Ecosystem changes revealed by land cover in the three-river headwaters region of Qinghai,China(1990–2015)

The Three-River Headwaters Region(TRHR) of Qinghai Province, in the Tibetan Plateau of China, is the main source of the Yangtze, Yellow, and Lancang rivers, and is very significant to the security of freshwater resources for China and southeastern Asia. It is a critical ecological region of China for its ecological functions, and has been changed or even degraded in recent decades owing to climate change and human pressure. To effectively protect and restore the degraded ecosystems, the Chinese government initiated a series of ecological conservation projects in TRHR. It is essential to quantitatively assess ecosystem changes and their relationship to driving factors for indepth understanding of long-term changes of ecosystems and effects of ecological restoration policies and offer practical insights for ecological restoration. Here, land cover data has been interpreted with the series data of Landsat during 1990–2015. The patterns of different ecosystems and their developing process have been derived from land cover change. The results show that ecosystem types in TRHR include forest, grassland, cropland,wetland, artificial surface and barren land, accounting for 4.51%, 70.80%, 0.15%, 9.47%, 0.16% and 14.90%,respectively. Barren land converted to wetland was the significant ecosystem change from 1990 to 2015. Increases in temperature and precipitation and implementation of ecological rehabilitation helped maintain relatively stable ecosystem patterns. It is necessary to continue ecological projects to improve and/or maintain the ecosystems in TRHR because there is still a risk of land degradation under increasing climate change and human activity.

Synthesis Analysis of Soil Erosion for Three-River Headwater Region Based on GIS

In this paper,based on the common soil erosion model,the Three-River Headwaters region was select for study object. GIS methods are applied to conduct Semi-quantitative assessment for different types of soil erosion,and some results are concluded. The water erosion occurs in High Mountain and extra-high mountain of Yushu,Nangqian,Banma and Jiuzhi County in the southeast and south of the Three-River Headwaters region. The degree of erosion is prone to topography,precipitation,river and human activity. The freeze-thaw erosion mainly distributes in the northwest of the Three-River Headwaters region. The area of middle and above middle erosion degree accounts for roughly 50%.

Changes in Grassland Ecosystem Service Values in the Three-River Headwaters Region,China

[Method] This study aimed to assess the changes in grassland ecosystem Service values in the Three-River Headwaters Region of China, the source of the Yangtze, Yellow （Huang He） and Lantsang （Mekong） rivers. [Method] Biophysical values of four services were monetized within the region, including water regulation, air quality regulation, climate regulation and soil conservation. [Result] The total ESVs were 884.97×10^8 Yuan, 1 302.06×10^8 Yuan and 1 299.49×10^8 Yuan in 2000, 2005 and 2008, respectively. The amount of value per unit area experienced a steep increase from 2000 to 2005（18.10×10^4 Yuan/km2）, and then remained almost unchanged from 2005 to 2008 （-0.31×10^4 Yuan/km2）. The ESV tended to decline from the southeastern to the northwestern. ESV in the eastern and central part increased faster than that in the south-central and western part of the TRHR from 2000 to 2008. It could be seen that the ecosystem condition of grassland in the TRHR improved signifi- cantly over the study period of 2000-2008. [Conelusion] The results provided good information to assess the effectiveness of current ecological protection measures in the TRHR and support regional sustainable management policies.

Grassland degradation in the ＂Three-River Headwaters＂ region, Qinghai Province

Supported by MSS images in the mid and late 1970s,TM images in the early 1990s and TM/ETM images in 2004,grassland degradation in the＂Three-River Headwaters＂region （TRH region）was interpreted through analysis on RS images in two time series,then the spatial and temporal characteristics of grassland degradation in the TRH region were analyzed since the 1970s.The results showed that grassland degradation in the TRH region was a continuous change process which had large affected area and long time scale,and rapidly strengthen phenomenon did not exist in the 1990s as a whole.Grassland degradation pattern in the TRH region took shape initially in the mid and late 1970s.Since the 1970s,this degradation process has taken place continuously,obviously characterizing different rules in different regions.In humid and semi-humid meadow region,grassland firstly fragmentized, then vegetation coverage decreased continuously,and finally＂black-soil-patch＂degraded grassland was formed.But in semi-arid and arid steppe region,the vegetation coverage decreased continuously,and finally desertification was formed.Because grassland degradation had obviously regional differences in the TRH region,it could be regionalized into 7 zones, and each zone had different characteristics in type,grade,scale and time process of grassland degradation.

Spatial patterns of ecosystem vulnerability changes during 2001–2011 in the three-river source region of the Qinghai-Tibetan Plateau, China

The three-river source region (TRSR, including Yangtze, Yellow and Lancang rivers), located in the Qinghai-Tibetan Plateau, China, is a typical alpine zone with apparent ecosystem vulnerability and sensitivity. In this paper, we introduced many interdisciplinary factors, such as landscape pattern indices (Shannon diversity index and Shannon evenness index) and extreme climate factors (number of extreme high temperature days, number of extreme low temperature days, and number of extreme precipitation days), to establish a new model for evaluating the spatial patterns of ecosystem vulnerability changes in the TRSR. The change intensity (CI) of ecosystem vulnerability was also analyzed. The results showed that the established evaluation model was effective and the ecosystem vulnerability in the whole study area was intensive. During the study period of 2001–2011, there was a slight degradation in the eco-environmental quality. The Yellow River source region had the best eco-environmental quality, while the Yangtze River source region had the worst one. In addition, the zones dominated by deserts were the most severely deteriorated areas and the eco-environmental quality of the zones occupied by evergreen coniferous forests showed a better change. Furthermore, the larger the change rates of the climate factors (accumulative temperature of ≥10°C and annual average precipitation) are, the more intensive the CI of ecosystem vulnerability is. This study would provide a scientific basis for the eco-environmental protection and restoration in the TRSR.

Assessing the effects of vegetation and precipitation on soil erosion in the Three-River Headwaters Region of the Qinghai-Tibet Plateau,China

Soil erosion in the Three-River Headwaters Region(TRHR)of the Qinghai-Tibet Plateau in China has a significant impact on local economic development and ecological environment.Vegetation and precipitation are considered to be the main factors for the variation in soil erosion.However,it is a big challenge to analyze the impacts of precipitation and vegetation respectively as well as their combined effects on soil erosion from the pixel scale.To assess the influences of vegetation and precipitation on the variation of soil erosion from 2005 to 2015,we employed the Revised Universal Soil Loss Equation(RUSLE)model to evaluate soil erosion in the TRHR,and then developed a method using the Logarithmic Mean Divisia Index model(LMDI)which can exponentially decompose the influencing factors,to calculate the contribution values of the vegetation cover factor(C factor)and the rainfall erosivity factor(R factor)to the variation of soil erosion from the pixel scale.In general,soil erosion in the TRHR was alleviated from 2005 to 2015,of which about 54.95%of the area where soil erosion decreased was caused by the combined effects of the C factor and the R factor,and 41.31%was caused by the change in the R factor.There were relatively few areas with increased soil erosion modulus,of which 64.10%of the area where soil erosion increased was caused by the change in the C factor,and 23.88%was caused by the combined effects of the C factor and the R factor.Therefore,the combined effects of the C factor and the R factor were regarded as the main driving force for the decrease of soil erosion,while the C factor was the dominant factor for the increase of soil erosion.The area with decreased soil erosion caused by the C factor(12.10×10^3 km^2)was larger than the area with increased soil erosion caused by the C factor(8.30×10^3 km^2),which indicated that vegetation had a positive effect on soil erosion.This study generally put forward a new method for quantitative assessment of the impacts of the influencing factors on soil erosion,and also provided a scientific basis for the regional control of soil erosion.

Aboveground biomass of the alpine shrub ecosystems in Three-River Source Region of the Tibetan Plateau

Though aboveground biomass(AGB) has an important contribution to the global carbon cycle,the information about storage and climatic effects of AGB is scare in Three-River Source Region(TRSR)shrub ecosystems. This study investigated AGB storage and its climatic controls in the TRSR alpine shrub ecosystems using data collected from 23 sites on the Tibetan Plateau from 2011 to 2013. We estimated the AGB storage(both shrub layer biomass and grass layer biomass) in the alpine shrubs as 37.49 Tg, with an average density of 1447.31 g m^(-2). Biomass was primarily accumulated in the shrub layer, which accounted for 92% of AGB, while the grass layer accounted for only 8%. AGB significantly increased with the mean annual temperature(P < 0.05). The effects of the mean annual precipitation on AGB were not significant. These results suggest that temperature,rather than precipitation, has significantly effects on of aboveground vegetation growth in the TRSR alpine shrub ecosystems. The actual and potential increase in AGB density was different due to global warming varies among different regions of the TRSR. We conclude that long-term monitoring of dynamic changes is necessary to improve the accuracy estimations of potential AGB carbon sequestration across the TRSR alpine shrub ecosystems.

Changing Spring Phenology Dates in the Three-Rivers Headwater Region of the Tibetan Plateau during 1960–2013

The variation of the vegetation growing season in the Three-Rivers Headwater Region of the Tibetan Plateau has recently become a controversial topic. One issue is that the estimated local trend in the start of the vegetation growing season(SOS)based on remote sensing data is easily affected by outliers because this data series is short. In this study, we determine that the spring minimum temperature is the most influential factor for SOS. The significant negative linear relationship between the two variables in the region is evaluated using Moderate Resolution Imaging Spectroradiometer–Normalized Difference Vegetation Index data for 2000–13. We then reconstruct the SOS time series based on the temperature data for 1960–2013.The regional mean SOS shows an advancing trend of 1.42 d(10 yr)during 1960–2013, with the SOS occurring on the 160th and 151st days in 1960 and 2013, respectively. The advancing trend enhances to 6.04 d(10 yr)during the past 14 years. The spatiotemporal variations of the reconstructed SOS data are similar to those deduced from remote sensing data during the past 14 years. The latter exhibit an even larger regional mean trend of SOS [7.98 d(10 yr)] during 2000–13. The Arctic Oscillation is found to have significantly influenced the changing SOS, especially for the eastern part of the region,during 2000–13.

Quantifying impacts of climate and human activities on the grassland in the Three-River Headwater Region after two phases of Ecological Project

The Three-River Headwater Region(TRHR)of China is a typical representative of the alpine environment in the Central Asian plateau and the alpine grassland in the world.Grassland degradation is one of its serious eco-logical problems.The purpose of this study is to quantify the joint impacts of climate and human activities on grassland changes in TRHR after two phases of Ecological Conservation and Construction Project(Ecological Project).Grassland vegetation coverage is selected as an indicator for analyzing grassland changes.We adopt Sen+Mann-Kendall trend analysis,residual trend analysis and correlation analysis methods to analyze the trends in spatial-temporal changes and driving factors of grassland in TRHR from 2000 to 2019.The results show that:(1)The grassland has been mainly restored,and the degraded grassland area only accounts for 1.66%of TRHR.After the implementation of the first phase of the Ecological Project,the percentage of restored grassland area has significantly increased from 8.82%to 24.57%,and slightly decreased during the second phase.(2)The establish-ment of national nature reserves and the implementation of the Ecological Project have changed the situation that“the grassland inside the reserve is worse than that outside the reserve”.(3)Grassland restoration is mainly af-fected by the joint effects of climate and human activities.Nevertheless,grassland degradation is mainly affected by human activities such as overgrazing and grassland reclamation.All of these findings can enrich our under-standing of grassland restoration in TRHR.Artificial measures have certain limitations in promoting grassland restoration.Natural restoration should be considered when human beings strengthen ecological conservation and transform their production and life styles.

Spatial and temporal change patterns of freeze-thaw erosion in the three-river source region under the stress of climate warming

The three-river source region(TRSR), located in the Qinghai-Tibet Plateau in China, suffers from serious freeze-thaw(FT) erosion in China. Considering the unique eco-environment and the driving factors of the FT process in the TRSR, we introduce the driving force factors of FT erosion(rainfall erosivity and wind field intensity during FT period) and precipitation during the FT period(indicating the phase-changed water content). The objective was to establish an improved evaluation method of FT erosion in the TRSR. The method has good applicability in the study region with an overall precision of 92%. The spatial and temporal changes of FT erosion from 2000 to 2015 are analyzed. Results show that FT erosion is widely distributed in the TRSR, with slight and mild erosion being the most widely distributed, followed by moderate erosion. Among the three sub-regions, the source region of the Yellow River has the slightest erosion intensity, whereas the erosion intensity of the source region of Yangtze River is the most severe. A slight improvement can be observed in the condition of FTerosion over the whole study region from 2000 to 2015. Vegetation coverage is the dominant factor affecting the intensity of FT erosion in the zones with sparse vegetation or bare land, whereas the climate factors play an important role in high vegetation coverage area. Slopes>28° also have a significant effect on the intensity of FT erosion in the zones. The results can provide a scientific basis for the prevention and management of the soil FT erosion in the TRSR.

Climate Change and Ecological Projects Jointly Promote Vegetation Restoration in Three-River Source Region of China

As the source of the Yellow River,Yangtze River,and Lancang River,the Three-River Source Region(TRSR)in China is very important to China’s ecological security.In recent decades,TRSR’s ecosystem has degraded because of climate change and human disturbances.Therefore,a range of ecological projects were initiated by Chinese government around 2000 to curb further degradation.Current research shows that the vegetation of the TRSR has been initially restored over the past two decades,but the respective contribution of ecological projects and climate change in vegetation restoration has not been clarified.Here,we used the Moderate Resolution Imaging Spectroradiometer(MODIS)Enhanced Vegetation Index(EVI)to assess the spatial-temporal variations in vegetation and explore the impact of climate and human actions on vegetation in TRSR during 2001–2018.The results showed that about 26.02%of the TRSR had a significant increase in EVI over the 18 yr,with an increasing rate of 0.010/10 yr(P<0.05),and EVI significantly decreased in only 3.23%of the TRSR.Residual trend analysis indicated vegetation restoration was jointly promoted by climate and human actions,and the promotion of human actions was greater compared with that of climate,with relative contributions of 59.07%and40.93%,respectively.However,the degradation of vegetation was mainly caused by human actions,with a relative contribution of71.19%.Partial correlation analysis showed that vegetation was greatly affected by temperature(r=0.62,P<0.05)due to the relatively sufficient moisture but lower temperature in TRSR.Furthermore,the establishment of nature reserves and the implementation of the Ecological Protection and Restoration Program(EPRP)improved vegetation,and the first stage EPRP had a better effect on vegetation restoration than the second stage.Our findings identify the driving factors of vegetation change and lay the foundation for subsequent effective management.

A method for determining vegetation growth process using remote sensing data: A case study in the Three-River Headwaters Region, China

Accurate measurements of the associated vegetation phenological dynamics are crucial for understanding the relationship between climate change and terrestrial ecosystems. However, at present, most vegetation phenological calculations are based on a single algorithm or method. Because of the spatial, temporal, and ecological complexity of the vegetation growth processes, a single algorithm or method for monitoring all these processes has been indicated to be elusive. Therefore, in this study, from the perspective of plant growth characteristics, we established a method to remotely determine the start of the growth season(SOG) and the end of the growth season(EOG), in which the maximum relative change rate of the normalized difference vegetation index(NDVI) corresponds to the SOG, and the next minimum absolute change rate of the NDVI corresponds to the EOG. Taking the Three-River Headwaters Region in 2000–2013 as an example, we ascertained the spatiotemporal and vertical characteristics of its vegetation phenological changes. Then, in contrast to the actual air temperature data, observed data and other related studies, we found that the SOG and EOG calculated by the proposed method is closer to the time corresponding to the air temperature, and the trends of the SOG and EOG calculated by the proposed method are in good agreement with other relevant studies. Meantime, the error of the SOG between the calculated and observed in this study is smaller than that in other studies.

Review of the Three-River Project

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Three-River Project Proceeds Smoothly

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Decadal expansion and contraction of permafrost in the Three-River Source Region,Qinghaie-Tibet Plateau(1901-2020)

Permafrost and its spatiotemporal variation considerably influence the surface and sub-surface hydrological processes,biogeochemical cycles,fauna and flora growth and cold region engineering projects in the Three-River Source Region(TRSR),Qinghai–Tibet Plateau.However,the dynamics of permafrost over a relatively long term duration(e.g.>100 years)in the TRSR is not well quantified.Thus,the spatial and temporal variations of the temperature at the top of the perennially frozen/unfrozen ground(TTOP),active layer thickness(ALT)in permafrost regions and the maximum depth of frost penetration(MDFP)in the seasonally frozen ground of the TRSR during 1901–2020 were simulated using the TTOP model and Stefan equation driven by the widely used reanalysis Climatic Research Unit 4.05 dataset.Results revealed that the permafrost in the TRSR over the past 120 years did not degrade monotonically but experienced considerable fluctuations in area with the decadal oscillations of climate warming and cooling:shrinking from 263.9×10^(3)km^(2)in the 1900s to 233.3×10^(3)km^(2)in the 1930s,expanding from 232.3×10^(3)km^(2)in the 1940s to 260.9×10^(3)km^(2)in the 1970s and shrinking again from 254.1×10^(3)km^(2)in the 1980s to 228.9×10^(3)km^(2)in the 2010s.The regional average TTOP increased from−1.34±2.74℃in the 1910s to−0.48±2.69℃in the 2010s,demonstrating the most noticeable change for the extremely stable permafrost(TTOP<−5℃)from 8%to 1%.The regional average ALT increased from 2.68±0.52 m to 2.87±0.46 m,with the area proportion of ALT>3.0 m by 12%from 1901 to 2020.Notably,minor changes were observed for the regional average MDFP,probably due to the increase in the area proportion of MDFP<3.0 m(caused by climate warming)and MDFP>3.5 m(owing to the transformation of permafrost to seasonally frozen ground)by 7.39%and 4.77%,respectively.These findings can facilitate an in-depth understanding of permafrost dynamics and thus provide a scientific reference for eco-environment protection and sustainable development under climate change in the TRSR.

Increased southerly and easterly water vapor transport contributed to the dry-to-wet transition of summer precipitation over the Three-River Headwaters in the Tibetan Plateau

The Three-River Headwaters(TRH)region in the Tibetan Plateau is vulnerable to climate change;changes in summer(June–August)precipitation have a significant impact on water security and sustainability in both local and downstream areas.However,the changes in summer precipitation of different intensities over the TRH region,along with their influencing factors,remain unclear.In this study,we used observational and ERA5 reanalysis data and employed a precipitation categorization and water vapor budget analysis to quantify the categorized precipitation variations and investigate their possible linkages with the water vapor budget.Our results showed an increasing trend in summer precipitation at a rate of 0.9 per year(p<0.1)during 1979–2020,with a significant dry-to-wet transition in 2002.The category‘very heavy precipitation’(10 mm d−1)contributed 65.1%of the increased summer precipitation,which occurred frequently in the northern TRH region.The dry-to-wet transition was caused by the effects of varied atmospheric circulations in each subregion.Southwesterly water vapor transport through the southern boundary was responsible for the increased net water vapor flux in the western TRH region(158.2%),while southeasterly water vapor transport through the eastern boundary was responsible for the increased net water vapor flux in the central TRH(155.2%)and eastern TRH(229.2%)regions.Therefore,we inferred that the dry-to-wet transition of summer precipitation and the increased‘very heavy precipitation’over the TRH was caused by increased easterly and southerly water vapor transport.

三江源区生物质资源沼气化利用潜力评价

分析和评价三江源区生物质能资源潜力,是建设庭院生态经济模式的基础。通过构建模型的方法,对三江源区的养殖业生产和牧区居民生活过程产生的畜禽粪便和人粪尿等生物质能源潜力进行了估算,分析结果表明,仅2011年,江河源区产生的牲畜粪便总量为5 819.31万t,人的粪便总量为135.92万t,合计5 955.23万t,如果进行沼气化利用,可产生沼气11.23-18.84亿m3,相当于7.97-13.38亿kg的标准煤,对三江源生态移民点和灾后恢复重建点发展能源型庭院生态经济模式具有重要作用。

青海省“三江源”地区植被退化原因及其保护策略

对治多县32年的降水和气温变化资料的分析表明,自20世纪90年代以来,由于出现了较明显的增温减水现象,大气干旱加重,空气中相对湿度呈明显的波动减少趋势,因而造成了该地区的气候干旱化,不利于该地区草地生态系统生产力的提高和维持。同时,由于人口和家畜数量的增加,每个羊单位占有可利用草地从1953年的2.3hm2降低到1994年的1.1hm2,使牧压成倍增加。与60年代相比,平均产草量降低了50%以上,而有毒有害类杂草增加了20%～30%。到目前为止,约有1/3以上的草地处于不同程度的退化状态,约有1万hm2的天然草地已经荒漠化或沙化,主要分布在水边、河岸附近、滩地、坡麓和居民点周围即冬季牧场,是局部的退化;但夏季牧场牧压较小,牧草利用率较低,因而保持相对良好状态。由此可见,草地退化的主要原因是超载过牧。但气候的干旱化给过牧对草地的影响起到了推波助澜的作用,其叠加效应加速了草地的退化沙化。同时,由于气候的干旱化可能导致高寒草甸面积的缩小,使高寒草原及荒漠草原的面积有扩大的趋势,从而导致该地区草地总生产力的下降。

适应、整合、创新与发展:三江源自然保护区生态移民研究的分析和思考

自2005年以来,随着三江源生态保护和建设工程正式启动,国内学界对三江源生态移民问题进行了深入的研究,取得了丰硕的研究成果,同时也存在着许多不足和空白,而随着社会的不断发展,三江源生态移民也面临着诸多的新形势、新情况和新问题。如何适应新的现实需求,发挥多学科优势,整合不同研究资源,创新研究思路与方法,拓展研究视野和领域,不断克服以往研究中存在的不足和缺陷,对三江源生态移民社会的健康可持续发展具有重大意义。