water system was greatly improved.
After months of efforts, nine suction dredgers completed all the waterway dredging operations and dredged more than 5 million cubic meters of sludge.
Workers clean sludge under the Ulansuhai Nur Lake. [Photo/sasac.gov.cn]
Improving living environment in rural areas
Civilizations are cradled along rivers, and Ulansuhai Nur is no exception.
As more and more people settled along the river, more domestic pollutants were noted. Therefore, treatment of pollutants produced from nearby villages were highlighted with attempts to eliminate them as underwater pollution source.
The project contractors guided villagers on how to scientifically handle wastes like waste mounds, dunghills, haystacks, slag dumps and garbage to improve the environment.
Meanwhile, renovation of old and dangerous walls and fences as well as roads had also been conducted. Various kinds of trees were planted along the roads and on activity squares for greening and sandstorm prevention.
Sewage treatment was a key part of the project. To realize full coverage, collection and treatment of sewage pipelines, several sewage treatment stations and facilities were built, through which every household is linked. All domestic sewage is transmitted through one single path.
Handling with the mine
The climate and ecology of the entire Ulansuhai Nur region depend much on both the Ural Mountains and the Ulansuhai Nur Lake.
The Ural Mountains is home to rich mineral resources. Mining was once a pillar of regional economic development.
However, the industry led to a series ecological and environmental issues such as frequent geological disasters, lowering water quality, desertification of the grassland and worsening farmland quality. Worse, a large amount of sediment and pollutants flowed into the Ulansuhai Nur Lake which intensified water issues. The ecological restoration of the Ural Mountains became extremely urgent.
Li Yijin, head of the Ural Mountains restoration project, said that the Ural Mountains area has little rain and barren soil. Adding to the fragile ecological environment and vast and scattered targeted areas, he said the project plan must be geared towards local conditions.
After repeated surveys and improved plans, the team finally made a decision to combine advanced treatment methods and the traditional approaches.
For example, the Xiaomiaozi ditch located in the southern foot of the Ural Mountains has high cliffs on both sides and rich resources. Unfortunately, the ditch experienced several mudslide disasters in recent years, resulting in damage to farmland, houses and roads.
The team adopted real-time video monitoring systems of the amount of precipitation, infrasound and mud and water levels based on the internet to provide accurate and reliable data and analysis as references for making decisions and reducing mudslide impacts.
In terms of restoration of barren land, that's where the traditional approaches came in.
According to Li, the team dug trenches on the side slopes vertical to the main wind direction and planted salix mongolica and reed straws, forming a grid wind-break wall. The wall can effectively restore plants eliminated in the mining areas and stabilize the sand.
(Executive editor: Wang Ruoting)
