Main ecological and environmental problems in water source area

3.2. 1 Water environment of water source area

The main tributaries of Danjiangkou Reservoir in Henan Province are Laoguan River and Danjiang River. Laoguan River in Nanyang is a mountainous river with a length of 146.4km and a drainage area of 2523km2. It has the characteristics of fierce flood, large amplitude, steep longitudinal slope and rich sandstone. Danjiang River originated in Languan, Qinling Mountains, Shangxian County, Shanxi Province, and entered Xichuan County, Henan Province from north to south, and joined the Han River in Danjiangkou, Xunxian County, Hubei Province. The total length of the main stream is 390km, and the catchment area at the junction of Henan and Hubei is 147 14km2. The length of the main stream of Henan Province is 1 17.4km, and the drainage area of Henan Province is 5592km2.

According to the results of "Functional Zoning of Surface Water Environment in Nanyang City", Xichuan County section of Danjiang River is Grade II water quality; The water quality above Xixia County of Laoguan River is Grade III, and the water quality below Xixia County to Dangziling is Grade IV (Dangziling section is the exit water quality control section of Laoguan River in Xixia, which accepts industrial wastewater from Xixia County and domestic sewage from the county); The water quality from Xichuan County to Zhang Ying is Grade III (Zhang Ying section is the control end of Laoguan River in Xichuan County entering Danjiangkou Reservoir, which mainly receives industrial wastewater from Xichuan County and domestic sewage from the county); The functional division of surface water in Danjiangkou reservoir area of Henan Province is Class II water quality (Table 3.8).

Table 3.8 Water Quality of Water Intake Source Catchment Control Section of Middle Route of South-to-North Water Transfer Project

According to the water quality monitoring results of Danjiangkou Reservoir catchment monitoring section and Laoguanhe monitoring section arranged by Nanyang Environmental Protection Department, the water quality of each section is as follows:

(1) jiepai section of Danjiang River, which exceeds Grade II water quality in wet season; Both the dry season and the annual average water quality meet the Class II water quality standard, which accords with the water quality category of functional zoning. The main influencing factors in rainy season are organic matter and ammonia nitrogen.

(2) In Shijiawan section of Danjiang River, the water quality in wet season is over Grade II; The water quality in dry season is Grade II; The annual average value exceeds Grade II water quality; Total nitrogen exceeded the standard.

(3) The water quality of the Dangziling section of Laoguanhe River meets the Class IV water quality standard in the wet season; In dry season, the water quality standard exceeds Class IV; The annual average value meets the Class IV water quality standard.

(4) The Zhang Ying section of Laoguan River exceeded the Class III water quality standard in the wet season, in which COD (chemical oxygen demand) was slightly exceeded, ammonia nitrogen exceeded the standard by 65,438 0.73 times, and total nitrogen exceeded the standard by 65,438 0.79 times; In the dry season, the water quality standard of Class III was exceeded, in which COD exceeded the standard by 2.97 times and CODMn (COD measured by potassium permanganate method) exceeded the standard by 2.02 times. The annual average value exceeds Class III water quality standard, with COD exceeding 2.25 times and CODMn exceeding 1.08 times. Point-source organic pollution is the main pollution in Dangziling section of Xixia County, while non-point source ammonia nitrogen pollution is the main pollution in Zhang Ying section of Xichuan in wet season, and point source organic pollution is the main pollution in dry season.

(5) The water intake at the head of the middle route of South-to-North Water Diversion Project exceeded the Grade II water quality standard in wet season, dry season and annual average, and the factors exceeding the standard were total nitrogen and total phosphorus, which were mainly caused by non-point source pollution.

3.2.2 The situation of environmental pollution in water sources is grim.

The environmental pollution of water source includes point source pollution and non-point source pollution. Industrial pollution is the main cause of point source pollution, and the extensive use of pesticides, fertilizers and agricultural films in agricultural production is the leading factor of non-point source pollution.

The middle route project of South-to-North Water Transfer Project requires the water quality in Danjiangkou reservoir area to meet the national Class II surface water quality requirements. It is stipulated that the total phosphorus, total nitrogen and ammonia nitrogen in the water source area of Danjiangkou Reservoir shall not exceed 0.02 mg/L, 0.04 mg/L and 0.5 mg/L respectively. According to the test results of water samples in Danjiangkou reservoir area, most indicators of water quality in the reservoir area meet the requirements of Class II water quality, among which the total phosphorus concentration is 0.02 ~ 0.05 mg/L, the total nitrogen concentration is 1.46 ~ 1.60mg/L, and the total phosphorus and total nitrogen obviously exceed the standard. The analysis of components exceeding the standard is mainly the non-point source pollution caused by sewage, pesticides, fertilizers, human and animal manure and domestic garbage pollution.

3.2.2. 1 industrial pollution

Industrial pollution in water source areas can not be ignored. First, the industrial structure is not reasonable. Paper-making, chemical, pharmaceutical and wine-making industries, which are seriously polluted, account for a relatively large proportion of the total industrial output value, and industrial wastewater is the main factor causing surface water pollution. Second, there are no domestic sewage treatment plants and garbage treatment plants in all towns in the water source area. With the acceleration of urbanization and the expansion of urban framework, domestic sewage and domestic garbage pollution will become increasingly serious. Third, the mountainous counties located at the source have local financial difficulties and insufficient investment in urban construction. There is no unified drainage system between the county seat and major towns. Industrial wastewater, domestic sewage and rainwater are not separated and discharged into surface water, but directly discharged into rivers, causing water pollution in Laoguan River and even Danjiangkou Reservoir. According to the monitoring results of Nanyang Environmental Protection Bureau, the discharge of wastewater pollutants in Xixia, Xichuan and Neixiang counties in 2003 is shown in Table 3.9.

Table 3.9 Discharge of Water Pollutants from Water Sources (2003)

Note: According to the Investigation Report of Non-point Source Pollution in Water Source Area of South-to-North Water Transfer Project of Nanyang Agriculture Bureau in 2004.

Pesticides and fertilizers are widely used in agricultural production in 3.2.2.2.

Nanyang reservoir basin belongs to the main agricultural producing area, and planting is dominant. According to the calculation, the annual input of chemical fertilizer in 36 towns114000 mu of cultivated land in the water source area of Danjiangkou Reservoir is 4.35× 104t (in pure terms), of which the largest amount is nitrogen and phosphorus fertilizer. According to the national average fertilizer utilization rate of 30% ~ 40%, the annual loss of soil fixation, air volatilization, groundwater infiltration and surface runoff reaches (2.61~ 3.045) ×104t; The annual application amount of pesticides in the water source area is 275t, most of which are pesticides, fungicides and herbicides. High toxic and high residue pesticides such as phosphorus, arsenic and mercury are harmful to the environment. In addition to 40% of pesticides being absorbed and decomposed by crops and pests, some of them are volatilized into the air, and most of them remain on the soil surface and infiltrate into groundwater or flow into the reservoir area with rainwater, causing pollution. According to the survey, the contribution rate of chemical fertilizers and pesticides to the total phosphorus in the reservoir area exceeds 75%. The annual coverage of agricultural film in the reservoir area of water source area is 2 1.32 million mu, and the amount of agricultural film is 704t t. Based on the average residual rate of 5.88%, the annual residual film is 41.39 t. The residual agricultural film in farmland is difficult to decompose, which affects farming. A small amount of decomposition products release harmful substances and pollute soil and groundwater.

The amount of livestock manure and domestic garbage in 3.2.2.3 is increasing year by year.

With the adjustment of agricultural production structure and the rapid development of animal husbandry, the problem of non-point source pollution caused by animal husbandry has become more and more prominent. According to investigation and statistics, there are more than 200 large-scale farms in Danjiangkou reservoir catchment, and livestock and poultry are widely distributed. The annual discharge of livestock manure exceeds 826× 104t, and the simple treatment rate of manure is only 59.5%. Feces are discharged at will, and a large number of nutrient-rich substances such as nitrogen, phosphorus and COD are directly or indirectly discharged into the reservoir area, which directly pollutes the environment and water quality. Domestic sewage and garbage in Danjiangkou reservoir catchment are discharged directly for a long time, polluting surface water and groundwater.

3.2.3 The ecological environment of the water source area is fragile.

Danjiangkou reservoir water source is located in the transitional zone between north and south and the junction of east and west in China, which is a relatively independent natural geographical unit. At present, the forest vegetation in this area is scarce, with poor quality and low water storage and soil consolidation capacity. In addition, unreasonable farming methods lead to the deterioration of ecological environment and serious soil erosion. According to the data, during the 20 years from 1979 to 1999, the total siltation of Danjiangkou Reservoir was 897 15.5× 104m3, with an average annual siltation of 4485.775× 104m3. According to this sedimentation rate, the service life of Danjiangkou Reservoir will be greatly shortened. The temporal and spatial distribution of precipitation and runoff is seriously uneven, and floods and droughts occur frequently. Frequent floods in rainy season, quicksand of earth and stone, drought and water shortage in winter and spring, water shortage in gullies and streams, and difficulty in drinking water for people and animals. In many places, people in mountainous areas often have to run dozens of kilometers to get water, which seriously restricts the economic development of water source areas. The frequency of floods and droughts has increased from 0.42 times a year in 1950s to 0.83 times a year at present. According to the investigation of Jingziguan, Vance, Dashiqiao and Taohe River in Xichuan County by Nanyang Water Conservancy Department, in recent years, fertile land has been reduced by more than 500 square kilometers due to floods. Since 1954, the cultivated land in Xixia County has been reduced by 0.7× 104km2 due to the flood disaster, and it has been increasing by 3.6% every year.

A large amount of land in the reservoir area was flooded, more than 20,000 square kilometers of fertile land were flooded, 74,000 immigrants moved out, and 654.38 million immigrants and anti-immigrants moved to hills and low mountains. Most of the hilly areas in the water source area are densely populated and lack of cultivated land resources. The per capita arable land in Xixia County is less than 0.047km2, which is far below the average level of the whole province and Nanyang City. The reserve resources of cultivated land are insufficient, the unused cultivated land resources are few, and the contradiction between man and land is very prominent. With the heightening of Danjiangkou reservoir dam, the submerged area will be expanded to 1050km2, and this contradiction will be further aggravated. Due to poor soil, single agricultural industrial structure and fragile ecological environment, the local people have not yet got rid of poverty and backwardness. The per capita annual grain possession is only 340 kilograms. In order to survive, farmers are forced to reclaim land, which leads to a sharp decline in forest resources, aggravates the deterioration of ecological environment, and makes mountain agriculture fall into a vicious circle of "getting poorer and poorer".

The periphery of Danjiangkou reservoir area is dominated by shallow hills, with vertical and horizontal gullies, complicated terrain and large slope. Vegetation is mostly young and middle-aged forests and inefficient forests, with low vegetation coverage, poor protection ability, low natural adjustment ability, interception of branches and leaves, decreased soil and water conservation ability of roots and fragile ecological environment.

3.2.3. 1 The soil properties of the water source area are poor.

The soil in the water source area is mainly yellow cinnamon soil, yellow clay or red clay, which is heavy in texture, easy to dry, shrink and crack, poor in permeability, loose and shallow in topsoil, drought-resistant and waterlogging-resistant, and easy to be eroded. Limestone and schist in shallow hills and hills have poor erosion resistance, severe weathering and weak rainfall impact resistance, which is easy to cause soil erosion.

Table 3. 10 Forest land unit in water source area: hm2

Table 3. 1 1 Forest area and volume in water source area

Table 3. 12 Classification of Forest Land in Water Source Area

Influence of climate and water resources in 3.2.3.2 water source area

Danjiangkou reservoir watershed has a subtropical monsoon continental climate, and the rainfall varies greatly during the year. Due to the influence of monsoon, the annual rainfall distribution is uneven, and the rainfall in flood season accounts for 58% ~ 62% of the annual rainfall. Heavy rain is concentrated, strong, short in duration and limited in infiltration, which is easy to scour and erode the surface. The tributaries of Danjiangkou Reservoir in Nanyang are all mountain rivers with large slope and little groundwater resources. The total water resources are mainly surface runoff, which is the main driving force of soil erosion. Soil erosion makes dust and residues of pesticides and fertilizers attached to the soil flow into the surface runoff and into the reservoir area, resulting in excessive suspended solids, nitrogen and phosphorus in the reservoir area, which has a great impact on the water quality in the reservoir area.

The problem of forest resources in water source areas of 3.2.3.3 is outstanding.

First, forest resources are unevenly distributed. People regard the forest as a natural resource, but they don't know enough about its regeneration, versatility and long renewal period. They are eager for quick success and instant benefit, taking more from the forest and using less, which makes the allocation of limited forest resources extremely unreasonable. Most of them are distributed in the source of rivers in the deep mountains, with small growth, and the ecosystem is in a state of structural and functional degradation, with poor protection benefits. However, it is located in the lower reaches of low mountains, hills and plains, with high population density, high reclamation index and few forest resources, and most of them are artificial young forests. In many places, the surface is exposed seriously, which is the hardest hit area of soil erosion. Second, the ecological benefits are low. Forest quality is not high, low-yield and inefficient shelterbelts account for a large proportion, and productivity level is low. Third, the structure of forest species and forest age is unreasonable. The structure of forest species is unreasonable, and the proportion of shelter forest as a whole is still small; In terms of age structure, there are more young adults, accounting for 95.8% and 89.4% of the total stand area and volume respectively. However, the area and volume of near-mature and over-mature forests account for 4.2% and 10.6% of the whole forest, respectively. See table 3. 10 to table 3. 12 for the forest resources in the water source area.

3.2.4 The water source area has serious soil erosion.

3.2.4. 1 Present situation of water and soil loss in water source area

Table 3. 13 gives different types of soil erosion and related data in the water source area. A large amount of soil erosion not only causes reservoir siltation, but also worsens water quality and makes eutrophication higher.

Table 3. 13 Types of Soil Erosion and Related Data in Water Source Area

According to the data of the third national remote sensing survey of soil erosion in 2000, the soil erosion area in Danjiangkou reservoir area and Nanyang in the upper reaches is 3369.0 1km2, and the average annual soil erosion is about 990× 104t. The degree of soil erosion in Zhongshan gradually changed from moderate to slight loss in shallow hills and hills to mild and slight loss, which mostly occurred in shallow hills and hills around Danjiangkou Reservoir and areas with concentrated population, poor vegetation, breeding and agricultural planting areas, convenient transportation and relatively concentrated development and construction projects. The average soil erosion modulus is 2938 t/km2 a, and the ditch density is 2.6 1km/km2. Strong soil erosion covers an area of 446.87km2, accounting for 7% of the soil erosion area, mainly distributed in barren hills, slopes and sloping farmland with low vegetation coverage, such as Xixia 3 12 national highway and Danjiangkou reservoir area in Xichuan, with surface erosion and gully erosion as the main forms. The area of moderate soil erosion is 1369.7km2, accounting for 2 1.5% of the soil erosion area, which is mainly distributed in the southern mountainous area of Xixia County, narrow areas along the banks of the river such as Laoguan River and Qihe River, and hilly areas around Danjiangkou Reservoir such as Xichuan, Neixiang and Dengzhou. The population density in this area is relatively high, and the vegetation coverage rate is low (

Table 3. 14 Classification area and loss of soil erosion intensity in Danjiangkou Reservoir and upstream Nanyang City

Note: According to the Water and Soil Conservation Plan of Danjiangkou Reservoir Area and Its Upstream in Nanyang City in 2003.

3.2.5 Geological Environment Problems of Water Source Mines

The mineral resources in the water source area are characterized by many kinds of minerals, many occurrences and concentrated distribution, but there are few large and medium-sized deposits, mostly small occurrences and mostly small private mining. Most mining methods are open-pit mining, which produces a lot of tailings and slag. At present, the active metal minerals are vanadium ore, iron ore, gold ore and stibnite. Non-metallic minerals include marble, limestone, graphite and dolomite. Limestone mine, marble mine and vanadium mine, etc. , mining is extremely rich, often forming a concentrated group of mining areas. Therefore, the mine environmental geological problems in the study area are outstanding.

3.2.5. 1 Environmental geological problems caused by mining

(1) Causing the destruction of land resources: mining occupies and destroys land. According to the survey, the area occupied by medium-sized mining areas is generally 2 ~ 9 hm2, and that occupied by small-sized mining areas is generally 1 ~ 6 hm2. For example, the area from Xichuan County to Ximiaogang is a ravine, which is a gathering place for marble stone processing. There are dozens of processing factories on both sides of G3 12. It covers an area of 20 ~ 50m wide and extends intermittently for nearly 20km. The phenomenon of abandoning slag and changing land to destroy land is more serious.

Figure 3.3 Distribution of Soil Erosion in the Study Area

(2) Damage to landform and landscape: Open-pit mining seriously damages landform and landscape, and damages vegetation and ecological environment. Traces left by mining can be seen in the visible range on both sides of the traffic trunk line, and there is a trend of continuous increase. The damaged area of vegetation in large mining areas is 15hm2, that in medium mining areas is generally 1.5 ~ 4.5hm2, and that in small mining areas is generally 0.5~2.0hm2. The landscape damage caused by mining in the water source area is mainly distributed in the following areas: ① Xichuan County-Maotang-Huang Xi area is a vanadium mine-intensive area with dozens of mining points. The mines are distributed along the vein, with a width of 6 ~10m, a depth of 5 ~ 8m, and an intermittent extension of nearly 50km, with a total area of about 100hm2. Slag piled up on the hillside. (2) Haoping-Dashiqiao area in Xichuan County is a marble mining intensive area with dozens of mine sites. The mine pits are distributed along the vein, with a width of 6 ~ 10m and a depth of 5 ~ 30m, with an intermittent extension of nearly 40km and a total area of about 80hm2. Mining slag is accumulated on the hillside, which seriously damages the mountain vegetation and land, has a certain impact on Danjiang scenic spot, and is also soil erosion.

(3) Frequent geological disasters: Slope instability, landslide and collapse often occur during the mining of limestone, marble and vanadium ore. The gold-iron ore mined underground is prone to pit collapse. A large number of slag and tailings discharged from mines are piled up, which not only occupies a lot of land, seriously pollutes water and soil resources and the atmosphere, but also often causes landslides, landslides and mudslides. In particular, some township collective and individual mining sites cut the riverbed and the mountains on both sides of the highway, which has a certain impact on the smooth flow of rivers and provided a solid source for the formation of debris flows.

Analysis of Soil Pollution in 3.2.5.2 Water Source Area

In order to understand the influence of vanadium ore on soil, two soil sampling profiles were laid out in Maotang-Xichun area where vanadium ore mining was intensive. According to the analysis results, it is concluded that the vanadium content far away from the mining point has a significant decreasing trend.

Analysis of Water Environment Quality in 3.2.5.3 Water Source Area

(1) Groundwater environmental quality analysis: Groundwater environmental analysis is mainly realized through groundwater quality evaluation and groundwater pollution evaluation.

1) Groundwater quality evaluation: This evaluation selects pH value, total hardness, total dissolved solids, sulfate, chloride, iron (Fe), manganese (Mn), copper (Cu), zinc (Zn), volatile phenol, anionic synthetic detergent, permanganate index, nitrate, nitrite, ammonia nitrogen (NH4) and fluoride. Based on the data of water quality analysis, the quality category of a single component is determined according to the classification index listed in People's Republic of China (PRC) Groundwater Quality Standard, which is a single factor evaluation method. According to the quality category of each individual component, the evaluation score Fi of each individual component is determined according to Table 3. 15.

Table 3. 15 Evaluation scores of individual components in various categories

Calculate the comprehensive evaluation score f according to formula (3. 1) and formula (3.2).

Theory, Method and Practice of Ecological Security of Land Resources in Henan Province

Where: f is the average value of each single component evaluation score Fi; Fmax is the maximum value in the single-component evaluation score Fi; N is the number of terms.

According to the calculated F value, the groundwater quality grade is divided according to Table 3. 16.

Table 3. 16 Determination of Groundwater Quality Grade

2) Groundwater pollution evaluation: 24 components in groundwater quality evaluation are selected as evaluation indexes. Taking the standard limit value of Class II water in People's Republic of China (PRC) Groundwater Quality Standard (GB/4848-93) as the background value, the inorganic pollution was evaluated by component synthesis method and pollution index method respectively.

The pollution index (I) of a single index shall be calculated according to formula (3.3).

Theory, Method and Practice of Ecological Security of Land Resources in Henan Province

Where: I is the pollution index of a pollutant; Ci is the measured content of pollutants; C0 is the background value or control value of a pollutant, and the upper and lower limits of the second-class water standard are taken this time.

If the Ci value is within the interval, let I= 1. If the I value is greater than the maximum value or less than the minimum value, divide the Ci value by the maximum value or the minimum value, respectively.

The comprehensive pollution index (PI) of multiple indicators is calculated according to Formula (3.4) and Formula (3.5).

Theory, Method and Practice of Ecological Security of Land Resources in Henan Province

Theory, Method and Practice of Ecological Security of Land Resources in Henan Province

Where: PI is the comprehensive pollution index of multiple components in a single sample; Is the average value of pollution index I of each single component; Imax is the maximum value of pollution index I of each single component; N is the number of terms.

According to the calculated PI value, the pollution levels are classified according to Table 3. 17.

Table 3. 17 Classification of Groundwater Pollution Levels

Finally, the maximum value of f is 7. 19 and the minimum value is 2. 15. The quality grades are divided into "good" and "poor", and the comprehensive evaluation results are consistent with the evaluation results of single components, that is, Class III water belongs to "good" grade, and Class IV and V water belongs to "poor" grade.

(2) Environmental quality assessment of surface water in water source area: According to 24 indexes in the standard limits of basic items in national standards, pH value, dissolved oxygen, permanganate index, chemical oxygen demand (CODcr), biological oxygen demand (BOD5), total phosphorus (in terms of P), total nitrogen (in terms of N), copper (Cu), zinc (Zn) and fluoride (in terms of F) are selected. According to the analysis results, the water environmental quality assessment of water source shows that the contents of dissolved total solids, total hardness, sulfate (s02-4), nitrate (NO3-), anionic synthetic detergent and hexavalent chromium (Cr6+) in groundwater components are quite different, and the contents are higher near mines and densely populated areas, and their distribution area is smaller; There are many areas with good groundwater quality. The water quality of some sections of surface water is poor. Danjiangkou Reservoir is Class II water of Danjiangkou Reservoir, Class V water of Qihe River and Class IV water of Laoguan River. The surface water sample of the water intake (Xichuan Taocha) of the Middle Route of South-to-North Water Transfer Project is Class II water, which meets the drinking water standard. Under the current conditions, the changes of groundwater and surface water quality caused by mining activities have caused different degrees of pollution to groundwater and surface water quality. Although the impact on the water quality of Danjiangkou Reservoir is not obvious, it should be highly valued.