The influence of water regulation on vegetation in the lower Heihe River

J. Geogr. Sci. 2010, 20(5): 701-711DOI: 10.1007/s11442-010-0805-6◎2010◆Science China Pres勾Springer-VerlagThe influence of water regulation on vegetationin the lower Heihe RiverJIANG Xiaohui', LIU Changming231. Yellow River Institute of Hydraulic Research, YRCC, Zhengzhou 450003, China;2. Collge of Water Sciences, Beiing Normal University, Beiing 100875, China;3. Institute of Geographic Science and Natural Resources Research, CAS, Being 100101, ChinaAbstract: Water regulation has been carried out by the Heihe River Bureau since 2000, whichaims to address the existing eco-environmental problems in the lower Heihe River. In the pastnine years, great changes in spatial-temporal distribution of water resources took place in thelower Heihe River. In order to objectively evaluate the influence of water regulation on theeco-environment, the changes of groundwater table, typical vegetation, landscape types aswell as East Juyan Lake have been analyzed in the lower Heihe River, by means of fieldsurveys and remote sensing. These results indicate that there are obvious effects of waterregulation on the eco-environment, which has been improved toward sustainability in thelower Heihe River.Keywords: water regulation; ecosystem; groundwater; the lower Heihe River1 IntroductionThe Heihe River is the second longest inland river in China, which is called“the MotherRiver" by the Hexi people. With a total drainage area of 142 900 km2 and a total length of821 km, the Heihe River originates from the north of the Qilian Mountain and flows throughQinghai Province, Gansu Province and Inner Mongolian Autonomous Region (including 11counties or banners): Its upper reach is from the above Yingluo Gorge, the middle reach isbetween Yingluo Gorge and Zhengyi Gorge, and the lower reach is from Zhengyi Gorgedownwards. The length of the lower reach is 333 km, and the drainage area is 80,400 km2.The lower reach is about 176 km from Zhengyi Gorge to Langxin Mountain, and is dividedinto the East River and the West River downwards from the diversion in Langxin Mountain.Finally it flows into the East Juyan Lake (Suoguonuoer) and the West Juyan Lake (Gashun-nuoer) respectively. The Ejina Delta oasis formed around the East and West rivers in the in-terior of the Gobi desert has been an important ecological defense against the sandstorms inReceived: 2009-02-27 Accepted: 2009-10-22Foundation: Key National Water Project funded jointly by the Ministng中国煤化工。-stry of Environ-mental Protection and Ministry of Water Resources, No.2:CHC N M H Gft Research In-stitutions Basic Scientifc Research Special Fund, No.HKYAuthor: Jiang Xiaohui (1972-), Ph.D and Senior Engineer, specialized in water resources and water environment.E-mail: jxh3412@163.comwww.scichina.comwww.springerlink.com702Joural of Geographical SciencesNorthwest China.According to historical records, there was abundant vegetation in the lower Heihe River.Furthermore, the famous ancient Juyan-Black City Oasis Culture was fostered in this regionin the 1000 years from the Han Dynasty to the Yuan Dynasty. During the period 1928- -1932,the water area of the East Juyan Lake and the West Juyan Lake spanned 35 km2 and 190 km2respectively, when the Chinese-Swedish Northwest Survey Team investigated the region. In1958, a wet year, the water area of the two lakes spanned 35.5 km' and 267 km' respectively.At that time, many species of plants, such as Populus euphratica, Elaeagnus angstifolia,Tamarix sp, Haloxylon ammodendron, Nitraria sibirica, Glycyrrhiza uralensis, Phragmitescommunis etc., flourished on both banks of the Ejina Delta and around the East Juyan, WestJuyan and Gurinai lakes. In the past 50 years, owing to water extraction in the upper andmiddle reaches, water supply for industrial and agricultural purposes, although the dischargein Yingluo Gorge has not significantly changed, the flow in Zhengyi Gorge has decreasedrapidly since the 1980s (Figure 1), and less water entered into the lower Heihe River. Owingto the lack of water in the lower Heihe River, the oasis became seriously desertified, lakesdried up, and the water quality deteriorated. The carrying capacity of pasture declinedsharply and several rare animals disappeared (Zhong et al, 2002; Cao et al, 2004; Yang etal, 2005; Zhang et al, 2002; Wang et al, 1998; Luo et al, 2003; Tang et al, 2009).2(1816， 14品12复108+Yingluo Gorge1954 1959 1964 1969 1974 1979 1984 1989 1994 1999 2004Figure 1 The 10 years moving average flow of Zhengyi Gorge and Yingluo Gorge from 1954 to 2004In order to increase water supply and avoid deterioration of the ecosystem in the lowerHeihe River, the unified management system and the new regulation were implemented inthe Heihe River. In 1999, the Heihe River Bureau of the Yellow River Conservancy Com-mission (YRCC) under the Ministry of Water Resources (MWR )was authorized andfounded. Since 1999, the water resources in this basin have been managed and regulateduniformly. Since the end of 1999, water resources uniform regulation has been initiated, andthe water user in the middle Heihe River reduce中国煤化ired to the lowerHeihe River. After several years of water regudistribution ofwater resources has changed dramatically in the ::TYHCNMHGutflow from themiddle reach has increased year by year. In terms of the relation of water diversion curve, itis calculated that when the average inflow at Yingluo Gorge is 1 .58 billion m', the averageoutflow at Zhengyi Gorge increased from the average discharge of 0.73 billion m3 beforeJIANG Xiaohui et al: The influence of water regulation on vegetation in the lower Heihe River703water regulation during the period 1997-1999 to 0.80 billion m3 in 2000, 0.83 billion m' in2001, 0.90 billion m' in 2002, and 0.95 billion m' in 2003 after water regulation. Especiallythe runoff reached the capital of Ejina town in 2001, to East Juyan Lake with the maximumwater area of 23.5 km2 in 2002 (where there has been no water for 10 years), and to WestJuyan Lake in 2003 (where there has been no water for 40 years) (Si et al, 2005; Yang et al,2003).By means of the unified water regulation for several years, the spatial-temporal distribu-tion of the water resources has significantly changed in the lower Heihe River, which hasproduced positive effects on the ecosystem in the lower reach. In this paper, by field surveysand applying remote sensing data, the influence on the vegetation has been analyzed in thelower Heihe River. The results provide scientific basis for the further water regulation andthe improved restoration of the ecosystem in the lower Heihe River.2 Influence of water regulation on the groundwater level2.1Influence of water regulation on the groundwater levelThe observation wells in the lower Heihe River were established in 1988 (Feng et al., 1998).These wells were mainly distributed in the oasis along the East and West rivers and rarely onthe edge of the oasis or the desert. These wells are more concentrated near the LangxinMountain in the upper reaches of both the East and West rivers, Jirigelangtu in the lowerreaches of the East River and near Saihantaolai in the lower reaches of the West River (Fig-ure 2). Figure 3 shows the variation of groundwater level in several typical wells in the up-per reaches of the East and West rivers, near Jirigelangtu and Saihantaolai in the lowerreaches of the East River, as well as in the Ejina Oasis (1995- 2004). It can be seen that theslow descending trend of groundwater level in the lower Heihe River has been held backafter water regulation for 5 years (Figure 3). Particularly, the groundwater level has beenrising to some degrees in the lower Heihe River since 2002. In 2004, the groundwater levelhas increased to near the historical maximum since 1995. Comparing the figure in 2004 withthat in 2002, the groundwater level rose by 0.22 m both in the East and West rivers, by 0.79m in Jirigelangtu, by 0.5 m in Saihantaolai, and by 0.42 m in the whole Ejina Oasis.2.2 Relationship between groundwater level and vegetationMany surveys indicate that there is a significant correlation between the evolvement ofnatural vegetation and groundwater level (Table 1). This is because rainfall is scarce, and thegroundwater is required to maintain the normal growth of the large variety of natural vegeta-tion. Therefore, it is necessary to meet this water demand for maintaining the normal growthof natural vegetation. Natural vegetation in the lower Heihe River could be protected andrehabilitated effectively, if water demand of natural vegetation is met by scientific waterregulation (Feng et al, 1998; Zhang et al, 2004; Wang et al.2003).中国煤化工3 Influence of water regulation on typical |YHCNMHG3.1 Response of Populus euphratica to water regulationAccording to the survey, after water regulation for 5 years in the Heihe River, the lateral704Joumnal of Geographical Sciencesselest Juyan LakeEast Juyan Lake2HloH29)SupozhuperWonong)Lake●5驴鸟/E1.E2S 34RoadXialezhuoer, ReseryoirSuan Lake{5 88ge Langtu63.EjhSaihantadls6_4#CaicaigeaobaBaodage|■County回TownOrdinary road曰Lake叫Small reservoirHydrometric station●Groundwater observation wellB1/682。B4B5B6。Special test observation wellB3B7Conservation arca of naturalforest- pasture色Ejinaqi .。BayinbaogedeDongfeng Reservoir,BejheranReeryoir3# 4/65#Jjayuguen, Lmm hersie Pojet( JiguenLengxIyShan中国煤化工、y1#MYHCNMHGyeFigure2 The distribution of the observation wells in the lower Heihe RiverJIANG Xiaohui et al: The influence of water regulation on vegetation in the lower Heihe River7050.1995 1996 1997 1998 1999 2000 2001 2002 2003 2004- + Upper reaches of East-West rivers一Saihantaolai巨1.0r Jirigelangtu号1.5Ejin 0Dasis2.0e 2.53.Figure 3 Inter-annual variations of groundwater level in the major regions of the lower Heihe RiverTable 1 Relation between water level and the growth of plants in Ejin bannerVegetation communityWater table and growth condition<4m4-6 m,hidebound, bald, the 6- 10 m, most of the plants>I0 m, all thePopulus euphraticanormal growth leaves fade even few plants die blastplants dieElaeagnus angstifolia2--3m45 m, hidebound, blasted, even 5- 6 m, most of the plants >6 m, most ofnormal growth few plants dieblast and degradedthe plants dieTamarix sp.<5m5- 7 m, degradation, blasted, 7- -8 m, degraded seriously,>8-10 m, allNitraria sibiricanormal growth even few plants diemost of the plants dieaffected area of water regulation on Populus euphratica extends to 800 m away from thewatercourse. Furthermore the affected area of water regulation on Populus euphraticachanges with different distances to the watercourse in different periods. During the 2nd yearof water regulation, 2001, the indexes of Populus euphratica within the region (100 m awayfrom the watercourse), such as the average height and the thorax diameter etc., increasedmarkedly. During the 3rd year, 2002, the indexes of Populus euphratica within the region(100- 200 m away from the watercourse) reached their peak. During the 4th year, 2003,Populus euphratica within the region (200- -300 m away from the watercourse) grew rapidly.Tables 2- 6 show the growth of Populus euphratica before or after water regulation at dif-ferent sites of the East and West rivers in terms of the field survey in August. 2005. The de-gree of growth is an important quantitative index to evaluate the recovery of PopulusTable 2 Survey results of the growth indexes for Populus euphratica at the CrOSs section near Weitong Bridge inDongfengchang before and after water regulationDistance to the Age of Populus Growth degree for 5 years Growth degree for 5 yearsConcomitant vegetationwatercourse (m) euphratica (year) before water regulation (mm) after water regulation (mm)Phragmites communis1001114.216.1Achnatherum splendensSophora alopecuroides20002.520013.226081soiunntherum splendens中国煤化工alopecuroidesFYHCNMHG5001612.313.210001310.810.9706Journal of Geographical SciencesTable 3 Survey results of the growth indexes for Populus euphratica at the left cross section of Yidao River nearDaxi'aobao before and after water regulationDistance to the Age of Populus Growth degree of the thorax Growth degree of the thorax Water levelWater levelwatercourseeuphraticadiameter for 5 years before diameter for 5 years after before water after water(m)water regulation (mm)regulation (m) regulation (m)8511.515.02.271.321002610.514.22.641.87200247.510.03.182.55300128.39.53.523.05500229.810.24.11357.4.674.55Table 4 Survey results of the growth indexes for Populus euphratica at the right cross section in th. middlereaches of the Liudao River before and after water regulationDistance to theAge of PopulusGrowth degree of the thorax Growth degree of the thoraxWater level Water leveleuphratica (year)water regulation (mm) regulation (m) regulation (m)0149.612.32.831.54313.23.142.011810.411.33.312.89200.33.853.646:.98.4.534.3210008.56.55.365.28Table 5 Survey results of the growth indexes for Populus euphratica near the right cross section near Lu. .chicin the upper reaches of the East River both before and after water regulationAge of PopuhusGrowth degree of the thorax Growth degree of the tho- Water level Water leve! aftediameter for 5 years before rax diameter for 5 yearsbefore water water regulatiorwater regulation (mm) after water regulation (mm) regulation (m)14.316.11.281312.513.41.981.882113.72.542.4600309.03.153.1252.87.93.633.5815007.24.694.64Table 6 Survey results of the growth indexes for Populus euphratica at the left cross section near Saihantaolai inthe West River both before and after water rcgulationGrowth degree of the thorax Growth degree of the thorax Water levcl be- Water level afterdiameter for 5 years before diamter for 5 years after fore water regu- water regulationlation (m)13.216.92.1511.8中国煤化工199.MHCNMHG4.058.58.84.384.02586.6.34.99JIANG Xiaohui et al: The influence of water regulation on vegetation in the lower Heihe River707euphratica. According to the survey results, the year of 2000 is the turning point of the in-fluence on Populus euphratica's growth. The nearer Populus euphratica is to the water-course, the more rapid its growth. There is a clear correlation between the growth degree andthe water level. However, the influence of water regulation on Populus euphratic is not sig-nificant in the region which is more than 1000 m away from the watercourse.3.2 Influence of water regulation on Tamarix sp.According to the field survey, the transverse influence of water regulation on Tamarix sp. isalso evident in that past 5 years. This influence changes according to the distance from thearea where the Tamarix sp. develops to the river course. Tables 7 and 8 show the growthindexes of Tamarix sp. at the cross sections of the East River and Yidao River before andafter water regulation.As shown in the two tables, when compared with the data before water regulation, thegrowth degree of the thorax diameter of Tamarix sp. at the section of the East River is a littlelarger than that at the section of the Yidao River. Similarly, at the cross section, the differ-ence in the growth degree of the thorax diameter is quite small when the distance away fromthe watercourse is longer.Table 7 Survey results of the growth indexes for Tamarix sp. at the cross section of the East River before and afterwater regulationDistance 10 theAge of TamarixGrowth degree of the subaerial Growth degree of the subaerialCoverage Concomitantwatercoursediameter for 5 years before water diameter for 5 years after water(m)sp. (year)regulation (mm)vegetation001011.311.570Sophoraalopecuroides1710.812.15010.511.94001211.7!111.060010.1431000010.210.3Table 8 Survey results of the growth indexes for Tamarix sp. at the cross section of the Yidao River before andafter water regulationDistance to theGrowth degree of the subaerial Growth degree of the subac-diameter for 5 years beforerial diameter for 5 years afterConcomitant vegetationsp. (ear)water regulation (mm)12.5Populus euphratica100148.910.0Kareliniacaspia (Pall.) Less.2008.6中国煤化Iphratica300CNMHC aspia (Pall) Less.C JopecuroidesMH50019.67.98.1708Jourmal of Geographical Sciences4 Infuence of water regulation on vegetation near the East Juyan Lake :The vegetation had been seriously degraded in or around the East Juyan Lake since the lakewas drying up in 1992. And there were a few of sapless Phragmites communities in the lakeand lots of dead Tamarix sp. around the lake before water regulation in July 2002. After theflow entered East Juyan Lake for the first time in July 2002, the water had been regulated tothe East Juyan Lake 6 times in the following 3 years, and even the maximal water area wasnearly 40 km', being the most obvious affected region in vegetation change by water regula-tion. According to the field survey, vegetation in the lower reaches has changed evidently,when compared to the start of water regulation with that of before water regulation. All thesurvey results are shown in Tables 9 and 10.Table 9 Survey results of vegetation in and around the East Juyan Lake before water regulationSpecimen positionDominant vegetationCoverage (%)Concomitant vegetationOther featuresIn the lake (dry)Phragmites commumis1The average height is 6cmAround the lakeTamarix sp.13Nitraria sibirica65% bald dieTable 10 Survey results of vegetation around the East Juyan Lake after water regulationCoverageThe average(%)height (cm)SouthwestermWithin 100 m to lake bankKalidium foliatum (Pall)Moq. Tamarix sp.bank100 m away from lake bankSuaeda heteroptera KitagKalidium folianum (Pall)Kareliniacaspia (Pall) Less.Within 60 m to lake bankMoq.and so onSouthermPhragmites communisWithin 60- -120 m to lake bank Kalidium foliatum (Pall)Mog.120 m away from lake bank Tamarix sp.18 Nitraria sibirica2830 m from bank to center in the lakes4Kalidium folaum (Pall,)Within 60 m to the lake edgeSuaeda heteropteraSoutheastemKitogAlhagi sparsifolia60 m away frorm lake bank3:17Within 100 m to both sides of the water inlet Tamarix sp.56 Suaeda heteroptera Kitag86It can be concluded from Tables 9 and 10, before water regulation, the coverage of vege-tation was low with less plant varieties, the categories were few, and most of the vegetationwas sapless in or around the East Juyan Lake. However, after water was regulated for threesuccessive years, both the coverage and varieties of plant increased evidently, and all thevegetation grew well. The reasons are that after waten Pewing n snhRet _uyan Lake, boththe lateral and vertical infiltration caused the incre中国煤化工and groundwaterlevel around the lake. Accordingly, water demand:YHC N M H G vegetation wasmet, and consequently the vegetation was successively improved.JIANG Xiaohui et al: The influence of water regulation on vegetation in the lower Heihe River7095 Remote sensing analysis for the influence of water regulation on theecosystemAs an important measure in monitoring the changes of geo-environment, satellite remotesensing has played an increasingly important role in geo-environment monitoring. In orderto further analyze the influence of water regulation on the eco-environment of the oasis inthe lower Heihe River Basin, remote sensing is applied to analyze the area and coverage ofpasture, Populus euphratica, shrub together with the variation of coverage of vegetation indifferent regions of the lower reaches, as well of the area changes of Gobi desert and salin-ized land. before and after water regulation.According to the statistic analysis of remote sensing, it is found that there are greatchanges on the area and coverage of both the pasture and the shrub, as well as the area ofGobi Desert and salinity, when comparing the statistic data in 1998 with that in 2004 (Table11). The conclusions can be drawn as follows: (1) After water regulation, the growth of for-est and pasture in Dingxin irrigation area became worse because of the decrease of watersupply from the Heihe River. At the same time, the area of salinized land reduced due to thedecrease of groundwater level. (2) The growth of forest and pasture in Dongfengchangchanged lttle except for those along the river, because there was no more water supply toDongfengchang after water regulation. (3) The eco-environment in the East and West rivershas been greatly improved since water regulation in the Heihe River. For example, the areasof Populus euphratica, pasture and shrub increased; the growth condition of vegetation wasimproved; and the areas of Gobi and desert decreased when compared with those beforewater regulation. The oasis in the East and West rivers is the core region in the lower HeiheRiver, and improvement of the eco-environment in the oasis indicates that the continuousdeterioration of the eco-environment in the lower reaches has been controlled effectively. (4)The benefits are the most obvious in the lake area, especially around the East Juyan Lake.Not only the water surface and water body always remained larger throughout the year ofTable 11 Increment statistics of remote sensing data in the lower Heihe River between 1998 and 2004(unit: km2)ItcmDingxin area Dongfengchang area East-West rivers area Two lakes areaPasture area with larger coverage1.750.192.151.19Pasture area with middle coverage6.450.042.967.15Pasture area with smaller coverage3.34-0.11.717.29Shrub area with larger coverage-1.722.075.9Shrub area with middlc coverage-1.45- 6.05-0.39Shrub area with smaller coverage0.01- -11.6- 0.82Populus euphralica area0.056.35with larger coveragePopulus euphratica area- -0.06-0.82with middle coveragewith smaller coverage中国煤化工Other forest area0.8MHCNMHGGobi area-0.42-0.03-10.77-9.99Desert-5.53-0.03 ;-1.67-12.92Salinized land-1.030710Jourmal of Geographical Sciences2004, but also the ecosystem around this region has been improved greatly. For instance, thedead and drying up Phragmites communis and Achnatherum splendens for years began toflourish. In summary the oasis in the lower Heihe River, where the pasture, Populus eu-phratica and shrub grow, increased by 40.16 km', of which pasture was 8.16 km*, Populuseuphratica, 4.84 km^ and shrub 25.33 km*. All these indicate that the desertified area wasdecreasing，while the area of oasis was increasing after water regulation. The trend ofshrinkage of the oasis in the lower reaches has been held back after water regulation.6 ConclusionsBased on the above analysis, the conclusions are summarized as follows:(1) The trend of continuous decrease of groundwater level has been held back in EjinaOasis after water regulation in the lower Heihe River. Even the groundwater level went upagain in some sites. Especially, the groundwater level in the lower Heihe River has increasedto some extent since 2002. In 2004, the groundwater level was near or up to the historicalmaximum since 1995. Comparing the figure in 2004 with that in 2002, groundwater levelhave increased by 0.22 m both in the East and West rivers, by 0.79 m in Jirigelangtu, by 0.5m in Saihantaolai, and by 0.42 m in the whole Ejina Oasis.(2) The influence of water regulation on Populus euphratica and Tamarix sp. was obvious.The rate of growth became higher. According to the survey for the growth CONDITIONS ofPopulus euphratica and Tamarix sp. within the affected region before and after water regu-lation, it is found that the rates of growth of both Populus euphratica and Tamarix sp. be-came obviously higher than those before water regulation. Moreover, the nearer the distanceis to the watercourse, the better the growing conditions.(3) The trend of shrinkage in vegetation at the Ejina Oasis in the lower Heihe River hasbeen held back, and the biodiversity has increased as well. The area of Populus euphraticaaround the East and West rivers, or in the lower Heihe River increased from 366 km' beforewater regulation to 375 km2 after water regulation. The area of pasture and shrub increasedby 6.8 km2 and 5 km2 respectively, while the area of Gobi and sandy land decreased by 1.67km' and 10.77 km^ respectively. Especially, the eco-environment has changed most obvi-ously in the East Juyan Lake. Not only the water area of the lake always maintained a largersurface throughout the year of 2004, but also the eco-environment around the lake was im-proved dramatically. During the period 1998- -2004, the area of pasture and shrub increasedby 15.6 km2 and 14.5 km2 respectively, and the area of Gobi and sandy land decreased by9.99 km2 and 12.92 km2 respectively. The biodiversity has been increasing in the Juyan Lakebecause many wild animals rehabitated the region.(4) Some achievements have been obtained since water regulation in the lower HeiheRiver. The trend of continuous deterioration of the eco-environment has been held back inthe Ejina Oasis, however, as the restored vegetation is located near the river, so the vegeta-tion which is far from the river made little progres中国煤化工alocate waterresources in the lower Heihe River, and get moremited water re-TYHCNMHGsources.JIANG Xiaohui et al: The influence of water regulation on vegctation in the lower Heihe River711ReferencesCao Wenbing, Wan Li, Zhou Xun, et al, 2004. Effects of variation in water environment on ecosystem in thelower reaches of the Heihe watershed. Hydrogeology and Engineering Geology, (5): 21-25. (in Chinese)Feng Qi, Chenf Guodong, Tang Zhigang, 1998. Study on relationship of vegetation growth and groundwater levelin Ejina oasis. Journal of Desert Research, 18(1): 107-109. (in Chinese)Luo Geping, Zhou Chenghu, Chen Xi, 2003. Process of land use/land cover change in the oasis of arid region.Acta Geographica Sinica, 58(1): 63. -72. 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