Speaking of Hedi Reservoir, friends in the north may not know much, but in the south, Hedi Reservoir is a well-known "treasure house" and is known as the largest "artificial sea" in Guangdong. Historically, the Leizhou Peninsula has been drought and water shortage, drought has occurred frequently, grain production has been reduced, land has been seriously abandoned, and it is urgent to build reservoirs to solve water demand.
At the end of the 1950s, the Hedi Reservoir was fully completed, and the water of the Kyushu River was intercepted and stored, and agriculture on the Leizhou Peninsula was revived. In the past 60 years, irrigation has become one of the primary goals of Hedi Reservoir, with an effective irrigation area of 1.27 million mu, and at the same time has a variety of functions such as flood control and power generation, with significant comprehensive benefits.
Hedi Reservoir is one of the five large drinking water sources in Guangdong Province, and water quality control has always been a top priority. Since the new century, the nitrogen pollution of Hedi Reservoir has improved, phosphorus pollution often exceeds the standard, the degree of eutrophication is not optimistic, and the overall trend is aggravated.
Taking the water quality in 2020 as an example, the water quality target in the reservoir area was originally Class II water, but in fact, it only met the standard of Class III water, and the reason for not meeting the standard was that the total phosphorus and chemical oxygen demand exceeded the standard. The "nutrient water" in the reservoir area is still a difficult problem, and the comprehensive sample state index is as high as 53.0, and it is currently in a mildly eutrophic state.
Catchment area of Hedi Reservoir
It is undeniable that eutrophication has become an important threat to lakes and reservoirs, and the consequences of the threat are even more serious for the Hedi Reservoir, which is the source of drinking water. If you let it go unchecked and let nitrogen and phosphorus be imported, it will inevitably lead to water blooms. In particular, cyanobacteria such as corydia and microcystins are harmful to human health and have endless troubles.
In May 2007, the "water crisis" in Taihu Lake shocked the country, and the cyanobacteria flood was the reason. Because the cyanobacteria density is too large and involves a wide range, it quickly spread to the northern part of the lake area (Gong Lake), resulting in a sharp deterioration of water quality, and the fishy odor drifts with the wind, which is a big problem to the scenery. Gonghu Lake is the water source of Wuxi City, and the outbreak of cyanobacteria has led to a water supply crisis in the local area, which has aroused great concern from all walks of life. To this day, the incident is still worth a wake-up call!
Eutrophication is a hotbed of cyanobacterial outbreaks, and only by protecting water quality and reducing nitrogen and phosphorus input can we prevent problems before they occur. To this end, Zhanjiang City has also "taken a hard hand" to rectify the source of pollution, and in March 2021 issued the "Regulations on the Protection of Drinking Water Sources in Hedi Reservoir in Zhanjiang City", which was officially implemented on May 1.
The Protection Regulations delineate a line of defence to ensure the quality of the water in the reservoir area. In terms of pollution prevention and control, it is clearly stipulated that the following activities are prohibited in the secondary protection zone of drinking water sources:
Planting of fast-growing eucalyptus trees, ponding, land reclamation, damming, mining, quarrying, sand mining, cage culture, driving of motorized ships unrelated to the protection of water sources, etc.
To protect the water quality of the reservoir area, why is eucalyptus trees planted in the surrounding area prohibited? I believe many people have doubts about this ban.
Eucalyptus is one of the common economic trees in Guangxi, Guangdong and other places in China, not a native tree species in China, but an "imported product", and the heat has not decreased in recent decades. Eucalyptus is native to Australia, Indonesia and the Philippines, with fast growth, short logging cycle, high economic value, and has been introduced in many parts of the world.
In 1890, Eucalyptus was introduced for the first time in China, and in the 1960s, a boom in eucalyptus planting was set off, and a large area of mountainous land was transformed into a fast-growing eucalyptus plantation forest. The scale of eucalyptus trees in Guangxi is second to none in the country, and the industrial benefits are remarkable: eucalyptus trees can generally be harvested in 4 to 6 years, and the production of timber per mu is more than 5m³, and planting eucalyptus and cutting eucalyptus has become the "rich code" of many mountain farmers.
As of 1990, the area of eucalyptus in China has grown to 670,000 hectares, compared with 4.5 million hectares in 2018. Behind the crazy expansion of eucalyptus planting area is the dissatisfaction, worry and even condemnation of all sectors of society. According to the investigation, some mountainous areas in the planting of eucalyptus trees using the method of refining mountains and preparing land, full reclamation, abuse of chemical fertilizers, is not conducive to soil and water conservation, some people have named eucalyptus trees as "ecological killers".
What's more, some people refer to eucalyptus trees as "pumping machines", "fertilizer pumping machines", "poison machines", and "trees that cut off children and grandchildren", which is a bit exaggerated, but the rumor that eucalyptus forests "do not fly birds on the top and no grass grows on the bottom" is not unfounded.
The cultivation of fast-growing eucalyptus does have certain harms, such as leading to a single tree structure and a decrease in ecological diversity. In contrast, the impact of human activities is even greater, such as blindly increasing fertilization for the pursuit of the economy, digging pits and mountains, weeding and logging, and so on.
The consequences can be imagined, soil erosion intensifies, and the nitrogen sources in the soil and fertilizers converge with the surface precipitation, and eventually enter the drinking water source or downstream rivers, which makes people invincible.
The State Forestry and Grassland Administration has also clearly issued instructions: in important areas such as the headwaters of rivers, important reservoirs (water sources), nature reserves, and urban functional areas, it is not suitable to plant fast-growing eucalyptus trees. In the Hedi Reservoir Secondary Protection Area, it is reasonable that eucalyptus trees are banned from planting, and the punishment is not low:
Where eucalyptus is planted, the local forestry department shall order rectification within a time limit and punish it. Where the planting area is less than 10 mu, a fine of 5,000 yuan shall be imposed on the unit and 500 yuan shall be imposed on the individual; where the planting area is more than 100 mu and less than 100 mu, a fine of 500 yuan per mu shall be imposed on the unit and 50 yuan per mu shall be imposed on the individual; where the planting area is more than 100 mu, a fine of 50,000 yuan shall be imposed on the unit and 5,000 yuan shall be imposed on the individual.
In low-lying areas of forest areas, a beach of "black water" sometimes appears, which is more common after rain. The black water here is called "forest black water", which generally refers to the rotten water body formed by the decomposition of branches, leaves and other withered substances in the accumulated water.
In eucalyptus forests, the phenomenon of black water also exists, and its mystery has aroused heated discussion in the media. Studies have found that black water in eucalyptus forests is an occasional phenomenon, often accompanied by a rainfall process, mostly in new logging areas. In 2013, domestic scholars such as Yang Calciren investigated the black water of eucalyptus forests, and concluded that the black water was actually a mixture of black rot lysate and surface runoff of eucalyptus trees.
In order to study the harm of eucalyptus black water to aquatic organisms, researchers injected black water into the pond, but the results were surprising: grass carp in the pond began to float a large number of heads, and then crucian carp and carp also began to float their heads; in the afternoon of the floating head, the grass carp belly turned upwards, and individually began to die; at 10 a.m. the next morning, more than 95% of the grass carp died, weighing 300 to 1500g, and the mortality rate of crucian carp and carp was also about 50%.
Images are for reference only
After testing, the introduction of black water led to a decrease in the dissolved oxygen content of pond water quality by 4.62 mg/L, a decrease of 82%, and the transparency of the water body decreased significantly. These black waters contain high concentrations of organic matter, water quality is more fertile, is a potential source of nitrogen and phosphorus pollution, decomposition in the water will compete with fish, shrimp and crabs for oxygen, serious will lead to fish and shrimp suffocation and death.
Combined with the Crane Land Reservoir and the terrain, topography and soil environment, it is even more necessary to ban the cultivation of eucalyptus trees.
The area around the Hedi Reservoir is mostly hilly terrain, with islands dotted around the reservoir and a tortuous shoreline of the reservoir, forming numerous reservoir bays and reservoirs. The hilly slopes are condescending, and if eucalyptus trees are planted, the so-called "black water" may be produced, which will go down with the rain and cause nutritional pollution to the reservoir area.
In terms of soil structure, the area around the reservoir area is mostly red loam, impact paddy loam, loam and black soil, the soil particle size porosity is large, the soil is fertile, suitable for pine, bamboo, eucalyptus and other plants to grow. Once eucalyptus trees are planted, the forest formation rate will be very fast, which will undoubtedly aggravate the local soil erosion, resulting in larger turbidity and poorer water quality in the reservoir area.
In short, the prohibition of eucalyptus trees around the reservoir area is a comprehensive move, starting from the details, not giving eutrophication an opportunity!
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