Quantitative contributions of climate change and human activities to vegetation dynamics in the Zoige Plateau from 2001 to 2020

Climate change and human activities such as overgrazing and rapid development of tourism simultaneously affected the vegetation of the Zoige Plateau.However,the spatiotemporal variations of vegetation and the relative contributions of climate change and human activities to these vegetation dynamics remain unclear.Therefore,clarifying how and why the vegetation on the Zoige Plateau changed can provide a scientific basis for the sustainable development of the region.Here,we investigate NDVI trends using the Normalized Difference Vegetation Index(NDVI)as an indicator of vegetation greenness and distinguish the relative effects of climate changes and human activities on vegetation changes by utilizing residual trend analysis and the Geodetector.We find a tendency of vegetation greening from 2001 to 2020,with significant greening accounting for 21.44%of the entire region.However,browning area expanded rapidly after 2011.Warmer temperatures are the primary driver of vegetation changes in the Zoige Plateau.Climatic variations and human activities were responsible for 65.57%and 34.43%of vegetation greening,and 39.14%and 60.86%of vegetation browning,respectively,with browning concentrated along the Yellow,Black and White Rivers.Compared to 2001-2010,the inhibitory effect of human activity and climate fluctuations on vegetation grew dramatically between 2011 and 2020.

Methane emissions from natural and drained peatlands in the Zoigê, eastern Qinghai-Tibet Plateau

Peatlands are one of the major natural sources of methane （CH4）, but the level of CH4 efflux is uncertain, especially in alpine peatlands. In this study, CH4 emission fluxes from natural and drained peatlands on the Qinghai- Tibet Plateau, southwest China, were measured from June to October in 2013 using the opaque static chamber technique and the Fast Greenhouse Gas Analyzer （DLT-100, Los Gatos Research Corp.）. CH4 emission fluxes ranged from 2.07 to 56.33 mg m^-2 h^-1 in natural peatlands and from 0.02 to 0.42 mg m^-2 h^-1 in drained peatlands. Mean CH4 emission flux was 19.13 mg m^-2 h^-1 in natural peatlands and 0.14 mg m^-2 h^-1 in drained peatlands. These results showed that drainage led to a significant decrease in CH4 emissions. CH4 emission fluxes for all sampling plots were significantly correlated with variation in water table depth for linear （R^2 = 0.453, P 〈 0.01） and exponential functions （R^2 = 0.429, P 〈 0.01）.

Analysis of Dynamics and Driving Factors of Wetland Landscape in Zoige,Eastern Qinghai-Tibetan Plateau

Zoige Wetland is one of the largest plateau wetlands in the world. This paper provides a dynamic analysis of spatial and temporal patterns of the wetland in Zoige, Eastern Qinghai-Tibetan Plateau, supported by ERDAS8.7 and ArcGIS9.0. It is the first comparative analysis of a system of rapidly changing wetland with landscape patterns in Zoige, using 3 classified landsat Thematic Mapper images of 1977, 1994 and 2001. The classified images were used to generate wetland distributing maps, and shape index （S）, diversity index （H）, dominance index （D）, evenness index （E）, fragmentation index （F） and fractal dimension （Fd） were calculated and analyzed spatiotemporally across pure grazing area in Zoige for each landscape type and in different periods （before 1977, during 1977-1994 and 1994-2001）, as well as the driving forces of natural and anthropogenic. The study shows that for a comprehensive understanding of the shapes and trajectories of the shrinking and desertificated land expansion of the wetland, a spatiotemporal landscape metrics analysis in different periods is an improvement than only with landscape changing rates. This type of analysis can also be used to infer underlying social, economic, and political processes that drive the observed wetland forms. The results indicate that wetland patterns can be changed over relatively short periods of time. The total area of lake reduced by 164.86 km^2, grassland extended by 141.74 km^2, semi-marsh extended by 105.94 km^2, marsh reduced by 86.00 km^2 the number of landscape patches reduced by 56, and their average area decreased by 2.68 km^2, the successions within lake, marsh, semi-marsh and grassland were found obviously. S decreased stepwise： D and F increased but H decreased： The changing rate after 1994 was 2.3 to 2.9 times greater than that before. The change of the wetland landscape patterns resulted in the interaction between socio-ceenomic and natural forces of positive and negative aspects; and natural factors affected as assistant aspect. Some important human activities in this period led to the change of the landscape patterns in this region directly. Some measurements made by government and NGO delayed the converting process partly.

Driving forces of land use and land cover change (LUCC) in the Zoige Wetland, Qinghai-Tibetan Plateau

The Zoige Wetland is located in the northeastern Qinghai-Tibetan Plateau, which is highly sensitive to global environment change and human disturbance because of its high elevation and cold environment, thus, it＇s a hotspot for land use and land cover change （LUCC） research. We used Landsat MSS images from 1975, Landsat ETM images from 2000, and Landsat TM images fi：om 1990 and 2005 to assess the LUCC in the study area, using GIS techniques, as well as topographic, vegetation, and soil maps combined with field investigations. The monitoring result shows that the study area＇s environment degraded rapidly between 1975 and 2005, including wetland shrinkage from 5,308 km2 to 4,980 lan2, sandy land expansion from 112 krn2 to 137 krn2, forest land decreasing from 5,686 km2 to 5,443 km2, and grassland degradation from 12,309 km2 to 10,672 km2. According to the analysis of meteorological data and social-economic statistical data, we concluded that the LUCC in the Zoige Wetland was caused by both natural and anthropogenic factors, but human activities were primarily responsible for the observed LUCC, thereby, we suggest human behaviors must be adjusted to control environmental degradation.

Rangeland Privatization and Its Impacts on the Zoige Wetlands on the Eastern Tibetan Plateau

The high Zoige Basin （Ruoergai Plateau） on the eastern Tibetan Plateau is a fault depression formed during intensive uplifting of the Tibetan Plateau. The wetland is globally important in biodiversity and is composed of marshes, bogs, fens, wet meadows and shallow water interspersed with low hills and sub-alpine meadows. Most of the Zoige wetlands have long been one of the most important grazing lands in China. Recent rangeland policy has allowed grazing, and usable wetland areas have been being legally allocated to individuals or groups of households on a long-term lease basis. Privatizafion of the wetland has impacted the Zoige wetlands in aspects of hydrologic condition, landscape and biodiversity. The uneven spatial distribution of water resources onprivatelands has led to the practice of extracting ground water, which has decreased the perched water table in Zoige. Fencing off the rangelands and grazing on expanding sand dunes have affected landscapes. Variation in the water table has led to the changes in vegetation diversity, resulting in the changes in wildlife and aquatic diversities and ecosystem processes. Making use all year round of the pasture that was previously grazed only in summer has shrunk the daily activity space of wildlife, and the newly erected fences blocked the movement of wild animals looking for food in the snow to lower and open areas. To maintain the favorable conditions of the Zoige wetland ecosystem, the author suggests that, in addition to biophysical research and implementation of conservation practices, there is an immediate need to initiate an integrated management program, increase public awareness of wetland functions and provide better training for the local conservation staff.

The Response of Vegetation Biomass to Soil Properties along Degradation Gradients of Alpine Meadow at Zoige Plateau

Alpine grassland of the Tibetan Plateau has undergone severe degradation, even desertification. However, several questions remain to be answered, especially the response mechanisms of vegetation biomass to soil properties. In this study, an experiment on degradation gradients was conducted in an alpine meadow at the Zoige Plateau in 2017. Both vegetation characteristics and soil properties were observed during the peak season of plant growth. The classification and regression tree model(CART) and structural equation modelling(SEM) were applied to screen the main factors that govern the vegetation dynamics and explore the interaction of these screened factors. Both aboveground biomass(AGB) and belowground biomass(BGB) experienced a remarkable decrease along the degradation gradients. All soil properties experienced significant variations along the degradation gradients at the 0.05 significance level. Soil physical and chemical properties explained 54.78% of the variation in vegetation biomass along the degradation gradients. AGB was mainly influenced by soil water content(SWC), soil bulk density(SBD), soil organic carbon(SOC), soil total nitrogen(STN), and pH. Soil available nitrogen(SAN), SOC and p H, had significant influence on BGB. Most soil properties had positive effects on AGB and BGB, while SBD and p H had a slightly negative effect on AGB and BGB. The correlations of SWC with AGB and BGB were relatively less significant than those of other soil properties. Our results highlighted that the soil properties played important roles in regulating vegetation dynamics along the degradation gradients and that SWC is not the main factor limiting plant growth in the humid Zoige region. Our results can provide guidance for the restoration and improvement of degraded alpine grasslands on the Tibetan Plateau.

Landscape Pattern Evolution Processes of Alpine Wetlands and Their Driving Factors in the Zoige Plateau of China

Zoige Plateau wetlands are located in the northeastern corner of the Qinghai-Tibet Plateau.The landscape pattern evolution processes in the Zoige Plateau and their driving factors were identified by analyzing the dynamic changes in landscape modification and conversion and their dynamic rates of alpine wetlands over the past four decades.The results showed that the landscape conversion between wetlands and non-wetlands mainly occurred during the period from 1966 to 1986.The marsh wetland area converted from lake and river wetlands was larger because of swamping compared to other wetland landscapes.Meanwhile,the larger area of marsh wetlands was also converted to lake wetlands more than other types of wetlands.The modification processes mainly occurred among natural wetland landscapes in the first three periods.Obvious conversions were observed between wetland and nonwetland landscapes(i.e.,forestland,grassland,and other landscapes) in the Zoige Plateau.These natural wetland landscapes such as river,lake and marsh wetlands showed a net loss over the past four decades,whereas artificial wetland landscapes(i.e.,paddy field and reservoir and pond wetlands) showed a net decrease.The annual dynamic rate of the whole wetland landscape was 0.72%,in which the annual dynamic rate of river wetlands was the highest,followed by lake wetlands,while marsh wetlands had the lowest dynamic rate.The integrated landscape dynamic rate showed a decreasing trend in the first three periods.The changes in wetland landscape patterns were comprehensively controlled by natural factors and human activities,especially human activities play an important role in changing wetland landscape patterns.

A Method for Alpine Wetland Delineation and Features of Border: Zoigê Plateau, China

Accurate wetland delineation is the basis of wetland definition and mapping, and is of great importance for wetland management and research. The Zoige Plateau on the Qinghai-Tibet Plateau was used as a research site for research on alpine wetland delineation. Several studies have analyzed the spatiotemporal pattern and dynamics of these alpine wetlands, but none have addressed the issues of wetland boundaries. The objective of this work was to discriminate the upper boundaries of alpine wetlands by coupling ecological methods and satellite observations. The combination of Landsat 8 images and supervised classification was an effective method for rapid identification of alpine wetlands in the Zoig6 Plateau. Wet meadow was relatively stable compared with hydric soils and wetland hydrology and could be used as a primary indicator for discriminating the upper boundaries of alpine wetlands. A slope of less than 4.5° could be used as the threshold value for wetland delineation. The normalized difference vegetation index （NDVI） in 434 field sites showed that a threshold value of 0.3 could distinguish grasslands from emergent marsh and wet meadow in September. The median normalized difference water index （NDWI） of emergent marsh remained more stable than that of wet meadow and grasslands during the period from September until July of the following year. The index of mean density in wet meadow zones was higher than the emergent and upland zones. Over twice the number of species occurred in the wet meadow zone compared with the emergent zone, and close to the value of upland zone. Alpine wetlands in the three reserves in 2014 covered 1175.19 kin2 with a classification accuracy of 75.6%. The combination of ecological methods and remote sensing technology will play an important role in wetland delineation at medium and small scales. The correct differentiation between wet meadow and grasslands is the key to improving the accuracy of future wetland delineation.

Classification of plant functional types based on the nutrition traits： a case study on alpine meadow community in the Zoigê Plateau

The ecological concept of Plant Functional Types（PFTs）, which refers to the assemblage of plants with certain functional traits, has been introduced for the study of plant responses to the environment change and human disturbance. Taking the alpine meadow community in the Zoigê Plateau as a study case, this paper classified PFTs in terms of plant nutrition traits. The sequential results are as follows.（1） The main herbages in the Zoigê Plateau included 16 species in 5 families. Among the five families, Cyperaceae vegetation accounted for 81.37%of herbage area in total, while the remaining 4families occupied less than 20%. As for the species,Kobresia setchwanensis Hand.-Maizz. was dominant,accounting for 48.74% of the total area; while the remaining 51.26% was comprised of Polygonum viviparum L., Anaphalis fiavescens Hand.-Mazz.,Stipa aliena Keng and other species.（2） By using the Principal Component Analysis（PCA）, the assessment of herbages nutrition was carried out based on the comprehensive multi-index evaluation model.Polygonum viviparum L. had the highest nutritional value score（1.43）, and Stipa aliena Keng had the lowest（-1.40）. Nutritional value of herbage species had a significantly positive correlation with altitude（P＆lt;0.01） in the Zoigê Plateau.（3） Based on the nutritional values, herbages in the Zoigê Plateau could be grouped into 3 nutrition PFTs（high, medium and low） by using the Natural Breaks（Jenks） method.

Sensitivity analysis of the De Nitrification and De Composition model for simulating regional carbon budget at the wetlandgrassland area on the Zoige Plateau,China

Although mathematical models(e.g., De Nitrification and De Composition(DNDC) provide a powerful tool to study regional carbon budget, it is still difficult to obtain accurate simulation results because there exists large uncertainties in modeling regional carbon budget. Through the investigation on the sensitivity of model output parameters to the input parameters, sensitivity analysis(SA) has been proved to be able to identify the key sources of uncertainties and be helpful to reduce the model uncertainties. However, some input parameters with discrete values(e.g., land use type and soil type) and the regional effect of the sensitive parameters were rarely examined in SA. In this paper, taking the Zoige Plateau as a case area, we combined the one-factor-ata-time(OAT) with Extended Fourier Amplitude Sensitivity Test(EFAST) to conduct a SA of DNDC for simulating the regional carbon budget, including Gross Primary Productivity(GPP), Net Primary Productivity(NPP), Net Ecosystem Productivity(NEP), autotrophic respiration(Ra), soil microbial heterotrophic respiration(Rh) and ecosystem respiration(Re). The result showed that the combination of OAT and EFAST could test the contribution of the input parameters with discrete values to the output parameters. In DNDC model, land use type and soil type had a significant impact on the regional carbon budget of the Zoige Plateau, and daily temperature was also confirmed to be one of the most important parameters for carbon budget. For the other input parameters, with the change of land use type or soil type at regional scale, the sensitive parameters of carbon budget would vary accordingly. The SA results would provide scientific evidence to optimize DNDC model and they suggested that we should pay attention to the spatial/temporal effect of SA and try to use the appropriate data in simulation of the regional carbon budget.

Responses of soil inhabiting nitrogen-cycling microbial communities to wetland degradation on the Zoige Plateau,China

The wetlands on the Zoige Plateau have experienced serious degradation,with most of the original marsh being converted to marsh meadow or meadow.Based on the 3 wetland degradation stages,we determined the effects of wetland degradation on the structure and relative abundance of nitrogencycling(nitrogen-fixing,ammonia-oxidizing,and denitrifying) microbial communities in 3 soil types(intact wetland:marsh soil;early degrading wetland:marsh meadow soil;and degraded wetland:meadow soil) using 454-pyrosequencing.The structure and relative abundance of nitrogen-cycling microbial communities differed in the 3 soil types.Proteobacteria was the predominant phylum in most soil samples but the most abundant soil nitrogenfixing and denitrifying microbial bacteria differed at the class,order,family,and genus levels among the 3soil types.At the genus level,the majority of nitrogenfixing bacterium sequences related to Bradyrhizobium were from marsh and marsh meadow soils;whereas those related to Geobacter originated from meadow soil.The majority of ammonia-oxidizing bacterium sequences related to Nitrosospira were from marsh(except for the 40-60 cm layer),marsh meadow and meadow soils;whereas those related to Candidatus Solibacter originated from 40-60 cm layer of marsh soil.The majority of denitrifying bacterium sequences related to Candidatus Solibacter and Anaeromyxobacter were from marsh and meadow soils;whereas those related to Herbaspirillum originated from meadow soil.The distribution of operational taxonomic units(OTUs)and species were correlated with soil type based upon Venn and Principal Coordinates Analysis(PCoA).Changes in soil type,caused by different water regimes were the most important factors influencing compositional changes in the nitrogen-fixing,ammonia-oxidizing,and denitrifying microbial communities.

基于NSGA-Ⅱ算法的若尔盖高原高寒湿地生态修复格局优化

随着全球气候变暖和人类活动增强,高寒湿地面临着面积萎缩、动植物生境恶化、生态系统结构和功能退化等环境问题。以若尔盖高原高寒湿地为研究对象,基于生态系统稳态转化理论,使用湿地景观演变函数和第二代非支配排序遗传算法(non-dominated sorting genetic algorithmⅡ,NSGA-Ⅱ)分析1980—2015年7期湿地动态变化,计算多情景多目标函数值,选择适宜目标并基于社会经济生态可持续性发展、湿地生态系统稳态平衡原则,制订湿地修复优化策略。结果表明,可持续发展区、过度关注区与过度扰动区呈围绕发展,分别占湿地总面积的45.25%、17.27%与37.48%;基于NSGA-Ⅱ算法评价无偏好(等权最优)、经济效益最大化、生态效益最大化、空间紧凑度最大化、修复适宜性最大化5个目标下的湿地修复策略,无偏好策略函数值在经济效益、生态效益与湿地修复适宜性方面分别提升41.45%、9.18%和1.65%;基于社会经济可持续性发展的需求,构建保护优先、自然恢复、近自然恢复和适度修复4类若尔盖高原湿地生态修复空间优化格局。

近20年若尔盖高原陆地水储量变化分析

黄河上游若尔盖高原湿地区多年来存在湿地退化萎缩的趋势,维持若尔盖地区的陆地水储量对湿地区生态环境保护和经济发展有重要意义。为更好地分析近20年来的若尔盖高原地区陆地水储量时空分布和变化情况,运用GRACE重力卫星数据,进行降尺度处理后,结合统计方法,对若尔盖高原地区2003-2020年的陆地水储量时空分布及其与降水的关系进行讨论和分析。研究结果表明:研究时段内,若尔盖陆地水储量呈上升趋势,增长速率为1.37 cm/a,且有明显季节性变化特征;小波分析显示11 a为陆地水储量变化的第一主周期;空间分布上,水储量有从东部地区向西部地区逐渐降低的趋势。计算降水与水储量变化之间的相关性系数为年际尺度0.497和年内尺度0.402,两者为中等相关关系,降水是陆地水储量变化的主要驱动因子之一。

基于^(31)P核磁共振探究退化高寒湿地土壤磷素演变特征及影响因素

探明高寒湿地不同退化程度土壤磷素组成特征及其形态演变的驱动机制对于湿地生态恢复过程中养分和碳汇的科学管理具有重要意义。以若尔盖自然保护区内相对原生沼泽(RPM)、轻度退化沼泽(LDM)、中度退化沼泽(MDM)、重度退化沼泽(HDM)为对象,采用液相31P核磁共振波谱技术、分段式结构方程模型研究了高寒湿地退化过程中土壤磷素演变特征及主要影响因素。结果表明,高寒湿地退化导致植物群落组成由湿生向中生演替,土壤有机质与氮含量降低。正磷酸盐和磷酸单酯含量随湿地退化呈先增加后降低的趋势,其中正磷酸盐在HDM中相较于RPM降低46.45%,磷酸单酯在LDM、MDM和HDM中相较于RPM分别增加27.02%、54.96%和41.74%;焦磷酸盐和磷酸二酯含量随湿地退化逐渐降低。分段式结构方程模型的拟合结果显示,植被生物量、土壤养分和微生物活性是影响湿地土壤磷素演变的主要因素,其中微生物活性是正磷酸盐、焦磷酸盐和磷酸二酯的正向影响因子,是磷酸单酯的负向影响因子,植物生物量是正磷酸盐和磷酸二酯的正向影响因子,土壤养分虽对各形态磷没有直接影响,但可通过调控微生物活性间接影响焦磷酸盐和磷酸二酯含量。综上所述,湿地退化通过改变植物群落组成、降低土壤养分含量和微生物活性,促进了土壤磷酸二酯分解;重度退化湿地土壤磷有效性因磷酸单酯矿化能力减弱、正磷酸盐含量降低而减小。

若尔盖高原四川片区陆生脊椎动物多样性研究

利用2012—2021年在若尔盖高原四川片区的调查和访问数据,结合历史文献资料,对区域内陆生脊椎动物多样性及其保护价值进行了分析和评估,在此基础上提出了保护建议.结果表明:研究区域已知有陆生脊椎动物319种,包括兽类53种、鸟类254种、爬行类7种、两栖类5种;物种多样性G-F指数鸟类最高,兽类次之,爬行类和两栖类均为0;区系特征方面鸟类和兽类均以古北界种类为优势,东洋界物种也表现出一定的渗透性;鸟类居留型方面,候鸟和旅鸟较为丰富(56.69%),表明研究区域是候鸟迁徙的重要目的地和停歇补给点;食肉目动物(17种)和猛禽(26种)等顶级消费者种类丰富,反映出区域食物链完整性较好;保护价值方面,国家级和省级重点保护比例27.59%、濒危野生动植物种国际贸易公约(CITES)附录收录比例13.17%、特有物种比例10.03%,《中国生物多样性红色名录》受威胁比例21.94%,陆生脊椎动物多样性保护价值指数V_(A)和珍稀濒危野生动物多样性保护价值指数V_(AT)分别为60.32和57.24,与华北、东北内陆湿地自然保护区以及邻近的三江源国家公园黄河源园区相比都更高,表明研究区域具有极高的物种多样性保护价值.建议加强对区域内野生动物的调查、监测、巡护和保护宣传力度,建立健全野生动物救护机制,合理设置野生动物安全通道,同时立足区域优势,大力发展高原特色农牧业和生态文化旅游,从根本上缓解人类活动对野生动物的影响.

泥炭地水位下降改变酚类物质对温度的响应

酚类物质作为抑制剂,可直接或间接参与泥炭地碳循环。为了解泥炭地碳输出对全球气候变化的响应,以若尔盖高原的红原县日干乔国家湿地公园附近3处不同地下水位[-1.9 cm(S1)、-10 cm(S2)、-19 cm(S3)]泥炭地为研究对象,在5、15和25℃下进行恒温培养,研究不同地下水位泥炭地土壤酚类物质与温度的复合响应格局。结果表明:随着水位下降,总酚、水溶性酚和简单酚含量均显著增加(P<0.05)。增温使S1、S2、S3总酚含量变化不一,但其增温后与增温前的比值均接近1;增温使S1水溶性酚显著增加约172%(P<0.05),且温度越高增幅越大,使S2略微增加、S3略微减少;增温使不同水位泥炭地简单酚含量均显著增加约312%(P<0.05),其中不同水位泥炭地增幅为S1>S2>S3,不同温度增幅为15℃>25℃>5℃。本研究发现增温使泥炭地简单酚和水溶性酚增加,且地下水位越低增量越小,而增温对总酚无明显影响,说明温度主要通过改变简单酚和水溶性酚含量来影响泥炭地酚类物质组成,且泥炭地水位下降减弱了简单酚和水溶性酚对温度的响应。

土壤有机磷矿化特征对高寒草甸退化及温度的响应

明晰退化草地土壤有机磷在不同温度下的矿化特征,可为退化草地生态恢复中的土壤磷养分科学调控提供基础数据与理论依据。采用恒温控湿好气培养法研究若尔盖高原未退化草甸(ND)、轻度退化(LD)、中度退化(MD)、重度退化(HD)草甸土壤有机磷矿化特征及温度效应。结果表明,4类草甸土壤5~15℃培养下,有机磷矿化速率在前期(0~30 d)无明显变化,中期(30~60 d)快速增加,后期(60~120 d)逐渐趋于稳定。低温(5~10℃)时,草甸退化对土壤有机磷矿化无显著影响,但在高温(≥15℃)时,草甸自中度退化开始显著降低了土壤有机磷矿化作用。与ND相比,15℃时MD和HD土壤有机磷净矿化速率分别显著降低52.8%、56.8%,表征土壤有机磷矿化快慢常数的B0值分别显著降低29.5%、40.4%。土壤有机磷矿化的温度敏感性随草甸退化程度加剧而逐渐降低,ND土壤有机磷矿化的温度敏感系数y″值分别比MD、HD显著升高221.1%、306.7%。由此可见,高寒草甸退化减小了土壤有机磷的矿化作用和温度敏感性,进而降低了土壤磷素有效性,还可能因全球继续变暖而诱发退化草地生态系统的磷限制问题。

近40年来若尔盖高原高寒湿地景观格局变化

基于Apack软件,通过选取景观面积指数、景观多样性指数和景观破碎化指数等景观格局指数,从景观水平上研究了近40a来若尔盖高原高寒湿地景观空间分布格局特征的动态变化过程。结果表明:(1)高寒湿地景观空间格局以自然湿地景观为主要特征,自然湿地景观的斑块数和平均斑块面积均明显高于人工湿地景观。沼泽湿地景观斑块数最多,面积最大,所占比例高于95%;(2)高寒湿地景观具有高度的空间异质性。若尔盖县湿地景观的面积最大,占该区湿地景观总面积的近50%,湿地率也居五县之首;红原县和玛曲县次之;阿坝县和碌曲县最小;(3)高寒湿地景观面积呈先减少后增加的变化趋势。但与20世纪60年代相比,2000年湿地景观面积仍呈萎缩状态,总面积减少59857.83hm2;(4)近40a来,若尔盖高原湿地景观呈集中连片分布,聚集度均高于0.95;优势度水平较高,但多样性指数水平较低。湿地景观的斑块数呈先下降后持平的变化趋势,而平均斑块面积则表现为增加的变化趋势;湿地景观分布质心也发生了明显的空间位移,经历了先向西北方向偏移12.54km;再向东南方向偏移了11.33km;最后又向北偏移了1.1km。

若尔盖高原沼泽湿地CH_4排放研究

若尔盖高原沼泽湿地海拔3400m,面积4038km2,是我国面积最大的高原沼泽湿地分布区。2001年5～9月的非冰冻期,其主要沼泽类型木里苔草沼泽的CH4排放通量范围是0.51～8.20mg/(m2·h),平均值为2.87mg/(m2·h);乌拉苔草沼泽CH4排放通量范围是0.36～10.04mg/(m2·h),平均值为4.51mg/(m2·h)。在空间分布上,不同沼泽类型之间CH4排放通量具有一定的差异。在季节变化上,没有明显的排放高峰。根据代表性观测点的CH4平均排放量、日数和沼泽总面积推算,非冰冻期若尔盖高原沼泽湿地CH4的排放量为0.052Tg/a。

若尔盖高原土地利用变化对生态系统服务价值的影响

运用G IS和遥感技术分析了若尔盖高原1990年、2000年和2005年的土地利用/覆盖特征,在此基础上,使用生态价值系数(C)计算出该区生态系统服务价值,并使用敏感性指数(CS)对所选的C值进行验证。结果表明,该区域1990—2005年间,高覆盖度草地、湿地和林地面积呈持续减少趋势,建设用地、荒漠、中覆盖度草地和耕地面积及土地利用综合程度呈持续增加趋势;生态系统服务价值从603.10×108元减少到586.07×108元,共损失17.03×108元,且损失量和损失幅度呈加速增加趋势;该区域生态系统服务价值中,废物处理价值最高,水源涵养价值次之,食物生产价值最低,且各服务类型的价值均呈持续减小趋势;若尔盖高原1990和2005年人均生态系统服务价值分别为38.93万元和27.03万元,表明若尔盖高原由于人口增长和土地退化,环境压力呈明显增大趋势。湿地和草地退化是导致该区域生态系统服务价值减少的主要原因,尤其是湿地退化。CS检验说明本文所选C值较为合理。