Relocation of the M_S≥2.0 Earthquakes in the Northern Tianshan Region, Xinjiang, Using the Double-Difference Earthquake Relocation Algorithm

We applied the double-difference earthquake rdocation algorithm to 1348 earthquakes with Ms ≥2.0 that occurred in the northern Tianshan region, Xinjiang, from April 1988 to June 2003, using a total of 28701 P- and S-wave arrival times recorded by 32 seismic stations in Xinjiang. Aiming to obtain most of these Ms ≥ 2.0 earthquakes relocations, and considering the requirements of the DD method and the condition of data, we added the travel time data of another 437 earthquakes with 1.5 ≤ Ms 〈 2.0. Finally, we obtained the relocation results for 1253 earthquakes with Ms ≥2.0, which account for 93 % of all the 1348 earthquakes with Ms ≥ 2.0 and includes all the Ms ≥ 3.0 earthquakes. The reason for not relocating the 95 earthquakes with 2.0 ≤ Ms 〈 3.0 is analyzed in the paper. After relocation, the RMS residual decreased from 0.83s to 0.14s, the average error is 0.993 km in E-W direction, 1.10 km in N- S direction, and 1.33 km in vertical direction. The hypocenter depths are more convergent than before and distributed from 5 km to 35 kin, with 94% being from 5km to 35 kin, 68.2% from 10 km to 25 kin. The average hypocenter depth is 19 kin.

Analysis of the Wave Velocity Ratio Anomalies in the Tianshan Region of Xinjiang

Based on the seismic observation report data provided by the Xinjiang Digital Seismic Network from 2009 to 2014,we calculate the wave velocity ratio and its background value for medium and small earthquakes by using the multi-station method in Tianshan,Xinjiang.This paper analyzes the variation of the wave velocity ratio disturbance value to highlight the abnormal,and also back-traces 7 moderate earthquakes at the research area.The results show that:(1)the background value of the wave velocity ratio is almost 1.70,the wave velocity ratio obviously decreases in the middle-eastern part of Tianshan and the region near the Puchang fault;(2)the wave velocity ratio disturbance value is mostly low in the epicenter before four earthquakes of M≥5.0 from 2011 to 2013 in the study area;(3)before 7 moderate strong earthquakes,the earthquake events with low value of the wave velocity ratio account for over 60% of corresponding total events near the epicenters,and the low value of the wave velocity ratio is relatively obvious before moderate earthquakes.

Paleozoic Tectono-Metallogeny in the Tianshan-Altay Region,Central Asia

The research on Paleozoic tectonics and endogenic metallogeny in the Tianshan-Altay region of Central Asia is an important and significant project. The Altay region, as a collision zone of the Early Paleozoic （500-397 Ma）, and the Tianshan region, as a collision zone of the early period in the Late Paleozoic （Late Devonian-Early Carboniferous, 385-323 Ma）, are all the result of nearly N-S trending shortening and collision （according to recent magnetic orientation）. In the Late Devonian-Early Carboniferous period （385-323 Ma）, regional NW trending faults displayed features of dextral strike-slip motion in the Altay and Junggar regions. In the Tianshan region, nearly EW-trending regional faults are motions of the thrusts. However, in the Late Carboniferous-Early Permian period （323-260 Ma）, influenced by the long-distance effect induced from the Ural collision zone, those areas suffered weaker eastward compression, the existing NW trending faults converted into sinistral strike-slip in the Altay and Junggar regions, and the existing nearly E-W trending faults transferred into dextral strike-slip faults in the Tianshan region. The Rocks of those regions in the Late Carboniferous-Early Permian period （323-260 Ma） were moderately ruptured to a certain tension-shear, and thus formed a number of world famous giant endogenic metal ore deposits in the Tianshan-Altay region. As to the Central Asian continent, the most powerful collision period may not coincide with the most favorable endogenic metallogenic period. It should be treated to ＂the orogenic metallogeny hypothesis＂ with caution in that region.

Alpine vegetation responses to snow phenology in the Chinese Tianshan mountainous region

Investigating the interrelation between snow and vegetation is essential to explain the response of alpine ecosystems to climate change.Based on the MOD10 A1 daily cloud-free snow product and MOD13 A1 NDVI(normalized difference vegetation index)data,this study analysed the spatial and temporal patterns of snow phenology including snow onset date,snow end date,snow cover days,and vegetation phenology including the start of growing season,the end of growing season and the length of growing season in the Chinese Tianshan Mountainous Region(CTMR)from 2002 to 2018,and then investigated the snow phenological effects on the vegetation phenology among different ecogeographic zones and diverse vegetation types.The results indicated that snow onset date was earlier at higher elevations and later at lower elevations,while snow end date showed opposite spatial distribution characteristics.The end of growing season occurred later on the northwest slope of the CTMR and the Yili Valley.The earliest end of growing season was in the middle part of the CTMR.A long growing season was mainly distributed along the northern slope and the Yili Valley,while a short growing season was concentrated in the middle part of the CTMR.The response of vegetation phenology to changes in snow phenology varied among vegetation types and ecogeographic zones.The effect of snow phenology on vegetation phenology was more significant in IID5(Yili Valley)than in the other ecogeographic zones.A negative correlation was observed between the start of growing season and snow end date in nearly 54.78%of the study area,while a positive correlation was observed between the start of growing season and the snow end date in 66.85%of the study area.The sensitivity of vegetation phenology to changes in snow cover varied among different vegetation types.Snow onset date had the greatest effect on the start of growing season in the four vegetation cover types(alpine meadows,alpine steppes,shrubs,and alpine sparse vegetation),whereas the snow cover days had the least impact.Snow end date had the greatest impact on the end of growing season in the alpine steppes and shrub areas.The study results are helpful for understanding the vegetation dynamics under ongoing climate change,and can benefit vegetation management and pasture development in the CTMR.

Horizontal movement and strain characteristics in Tianshan and its adjacent region with GPS deformation data

Based on the multiple-term horizontal velocity solutions of 230 GPS monitoring sites in Tianshan and its adjacent region, the GPS site velocity fields and crustal horizontal strain fields in the area have been obtained. The results show that the crustal shortening rate of Tianshan, with the longitude （77°±1°）E as the boundary, gradually decreased towards two sides, from the south to the north, indicating that the pushing force of plate becomes weaker along with the fold deformation decreasing of the Tianshan. The direction of principal compressive strain of Tianshan and its adjacent area, nearly NNW, is basically perpendicular to the Tianshan cordillera trend, suggesting the distribution and variation of maximum principal compressive stress in Tianshan and its adjacent region resulted from collision and extrusion of Indian Plate. This paper indicates that the maximum shear strain field mainly con- centrates on two areas, one is Isyk lake of North Tianshan, Kyrgyzstan, and the other is the juncture of Jiashi （South Tianshan） and Pamir arc faults. In the above areas, it can be shown from the epicentral distribution that the strong earthquakes mostly occurs at the high shearing strain accumulation filed or its edge.

天山地区史前房屋墙壁的初步研究

天山沿线的史前房址数量丰富,结构各异。本文以这些房屋的墙壁作为研究对象,根据考古发现的堆积与遗迹遗物现象,结合民族学调查,将天山地区史前房址的墙壁分为直立墙体、毡墙、地坑壁三大类,直立墙体又分为单一结构和复合结构两类。文章详细讨论了各类墙壁的结构,复原了构筑过程。最后探讨了墙壁与房屋的建造方式、结构、规模、功能,以及与人类居住形态之间的联系。

Polyphase Tectonic Events and Cenozoic Basin-Range Coupling in the Tianshan Belt,Northwestern China

Studies show that the Tianshan orogenic belt was built in the late stage of the Paleozoic, as evidenced by the Permian red molasses and foreland basins, which are distributed in parallel with the Tianshan belt, indicating that an intense folding and uplifting event took place. During the Triassic, this orogenic belt was strongly eroded, and basins were further developed. Starting from the Jurassic, a within-plate regional extension occurred, forming a series of Jurassic-Paleogene extensional basins in the peneplaned Tianshan region. Since the Neogene, a collision event between the Indian and the Eurasian plates that took place on the southern side of the Tianshan belt has caused a strong intra-continental orogeny, which is characterized by thrusting and folding. Extremely thick coarse conglomerate and sandy conglomerate of the Xiyu Formation of Neogene System were accumulated unconformably on the Tianshan piedmont. Studies have revealed that the strong compression caused by the Indian-Eurasian collision had a profound influence over the orogenic belt in the hinterland, and MesozoiC-Cenozoic brittle deformed structures superposed on the ductile deformed Paleozoic rocks. The Mesozoic extensional basins were converted into Cenozoic compressional basins. The deformation in the basins is featured by step thrusts and fault-related folds. Statistics of joints show that the principal compressive stress since the Neogene is in a N-S direction. Meanwhile, owing to the underthrusting of the basin toward the orogenic belt, the Paleozoic strata were thrust on the Meso-Cenozoic rocks as tectonic slices, revealing distinct kinematic features in different geologic units. The basin-range coupling zones are characterized by intensive compression, folding and thrusting, accompanied by local sub-E-W-trending strike-slip faults. In the Tianshan region, Cenozoic thrusting is the most common basin-range coupling mode. The folding and faulting of Mesozoic sedimentary rocks, spontaneous combustion of Jurassic coal layers and formation of sintered rocks, the Cenozoic earthquakes and active faulting, and the unique mosaic pattern of basin-range framework of Xinjiang are all products of tectonism since the Neogene.

新疆东天山康古尔一带金矿地质特征及成矿机制

新疆康古尔一带的金矿床位于塔里木板块北缘的东天山秋格明塔什—黄山韧性剪切带南缘,是新疆的重要金成矿区。二叠纪早中期,在SN向推覆韧性剪切和右行走滑韧-脆性剪切基础上,地壳快速抬升在韧性变形构造上叠加脆性破裂,一系列张性断裂成为主要容矿构造;同构造期侵位的中酸性浅成斑岩体(如石英斑岩)提供了充足的成矿热源和部分水源及成矿物质来源;康古尔一带金矿矿化型式各不相同,既有产于构造破碎带中的蚀变岩型金矿、石英脉金矿,也有产于火山角砾岩筒中的脉状金矿,还有产于斑岩体边缘或产于岩体内部的斑岩型金矿;但成矿流体的物理化学特征均具中低温、低盐度、中低压力的特点;金矿的形成分为2个热液成矿阶段,其中晚期阶段是金的主要形成阶段。本文对该区金的成矿物理化学环境进行了讨论,并总结了成矿机制,认为康古尔一带金矿形成于统一的岩浆热液成矿系统,成矿作用与区域构造的脆性构造活动同步发生,金矿成矿时段大致在二叠纪晚期(263 Ma—243 Ma);下一步找矿工作应在有利的物化探异常中预测和寻找不同地质产状的中低温浅成热液型金矿。

新疆南天山乌宗布拉克铅锌矿床地质特征及矿床成因探讨

新疆南天山乌宗布拉克铅锌矿床地处艾尔宾山(残余海盆)成矿带的东段,经过多年来地质探矿,矿床规模在不断扩大,铅锌矿体产于中泥盆统萨阿尔明组大理岩与绢云千枚岩的岩性界面附近,其含矿性与地层层位、特定的岩性关系密切,成矿作用与石炭二叠纪岩浆岩关系密切,该铅锌矿体显示出明显的热液交代充填成矿作用的特征。本文从矿区地质特征入手,结合前人资料,对乌宗布拉克铅锌矿床成矿条件、矿石特征等进行研究,认为乌宗布拉克铅锌矿床为产于泥盆系碳酸盐岩地层中的中低温热液铅锌矿床,属于沉积热液改造型复成因矿床。

新疆塔乌尔别克金矿矿床地质及稳定同位素地球化学特征

新疆塔乌尔别克金矿位于西天山吐拉苏断陷盆地,与阿希金矿相邻。金矿体主要赋存于下石炭统大哈拉军山组第五岩性段的火山岩类中,受4个环形构造及伴生的线性构造控制。本文在阐述塔乌尔别克金矿床地质特征的基础上,论述了金矿石的碳、氢、氧、硫、铅等稳定同位素地球化学特征。认为成矿流体中的碳的主要为岩浆来源,但是较为复杂,部分受到深部碳酸盐岩同位素交换的影响;成矿流体中的水源来自岩浆热液和大气降水的混合;矿石中的硫来自于深部岩浆;铅则显示造山带的特征,主要来自上地壳。分析稳定同位素特征,结合矿床地质特征,塔乌尔别克金矿的矿床类型确定为低硫型浅成低温热液斑岩型金矿。矿床稳定同位素的研究不仅能深化矿床地质的研究,还可对进一步的找矿工作提供珍贵信息。

Tectonic Framework of Late Paleozoic Intrusions in Xingxingxia： Implications for Final Closure of South Tianshan Ocean in East Tianshan

This work carried out systematic geological field investigation, petrography observation, zircon geochronology and whole rock geochemistry on Late Paleozoic intrusions in the Xingxingxia region near the Xinjiang-Gansu provincial boundary, western China, aiming to constrain the Late Paleozoic tectonic framework of the Xingxingxia region and the final closure time of South Tianshan Ocean in the East Tianshan. The Xingxingxia area is located in the east part of the Tianshan orogen, and adjacent to the north of the Tarim Basin. The Late Paleozoic magma activities in the Xingxingxia region can be mainly divided into three stages. The first stage includes intrusive magma activities under a collision setting between Late Ordovician to the Late Devonian. The second stage is intrusive magma activities under a subduction setting during（304±3）–（278±3） Ma, and the third stage involves intrusive magma activities under a collision and post-collision setting during（268±5）–（259.9±2.6） Ma. The final suture zone of South Tianshan Ocean should be between the Central Tianshan Block and South Tianshan accretionary complex. Based on previous work, both the first stage magma activities（i.e., intrusive magmatic activities between the Late Ordovician to Late Devonian） and the Hongliuhe ophiolitic complex indicate a close event between Central Tianshan Block and South Tianshan Accretionary Complex. The 304±3 Ma dioritic metamorphic gneiss of the XingX ingxia complex and the 278±3 Ma diorite are all island arc calc-alkaline rocks, the 289±3 Ma gabbro is island arc tholeiitic gabbro formed by magma from metasomatic enrichment mantle. All these results indicate that the second stage of magmatic activities is under a subduction setting. The third stage magma activities i.e. the granitic magma activities of（268±5）–（259.9±2.6） Ma occurred at a transitional setting from compressional to post-collision extensional tectonic setting. Thus, around（268±5）–（260±3） Ma, the final closure of the South Tianshan Ocean occurred and the Tianshan orogen shifted into the intracontinental evolution stage. During and after the closure process, a wide range of metamorphism and large dextral strike-slip faults developed.

Projected change in precipitation forms in the Chinese Tianshan Mountains based on the Back Propagation Neural Network Model

In the context of global warming,precipitation forms are likely to transform from snowfall to rainfall with a more pronounced trend.The change in precipitation forms will inevitably affect the processes of regional runoff generation and confluence as well as the annual distribution of runoff.Most researchers used precipitation data from the CMIP5 model directly to study future precipitation trends without distinguishing between snowfall and rainfall.CMIP5 models have been proven to have better performance in simulating temperature but poorer performance in simulating precipitation.To overcome the above limitations,this paper used a Back Propagation Neural Network(BNN)to predict the rainfall-to-precipitation ratio(RPR)in months experiencing freezing-thawing transitions(FTTs).We utilized the meteorological(air pressure,air temperature,evaporation,relative humidity,wind speed,sunshine hours,surface temperature),topographic(altitude,slope,aspect)and geographic(longitude,latitude)data from 28 meteorological stations in the Chinese Tianshan Mountains region(CTMR)from 1961 to 2018 to calculate the RPR and constructed an index system of impact factors.Based on the BNN,decision-making trial and evaluation laboratory method(BP-DEMATEL),the key factors driving the transformation of the RPR in the CTMR were identified.We found that temperature was the only key factor affecting the transformation of the RPR in the BP-DEMATEL model.Considering the relationship between temperature and the RPR,the future temperature under different representative concentration pathways(RCPs)(RCP2.6/RCP4.5/RCP8.5)provided by 21 CMIP5 models and the meteorological factors from meteorological stations were input into the BNN model to acquire the future RPR from 2011 to 2100.The results showed that under the three scenarios,the RPR in the number of months experiencing FTTs during 2011-2100 will be higher than that in the historical period(1981-2010)in the CTMR.Furthermore,in terms of spatial variation,the RPR values on the south slope will be larger than those on the north slope under the three emission scenarios.Moreover,the RPR values exhibited different variation characteristics under different emission scenarios.Under the low-emission scenario(RCP2.6),as time passed,the RPR values changed slightly at more stations.Under the mediumemission scenario(RCP4.5),the RPR increased in the whole CTMR and stabilized on the north slope by the end of this century.Under the high-emission scenario(RCP8.5),the RPR values increased significantly through the 21 st century in the whole CTMR.This study may help to provide a scientific management basis for agricultural production and hydrology.

Spatial variability of glacial changes and their effects on water resources in the Chinese Tianshan Mountains during the last five decades

Changes in glaciers in the Chinese Tianshan Mountains have been analyzed previously. However, most previous studies focused on individual glaciers and/or decentralized glacial basins. Moreover, a majority of these studies were published only in Chinese, which limited their usefulness at the international level. With this in mind, the authors reviewed the previous studies to create an overview of glacial changes in the Chinese Tianshan Mountains over the last five decades and discussed the effects of glacial changes on water resources. In response to climate change, glaciers in the Tianshan Mountains are shrinking rapidly and are ca. 20% smaller on average in the past five decades. Overall, the area reduction of glacial basins in the central part of the Chinese Tianshan Mountains is larger than that in the eastern and western parts. The spatial differentiation in glacial changes are caused by both differences in regional climate and in glacial factors. The effects of glacial changes on water resources vary in different river basins due to the differences in glacier distribution, characteristics of glacial change and proportion of the glacier meltwater in river runoff.

基于矿质元素的赤霞珠葡萄酒产地溯源

为探讨基于矿质元素的赤霞珠葡萄酒产地溯源的可行性,分析新疆天山北麓产区与其他4个产区(宁夏、甘肃、河北、山东)赤霞珠葡萄酒中的23种矿质元素含量,结合多元统计方法,构建有效的葡萄酒产地溯源模型。结果表明:天山北麓与宁夏、甘肃、河北、山东产区葡萄酒中P、Mg、Sr、Ti、Al、Cu、Ba具有显著(p<0.05)或极显著差异(p<0.01),可以作为区分不同产区葡萄酒的特征性元素。以23种矿质元素为依据的Fisher判别分析,筛选出P、Sr、Al 3种对产地判别显著的元素,建立的判别函数对天山北麓和其他4个产区葡萄酒的初始验证和交叉验证整体正确判别率分别为96.43%和89.29%。基于矿质元素分析能够对赤霞珠葡萄酒进行产地溯源,区分新疆天山北麓与宁夏、甘肃、河北、山东产区的葡萄酒。

红柯小说中的西域景观和丝路精神

红柯是执着于书写西域景观的当代陕西作家,新疆十年的生活阅历成为他创作生涯中重要的写作素材,“天山——丝绸之路”系列小说正是他留给当代文坛的力作。从陕西关中平原到新疆天山脚下,地域空间的变换和文化语境的差异对红柯的创作产生了巨大的影响,尤其是丝绸之路的时空和文明体系成为他重要的创作背景和精神资源。红柯的独特之处就在于,以宏阔的视野向读者呈现出丝绸之路上的文化、史诗、神话传奇,彰显出浓郁的西域风情、质朴刚硬的气质和诗性的浪漫底蕴。红柯对丝绸之路的文学表达和其作品中蕴含的丝路精神,仍有可待研究的空间。

复杂造山带多尺度构造变形的观测方法——来自南天山库米什地区研究的启示

复杂造山带的构造解析需要精准识别并融合分析多类型构造要素。为了提高构造观测的精度和效率,本文引入高分辨率卫星遥感影像解译、无人机航拍超高分辨率影像解译,以及数据综合处理等观测技术,将其与常规露头实地观测相结合,提出了多方法相结合、多尺度相衔接的地质观测技术解决方案。在南天山库米什地区的构造观测中,精细刻画了大规模蛇绿混杂岩、大型断裂及韧性剪切带、酸性和中基性岩浆活动的空间分布,并且识别出较小规模的酸性及中基性岩脉、岩体内部节理等脆性变形等。研究认为,蛇绿岩之后发育多期次岩浆活动及多类型构造变形的叠加改造。研究验证了可推广的构造变形观测技术,也为继续深入研究天山造山带演化过程提供了新证据。

西天山地区一次冷锋暴雪微物理特征分析

基于二维视频雨滴谱仪联合毫米波云雷达、风廓线雷达、微波辐射计、GPS/MET水汽等垂直探测设备,对2020年2月18~19日西天山地区一次冷锋暴雪过程进行了微物理特征研究。本文设计了雪花及霰粒子分类算法,用于定量研究降雪微物理特征。结果表明:(1)冷锋入侵、动力强迫阶段,降雪粒子类型主要为雪花,微物理过程主要为凝华增长及聚并增长;(2)冷锋控制、大风降温阶段,降雪粒子类型主要为雪花、霰粒子,微物理过程主要是聚并增长及凇附过程,同时聚并增长有利于凇附过程的发生;(3)在冷锋过境阶段,由于云顶温度升高、大气冰核减少、充足的过冷水,有利于凇附过程的发生。不同于南京地区的降雪,西天山地区降雪,雪花直径及雪强偏小,但霰粒子对雪强有较大贡献。通过两种融化模型,拟合出相应的雨滴谱及其Gamma分布,发现与本地层状云降水的特征相似。

基于Ka波段云雷达观测的中国西天山降雨云宏微观物理特征研究

利用Ka毫米波云雷达与自动气象站降雨资料,研究了西天山地区2019年和2020年5~8月的降雨云宏微观特性。结果表明:(1)降雨主要发生在夜间,累积降雨量集中在21:00(北京时间,下同)至次日07:00,降雨频次和累积降雨量相关系数为0.71。大雨强频次虽最少,但对总累积降雨量贡献较显著。(2)小雨强、中雨强、大雨强平均反射率因子最大值分别为30 dBZ、35.8 dBZ和39.5 dBZ,最大平均液态水含量分别为1.5 g m^(-3)、4.2 g m^(-3)和7.3 g m^(-3)。(3)不同降雨强度对应的反射率因子都有两个集中区域,2.0~4.4 km反射率因子集中在15~26 dBZ,地面附近的小雨强、中雨强、大雨强对应的反射率因子分别集中在24~32 dBZ、29~38 dBZ和31~42 dBZ。1.75 km以下中雨强和大雨强液态含水量小于1gm^(-3)的频率明显少于小雨强,降雨强度的越大降雨粒子径向速度越集中。

2014年伊犁地区天山云杉分布区生态因子数据集

天山云杉(Picea schrenkiana var.tianschanica)是新疆山地涵养水源、防风固沙的重要树种,对新疆森林生态系统的形成和维护等方面具有举足轻重的作用。温度、降水量、土壤、地形等生态因子是研究森林生态系统的重要数据基础。本数据集以新疆伊犁地区的遥感影像、DEM、气象和土壤等多源数据为基础,采用多尺度分割、最近邻分类和空间分析等方法,生成了2014年伊犁地区天山云杉分布区生态因子数据集,包含温度、降水量、日照时间、坡度、坡向、土壤类型6种生态因子。本数据集采用TTA Mask精度验证等方法进行了严格的数据质量控制,确保了数据的准确性和可靠性,可为森林生态系统的健康评价提供数据支持。

天山-帕米尔地区生态安全格局时空演变及其影响因素

【目的】天山-帕米尔地区以其独特的地理位置和丰富多样的生态系统,在中国生态安全方面发挥着重要的屏障作用,但近30 a来区域经济和生态环境发生了很大变化,开展基于自然及人为压力状态下天山-帕米尔地区生态安全格局时空演变及其影响因素研究,为区域生态保护、生态建设以及协同发展提供科学依据。【方法】以天山-帕米尔地区作为研究区,运用压力-状态-响应(PSR)模型以及地理探测器方法,选取20个关键指标,对天山-帕米尔地区1990—2018年的生态安全及其影响因素进行分析。【结果】天山-帕米尔地区区域生态安全的分布格局并没有发生显著变化,但不同市(县)的生态安全等级差异较大;1990—2018年天山-帕米尔地区生态安全处于Ⅲ级及以上的面积占比始终在60%及以上,2010年达80%,区域生态环境改善显著;其中有5个因子对天山-帕米尔地区生态安全的影响较为稳定,其他各因子的影响各有差异;3个子系统影响从大到小依次为响应、压力、状态,状态指数和压力指数变化趋势相似。【结论】天山-帕米尔地区生态安全状况逐步向好,但也存在一些生态破坏的现象。其中博乐市、精河县、温泉县、塔什库尔干塔吉克自治县生态安全状态改善显著,响应能力的提高对缓解生态压力具有较大贡献。