Spatio-temporal evolution and topographic gradient effect of land use and ecosystem service value in the Lhasa River Basin

The Lhasa River Basin forms an essential human settlement area in the southern part of the Qinghai-Tibet Plateau.This study employed ecosystem service value(ESV)evaluation model,terrain gradient grading,and Geodetector to analyze land use and ESV in the Lhasa River Basin from 1985 to 2020.The findings reveal that:(1)From 1985 to 2020,grassland was the dominant land use.There was a trend of grassland reduction and the expansion of other land types.(2)ESV has increased over the research period(with a total increase of 0.84%),with higher values in the southeast and lower values in the northwest.Grassland contributed the most to ESV,and climate regulation and hydrological regulation were the ecosystem services that contribute the most to ESV.(3)Natural factors like NDVI and altitude,as well as economic factors like population density and distance from roads,influenced the spatial differentiation of ESV,the explanatory power of NDVI reached up to 0.47.The interaction between factors had a greater impact than individual factors.These research results can provide theoretical support for national spatial planning and ecological environment protection in the Lhasa River Basin and other similar areas.

Alpine wetlands in the Lhasa River Basin, China

The Lhasa River Basin is one of the typical distribution regions of alpine wetlands on the Tibetan Plateau. It is very important to get a better understanding of the background and characteristics of alpine wetland for monitoring, protection and utilization. Wetland construction and distribution in the basin were analyzed based on multi-source data including field investigation data, CBERS remote sensing data and other thematic data provided by 3S technology. The results are （1） the total area of wetlands is 209,322.26 hm^2, accounting for 6.37% of the total land area of the basin. The wetlands are mainly dominated by natural wetland, with artificial wetland occupying only 1.09% of the wetland area; marsh wetland is the principal part of natural wetland, dominated by Kobresia littledalei swampy meadow which is distributed in the river source area and upstream of Chali, Damshung and Medro Gongkar counties. The ratio and type of wetlands in different counties differ significantly, which are widely distributed in Chali and Damshung counties （accounting for 62% of the total wetland area）. （2） The concentrated vertical distribution of wetlands is at an elevation of 3600-5100 m The wetlands are widely distributed throughout the Yarlung Zangbo River Valley from river source to river mouth into the Yarlung Zangbo River. Marsh wetland is dominant in the source area and upstream of the river, with the mosaic distribution of lakes, Kobresia litUedalei and Carex moorcroftii swampy meadow, shrubby swamp and river; as for the middle-down streams, the primary types are river wetland and flooded wetland. The distribution is in a mosaic pattern of river, Kobresia humilis and Carex moorcroftii swampy meadow, Phragmites australis and subordinate grass marsh, flooded wetland and artificial wetland.

The trend on runoff variations in the Lhasa River Basin

Taking the Lhasa River Basin above Lhasa hydrological station in Tibetan Plateau as a study area, the characteristics of the annual and monthly mean runoff during 1956-2003 were analyzed, based on the hydro-data of the two hydrological stations （Lhasa and Tanggya） and the meteorological data of the three meteorological stations （Damxung, Lhasa and Tanggya）. The trends and the change points of runoff and climate from 1956 to 2003 were detected using the nonparametric Mann-Kendall test and Pettitt-Mann-Whitney change-point statistics. The correlations between runoff and climate change were analyzed using multiple linear regression. The major results could be summarized as follows： （1） The annual mean runoff during the last 50 years is characterized by a great fluctuation and a positive trend with two change points （around 1970 and the early 1980s）, after which the runoff tended to increase and was increasing intensively in the last 20 years. Besides, the monthly mean runoff with a positive trend is centralized in winter half-year （November to April） and some other months （May, July and September）. （2） The trends of the climate change in the study area are generally consistent with the trend of the runoff, but the leading climate factors which aroused the runoff variation are distinct. Precipitation is the dominant factor influencing the annual and monthly mean runoff in summer half year, while temperature is the primary factor in winter season.

Distribution and land use characteristics of alluvial fans in the Lhasa River Basin,Tibet

In Lhasa River Basin(LRB),land suitable for settlement or living is experiencing a shortage of resources.Alluvial fans have the potential to alleviate this problem.However,basic information,such as the distribution and land use types of alluvial fans,is rarely studied.In this study,Google Earth,ArcGIS and visual interpretation were used to obtain the outlines,areas,quantities and distribution of alluvial fans.Meanwhile,to show the utilisation potential of alluvial fans,we analysed the land use,their distance from the roads,places(town and village)and rivers.The results showed 826 alluvial fans exist in LRB,with a total area of 1166.03 km2.The number of alluvial fans with areas between 0.1 and 1 km2 is 517,accounting for 62.59%of the total number of alluvial fans.Grassland is the dominant land use type,accounting for 68.70%of the total area of alluvial fans.The cropland area accounted for 2.16%of alluvial fans and accounted for 18.98%of the total cropland area in LRB.Exactly 93.70%,53.63%and 61.86%of the total number of alluvial fans were located within 5 km from the tertiary road,village,and river,respectively.To sum up,our survey results showed that alluvial fans are important land resources in LRB and may have huge utilisation potential.

Machine learning-based identification for the main influencing factors of alluvial fan development in the Lhasa River Basin,Qinghai-Tibet Plateau

Alluvial fans are an important land resource in the Qinghai-Tibet Plateau with the expansion of human activities. However, the factors of alluvial fan development are poorly understood. According to our previous investigation and research, approximately 826 alluvial fans exist in the Lhasa River Basin(LRB). The main purpose of this work is to identify the main influencing factors by using machine learning. A development index(Di) of alluvial fan was created by combining its area, perimeter, height and gradient. The 72% of data, including Di, 11 types of environmental parameters of the matching catchment of alluvial fan and 10 commonly used machine learning algorithms were used to train and build models.The 18% of data were used to validate models. The remaining 10% of data were used to test the model accuracy. The feature importance of the model was used to illustrate the significance of the 11 types of environmental parameters to Di. The primary modelling results showed that the accuracy of the ensemble models, including Gradient Boost Decision Tree,Random Forest and XGBoost, are not less than 0.5(R^(2)). The accuracy of the Gradient Boost Decision Tree and XGBoost improved after grid research, and their R^(2) values are 0.782 and 0.870, respectively. The XGBoost was selected as the final model due to its optimal accuracy and generalisation ability at the sites closest to the LRB. Morphology parameters are the main factors in alluvial fan development, with a cumulative value of relative feature importance of 74.60% in XGBoost. The final model will have better accuracy and generalisation ability after adding training samples in other regions.

Determining Critical Support Discharge of a Riverhead and River Network Analysis： Case Studies of Lhasa River and Nyangqu River

A riverhead is the demarcation point of continuous water channel and seasonal channel, which is characterized by a criti- cal flow that can support a continuous water body. In this study, the critical support discharge （CSD） is defined as the critical steady flows required to form the origin of a stream. The CSD is used as the criterion to determine the beginning of the riverhead, which can be controlled by hydro-climate factors （e.g., annual precipitation, annual evaporation, or minimum stream flow in arid season）. The CSD has a close correlation with the critical support/source area （CSA） that largely affects the density of the river network and the division of sub-watersheds. In general, river density may vary with regional meteorological and hydrological conditions that have to be considered in the analysis. In this paper, a new model referring to the relationship of CSA and CSD is proposed, which is based on the physical mechanism for the origin of riverheads. The feasibility of the model was verified using two watersheds （Duilongqu Basin of the Lhasa River and Beishuiqu Basin of the Nyangqu River） in Tibet Autonomous Region to calculate the CSA and extract river networks. A series of CSAs based on different CSDs in derived equation were tested by comparing the extracted river networks with the reference network obtained from a digitized map of river network at large scales. Comparison results of river networks derived from digital elevation model with real ones indicate that the CSD （equal to criterion of flow quantity （Qc）） are 0.0028 m3/s in Duilongqu and 0.0085 m3/s in Beishuiqu. Results show that the Qc can vary with hydro-climate conditions. The Qc is high in humid region and low in arid region, and the optimal Qo of 0.0085 m3/s in Beishuiqu Basin （humid region） is higher than 0.0028 m3/s in Duilongqu Basin （semi-arid region）. The suggested method provides a new application approach that can be used to determine the Qo of a riverhead in complex geographical regions, which can also reflect the effect of hydro-climate change on rivers supply in different regions.

拉萨河流域土地利用与生态系统服务价值时空演变及驱动因素

土地利用变化对生态文明建设产生强烈影响,进而威胁经济社会与生态环境的可持续发展。基于高精度土地利用数据,分析了拉萨河流域2000—2020年土地利用和生态系统服务价值(Ecosystem Service Value,ESV)时空演变特征,并借助PLUS模型和地理探测器分别探索了土地利用变化和ESV空间分异的驱动因素。结果表明:(1)2000—2020年拉萨河流域土地利用以草地为主,占流域总面积的85.23%。土地利用呈草地缩减,其余地类扩张的趋势。其中,草地减少2.45%,建设用地、水域和林地分别扩张199.72%、44.64%和21.97%。(2)流域土地利用变化受海拔、年均地温、距湖泊和水库距离等因素影响,其中,海拔对耕地、林地、水域和建设用地扩张的贡献度分别高达0.18、0.11、0.28和0.13,坡度和年均地温对草地和未利用地变化的贡献度分别为0.14和0.15。(3)2000—2020年流域ESV总体增加1.14%(14.96×108元),草地和气候调节分别为ESV贡献最突出的土地利用类型和生态系统服务类型,两者的贡献率分别为87.13%和25.50%。(4)流域ESV具有显著空间分异性,受NDVI、海拔、年均风速和年均气温等因子影响。其中,NDVI的解释力高达0.46,任意两两因子的交互均会增强ESV的分异性。研究结果可为拉萨河流域及类似区域国土空间规划和生态文明建设提供科学参考。

基于VIC_glacier模型的拉萨河水文模拟及冰川径流研究

拉萨河作为青藏高原南部雅鲁藏布江最大的支流,冰川融水是其径流的重要组成部分。本文基于VIC模型和度日模型构建的VIC_glacier模型,模拟了1990—2010年拉萨河流域径流过程。结果表明:(1)与VIC模型相比,VIC_glacier模型在研究区的径流模拟效果更好,日径流模拟值与观测值的相关系数接近0.8,纳什效率系数在0.75以上;(2)从上游到下游,冰川融水对径流的贡献率分别为21.4%(旁多站)、17.7%(唐加站)、14.5%(拉萨站),呈逐渐减少趋势;(3)冰川径流和非冰川径流年内变化均呈现“单峰型”形态,且在8月份达到峰值;(4)1990—2010年间,年冰川径流量整体呈现上升趋势,与同期气温上升的变化规律一致;年冰川融水对径流的贡献率与年降水量呈反比关系。研究成果可为拉萨河流域的水资源管理提供参考。

基于生态系统服务的水电开发利益相关者分析

水电开发对流域生态系统服务有重要影响。生态系统服务的供给区、水电企业和周边的农牧民构成了流域水电开发的利益主体。准确识别这些利益相关者在流域水电开发中扮演的角色对于建立和执行生态补偿机制至关重要。已有研究大多对利益相关者进行定性划分,定量分析侧重在经济损益,未考虑生态系统服务对利益相关者的影响。以西藏自治区拉萨河流域为研究区,评估了与水电开发关系密切的产水服务、土壤保持服务和洪水缓解服务。通过社会网络分析方法,探讨了在水电开发背景下,生态系统服务的供给者和需求者内部的中心性与凝聚子群,揭示了不同利益相关者之间的网络结构和联系强度。结果表明:(1)墨竹工卡县、林周县和嘉黎县是生态系统服务的主要供给区,位于生态系统服务供给社会网络的中心,中心度分别为1.75、1.48和1.30。(2)直孔水电站和旁多水电站处于三项生态系统服务需求网络中心,中心度、中心势最高,分别为0.37和0.35、0.41和0.38。(3)甘曲村和宁布村位于农牧民对水电开发影响感知的社会网络中心,中心度分别为3.54和2.41。本研究通过将生态系统服务评价与社会网络分析方法结合,清楚地描绘了拉萨河流域水电开发中不同利益相关者的相互关系,为制定水电开发的生态补偿策略提供了科学依据。

考虑生态流量的梯级水库主从博弈优化调度研究

针对传统集中式多目标优化范式未充分考虑多利益相关主体博弈关系对水库调度决策的影响,导致难以保障河道生态流量的现实问题,设置了共同保障和单独保障两种生态流量保障情景,构建了发电服从防洪调度原则下的梯级水库主从博弈优化调度模型,并在拉萨河流域旁多直孔梯级水库开展了实例研究。结果表明:梯级水库在共同保障生态流量下综合效益最优,仅由直孔水库单独保障生态流量造成调度效益难以凸显,其中防洪效益降低4.35%,整体发电效益降低1.66%;效益降低的主要原因在于单库保障模式下枯水期旁多水库倾向于蓄水而减少下泄,导致直孔水库过度下降水位来保障生态流量。

拉萨河流域梯级电站水光互补调度对水文情势的影响分析

梯级电站水光互补调度能提高光伏消纳能力和系统总发电量,但也要求调整梯级电站的调度规则,进而会加剧梯级电站下游的水文情势改变。为定量评价水光互补调度对水文情势的影响,以系统总发电量和总保证出力最大为目标,构建了拉萨河流域梯级电站水光互补优化调度模型,提出了基于水光互补的梯级电站优化调度方案,分析评价了不同优化调度方案的水文情势改变度。结果表明:梯级电站的水光互补优化调度能有效提升电力系统的总发电量和总保证出力;水光互补后拉萨河水文情势的综合改变度略大于水光互补之前,处于轻度至中度改变的临界值附近。研究成果可为拉萨河的水光互补调度及流域综合管理提供科学方法和依据。

拉萨河流域湿地植物群落多样性对草地生态系统功能的影响

湿地植物群落多样性能够反映湿地生态系统的健康状况和生态功能。因此,研究湿地植物群落多样性对草地生态系统功能的影响,对于保护湿地植物资源、促进草地生态系统健康发展具有重要意义。本文通过对拉萨河流域湿地植物群落多样性进行剖析,分析不同植物群落结构对草地生态系统功能的影响,提出维护湿地植物群落多样性的措施,为保护拉萨河流域湿地植物资源、促进草地生态系统的健康发展提供科学依据。

拉萨河中下游流域典型湿地植物群落的数量分类与排序

为了更好的保护和修复拉萨河流域湿地生态系统,提升湿地的生态和社会价值。以拉萨河中下游流域5种典型湿地的植被群落为研究对象,共布置100个样方。运用群落类型划分方法、CCA排序和NMDS分析方法,探讨拉萨河中下流域5种典型湿地的植物群落数量分类及分布与环境梯度间的关系。结果表明:(1)拉萨河中下流域5种典型湿地的植物群落可划分为3种类型,即高山嵩草、蕨麻委陵菜草本群落为研究区的主要群落,沿线植被分布与环境梯度间的关系显著。(2)CCA二维排序图、NMDS分析将样地分为3个生态类型,间接验证了SPSS群落类型划分的结果。(3)研究区内地形复杂,小气候作用显著,考虑到环境因子数据的CCA排序效果好于仅采用植物样方数据的SPSS群落类型划分。因此,将CCA二维排序与SPSS聚类分析结合使用,能很好反映物种与环境因子间的生态关系。

拉萨河流域近50年来径流变化趋势分析

以拉萨水文站以上流域为研究区,基于拉萨水文站和唐加水文站的水文实测数据和当雄县等3个气象站的气候观测数据,统计分析了1956￣2003年研究区径流的年内、年际变化,利用Mann-Kendall趋势分析法和Pettitt变点检验法分析了拉萨河流域径流的变化特征,采用多元回归方法分析了气候因素(气温、降水)对径流变化的影响。结果表明:(1)研究时段内,径流年际变化波动较大,在1970年前后径流发生了较大的突变,呈现出明显的增加趋势,尤以近20年来的趋势最大;月均径流的年际变化中,有增加趋势的主要分布在冬半年(11～4月)和夏半年的个别月份(5、7、9月);(2)流域内气候变化趋势与径流变化趋势基本一致,但不同月/年均径流受不同气候因素影响,主要表现在年平均尺度上受降水影响较大,在月平均尺度上,夏半年径流增加趋势受降水增加影响较大,而冬半年径流变化则主要与气温有较显著相关性,其主要原因可能是全球变暖导致冰川融水增加。

土地覆被和气候变化对拉萨河流域径流量的影响

以拉萨水文站上游流域为研究对象,利用分布式水文模型SWAT对拉萨河流域水文过程进行模拟,分别用1995～2000和2003～2006年两个时间段的实测数据对模型进行校准和验证。结果显示月径流模拟相关系数和模拟效率系数分别为0.88和0.84。在此基础上通过建立情景模拟,探讨拉萨河流域气候波动和土地覆被变化对径流产流量的影响。结果表明:气候变化对年径流量影响显著,在各种模拟假设情景中最多可以使径流量增加89%。土地覆被变化相对于气候变化对径流量的年际影响较弱,但对径流量的季节变化影响显著。

西藏拉萨河流域巴嘎雪湿地水化学特征

以西藏拉萨河流域主要天然湿地之一的巴嘎雪湿地作为研究对象,对该湿地水体的p H值、水温、溶解氧(DO)、色度、浊度和15种金属元素的含量进行了分析检测.结果表明,巴嘎雪湿地水的p H、DO平均值分别为7.68、7.01mg/L;湿地水中15种金属元素含量均较低,汞、锡两种金属元素未能检出,其他13种金属元素的含量顺序为:Fe>Cr>V>Ni>Mn>As>Sb>Mo>Pb>Zn>Cu>Co>Cd,并均达到了国家《地表水环境质量标准》(GB3838-2002)Ⅰ类水质标准.通过比较湿地进水和出水水质的发现,巴嘎雪湿地对色度、浊度和部分金属元素的去除效果显著.对色度、浊度的去除率分别达到了51.73%、94.8%,对不同金属元素的去除效果不同,Cu、Pb、Zn、Mo、As、V的去除率分别为64.2%、36.9%、40.7%,28.2%、31.9%、67%.

拉萨河流域外来鱼类的分布、群落结构及其与环境的关系

为揭示当前拉萨河流域外来鱼类的现状及其主要影响因素,于2010、2012及2014年对该流域的鱼类群落结构及水体环境进行了调查。共捕获4目6科17属25种鱼类,包括13种外来鱼类和12种土著鱼类。在42个采样点中的19个发现了外来鱼类,包括12处的湿地、6处的河流及1处水库采样点。外来鱼类基本都分布在下游,除了鲫(Carassius auratus)分布到了上游,鲤(Cyprinus carpio)、鳙(Aristichthys nobilis)和泥鳅(Misgurnus anguillicaudatus)分布到了中游。分布最广、数量最多的土著鱼类是拉萨裸裂尻鱼(Schizopygopsis younghusbandi younghusbandi)、东方高原鳅(Triplophysa orientalis)和西藏高原鳅(Triplophysa tibetana),最常见的外来鱼类为泥鳅、鲫和麦穗鱼(Pseudorasbora parva)。典范对应分析表明,该流域的鱼类群落同时受局域和区域环境因素的作用,二者对鱼类群落变异的总解释量为33.9%。海拔、圆石的比例和沙的比例与鱼类群落结构的关系最为紧密。今后应当开展外来鱼类的监控和清除工作,减少人为活动对河流生态系统的干扰,以促进该地区外来鱼类的防控工作及土著鱼类的保护。

拉萨巴嘎雪湿地土壤重金属分布及生态风险评价

巴嘎雪湿地是西藏拉萨河流域的代表性湿地之一.文章为了解巴嘎雪湿地的重金属分布特征,在2018年10月采集了巴嘎雪湿地的表层土壤样品,对土壤中的Cu、Zn、Cr、Ni、Pb、Cd、As、Hg重金属的含量进行了检测.巴嘎雪湿地表层土壤的重金属污染评价采用的方法主要包括内梅罗综合污染指数法、地积累指数法和潜在生态风险指数法.结果表明,重金属Cu、Zn、Cr、Ni、As、Hg含量的平均值低于国家土壤环境质量标准(一级),但Pb、Cd的含量略偏高;Ni、As、Cr、Hg的平均含量低于拉萨市环境背景值,但Cu、Zn、Pb、Cd平均含量高于环境背景值.该研究区域的内梅罗综合污染指数平均值P_(N)=1.50,说明湿地整体处于轻度污染;按照国家土壤环境质量标准(二级)作为背景值,得到的P_(N)=0.64,属于安全水平.地积累指数平均值在-2.587到-0.744范围内,I_(geo)<0区域整体上无污染;潜在生态风险指数的平均值RI=72.779,属于低风险.各元素组合之间总体相关性不足,说明重金属累积方式具有多源性特点.巴嘎雪湿地整体生态环境优于国内大部分湿地,其表层土壤中Hg、Pb、Cd元素为强度变异,在部分位点中存在明显富集,受到人类活动影响,应加强关注.

拉萨河流域蒸发力估算:改进道尔顿模型

在地势变化剧烈、影响因素空间分布不均匀的高山深谷地区,蒸发力具有显著的空间差异性,造成了空间分布的困难.本文在分析拉萨河流域蒸发力与水汽压差、水-气温差、气温、风速等实测气象因子相关性的基础上,检验了基于水-气温差修正的道尔顿模型结构(全国通用公式)的适用性,提出了基于水-气温差和气温修正的道尔顿模型.残差分析和模型验证表明,新模型满足回归模型充分性假设,适用于拉萨河流域,从而为测站稀疏的拉萨河流域蒸发力的空间分布研究奠定了基础.

拉萨河流域不同土地利用方式下土壤动物的群落特征

对拉萨河流域下游6个不同土地利用方式下土壤动物的群落特征进行了研究.结果表明:由于土地利用方式的不同,土壤动物群落组成存在一定的差异.节跳虫科、辐螨亚目、革螨亚目和甲螨亚目在6个群落中均为优势类群或常见类群,这些类群不仅数量大,分布也较为均匀,是该地区的广布类群;稀有类群在各群落中分布各异.土壤动物垂直分布具明显的表聚性,个体数表聚性更为突出,2个草场土壤动物的个体数量主要聚集在表层,4个农田垂直分布递减的较为缓慢,这与生境中的食物来源有关.割草场和青稞田土壤动物群落的多样性较高;土地利用方式的不同,土壤动物群落的相似程度亦不同,其中小麦田与青稞田、割草场与放牧场生境最为相似.