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1.
Land cover type is critical for soil organic carbon(SOC) stocks in territorial ecosystems. However, impacts of land cover on SOC stocks in a karst landscape are not fully understood due to discontinuous soil distribution. In this study, considering soil distribution, SOC content and density were investigated along positive successional stages(cropland, plantation, grassland, scrubland, secondary forest, and primary forest) to determine the effects of land cover type on SOC stocks in a subtropical karst area. The proportion of continuous soil on the ground surface under different land cover types ranged between 0.0% and 79.8%. As land cover types changed across the positive successional stages, SOC content in both the 0–20 cm and 20–50 cm soil layers increased significantly. SOC density(SOCD) within 0–100 cm soil depth ranged from 1.45 to 8.72 kg m-2, and increased from secondary forest to primary forest, plantation, grassland, scrubland, and cropland, due to discontinuous soil distribution. Discontinuous soil distribution had a negative effect on SOC stocks, highlighting the necessity for accurate determination of soil distribution in karst areas. Generally, ecological restoration had positive impacts on SOC accumulation in karst areas, but this is a slow process. In the short term, the conversion of croplandto grassland was found to be the most efficient way for SOC sequestration.  相似文献   

2.
我国南方喀斯特地区岩石裸露率高、土层浅薄且分布不均,这种特殊的岩土组构如何影响水文过程对于准确估算岩溶碳通量具有重要意义。水化学径流法是计算流域尺度岩溶碳通量的常用方法,其中流域面积和流量作为2个重要参数在喀斯特地区往往难以准确获取。在普定喀斯特生态系统观测研究站设计了一组岩土比(1:1和4:1)和一组土层厚度(5,20,100 cm)共计5种岩土组构的模拟试验场。通过一个完整水文年的流量和水化学监测,定量研究了岩石裸露率和土层厚度对水文过程以及岩溶碳通量的影响。研究结果表明,5个模拟试验场岩溶碳通量平均值为(17±3) gC/m2/a,受渗漏量控制,雨季(5-10月)约占95%;岩石裸露率(2组岩土组构之间)对渗漏量的影响可达14%,且随着岩石裸露率增加,入渗系数也相应增加;土层厚度对渗漏量的影响仅在1%~2%之间。此外,对8个野外流域观测数据的分析发现,入渗系数与岩溶碳通量的相关性最为显著,说明入渗系数是喀斯特地区不同岩土组构地质背景影响和控制岩溶碳通量的主要因素,同时这种影响可能随降雨量变化而变化,即入渗系数并非常数。   相似文献   

3.
1INTRODUCTIONDesertification is one of the most serious land degrada-tion, which results in the deterioration of physical, che-mical, and biological characteristics of soils (UNEP, 1992). Soil organic carbon (SOC) was considered to be a key index in evaluation of soil quality, soil degradation and soil C sequestration(SCHLENGSINGER etal., 1990; FENG etal., 2002; WANG etal., 2003). Many researchers have reported the correlations among desertification restoration, soil C s…  相似文献   

4.
Soil organic carbon (SOC) was considered to be a key index in evaluation of soil degradation and soil C sequestration. To discuss the spatial-temporal dynamics of SOC in arable layer in reversed desertification area, a case study was conducted in Yulin City, Shaanxi Province, China. Data of SOC were based on general soil survey in 1982 and repeated soil sampling in 2003. Soil organic carbon content (SOCC) was determined by K2Cr3O2-FeSO4 titration method, and soil organic carbon density (SOCD) was calculated by arithmetic average and area weighted average method, respectively. On average, SOCC and SOCD of the arable layer in the study area from 1982 to 2003 had increased 0.5 Ig/kg and 0.16kg/m2, respectively. Considering main soil types, the widest distributed Arid-Sandic Entisols had lowest values and increments of SOCC and SOCD during the study period; while the second widest Los-Orthic Entisols had higher values and increments of SOCC and SOCD, compared to the mean values of the whole region. The results indicated that reversed desertification process was due to the modification of land use and management practices, such as natural vegetation recovery, planting grass, turning arable land to grassland, and soil and water conservation etc., which can improve SOCC and SOCD and thus enhance soil C sequestration.  相似文献   

5.
准确预测未采样区域SOC密度,是研究SOC演变趋势和探索土壤固碳作用对缓解全球气候变化的基础。采用泛克里格法(Universal Kriging,UK)和土壤类型法(pedological professional knowledge-based method,PKB),分别对长兴县水稻土有机碳密度进行了预测,其中,UK直接以长兴水稻土剖面资料为源数据、PKB以长兴水稻土剖面数据和长兴1∶5万数字土壤图为源数据进行预测。根据平均绝对误差(MAE)及均方根误差(RMSE)大小,评价了两种方法在县域尺度土壤有机碳密度空间预测效果。结果表明:UK的MAE(31.2)、RMSE(52.5)均大于PKB的MAE(24.7)、RMSE(43.1),说明PKB法的预测效果较好,UK法相对较差。研究表明,对土壤类型、土壤母质,以及剖面点位置等信息的综合考虑能使PKB法更好地表达土壤属性的空间特征,也更适于县域尺度土壤有机碳密度的空间预测。  相似文献   

6.
土壤分层信息,特别是表土层结构,对土地生产力具有重要影响,是评价土壤质量的一个重要指标。为了快速、准确地获取土壤分层信息,本文利用探地雷达对分层土壤进行了回波信号采集,并分别在时域和频域分析土壤层位置和层厚信息。首先在信号预处理的基础上,借助包络检波方法确定在土壤分层界面在时域上的位置;然后获取电磁波速度,得到土壤分层厚度。考虑到土壤介电常数与电磁波在土壤中传播速度的相关性,采用短时傅里叶变换方法（Short-time Fourier Transform,STFT）获取各土壤层时频域特征值,并利用回归分析建立特征值与介电常数之间的数学关系,实现对各土壤层的介电常数估算,从而计算出电磁波传播速度,进而确定土壤各层厚度。为验证算法的有效性,分别对理想模拟实验环境和农田环境进行了探地雷达实验,结果表明利用包络检波对探地雷达回波信息进行分析,土壤层检出率达到94.5%,借助STFT谱分析进行探地雷达回波速度估计,对于70 cm深度以上土层厚度计算误差大都保持在10%以下,但随着土壤深度的增加,误差变大。总体来说,本方法能有效识别浅层土壤的分层信息,可应用于实际生产中耕层厚度的估测。  相似文献   

7.
Grassland is a major carbon sink in the terrestrial ecosystem. The dynamics of grassland carbon stock profoundly influence the global carbon cycle. In the published literatures so far, however, there are limited studies on the long-term dynamics and influential factors of grassland carbon stock, including soil organic carbon. In this study, spatial-temporal substitution method was applied to explore the characteristics of Medicago sativa L.(alfalfa) grassland biomass carbon and soil organic carbon density(SOCD) in a loess hilly region with different growing years and management patterns. The results demonstrated that alfalfa was the mono-dominant community during the cutting period(viz. 0–10 year). Community succession began after the abandonment of alfalfa grassland and then the important value of alfalfa in the community declined. The artificial alfalfa community abandoned for 30 years was replaced by the S. bungeana community. Accordingly, the biomass carbon density of the clipped alfalfa showed a significant increase over the time during 0–10 year. During 0–30 year, the SOCD from 0–100 cm of the soil layer of all 5 management patterns increased over time with a range between 5.300 ± 0.981 kg/m2 and 12.578 ± 0.863 kg/m2. The sloping croplands had the lowest SOCD at 5.300 ± 0.981 kg/m2 which was quite different from the abandoned grasslands growing for 30 years which exhibited the highest SOCD with 12.578 ± 0.863 kg/m2. The ecosystem carbon density of the grassland clipped for 2 years increased 0.1 kg/m2 compared with the sloping cropland, while that of the grassland clipped for 10 years substantially increased to 10.30 ± 1.26 kg/m2. Moreover, the ecosystem carbon density for abandoned grassland became 12.62 ± 0.50 kg/m2 at 30 years. The carbon density of the grassland undisturbed for 10 years was similar to that of the sloping cropland and the grassland clipped for 2 years. Different management patterns imposed great different effects on the accumulation of biomass carbon on artificial grasslands, whereas the ecosystem carbon density of the grassland showed a slight increase from the clipping to abandonment of grassland in general.  相似文献   

8.
The dynamics of soil organic carbon(SOC)in cropland is one of the central issues related to both soil fertility and environmental safety. However, little information is available at county level regarding the spatiotemporal variability of SOC in the southwestern mountainous region of China. Thus, this study aimed to explore spatiotemporal changes of SOC in the cultivated soil layer of dry land in Mojiang County,Yunnan Province, China. Data were obtained from the second national soil survey(SNSS) of 1985 and soil tests for fertilizer application carried out by the Mojiang Agricultural Bureau in 2006. The ANOVA test was applied to determine any significant differences between the datasets, while semivariogram analysis was performed on geostatistics via an ordinary Kriging method in order to map spatial patterns of soil organic carbon density(SOCD). The results revealed that SOCD in the cultivated soil layer significantly decreased from 3.93 kg m~(-2) in 1985 to 2.89 kg m~(-2) in 2006, with a total soil organic carbon stock(SOCS) decrease of 41.54×10~4 t over the same period. SOCS levels fell most markedly in yellow-brown soil at a rate of51.52%, while an increase of 8.70% was found in the analysed latosol. Geostatistical analysis also showed that the recorded changes in SOCD between 1985 and2006 were spatially structured. The decreasing trend might be attributed to the combined action of intense cultivation, major crop residue removal without any protective tillage measures, unreasonable fertilization and natural climatic diversity inducing a large decrease in SOC in the studied cultivated dry land region of Mojiang County. Therefore, management measures such as protective tillage should be undertaken in order to enhance soil C sequestration.  相似文献   

9.
Soil structure plays an important role in understanding soil attributes as well as hydrological processes. Effective method to obtain high quality soil map is therefore important for both soil science research and soil work ability improvement. However, traditional method such as digging soil pits is destructive and time-consuming. In this study, the structure of headwater hillslopes from Hemuqiao catchment (Taihu Basin, China) have been analyzed both by indirect (ground penetrating radar, GPR) and direct (excavation or soil auger) methods. Four transects at different locations of hillslopes in the catchment were selected for GPR survey. Three of them (#1, #2, and #3) were excavated to obtain full-scale soil information for interpreting radar images. We found that the most distinct boundary that can be detected by GPR is the boundary between soil and underlain bedrock. In some cases (e.g., 8–17m in transect #2), in which the in situ soil was scarcely affected by colluvial process, different soil layers can be identified. This identification process utilized the sensitive of GPR to capture abrupt changes of soil characteristics in layer boundaries, e.g., surface organic layer (layer #1) and bamboo roots layer (layer #2, contain stone fragments), illuvial deposits layer (layer #3) and regolith layer (layer #4). However, in areas where stone fragments were irregularly distributed in the soil profile (highly affected by colluvial and/or fluvial process), it was possible to distinguish which part contains more stone fragments in soil profile on the basis of reflection density (transect #3). Transect #4 (unexcavated) was used to justify the GPR method for soil survey based on experiences from former transects. After that, O horizon thickness was compared by a hand auger. This work has demonstrated that GPR images can be of a potential data source for hydrological predictions.  相似文献   

10.
《山地科学学报》2020,17(7):1636-1651
The soil carbon pool which is the sum of soil organic carbon(SOC) and soil inorganic carbon(SIC) is the second largest active store of carbon after the oceans and it is an important component of the global carbon cycle. Hence, accurate estimation of SOC and SIC as important carbon reservoirs in terrestrial ecosystems using fast, inexpensive and non-destructive methods is crucial for planning different climate change policies. The aim of the current research was to examine the effectiveness of Vis-NIR(visible and near-infrared spectroscopy: 350-2500 nm) and MIR(mid-infrared spectroscopy: 4000-400 cm~(-1)) to characterize and estimate soil organic matter(SOM) and carbonates as main components of soil carbon stocks in Juneqan, Charmahal va Bakhtiari, Iran. To do so, a total of 548 soil samples from this area were collected(October 2015) and analyzed in laboratory(August 2017). In order to develop models capable of predicting SOM and carbonates content, seven spectral preprocessing methods comprising Absorbance(Abs), De-trending(Det), Continuum removal(CR), Savitzky-Golay derivatives(SGD), standard normal variate transformation(SNV), multiplicative scatter correction(MSC) and Normalization by range(NBR) were conducted along with five multivariate methods including Random Forest(RF), Partial Least-Squares Regression(PLSR), Artificial Neural Network(ANN), Support Vector Machine(SVM) and Gaussian Process Regression(GPR). The content of carbonates caused spectral reflectance intensity to augment on several ranges of spectrum and strong absorption feature at 2338 nm in the Vis-NIR and 714, 850, 870, 1796, 2150 and 2510 cm~(-1) in the MIR spectra range. SOM absorbed energy in several ranges, but also showed specific peaks in MIR. Both facts are associated with the structure of carbonates and SOM and its interaction with energy. The best combination of preprocessing and calibration models for carbonates quantification in Vis-NIR spectra was Det/PLSR(R~2= 0.74, RPD= 2.19, RMSE= 6.45). For SOM, it was Det/PLSR(R~2= 0.82, RPD= 2.41, RMSE= 0.75). The Det/RF(R~2= 0.87, RPD= 2.44, RMSE= 0.66) for the quantification of SOM and MSC/RF(R~2= 0.84, RPD= 2.84, RMSE= 5.50) for carbonates in MIR spectra range showed the greatest results. The stronger occurrence of spectral bands in MIR as well as the specificity of the absorption features indicated that this range produced better predictions. The obtained results highlighted the significant role of soil spectroscopy technique in predicting SOC and soil carbonates as key components of soil carbon stocks in the study area. Therefore, this technique can be used as a more cost-effective, time saving and nondestructive alternative to traditional methods of soil analysis.  相似文献   

11.
Rapid urbanization results in the conversion of natural soil to urban soil,and consequently,the storage and density of the soil carbon pools change.Taking Chongqing Municipality of China as a study case,this investigation attempts to better understand soil carbon pools in hilly cities.First,the vegetated areas in the study area were derived from QuickBird images.Then,topsoil data from 220 soil samples(0-20 cm) in the vegetated areas were collected and their soil organic carbon(SOC) densities were analyzed.Using the Kriging interpolation method,the spatial pattern of SOC was estimated.The results show that the SOC density exhibited high spatial variability in the urban topsoil of Chongqing.First,the SOC density in topsoil decreased according to slope in the order 2°-6° < 25°-90° < 0°-2° < 6°-15° < 15°-25°.Second,the newly developed areas during 2001-2010 had a lower SOC density than the areas built before 1988.Third,urban parks and gardens had a higher SOC density in topsoil,residential green land followed,and scattered street green land ranked last.For hilly cities,the variability of terrain affects the distribution of SOC.The Kriging results indicate that Kriging method combining slope with SOC density produced a high level of accuracy.The Kriging results show that the SOC density to the north of the Jialing River was higher than the south.The vegetated areas were estimated to amount to 73.5 km2 across the study area with an SOC storage of 0.192 Tg and an average density of 2.61 kg/m2.  相似文献   

12.
六盘水市土壤侵蚀时空特征及影响因素分析   总被引：1，自引：0，他引：1  
六盘水市是我国生态地位极其重要,水土流失又较为严重的城市。近些年,六盘水市实施了一系列生态工程,为了定量分析六盘水市土壤侵蚀状况及其影响因素,本文基于RUSLE模型,利用降雨数据、遥感影像数据、土地利用数据等,对贵州省六盘水市1990-2015年土壤侵蚀模数和土壤侵蚀量进行定量模拟,分析其时空动态变化,利用地理探测器定量分析影响因素,并进行空间相关性分析,结果表明： ① 六盘水市土壤侵蚀以微度和中度侵蚀为主。土壤侵蚀严重地区主要分布在北盘江流域与南盘江流域交界处以及喀斯特山地地区,煤矿开采使植被覆盖等抑制土壤侵蚀因子减少作用,使局部地区土壤侵蚀程度加剧。② 1990-2010年平均土壤侵蚀模数整体为下降趋势,2010-2015年为上升趋势。其中2000年平均土壤侵蚀模数最大,2010年平均土壤侵蚀模数最小。该变化由降雨可蚀性因子和植被覆盖度因子综合影响所致。③ 植被覆盖度因子和多年平均降雨量因子是影响区域土壤侵蚀空间分布的重要因素。未利用土地、植被覆盖度小于0.3、坡度在25°以上和降雨量在1543~1593 mm之间的地区为高风险侵蚀区域。④ 植被覆盖度与土壤侵蚀在空间上全部呈负相关性,降雨因子与土壤侵蚀在空间上存在负相关性和正相关性。⑤ 土壤侵蚀改善区域大多分布在生态工程区域内,生态工程建设能够改善土壤侵蚀情况,不同生态工程保护侧重点不同导致土壤侵蚀改善程度不同。退耕还林还草工程对六盘水市土壤侵蚀的改善具有重要意义,六盘水市更宜退耕还林。  相似文献   

13.
Carbon sequestration occurs when cultivated soils are re-vegetated. In the hilly area of the Loess Plateau, China, black locust(Robinia pseudoacacia) plantation forest and grassland were the two main vegetation types used to mitigate soil and water loss after cultivation abandonment. The purpose of this study was to compare the soil carbon stock and flux of these two types of vegetation which restored for 25 years. The experiment was conducted in Yangjuangou catchment in Yan′an City, Shaanxi Province, China. Two adjacent slopes were chosen for this study. Six sample sites were spaced every 35–45 m from summit to toe slope along the hill slope, and each sample site contained three sampling plots. Soil organic carbon and related physicochemical properties in the surface soil layer(0–10 cm and 10–20 cm) were measured based on soil sampling and laboratory analysis, and the soil carbon dioxide(CO2) emissions and environmental factors were measured in the same sample sites simultaneously. Results indicated that in general, a higher soil carbon stock was found in the black locust plantation forest than that in grassland throughout the hill slope. Meanwhile, significant differences in the soil carbon stock were observed between these two vegetation types in the upper slope at soil depth 0–10 cm and lower slope at soil depth 10–20 cm. The average daily values of the soil CO2 emissions were 1.27 μmol/(m2·s) and 1.39 μmol/(m2·s) for forest and grassland, respectively. The soil carbon flux in forest covered areas was higher in spring and less variation was detected between different seasons, while the highest carbon flux was found in grassland in summer, which was about three times higher than that in autumn and spring. From the carbon sequestration point of view, black locust plantation forest on hill slopes might be better than grassland because of a higher soil carbon stock and lower carbon flux.  相似文献   

14.
Plant invasion alters the fundamental structure and function of native ecosystems by affecting the biogeochemical pools and fluxes of materials and energy. Native (Suaeda salsa) and invasive (Spartina alterniflora) salt marshes were selected to study the effects of Spartina alterniflora invasion on soil organic carbon (SOC) contents and stocks in the Yellow River Delta. Results showed that the SOC contents (g/kg) and stocks (kg/m2) were significantly increased (P < 0.05) after Spartina alterniflora invasion of seven years, especially for the surface soil layer (0–20 cm). The SOC contents exhibited an even distribution along the soil profiles in native salt marshes, while the SOC contents were gradually decreased with depth after Spartina alterniflora invasion of seven years. The natural ln response ratios (LnRR) were applied to identify the effects of short-term Spartina alterniflora invasion on the SOC stocks. We also found that Spartina alterniflora invasion might cause soil organic carbon losses in a short-term phase (2–4 years in this study) due to the negative LnRR values, especially for 20–60 cm depth. And the SOCD in surface layer (0–20 cm) do not increase linearly with the invasive age. Spearman correlation analysis revealed that silt + clay content was exponentially related with SOC in surface layer (Adjusted R2 = 0.43, P < 0.001), suggesting that soil texture could play a key role in SOC sequestration of coastal salt marshes.  相似文献   

15.
Vertical distribution of soil nematode communities under conventional tillage (CT),no-tillage (NT) and fallow field (FF) treatments in the Lower Reaches of the Liaohe River was investigated at six soil depths (0-5 cm,5-15 cm,15-30 cm,30-50 cm,50-75 cm and 75-100 cm). The results show that total nematode abundance gradually decreases with depth,and the highest number of total nematodes is observed at 0-5 cm depth under NT and FF treatments. The number of fungivores and plant parasites is significantly higher...  相似文献   

16.
灰岩分布区易发生岩溶塌陷等地质灾害,高密度电阻率法是岩溶地质调查的重要手段。以某一段穿越岩溶发育区的公路为例,应用高密度电法对区内暗河、槽谷型岩溶塘、落水洞等灾害地质体进行了探测,结果显示拟建路段覆盖层厚度大约为2~20 m,基岩内岩溶极发育,岩石地表起伏大,溶沟、溶槽、岩溶塌陷、落水洞发育;岩石中溶蚀裂隙、溶洞发育。表明高密度电阻率法能够有效地判定岩溶的发育情况,可以为地质灾害评估提供科学客观的依据。  相似文献   

17.
Soil organic carbon is of great importance to terrestrial ecosystems.Studies on the amount and spatial distribution of soil organic carbon stock in various types of soil can help to better understand the role of soil in the global carbon cycle and provide a scientific basis for the assessment of the magnitude of carbon stored in a given area.Here we present estimates of soil organic carbon stock in soils in the upper reaches of the Yangtze River based on soil types as defined by Chinese Soil Taxonomy and recently compiled into a digital soil database.The results showed that the total soil organic carbon stock of the upper Yangtze River to a depth of 100 cm was 1.452×1013kg.The highest soil organic carbon stock was found in felty soils(2.419×1012kg),followed by dark brown soils(1.269×1012kg),and dark felty soils(1.139×1012kg).Chernozems and irrigation silting soils showed the lowest soil organic carbon stock,mainly due to the small total area of such soils.The soil organic carbon density of these major soil types ranged from 5.6 to 26.1 kg m-2.The average soil organic carbon density of the upper reaches of the Yangtze River was 16.4 kg m-2,which was higher than that of the national average.Soil organic carbon density indicated a distinct decreasing trend from west to east,which corresponds to the pattern of increasing temperature from cold to subtropical.  相似文献   

18.
Soil carbon and nutrient contents and their importance in advancing our understanding of biogeochemical cycling in terrestrial ecosystem, has motivated ecologists to find their spatial patterns in various geographical area. Few studies have focused on changes in the physical and chemical properties of soils at high altitudes. Our aim was to identify the spatial distribution of soil physical and chemical properties in cold and arid climatic region. We also tried to explore relationship between soil organic carbon (SOC) and total nitrogen (TN), total phosphorus (TP), available nitrogen (AN), available phosphorus (AP), soil particle size distribution (PSD). Samples were collected at 44 sites along a 300 km transect across the alpine grassland of northern Tibet. The study results showed that grassland type was the main factor influencing SOC, TN and TP distribution along the Gangdise Mountain-Shenzha-Shuanghu Transect. SOC, TN and TP contents were significantly higher in alpine meadow than alpine steppe ecosystems. SOC, TN, TP and AN contents in two soil layers (0-15 cm and 15-30 cm) showed no significant differences, while AP content in top soil (0-15 cm) was significantly higher than that in sub-top soil (15-30 cm). SOC content was correlated positively with TN and TP content (r = 0.901 and 0.510, respectively). No correlations were detected for clay content and fractal dimension of particle size distribution (D). Our study results indicated the effects of vegetation on soil C, N and P seem to be more important than that of rocks itself along latitude gradient on the northern Tibetan Plateau. However, we did not found similar impacts of vegetation on soil properties in depth. Inaddition, this study also provided an interesting contribution to the global data pool on soil carbon stocks.  相似文献   

19.
Frozen ground degradation under a warming climate profoundly influences the growth of alpine vegetation in the source region of the Qinghai-Tibet Plateau. This study investigated spatiotemporal variations in the frozen ground distribution, the active layer thickness(ALT) of permafrost(PF) soil and the soil freeze depth(SFD) in seasonally frozen soil from 1980 to 2018 using the temperature at the top of permafrost(TTOP) model and Stefan equation. We compared the effects of these variations on vegetation growth among different frozen ground types and vegetation types in the source region of the Yellow River(SRYR). The results showed that approximately half of the PF area(20.37% of the SRYR) was projected to degrade into seasonally frozen ground(SFG) during the past four decades; furthermore, the areal average ALT increased by 3.47 cm/yr, and the areal average SFD decreased by 0.93 cm/yr from 1980 to 2018. Accordingly, the growing season Normalized Difference Vegetation Index(NDVI) presented an increasing trend of 0.002/10 yr, and the increase rate and proportion of areas with NDVI increase were largest in the transition zone where PF degraded to SFG(the PF to SFG zone). A correlation analysis indicated that variations in ALT and SFD in the SRYR were significantly correlated with increases of NDVI in the growing season. However, a rapid decrease in SFD(-1.4 cm/10 yr) could have reduced the soil moisture and, thus, decreased the NDVI. The NDVI for most vegetation types exhibited a significant positive correlation with ALT and a negative correlation with SFD. However, the steppe NDVI exhibited a significant negative correlation with the SFD in the PF to SFG zone but a positive correlation in the SFG zone, which was mainly limited by water condition because of different change rates of the SFD.  相似文献   

20.
Snow cover is characterized by the high albedo, low thermal conductivity, and notable heat transition during phase changes. Thus, snow cover significantly affects the ground thermal regime. A comparison of the snow cover in high latitudes or high-altitude snowy mountain regions indicates that the eastern Tianshan Mountains (China) show a characteristically thin snow cover (snow depth below 15 cm) with remarkable temporal variability. Based on snow depth, heat flux, and ground temperature from 2014 to 2015 in the Urumqi River source, the spatialtemporal characteristics of snow cover and snow cover influences on the thermal conditions of active layer in the permafrost area were analyzed. During the autumn (Sept. - Oct.), thin and discontinuous snow cover can noticeably accelerate the exothermic process of the ground, producing a cooling effect on the shallow soil. During the winter (Nov. - Mar.), it is inferred that the effective thermal insulation starts with snow depth exceeding 10 cm during early winter. However, the snow depth in this area is generally below 15 cm, and the resulting snow-induced thermal insulation during the winter is very limited. Due to common heavy snowfalls in the spring (Apr. to May), the monthly mean snow thickness in April reached to 15 cm and remained until mid-May. Snow cover during the spring significantly retarded the ground warming. Broadly, snow cover in the study area exerts a cooling effect on the active layer and plays a positive role in the development and preservation of permafrost.  相似文献   

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