What are the main ecological and environmental problems facing Shiyang River Basin at present?

Main ecological and environmental problems in Shiyang basin

Oasis promotion

Oasis refers to the process of artificially cultivating oasis to irrigate soil under desert conditions. In the past, Shiyang River basin was mostly desert land with poor natural conditions and low productivity. After human reclamation and irrigation, the soil has changed from the original dry habitat to the wet habitat. Through the cultivation, maturity and cultivation of crops, the physical, chemical and biological characteristics of soil have been improved, and the fertility has been improved, thus forming oasis irrigation soil. According to the survey, in the early 1980s, the irrigated area in Wuwei Basin was 145800 hm2, increasing by 1950 127300 hm2. According to research, since the 1950s, the frequency of sandstorms has increased, with more than 60 occurrences in only half a century, and the harm has increased. For example,1May 5, 1993, a very strong sandstorm swept through five cities in Hexi, our province, with a wind speed of 25m/s, affecting Central China and the Pacific Ocean. Experts organized by the former Ministry of Forestry investigated and evaluated the hazards caused by the sandstorm, and the results showed that the direct economic loss was 5.3 billion yuan, and the direct economic loss of Hexi Corridor alone reached 236 million yuan. In April of 20 10, a particularly strong sandstorm occurred in Minqin, with a wind speed of 28m/s and serious losses. In a short period of 18 years, two extremely strong sandstorms occurred, which is rare in history. Sandstorm not only has a serious impact on the production and construction in this area, but also poses a direct threat to the safety of people's lives and property and the living environment, and has a more and more serious impact on the surrounding areas and even the global ecological environment.

4. Reduced water resources

In arid inland areas, water resources are the most critical factor affecting oasis society, economy and ecology [1]. Shiyang River Basin, as an independent water resource unit, its flow continues to decrease year by year. From the analysis of hydrological data for many years, the river runoff shows a decreasing trend year by year. In 1950s, the average annual runoff of six scenic rivers in Wuwei City of Shiyang River Basin was124.6 million m3, but it decreased to 859 million m3 in 1990s, which was nearly 1/3. Especially, the amount of water entering Minqin was 594 million m3 in 1950s, decreased to 230 million m3 in 1980s, only 65.438+50 million m3 in 1990s, and only 65.438+0 million m3 in 2000, less than the original 65.438+0/5. The per capita water resources of Wuwei City in Shiyang River Basin are less than 700m3 for many years, and the average water resources per unit area of cultivated land are about 3300 m3/hm2, which are 1/2 at the provincial level and 1/3 at the national level respectively. In particular, the average water resources per unit area of cultivated land is far below the drought limit standard. Because of the decrease of upstream water supply, Minqin can only continuously increase the over-exploitation of groundwater. Since 1970s, the county has drilled more than 1 1000 wells, and in recent years, it has pumped 600 million m3 of groundwater annually (the reasonable pumping amount is1200,000 m3). Over-exploitation of groundwater leads to the rapid decline of groundwater level and the increase of salt content, which is generally above 3g/L and as high as 10g/L in some areas. As a result, the quality of groundwater is getting worse.

5. Vegetation degradation

Due to unreasonable development and utilization, vegetation tends to evolve into drought type. With deforestation and overgrazing, the forest vegetation in Qilian Mountain has evolved into grassland, and grassland has evolved into desertification. The forest coverage rate of Qilian Mountain in Gansu Province has decreased from 22.4% in the 1940s to 14.4% at the beginning of this century, and the forest area has decreased from 310.6 million hm2 to10.2 million hm2. The cultivated forest and grassland are nearly 1.500 km2, the water source forest is less than 550km2, and the vegetation coverage rate is only about 40%. The growth of farmland shelterbelts in the middle and lower reaches is weakened and withered, a large number of trees die, harmful organisms breed and spread, and the protective ability is reduced. The disastrous weather such as low temperature frost and dry hot wind is increasing day by day, which has increasingly affected agricultural production. The climate in the lower reaches of the basin is dry and rainy, and sandstorms are frequent. The amount of grass in windbreak and sand-fixation forest on the edge of desert and the periphery of oasis is decreasing year by year, and the psammophytes in sand-protection area are declining and dying, and the vegetation coverage is decreasing. The shrubs and shrub meadows in this area have been degraded in a large area, and gradually replaced by xerophytic and ultra-xerophytic meadow vegetation such as camel thorn and red sand. According to the research, the vegetation community composition of Minqin Oasis in the lower reaches of Shiyang River is more arid and biochemical, and the complexity of community structure is reduced. The vegetation types are reduced from 19 desert vegetation groups in 1950s to 9 at present, and the vegetation degradation is obvious.

6. Soil erosion has intensified, and water conservation capacity has declined.

Qilian Mountain has diverse vegetation types, rich forest and grassland resources and powerful water conservation function. It has become a natural "reservoir" in Qilian Mountain, providing the main water source for Shiyang River. In recent years, due to population increase and over-exploitation, the contradiction between forest, animal husbandry, agriculture and mining is prominent, forest and grassland are degraded, vegetation coverage is reduced, water conservation function is reduced, water and soil conservation capacity is weakened, and soil erosion is intensified. In the rainstorm season, the formation time of flood peak is short, the shearing force is strong and the destructive power is great. Sediments and boulders are often deposited on river beds and reservoirs. According to the calculation, the sediment concentration of the flood is as high as 590kg/m3, and more than 0 reservoirs in the upper reaches of the whole basin 1/5 ~ 1/8 have reduced their effective stocks to varying degrees, which has brought huge losses to the regional economy and society.