Mu Minxia ，Wang Wenke ，Du Dong ，Zhao Shunyang ，Yang Lijun

School of Environmental Science and Engineering, Chang’an University，Xi’an 710054, China

 

Abstract：The Kuitun river basin is situated in Xinjiang in the arid regions of northwest of China With the increase of population and the development of economy, the national-economy water demand and the ecological water demand has become the principal contradictions of development and utilization of water resources of basin and ecological environmental protection. So, in order to realize the sustainable utilization of water resources in the Kuitun river basin and sustainable development of national economy, the ecological water demand should be studied immediately. In this paper, with the purpose of coordinated growth between the social economy and the eco-environment of this area, it analyzed the main eco-environment problems of the Kuitun River basin. At the basis of conception and classify of ecology water demand in arid areas, it imposed restrictions on ecology water demand of Kuitun River basin. On the premise of this, it proceeded from the current situation of this basin’s eco-environment and the future demand, using different computing technologies and calculating its ecology water demand. It provides the scientific basis for basin water resources rational distribution and constructions of eco-environment.

The result showed that the ecological water demand in the Kuitun River basin reached 4.39*10⁸m³ ,which occupies 24.6% of the whole water resource about 17.83*10⁸m³, and 26.0% of the whole runoff about 16.79*10⁸m³. In which the nature oasis ecological water demand reached 2.59*10⁸m³，occupied 59% of the ecological water demand; the artificial oasis ecological water demand reached 1.8*10⁸m³，occupied 41% of ecological water demand.

Keyword: eco-environment problems; ecological areas; calculate method; ecological water demand; the Kuitun River basin; Xinjiang

 

1 Brief Introduction of the Kuitun River Basin

The study area is located at the northern foot of Tianshan Mountain, the southwest edge of Zhungaer basin. The landform is high at the south and low at the north, with high mountains, hills, alluvial and diluvial plain, desert and other various topographies. The climate has a typical continent arid climate feature, and the irrigation for agricultural production is by artificial canal or takes out underground water. According to the statistical information from  meteorological station of Kuitun, Wusu and Chepaizi the long-term annual average temperature is 7.0℃, average yearly precipitation only 160mm, average yearly evaporation 1810 mm. The winter is severe cold and long and the summer is hot and short, the spring and the autumn is changed greatly, with long sunshine and big temperature difference.

All rivers in the study area belong to Aibi lake water system, originated from Tianshan Mountains flowing from south to north leading to the Aibi Lake, which is supplied mainly by snowmelt and rainfall fromTianshan Mountains. There are three major rivers in the study area. They are Kuitun river, Sikeshu river and Gurtu River.  The  annual  average  flow  volume respectively is 644 million m³ , 289 million m³ and 338 million m³. These rivers contain water throughout the year, while most of the water volume is intercepted upstream for agriculture irrigation.

The remaining flow tends to be minimal, sometimes disappearing completely. The total trunk stream is 360km in length, covers a total area of 2.54*10⁴km².

2 Main Ecological Environmental Problems in the Study Area

With the population growth and rapid economic development in the study area and increasing trend of development and utilization of water resources, the ecological environmental problems are becoming increasingly serious and mainly manifested in the following aspects:

2.1 Dry-up of watercourses at the lower reaches

With the population growth and large-scale exploitation of water and soil, a good many projects of piloting, storing, and delivering have been built along Kuitun River, Sikeshu River and Guertu River, from 1950s to 1970s. By 2003, the population in the  study area had reached 560,000, up by nearly 10 times over that in the 1950s; irrigation area 2.75 million mu, the second largest oasis formed at the north foot of Tianshan Mountain after the 1950s; 8 piloting hinges, with the designed piloting capacity being 380 m³/s and annual piloting volume being 11.27*10⁸ｍ³; 14 plain reservoirs, with the designed storage capacity being 3.22*10⁸ｍ³; 666kmtrunk channels, of which 377km have been processed with anti-seepage materials, with anti-seepage rate being 57%; and 5,407km drainge canals. Because of the sharp rise of population in the drainage area and the continuous increase of piloting volume at the upper reaches, the watercourses at the lower reaches have been dried up.

2.2 Deterioration of natural vegetation

Due to the water piloting in the upper reaches, water flowing into Ganjiahu at the lower reaches of Kuitun River, Sikeshu River and Guertu River began to decline, which resulted in the drop of underground water table and the reduction of natural vegetation in the area. Before the 1950s, the haloxylon ammodendron forest around Aibi Lake covered a total area 6.67*10⁴hm², with the coverage being 60% to 70%; populus euphratica forest 3.78*10⁴hm², with the coverage of medicinal plants being 70%, such as radix liquiritiae and herba cistanches; reed 4.6*10⁴hm², with the coverage being above 80%; and grass farm 1.0*10⁴hm², along with desert grass land of 2.67*10⁴hm² and desert secondary forest of 13.67*10⁴hm². With the growth of population and the increase of water development for agriculture, the water volume in the lake has declined, water table dropped, but the cultivation of farmland lifted and animal grazing area expanded, all of which led to the serious damages to forests of haloxylon ammodendron, populus euphratica, and reed. According to statistics, the total area of haloxylon ammodendron and populus euphratica forests dropped to 3*10⁴hm² and reed to 0.26*10⁴hm² in 1990. The degeneration of grassy marshland was extremely serious.

2.3 Lake shrinkage

The reasons for the shrinkage of the water area of Aibi Lake are multifold, including structure movement, climate and water resources change, and artificial factor. In the past, the study area of Kuitun Riveraccounted for 44% of the surface water amount entering the Aibi Lake. However, Kuitun River has been dried up at the lower reaches since the 1970s, and there is no surface water flowing into Aibi Lake in ordinary years. The changes of water area of Aibi Lake are detailed as chart 1:

Chart 1 reveals that the water area of Aibi Lake is showing a trend of gradual shrinkage, down by half from the 1950s to the mid 1980s, with the annual average reduction being 15km²; maintaining around 500～600 km² after the mid 1980s in spite of slight fluctuations.

Fig.1 Variation of water areas of Aibi Lake from 1950 to 2003

2.4 Soil salinization aggravates

Since the 1950s, people began to reclaim wastelands, channel water and construction of plain reservoirs along the two banks of rivers in a big way. A great deal of surface water drawn into irrational irrigation had led the obvious change of hydro geological condition of the irrigation area. The underground water table of irrigation region rises at large. The hydro geological mapping in 2003 shows that the underground water table in about 60% of the whole irrigation region is higher than 2m, the agricultural production is difficult to get rid of the obsession of salinization. The intense capillarity and evaporation resulted in the salinization of soil in the irrigation areas, and the cultivated land was hence wasted again, houses toppled down, and residents removed. The point can also be illustrated with remote-sensing interpretation results in different periods, with details seen Table 1.

Table 1 Statistic of salina and wetland areas in differ period of the Kuitun River basin   

Year	Areas of salina（km2）	Areas of wetland（km2）
1970	37.2	135.3
1990	1245.4	180.2
2000	785.7	32.4

Table 1 reveals that the areas of saline-alkali land and swampland in the study area had increased by 33 times and 1.3 times from 1970 to 1990 separately, and the area of saline-alkali land, in particular, increased sharply; because of the construction of drainge canals, the areas of saline-alkali land and swampland had declined to different degrees from 1990 to 2000.

2.5 Aggravation of land desertification

Because of the continuous interception of water flows at the upper reaches of Kuitun River, Guertu River and Sikeshu River and the anarchic mining of gold diggers in the past forty years, the water source of forest area of Ganjiahu could not be suppllied efficiently, and most of vegetables began to wither up. Meanwhile, the perennial wind at the mouth of Ala Mountain makes the sand dune between Guertu River and Ganjiahu move eastward at the speed of 12 meters every year. A green barrier of over tens of millions mu has been reduced to 740*10⁴ mu. The moving of desert deteriorated the ecological environment at the lower reaches of Kuitun River year by year, and the land desertification was aggravated.

In allusion to ecological environment problems in the study area of Kuitun River, water becomes the most active and sensitive factor restricting the sustainable development of the social economy and the protection of the ecological environment on the premise that the aggregate water volume is not changed. Therefore, the paper will, on the basis of the concept and categorization of ecological water demand in the arid zone, analyze and calculate the ecological water demand in the study area of Kuitun River with different methods.

3 Concept and Categorization of Ecological Water Demand

3.1 Concept of ecological water demand

There are a variety of definitions and studying methods of ecological water demand, but not a single one is adopted unanimously. Ecological water demand in a broad sense refers to the water needed in maintaining the water balance of the earth biological, geographical, and ecological systems, including water-heat balance, water-sand balance, and water-salt balance etc. ^[1]. In a narrow sense, it refers to the water consumed in the stabilization of the ecosystem, the protection of natural ecology, and the construction of artificial ecology^[2]. In terms of the definition, the current study result deems that the ecological water demand in arid areas refers to the minimum volume of water needed in maintaining the ordinary subsistence and multiplication of natural oasis, ecological systems in watercourses (bank vegetation, valley forest, and water quality), and protection vegetation systems in artificial oasis in the drainage area in a certain period of time. Hence, we can conclude that ecological water demand is closely related to ecological types: water demand varies from ecological type to ecological type. Based on this, the understanding of the ecological water demand in the drainage area of Kuitun River is: under the condition of sharing water resource by production, living, and ecology, ecological water demand needed in maintaining the existing ecological system should give priority to the guarantee of the groundwater volume of Aybi Lake and the minimum water resource needed in maintaining the ordinary subsistence and multiplication of protection vegetation systems in the artificial oasis. Meanwhile, the haloxylon ammodendron forest will not degenerate in the natural protection areas of Hena Forest, Hegu Forest, and Ganjiahu at the lower reaches of Kuitun River. This indicates that the priority should be given to ecological environment in the configuration of water resource in the drainage area of Kuitun River. The ecological water demand will not continue to decline in the future, and regions of partial ecological environmental worsening should increase somewhat. Only in this way can the coordinated development of regional economy and ecological environment be ensured.

3.2 Categorization of ecological water demand

The water demand in the drainage area of Kuitun River falls into two categories, namely national economical water demand and ecological water demand. This paper mainly dwells on the latter.

Ecological water demand includes artificial ecological water demand and natural ecological water demand. The former refers to the water needed in the ecosystem under the direct or indirect effect of people; the latter refers to the water needed in the ecosystem basically without the artificial effect. In terms of the actual situation of Kuitun River, artificial ecological water demand includes ① shelterbelt, ② irrigation grass farm, and ③ urban greening etc. Natural ecological water demand includes ① desert river bank forest, ② river valley forest, ③ low-land grassy marshland, ④ desert vegetation, and ⑤ river and lake etc. In the light of the above analysis, the ecological water demand in the drainage area of Kuitun River can be concluded as Table 2.

Table 2  Classification of water demand of ecological system in Kuitun River basin

artificial ecological water demand			Natural ecological water demand
shelterbelt	irrigation grass farm	urban greening etc.	desert river bank forest	river valley forest	low-land grassy marshland	desert vegetation	river and lake etc.

4 Analysis of Ecological Water Demand

In terms of sources, ecological water demand in Table 2 can be divided into three categories: ① ecological water demand of artificial oasis, supplied by surface water in the way of irrigation; ② ecological water demand of natural oasis, supplied by groundwater in the way of phreatic groundwater evaporation; and ③ ecological water demand of rivers and lakes, supplied by both surface water and groundwater.

Since the components of the first category of ecological water demand have the same requirements on their growth as those on crops under their shield, the volume can be obtained through the direct calculation method, namely that component areas multiply irrigation ration.

With regard to the second category of ecological water demand, it is mainly for the mesoxerophytes and mesophyte, which are distributed in bottomland, low-step land, lakeside, and swale with high underground water table. The vegetables rely on groundwater to maintain their lives, and the main form is the transpiration in the growth period. So the water volume can be determined through transpiration method. At present, there are a variety of ways of calculating vegetation transpiration volume, which are measurement transpiration method, Aweiyangnuo formula, Shen Lichang formula, Penman formula, SPAC model, ecological water demand quota method, and ecological water demand method based on remote sensing and GIS. In the light of the actual situation of Kuitun River, this paper calculates the evaporation volume of phreatic groundwater with ecological water demand quota method, phreatic groundwater transpiration method, Aweiyangnuo formula, and Shen Lichang formula separately, and then obtains the ecological water demand on the basis of calculation results.

The last category is the ecological water demand of lakes and rivers. Since Kuitun River has dried up at the lower reaches in the 1970s, and there were no surface water flowing into the lake, the water of Aibi Lakeis mainly supplied by Boertala River and Jing River. Therefore, in light of Criteria on Planning Environment Evaluation of River Basin, Planning of Boertala River Basin and Jinghe River Basin, and Planning of Kuitun River Basin, apt the lake water area should be established as the goal to attain so as to ensure the ecological environment of Aibi Lake. In the past twenty years (since 1985), the water area of Aybi Lake has been maintained around 500～600km². Based on this and in consideration of the status of the environment around the lake and the water demand of the regional economic development, the volume of Kuitun Rivergroundwater flowing into Aibi Lake should be no less than 0.42*10⁸m³ every year in the light of Investigation and Evaluation on Groundwater Resource and Environment Problem in Zhungaer Basin.

4.1 Artificial ecological water demand

Based on the land utilization of the drainage area of Kuitun River and in the light of remote-sensing data, we first gather the statistics of distribution areas of artificial shelter forest, irrigation grassland, and urban greening in each administrative area separately, and then calculate the concrete water demand in terms of farm irrigation quota of each irrigation area in the drainage area of Kuitun River and the coefficient method of irrigation water comprehensive utilization, with result detailed in Table 3.

4.2 Natural ecological water demand

Calculate natural ecological water demand with different methods.

4.1.1 Quota method

The ecological water demand quota of vegetation is related not only to natural factors such as climate condition and soil substance, but to group type and vegetation category as well. Directed to different ecological water demand types, typical species are selected as the reference species, and their ecological water demand quotas are taken as the quota for the type. The paper, on the basis of the evapotranspiration study result of different tree species in natural oasis of arid zones and in the light of the distribution area of natural oasis vegetation in the drainage area of Kuitun River, the paper calculates the ecological water demand volume with quota method, with result detailed in Table 4.

Table 3 Result of water demand by artificial oasis eco-system in Kuitun River basin

Table 4 Results of eco-demand water of natural oasis by quota calculated

        Table 4 reveals that the ecological water demand of natural oasis calculated with ecological water demand quota method is 2.03*10⁸m³, of which the volume of river valley forests is 1.52*10⁸m³, accounting for 75% of the total. The ecological water demand of desert forests is not included in the table, because desert forests in the study area are mainly distributed in the natural protection area of Ganjiahu. The main species include haloxylon ammodendron, white haloxylon ammodendron, red lauan, and reaumuria soongonica, of which haloxylon ammodendron and white haloxylon ammodendron take the predominance. In the light of studies, the ecological water demand quota of natural haloxylon ammodendron forest is 1,095 m³/hm² when the coverage is 30%. But the annual average rainfall in the area of Ganjiahu is 144.1mm or 1441 m³/hm², above the quota. This indicates that haloxylon ammodendron forest can relies on rainfall to maintain its life. Therefore, the ecological water demand of desert haloxylon ammodendron forest is not calculated.

4.2.2 Phreatic water transpiration method

To multiply the area of a vegetation type at a given depth of groundwater buried by the evaporation at the phreatic water level and vegetation coefficient:

In the formula:  is the ecological water demand of vegetation typeｉ;  is the distribution area of vegetation type ｉ;  is the phreatic water evaporation of vegetation type ｉ at a given depth of groundwater buried （m）; K is the vegetation coefficient.

Calculation formula of phreatic water evaporation:

 ｎ=2.15±0.025

In the formula:  is the extreme critical depth of phreatic water evaporation (m);  is the water surface evaporation of a 20ｍ² evaporation tank (m); and  is the depth of groundwater buried (m).

Research shows that the extreme critical depth of phreatic water evaporation in the study area is 5m. The experimental data of Hadi Slope in the valley of Toutun River also at the north foot of Tianshan Mountain are adopted as the values of  and . The calculation results are detailed in Table 5.

Table 5   Result of eco-demand water of natural oasis in different vegetation types

Types	The range of depth of groundwater buried  (ｍ)	h (ｍ)	areas（km2）	vegetation coefficient k	water demand（104m3）
Desert river bank forest	2～3	2.5	135	1.47	4112
River valley forest	1～3	2.0	290	1.62	15266
Low-land grassy marshland	1～2	1.5	34	1.77	3370
Total of water demand（104m3）			459		22748

4.2.3 Shen Licheng formula and Aweiyangnuo formula

4.2.3.1 Shen Licheng formula:

In the formula:  is the phreatic water evaporation at a depth of phreatic water buried h (m);  is the surface evaporation (m).

4.2.3.2 Aweiyangnuo formula

In the formula:  is the phreatic water evaporation at the phreatic water buried depth h (m);  is the surface evaporation (m);  is the extreme critical depth of phreatic water evaporation (m).

Ecological water demand W, the water volume needed in maintaining a given area of vegetation, can be expressed with the product of the area S of natural vegetation to be protected and the evapotranspiration E of unit area vegetation (nearly equal to the evaporation of phreatic groundwater), namely . Please see Table 6 for details.

Table 6 Result of eco-demand water of natural oasis by different method (10⁴m³)

depth of groundwater buried（m）	areas（km2）	Aweiyangnuo formula	Shenlichang formula
1～3	1014	21402	18830
3～5	1462	769	2351.5
Total		22171	21181.5

It can be known from the above calculations that the ecological water demand in the drainage area of Kuitun River is 4.39*10⁸m³.

 

5 Requirements on Ecological Water Demand in the valley project of Kuitun river

Practices show that the economic development in arid zones is actually on the basis of damaging natural vegetation growth and consuming water resource; the consideration of ecological water demand in the planning and management of drainage areas and taking it as the water-supply subject indicate the start of the rational understanding of ecology, and the ultimate purpose is to maintain the coordinated development between the sustainable growth of regional economy and the protection of ecological environment.

The ecological water demand index was firstly put forward in the valley project of Kuitun River started in 2001, and ecological water demand was taken as the water-supply object in the supply-demand balance of water resource in the area. The annual average runoff of the three main rivers in the drainage area of Kuitun River is 12.19*10⁸ｍ³, which has been consumed up in irrigation areas. The following principles are defined in the drainage planning: in ordinary years, the ecological water demand of natural vegetation at the lower reaches should not be less than 20% of the runoff, and water is mainly delivered to watercourses at the lower reaches in flood season. When external water flows into the drainage area, the ecological water demand of natural vegetation at the lower reaches should not be less than 35% of the runoff. Hence, it can be calculated that the ecological water demand of natural vegetation in the lower reaches should be 2.44*10⁸ｍ³ at least in ordinary years.

6 Result & Discussion

(1) The ecological water demand in the drainage area of Kuitun River calculated with different methods is 4.39*10⁸ｍ³.

(2) It can be known from the calculation result that the natural ecological water demand in the drainage area of Kuitun River calculated with different methods is around 2.59*10⁸ｍ³, and the ecological water demand of natural vegetation in the lower reaches of the drainage area determined in the planning should not be less than 2.44*10⁸ｍ³. So the natural ecological water demand calculated in the paper can be taken as the reference and basis for the optimized configuration of water resource.

(3) It can be known from the calculation result that the ecological water demand in the drainage area of Kuitun River is 4.39*10⁸ｍ³, of which the natural ecological water demand is around 2.59*10⁸ｍ³, accounting for 59%, and artificial ecological water demand is 1.8*10⁸ｍ³, accounting for 41%. In the light of the actual situation of the drainage area of Kuitun River, the natural oases are all at the outside of artificial oasis, so they are the natural barrier of artificial oasis and the fundamental guarantee for the sustainable development of artificial oasis. And water is the most active and sensitive factor in the environment. Under the condition that the overall quantity of water resource is unchanged, natural oasis and artificial oasis are competing for water consumption.

(4) In terms of the internal artificial oasis and natural oasis, shelter forests require the biggest water demand, being 1.62*10⁸ｍ³, accounting for 90% of the total ecological water demand of artificial oasis. And irrigation grassland and urban greening objectively play a positive role in the maintenance and improvement of the ecological environment of artificial oasis, but the water demand is rather small, only 10% of the total. In the ecological water demand of natural oasis, river valley forests require the biggest water demand, being 1.55*10⁸ｍ³. Since they are at the outside of oasis and of great importance to the stabilization of oasis production and ecological environment, their ecological water demand is the biggest.

(5) In terms of calculation method, the phreatic water evapotranspiration of each climate zone, each depth area, each forest, and each grassland should be calculated separately in theory when indirect ascertaining method is applied. Only results calculated in this way are perfectly accurate. But the method is infeasible because of the shortage of measurement data. In the case, this paper estimates the ecological water demand in terms of different forests, grasslands, the most important species, vegetation, and depth. In the light of the calculation result, indirect ascertaining model may reflect the water demand of each ecological water demand type at length, but it needs too many parameters, and the parameters have to be modified for different areas. Therefore, although it is allowed to calculate ecological water demand in arid zones through direct estimation method and indirect ascertaining model, further studies are still needed.

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