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941.
The forest litter is an essential reservoir of nutrients in forests, supplying a large part of absorbable base cations(BC) to topsoil, and facilitating plant growth within litter-soil system. To characterize elevational patterns of base cation concentrations in the forest litter and topsoil, and explore the effects of climate and tree species, we measured microclimate and collected the forest litter and topsoil(0-10 cm) samples across an elevational range of more than 2000 m(1243 ~ 3316 m a.s.l.),and analyzed the concentrations of BC in laboratory. Results showed that: 1) litter Ca concentration displayed a hump-shaped pattern along the elevational gradients, but litter K and Mg showed saddle-shaped patterns. Soil Ca concentration increased with elevation, while soil K and Mg had no significant changes. 2) Ca concentration in the forest litter under aspen(Populus davidiana) was significantly higher than that in all other species, but in topsoil, Ca concentration was higher under coniferous larch and fir(Larix chinensis and Abies fargesii). Litter K and Mg concentrations was higher under coniferous larch and fir, whereas there were nosignificant differences among tree species in the concentrations of K and Mg in topsoil. 3) Climatic factors including mean annual temperature(MAT), growing season precipitation(GSP) and non-growing season precipitation(NGSP) determined BC concentrations in the forest litter and topsoil. Soil C/N and C/P also influenced BC cycling between litter and soil. Observation along elevations within different tree species implies that above-ground tree species can redistribute below-ground cations, and this process is profoundly impacted by climate. Litter and soil Ca, K and Mg with different responses to environmental variables depend on their soluble capacity and mobile ability.  相似文献   
942.
Detecting and attributing vegetation changes in Taihang Mountain,China   总被引:1,自引:0,他引:1  
Attributing vegetation changes provide fundamental information for ecosystem management,especially in mountainous areas which has vulnerable ecosystems. Based on the Normalized Difference Vegetation Index(NDVI) data, the spatial-temporal change of vegetation was detected in Taihang Mountain(THM) from 2000 to 2014. The topographical factors were introduced to interpret the response of vegetation variation to climate change and human activities. Results showed that the avegaged NDVI during growing season showed a single-peak curve distribution, with the largest value(0.628) among 1600-1800 m. A significant greening trend was detected in THM, with the largest increasing rate(0.0078 yr~(-1)) among the elevation of1600-1800 m and slope gradient between 3~5°. The partial correlation and multiple correlation analyses indicated that vegetation variation in more than81.8% pixels of the THM was mainly impacted by human activities. In the low elevation zones less than1000 m, increasing precipitation is the principle factor promoting vegetation restoration, whereas in the high elevation zones of THM, temperature is the restricted factors impacting vegetation variation.Considering the dramatic climate change in the future,further studies should be conducted to explore inherent mechanism of vegetation growth to dynamic environment changes.  相似文献   
943.
鄂尔多斯盆地前寒武纪末期古地貌控制着后期沉积体系的空间配置与古地理展布。通过野外剖面、岩芯分析、测井数据等建立鄂尔多斯盆地寒武系层序地层格架;选取寒武纪SS1最大海泛面(徐庄组沉积晚期地层)为标志层,通过残余厚度印模法,并结合古地质图分析,对研究区前寒武纪进行古地貌恢复,明确了前寒武纪沉积背景、构造格局及物源方向。总体上,前寒武纪鄂尔多斯盆地南、北濒临秦祁海和兴蒙海,东、西被贺兰和晋豫陕坳拉槽所夹持,古地貌东北高、西南低,受秦祁海影响最大,可将其划分为3个古构造地貌单元:高地剥蚀区、受古构造控制形成的坳陷区以及处于剥蚀与沉积过渡地带的斜坡阶地区。通过研究前寒武纪末期古地貌与寒武纪早期烃源岩分布认为,拉张活动背景下的坳陷带以及斜坡带是鄂尔多斯盆地寒武纪早期烃源岩发育的有利区块,前寒武纪古地貌格局影响了寒武纪早期烃源岩发育与分布。恢复古地貌形态对于揭示物源供给,研究沉积物搬运、平面和纵向展布特征,探究沉积、沉降中心的迁移规律,以及进一步揭示生储盖组合和分布具有重大意义。  相似文献   
944.
The loess area in the northern part of Baoji City, Shaanxi Province, China is a region with frequently landslide occurrences. The main aim of this study is to quantitatively predict the extent of landslides using the index of entropy model(IOE), the support vector machine model(SVM) and two hybrid models namely the F-IOE model and the F-SVM model constructed by fractal dimension. First, a total of 179 landslides were identified and landslide inventory map was produced, with 70%(125) of the landslides which was optimized by 10-fold crossvalidation being used for training purpose and the remaining 30%(54) of landslides being used for validation purpose. Subsequently, slope angle, slope aspect, altitude, rainfall, plan curvature, distance to rivers, land use, distance to roads, distance to faults, normalized difference vegetation index(NDVI), lithology, and profile curvature were considered as landslide conditioning factors and all factor layers were resampled to a uniform resolution. Then the information gain ratio of each conditioning factors was evaluated. Next, the fractal dimension for each conditioning factors was calculated and the training dataset was used to build four landslide susceptibility models. In the end, the receiver operating characteristic(ROC) curves and three statistical indexes involving positive predictive rate(PPR), negative predictive rate(NPR) and accuracy(ACC) were applied to validate and compare the performance of these four models. The results showed that the F-SVM model had the highest PPR, NPR, ACC and AUC values for training and validation datasets, respectively, followed by the F-IOE model.Finally, it is concluded that the F-SVM model performed best in all models, the hybrid model built by fractal dimension has advantages than original model, and can provide reference for local landslide prevention and decision making.  相似文献   
945.
Rainfall can cause serious soil loss in the Loess Plateau hilly and gully region, but little focus has been placed on the extreme rainstorm effects on unpaved loess road soil erosion. A field survey method was used to investigate the erosional effects of the "7·26" heavy rainfall event on unpaved loess roads in the Jiuyuangou watershed of the Loess Plateau, China. The results showed that the average and maximum widths of the eroded gullies that formed on the unpaved roads were 0.65-1.48 m and 1.00-3.60 m, respectively. The average and maximum depths of theeroded gullies were 0.42-1.13 m and 0.75-4.30 m, respectively. The average width-to-depth ratio was 1.31, indicating that the widening effect was greater than the downcutting effect in the eroded gullies. In addition, the gully density ranged from 0.07 to 0.29 m m~(-2), and the road surface dissection degree ranged from 0.03 to 0.41 km~2 km~(-2). Eroded gullies generally developed at the slope toe of the cut bank side. The average eroded gully width and depth at turns in the road were 1.47-2.64 times and 1.30-3.47 times greater, respectively, than those in other road sections. The road erosion modulus increased from the upper section to the lower section of the roads. The average road erosion modulus of the study catchment was 235,000 t km~(-2). Turns in the road were associated with collapses, sinkholes and other gravitational erosion phenomena. The amount of road erosion under extreme rainfall conditions is mainly related to the interactions among road length, width, slope and soil bulk density. Our results provide a useful reference for developing further measures for preventing road erosion on the Loess Plateau.  相似文献   
946.
The availability of high-resolution satellite precipitation measurement products provides an opportunity to monitor precipitation over large and complex terrain and thus accurately evaluate the climatic, hydrological and ecological conditions in those regions. The Global Precipitation Measurement(GPM) mission is an important new program designed for global satellite precipitation estimation, but little information has been reported on the applicability of the GPM’s products for the Tibetan Plateau(TP). The object of this study is to evaluate the accuracy of the Integrated Multi-Satellite Retrievals for GPM(IMERG) Final Run product under different terrain and climate conditions over the TP by using 78 ground gauges from April 2014 to December 2017. The results showed the following:(1) the 3-year average daily precipitation estimation in the IMERG agrees well with the rain gauge observations(R~2=0.58, P0.01), and IMERG also has a considerable ability to detect precipitation, as indicated by a high probability of detection(78%-98%) and critical success index(65%-85%);(2) IMERG performed better at altitudes from 3000 m to 4000 m with a small relative bias(RB) of 6.4%. Precipitation change was not significantly affected by local relief;(3) the climate system of the TP was divided into four climate groups with a total of 12 climate types based on the K?ppen climate classification system, and IMERG performed well in all climate types with the exception of the arid-desert-cold climate(Bwk) type. Furthermore, although IMERG showed the potential to detect snowfall, it still exhibits deficiencies in identifying light and moderate snow. These results indicate that IMERG could provide more accurate precipitation data if its retrieval algorithm was improved for complex terrain and arid regions.  相似文献   
947.
Ascertaining the relationship between "source-sink" landscape and non-point source(NPS) pollution is crucial for reducing NPS pollution, however, it is not easy to realize this target on cell unit scale. To reveal the relationships between "sourcesink" landscape and NPS pollution based on cell units of a small catchment in the Three Gorges Reservoir Region(TGRR), the runoff and nutrient yields were simulated first by rainfall events on a cell unit scale based on the Annualized AGricultural Non-Point Source Pollution Model(AnnAGNPS). Landscape structure and pattern were quantified with "sourcesink" landscape indicators based on cell units including landscape area indices and locationweighted landscape indices. The results showed that:the study case of small Wangjiagou catchment highlighted a good prediction capability of runoff and nutrient export by the AnnAGNPS model. Throughout the catchment, the spatial distribution trends of four location-weighted landscape indices were similar to the trends of simulated total nitrogen(TN) and total phosphorus(TP), which highlighted the importance of spatial arrangement of "source" and "sink" landscape types in a catchment when estimating pollutant loads. Results by Pearson correlation analysis indicated that the location-weighted landscape index provided a more comprehensive account of multiple factors, and can better reflect NPS-related nutrient loss than other landscape indices applied in single-factor analysis. This study provides new findings for applying the "source-sink" landscape indices based on cell units in small catchments to explain the effect of "source-sink" landscape on nutrient export based on cell unit, and helps improve the understanding of the correlation between "source-sink" landscape and NPS pollution.  相似文献   
948.
以祁连山排露沟流域青海云杉林为研究对象,研究了海拔梯度上土壤肥力因子的分布特征及变化规律,并运用主成分分析法对青海云杉林土壤肥力状况进行了评价。结果表明:(1)研究区土壤呈碱性,pH值均大于8.0;高海拔地区(3 300 m)含水量达到过饱和状态,各土层含水量均大于100%;随海拔升高,全氮含量呈增大趋势,全钾含量呈减小趋势,而全磷含量呈先减小后增大趋势;不同海拔梯度速效磷含量差异不显著(P>0.05),海拔3 300 m处速效钾含量显著高于其他海拔段(P<0.05)。(2) 不同海拔梯度下土壤有机质、全氮、全磷、全钾、速效磷和速效钾含量都有明显的“表聚效应”,其中3 300 m处0~10 cm土层有机质含量高达325.93 g·kg-1,是本海拔段其他土层的1.6~1.8倍,是同土层其他海拔段的1.3~2.0倍。(3) 土壤肥力因子间关系密切,土壤含水量与有机质、全氮呈极显著正相关关系,与土壤容重、pH和全钾呈极显著负相关关系,土壤养分含量之间存在不同程度的显著正相关关系。(4) 不同海拔梯度土壤肥力质量为:3 300 m>3 200 m>3 100 m>3 000 m>2 900 m。  相似文献   
949.
粒度特征揭示的中全新世以来毛乌素沙地演化过程   总被引:1,自引:1,他引:0  
通过对毛乌素沙地现代固定沙丘、半固定沙丘、半流动沙丘和流动沙丘的粒度特征分析,发现研究区沙地变化敏感粒度是>245 μm的沉积物粒度组分,尝试性地将其用于地质时期沙地演化研究。结合区域典型风成砂-古土壤剖面的沉积相特征,探讨了中晚全新世以来毛乌素沙地的时间演化过程及其特征。结果表明:中全新世以来毛乌素沙地存在多次活化扩张和固定萎缩事件,除7.5 ka BP前为流动沙地占优势以外,其余阶段多在半流动沙地、半固定沙地和固定沙地之间频繁转换,即使在全新世适宜期古土壤大规模发育期间仍存在局地短时间的沙地活化事件。  相似文献   
950.
放牧对浑善达克沙地丘间低地植被群落及土壤的影响   总被引:1,自引:1,他引:0  
詹瑾  李玉霖  韩丹  杨红玲 《中国沙漠》2019,39(6):184-191
为探究放牧对丘间低地植被群落及土壤的影响,分析了浑善达克沙地丘间低地在重度和轻度放牧下植被的地上生物量、物种重要值、物种丰富度、Shannon-Wiener多样性指数、Pielou均匀度指数、Simpson生态优势度指数及0~10 cm土壤中黏粒、粉粒、砂粒、有机碳和全氮含量。结果表明:(1)植被地上生物量、土壤黏粒、粉粒、砂粒、土壤有机碳和全氮含量在不同放牧程度下存在极显著差异(P<0.01),物种丰富度、Shannon-Wiener多样性指数和Pielou均匀度指数在不同放牧程度下差异不显著(P>0.05),Simpson生态优势度指数在不同放牧程度下差异显著(P<0.05)。(2)放牧区植被以禾本科为主,禾本科植被地上生物量占整个植被群落的54.88%~57.76%;重度放牧区植被地上生物量为63.59 g·m-2,比轻度放牧区低26.61%。(3)羊草(Leymus chinensis)和狗尾草(Setaria viridis)是放牧区的优势种,其重要值依次为14.16%(重度放牧区)和19.10%(轻度放牧区)、13.40%(重度放牧区)和15.42%(轻度放牧区),重度放牧下雾滨藜(Bassia dasyphylla)、克氏针茅(Stipa krylovii)和猪毛蒿(Artemisia scoparia)的重要值较显著高于轻度放牧区,而羊草则低于轻度放牧区。(4)重度放牧加剧了土壤沙漠化,使砂粒含量增加,草地生产力下降,土壤有机碳和全氮含量降低。  相似文献   
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