Water resources and ecological conditions in the Tarim Basin

Vol. 45 Supp.SCIENCE IN CHINA (Series D)December 2002Water resources and ecological conditions in the Tarim Ba-sinSONG Yudong (宋郁东), WANG Ranghui (王让会)P3 A& PENG Yongsheng (彭永生)Xinjiang Institute of Ecology and Geography, Chinese Academy of Sciences, Urumqi 830011, ChinaCorrespondence should be addressed to Wang Ranghui (email: rhwang@ ms xjb.ac cn)Received September 15. 2002AbstractTemporal sequential analyses of the hydrological observational data in the Tarim Ba-sin over the last forty years revealed an annual increase of 2X 10 m' in the water quantities at thethree headstreams of the upper courses and an annual decrease of 3X 10'm3 in the water flowfrom Alaer, which is on the upper main stream. A prediction of the trends indicates that there canbe severe situations under which intrmittent water interceptions occur. By means of approximateestimations on vegetative water consumption through phreatic evaporation combined with a quotaassessment, the ecological water demands required to maintain the ecological environment in themainstream area over the three difterent targeted years of 2005, 2010 and 2030 are defined asstanding at 31.86X 109m"?, 36.27x10*m3 and 41.04X 10°m3 respectively. Ecological fragility in.dexes are established on the basis of the selection of environmental sensitivity factors. Rationalevaluations give proof that the lower reaches of the mainstream have already turned into zoneswhere their ecological environments are gravely damaged. Muti-objective optimization should beconducted and protective schemes be framed within the threshold limits of the bearing capacitiesof water resources and the environment.Keywords: Tarim Basin, hydrological characteristics, ecological water demands, ecological environment.1 A survey of the Tarim BasinThe Tarim River, the longest inland waterway in China, runs west-east through the Tarim Ba-sin along the northem edge of the Taklimakan Desert. Located in the south of Xinjjang UygurAutonomous Region and between the Tianshan Mountains and the Kunlun Mountains, the TarimBasin, along with the 105X 10* km2 of is mountainous peripheral segments, accounts for 63% ofthe total area of Xinjiang. The basin itself is 53X 10* km2 in area and the central Taklimakan De-sert 33.76x 10* km，while the pediment plains and oasis scarcely 19.24 km2. Affected by diversefactors, the Tarim River mainly relies on, at the present time, the three streams of Aksu, Hotan andYarkant on its upper course and the Peacock on its lower reaches as supply of its surface runoff.The Tarim River system has undergone distinct evolutions, the main features of which are thesuccessive development of man-made oasis in the source area. The subsequent divorce of somesource flows from the main stream caused a gradual break-up of the Tarim water system and espe-cially an ecological deterioration and shrinkage of the channel bed at the lower reaches of the中国煤化工MYHCNMHG2SCIENCE IN CHINA (Series D)Vol. 45trunk stream. The evolution of the Tarim River system directly leads to the grave degradation ofthe ecological environment' . The composition of the water flows from the Tarim watercourse isillustrated in table 1.Table | Current water flow compositon of the Tarim mainstream (1981- - 1993)Water compositionWater systemTarim mainstreamAksuYarkantHotanPeacockFlow volume/10* km'45.1133.580.232.12Proportion (%)10074.440.5120.354.70The Tarim trunk is 1321 km long, sectionalized into the upper, middle, and lower reaches atthree locations successively: Alaer, Yingbazha, and Kala. The watercourse of the lower segmentextends approximately 428 km and is labeled“the Green Corridor". The water flow from Kala(excluding that from Kuta) has decreased from 12X 10* m' in the 1950- 1960's (1957- -1967) to2.7X 10* m' in the 1980- - 1990's (1986- 1995). Years of water interception at the hinder segmentof the lower course, combined with the burying force of drift sand rendered the devastating deathof the preexisting desert poplar trees. Further downstream Yingsu, vegetation degradation, seriousdesertification and deteriorated eco-environment are normal phenomena. The ecological and en-vironmental issues of“the Green Corridor" at the lower reaches of the Tarim mainstream, conse-quently, have been ones that capture both domestic and foreign attention.2 Hydrological characteritics and the evolution of water qualityStarting from the end of the 19th century and particularly the second half of the 20th century,studies on the temporal and spatial variation of surface flows and the coupling of water and saltentered a new stage. But being influenced by various factors and based on nothing more than themere data obtained from hydrological observations, analyses are superficial so that it is hard tograsp the laws of the variational source flows over years.2.1 Trends on the variation of surface flowsOn the basis of the current data at hand, termporal sequential analyses are unprecedentedlyconducted on the 1957(1965)- -1995 series of annual runoffs at the 5 mountain-pass observationstations on the 3 sources and the 4 stations on the mainstream of the Tarim River (fig. 1). Mean-while, trends on and charateristics of the origin and formation of the water resources in the TarimRiver are presented, and also are the corresponding quantitative results, which reveal an annualincrease of2X 107 m' and 5X 10' m' in the water flows and water consumption respectively at thethree headstreams of the upper courses and an annual decrease of 3X 107 m' in the water flowsfrom Alaer, which is on the upper main stream.With regard to annual runoff entering the Tarim Basin from 1959 to 1995, the Aksu thatoriginated from the Tianshan Mountains indicates an evident yearly increase, while the Yarkant中国煤化工MYHCNMHGSupp.WATER RESOURCES & ECOLOGICAL CONDITIONS IN TARIM BASIN0一≌40-Alaer昌30平XinqimanYinghazha世Kala'19s51965ig. I. Annual runoft and the corresponding variational tendency as recorded alt the dfferent observationalstations on the Tarim mainstream.and the Hotan, both originating from the Kunlun Mountains, exhibit their stability over years, im-plicitly increasing and decreasing respectively. The impact of climatic changes on water resourcesis manifested in their impact on the supplying capacity of water resources and on water de-mands The annual runoff of the Alaer, one of the Tarim River's mainstreams, decreased from 6X 10' m' during the 1930- 1940s of the 20th century to the present 4.3X 10° m' and the trend isstill continuing at a rate of 3X 10 m'. As is well known, the decrease in water runoff in the main-stream results from increased water consumption rather than decreased water flow itself in thesource areas of the Tarim River, the annual average from the 1950- -1960s to the 1980- 1990sstanding at approximately 0.8-1X 10° m'.An analysis of the water consumption tendency at the various reaches of the Tarim main-stream by building models indicates an evident annual increase of 1.3X 10' m' at both the upperand middle reaches (able 2). Intermittent set-off at the different observational sections on themainstream is predicted at 2000- 2020 in Kala, 2050- -2070 in Yingbazha, 2075- 2095 in Xin-quman and 2120- 2140 in Alaer, presenting severity in the temporal and spatial changes of waterresourcesls.61.Table2 Average anual water consmption and every kilometer water consumption in the main stream of Tarim RiverUpper reachesMiddle reachesUpper and middle reachesRiver segmentsfront segmenthinder segmenttotal___ Yingbazha KalaAlaer-KalaLength/km189258447845Yearly average waterConsumption /10* m'7.858.7423.04Water consumptionper km/10*m'0.04150.03390.03710.05800.04692.2 The changing features of water qualityResearches have indicated that the variation of salinity in surface flows has close coupling中国煤化工MYHCNMHG14SCIENCE IN CHINA (Series D)Vol. 45Table 3 Variation of salinity of the surface and ground water at the representative cross- sctionson the mainstream of the Tarim RiverLocationGPS positional coordinateSalinity---Alaer hydrological station (riverside)E 81°21'. N 40933'0.40Xinquman hydrological station (nearby)0.72YinghazhaE84°14'. N 40°10' .1.01Kala reservoir (nearby)E 86*40'.N 41901'2.00Daxihaizi reservoir (neartby)E87°33', N 40*35'2.30Yingsu riverbedE8757'. N 40*26'5.90Kiaerdayi riverbedE 88*10'.N 40°23'9.40AlaganE 88*21'. N 40°09'9.70Yiganbujima riverbedE 823'. N 39*48'1.11LuobuzhuangE 88°16'.N 39*27'37.28relations with the mineralized degree and chemical features of water (table 3). Prior to the end ofthe 1950s, the Tarim mainstream boasted comparatively high-quality water whose salinity wasbelow 1.0 g/L. The reasons for the continuous rise of water salinity and the deterioration of waterquality afterwards may possibly include these facts: hydrological features hold a highly sensitiveresponse to changes in land utiliation"'; flows from the mainstream decreased with the exploita-tion of water and land resources in the river basin; and irigated areas discharged a large quantityof water of high salinity. According to an analysis of the 1985- -1998 data obtained from observa-tions on the chemical conditions of the river water, the mean annual salinity at Alaer and Kalastood at 1.85 g/L and 1.34 g/L respectively; a salinity below 1.0 g/L appeared only in August andthe salinity in other months of the year was higher than that. Fig. 2 shows the composition of wa-ter of different salinity at the two typical sec-tions at Alaer and Kala, while table 3 system-口<1atically reflects the salinity characteristics of四1-3the surface and ground water (downstream3-5Yingsu) at the representative cross-sectionson the mainstream. At the same time, moni-Alaer 1985- 1995Kala 1985-1995toring and assessment suggest that the con-Fig.2. Water qualily conposition at the two cosctienis of tamination degree is at 5 in Alaer and Ying-Alaer and Kala.bazha, and 4 in Kala. Such indexes as chlo-ride, sulfate, salinity, hardness and fluoride largely surpassed their normal standards.3 Estimation of ecological water demandsIn recent years, models for estimation of ecological water demands and the exploration forecologically sustainable water demand theories have been in their progressive development8-I0I.In a large spatial dimension, given stabilized evaporation on soil, not only the surface evaporationstrength maintains stable, but also the content of water in soil does not change with time. That is中国煤化工MYHCNMHGSupp.WATER RESOURCES & ECOLOGICAL CONDITIONS IN TARIM BASIN1:to say, the phreatic water, soil water flux and evaporation on soil are equal to each other. Liningthe two sides of the Tarim River are mesophytic and xerophytic azonal vegetation whose lives aremaintained by groundwater. Therefore, the ecological water demand that is needed to maintain thenatural vegetation can be approximately estimated through phreatic water evaporation, a funda-mental principle on the estimation of ecological water demand by applying vegetation water con-sumption.In the course of the estimation, types of vegetation are assorted according to growth condi-tions, serving the defining of their range and depth of burial, and of evaporation and mean quan-tity at different depths by using Aweiliyangnuofu formula. Then, quantities of water consumptionare respectively calculated according to areas of different vegetation types, making it possible toestimate the minimum water consumption required to keep the ecological environment from wors-ening. But there is still distinction between water consumption and water demand for naturalvegetation. Normally, these two are not the same and the latter is greater than the former. Thepurpose of estimating ecological water consumption is to provide theoretical basis and referencemodels for the rational estimation of ecological water demanding. A rational estimation of theminimum water demand to maintain the living of natural vegetation also needs to take the follow-ing factors into consideration: the climatic, topographic, hydrological, and soil conditions in theTarim Basin; the present state of hydraulic engineering and targets of ecological construction inthe basin area; the uilizing eficiency of water as well as theoretical research and practical ex-perience. According to estimations by various models, the ecological water demands in the Tarimmainstream area in the three targeted years of 2005, 2010 and 2030 are at 31.86X 10* m', 36.27X10* m' and 41.04X 108 m' respectively.4 Assessment of the eco-environmental conditions in the Tarim BasinAlthough researches on ecological sensitivity and fragility have been crried out in recentyears, there are no models to follow concerning the establishment of ecological fragility indexesand quanitative asessment. The index system of the asessment of fragile eco-environment iscomposed of 20 individual indexes, 5 in each of the four systems of water, land, biological andenvironmental resource systems respectively. This requires the consideration of the regional dis-crepancy of the natural resources and ecological environment in the river basin, the instruction ofsystem approach and information theory as well as quantitative methods and fuzzy mathematics.In order to study the quality of fragile ecological environmnents in a quantitative method,ecological fragile index (EFI) is created, comprehensively rflcting the quality of ecological en-vironments in different zones.CciiEFI= =Zai=l中国煤化工MYHCNMHG6SCIENCE IN CHINA (Series D)Vol. 45We know that the value of the EFI index is corresponding to the quality of the environment,and this is precisely the connotation of the ecological fragile index. The ecological fragility in theTarim Basin is classified into four grades, namely: seriously fragile (EFI≥0.5), moderately fragile(0.3≤EFI< 0.5), generally fragile (0.1≤EFI< 0.3), and none-fragility (EFI< 0.1). They indi-vidually correspond to damaged, disadjust, balanced and bettered environmental zones (as illus-trated by table 4).Table4 The assment resuls of ecological fagility in Tarim River BasinUpper reachesMiddle reaches Lower reachesAksu RiverYarkantHotanRiver basinsof the TarimBasinRiver BasinRiverFI0.080.230.250.320.87Fragilitylightly fragilegenerallygenerally fragile moderately fragilemoderatelyseriouslyfragileEcologicalred ecologicalgreen ecological zoneyellow ecological zonez0ne____5 Overall thinking on ecological construction and the existing problems5.1 Basic thinking on the regulation of ecological environmentsThe basic thinking on the regulation of the ecological environments in the Tarim Basin andits targets are as follows:To curb the ecological and environmental deterioration at the lower reaches of the TarimRiver by 2005; to preliminarily improve the ecological environments at the lower reaches of theTarim River by 2010; and by 2030 the ecological environments at the lower reaches of the TarimRiver will have been effectively protected and reasonably rehabilitated. Furthermore, through thegradual implementation of a series of ecological construction projects at the source area, main-stream area and other related areas, the social economy, people's living standards as well as thequality of the ecological environment in the Tarim Basin will have been greatly improved.Therefore, in the year 2000, under the common efforts by the govermment departments con-cerned, water was urgently transferred from the Bosten Lake to the Tarim River, directed to theDaxihaizi Reservoir, from which 9.88318X 10' m' of water was discharged between May and July.The water head reached as far as 102 km, playing an important role in relieving the increasingdeterioration of ecological environments. Presently, the 2000- 2001 water transfer has completed,the water amount exceeding 2.0X 10* m' and the water head reaching Kaogan, which is on thehinder segment of the lower reaches. All the practice in ecological construction is inspiring.5.2 Existing problemsAlthough rational understanding has now been achieved on such isues as the natural re-sources, environment and social economy in the Tarim Basin. Under the present situations,batches of major issues conceming the Tarim Basin are to be solved: the hydrological features and中国煤化工MYHCNMHGSupp.WATER RESOURCES & ECOLOGICAL CONDITIONS IN TARIM BASINevolution of water quality; rules of ecological water demand and the assessing models; the evolu-tion of river beds and rules of sedimentary transportation; the transition of wetlands; the evalua-tion of ecological value; the rehabilitation and reconstruction models for degraded eco-systems;and the establishment of information system models for resource and environmental management.At the same time, there is controversy over the regulation of the Tarim River. Some advocate thatthe“Green Corridor" at the lower reaches be abandoned and give the middle reaches priority withregards to water resources and potential exploitation; others argue that there is need to protect thelower reaches. But they cannot reach an agreement on whether the Daxihaizi or Alagan or eventhe Taitema Lake should be the object of protection. With the implementation of water-ransferprojects in recent years, however, some experts are convinced that there can be no doubt intransferring water to Taitema and thus rehabilitating the ecological environments back to the levelof the 1950s. In fact, the rehabilitation and reconstruction is a hard task due to radical changes intopographical features, soil properties and growth conditions for vegetation. Even under the as-surance of adequate water resources, which is normally difficult, the gradual improving of ecologyis not easy.AcknowledgementsHeartel thanks shall be extended to Lei Zhidong, Yang Shixiu. Fan Zili, Zhang Fawang. MaYingie and Ji Fang for their active participation in the rescarch, which was sponsored by the Ninth National Five- Year-Plan KeyProjects (Grant No. 96-912-02-02) and Major Projects Planned for National Fundamental Research (Grant No. G19990435) andCAS Knowledge Innovation Project (Grant No. KZCX-XJ02 02).References1. The Takelamagan Desert Comprehencsive Expedition Team. the Chinese Academy of Sciences, Catalog of ResearchDocuments on the Takelimakan Desert (in Chinese), Beijing: Science Press, 1993.2. Sven Hedin. Wang Anhong. Chui Yanhu. Expedition into the West of China- -Unveiling the Mysterious Luobu Lake (inChinese), Urumqi: Xinjang People's Press,. 1997.3. Tang Guoqiang. Li Xiubin, Liu Yanhua, The fagility of water resources and its evaluation methods given the global climatic changes, Progress in Earth Science (in Chinese), 2000. 15(3): 313- -317.4. Qian Zhengying. 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