基于水热变化的青藏高原土壤冻融过程研究进展

青藏高原近地层土壤冻融过程是高原地表最显著的陆面特征之一,也是判断冻土发育、存在以及反映气候变化的重要指标。近地层土壤昼夜、季节性的冻结、融化会导致青藏高原陆—气间能水平衡的变化甚至异常,从而显著影响高原地表水文过程、生态环境、碳氮循环以及高原及其周边区域的天气和气候系统。论文从观测、模拟以及对气候的影响3个角度来探讨1990年以来青藏高原土壤冻融过程的最新研究进展。结果表明：① 在一个完整的年冻融循环过程中,近地表各层土壤大体都经历了夏季融化期、春秋季融化—冻结期、冬季冻结期4个阶段。受局地因素的影响,不同站点的冻结或消融起止时间、速率、类型均有差异。② 多年冻土区和季节冻土区的日冻融循环过程差异较大,主要体现在日冻融循环持续时间上。③ 不同陆面模式都可以很好地抓住冻融过程中物理量的时空变化,但都需要针对高原陆面过程的特点进行参数化改进。④ 规避不稳定的迭代计算并根据热力学平衡方程确定冻融临界温度可以改进不合理的冻融参数化方案。基于已有研究回顾,发现增加高质量的观测站,利用卫星遥感等多种手段来反演高原土壤冻融过程以及加强陆面模式与区域气候模式和全球气候模式的耦合,并立足于高原冻融过程的特点发展相适应的参数化方案以及模拟结构的调整,能够有助于高原冻融过程的模拟。     

冻融及牲畜排泄物作用下的高寒草地土壤物理特性和氮磷变化

在青藏高原高寒草地生态系统中,牲畜排泄物自身冻融及其降解过程调控其养分释放及返还效率,影响草地土壤养分平衡和植被生长的养分供应.当前关于季节性冻融区草地土壤理化特性的研究,多通过定点监测和室内冻融模拟等方式分析冻融循环对土壤物理结构、水热变化及碳氮动态等方面的影响,尚缺乏关于草地土壤季节性冻融与牲畜排泄物耦合效应和作用...     

艾比湖地区冻融作用对梭梭群落土壤酶活性及微生物数量的影响

冻融作用对酶和微生物活性具有重要影响,进而影响植物群落的生长发育。为深入了解荒漠优势种梭梭群落冬季土壤生态过程,于2012年10月~2013年10月,对土壤冻融期、冻结期、融冻期和生长季的艾比湖典型样地进行野外实地观测、采样和室内分析。通过对比分析不同冻融阶段土壤含水量、pH值、有机质、全氮、酶活性和微生物数量的变化特征。结果表明:(1)土壤含水量,融冻期 >冻结期 >冻融期 >生长季,土壤pH值,生长季 >融冻期 >冻融期 >冻结期,各土层土壤含水量以浅层土表现最为显著(P <0.05),不同冻融阶段各土层pH值差异性较大,冻融期、冻结期和生长季表层土壤pH值较大,融冻期浅层土壤pH值较大。(2)土壤有机质和全氮含量的波动状况相似,分别在融冻期和生长季呈现波峰和波谷,不同土层间全氮和有机质含量差异性较小,以冻融期和生长季表现最为显著(P <0.05)。(3)土壤酶活性的变化中,过氧化氢酶、脲酶和蛋白酶在融冻期含量最大,冻融期次之,蔗糖酶在冻结期活性最大,土壤微生物数量的变化以融冻期最大,除此之外,各冻融阶段细菌和放线菌占主导,真菌含量相对较少。(4)冻融循环次数分布于冻融期和融冻期,对土壤酶活性和微生物数量具有一定的影响,致使融冻期土壤各因子大于冻融期。     

近30年来青海省风蚀气候侵蚀力时空差异及驱动力分析

青藏高原气候寒冷、多大风,冻融、风化和风蚀作用强烈,易发生土壤风蚀。气候对土壤风蚀的影响可用风蚀气候因子指数（C）度量。基于联合国粮农组织（FAO）提出的C计算方法,根据1984-2013年间连续完整的青海省气象站地面观测数据,应用地理加权回归模型（GWR）、重心及其转移模型,并结合本文定义的有效敏感性指数、有效影响面积等指标,得到全省风蚀气候侵蚀力及其影响因子的时空分布及其演化规律,并对其驱动力和机理进行了初步分析。结果表明：30年来,全省风蚀气候侵蚀力总体特征是西北高东南低并呈下降趋势,风蚀气候侵蚀力强的区域明显向西南扩展,20世纪80年代是柴达木盆地,90年代扩展到青南高原西北部边缘,21世纪基本涵盖了青南高原的西部;风速是影响风蚀气候侵蚀力的主导因子,其有效敏感区重心从柴达木盆地西南部边缘,移动到海拔较高的青南高原西部地区,这与高原近地面气旋系统中心总体移动趋势相反;其次是气温,其有效敏感区重心从海拔较低的青海省中部地区向海拔较高的青南高原移动,这与青南高原地区的海拔梯度式增温规律有关,即从高原边缘向高原腹地升温,且海拔越高,增温越快;降水主要影响柴达木盆地的侵蚀力,其有效敏感区重心向东南扩展,这可能与高原夏季风进退有关。研究结果可为青藏高原土壤风蚀灾害的预防、评估以及预测提供区域性差异化的技术支持与理论指导,也可为青藏高原乃至全球生源要素（C、N、P、S等）循环的大尺度驱动力研究提供新的研究视角。     

黄土高原面积-高程分析及其侵蚀地貌学意义

黄土高原是中国乃至世界最为著名的水土流失区之一,黄河的泥沙主要来源于此.面积-高程积分(Hypsometric integral,HI)分析常被用于侵蚀地貌区的地貌发育阶段判定.通过探讨HI与DEM分辨率、分析窗口之间的尺度效应,分析了黄土高原HI空间格局和发育阶段性,并在此基础上揭示了侵蚀产沙和地貌发育关系.研究表明:利用不同分辨率DEM计算的HI具有很好的稳定性,HI对DEM分辨率不具有依赖性;然而,利用不同分辨率的分析窗口所计算的黄土高原原HI值,表现出随着分析窗口的增大,HI表现出按照乘幂函数关系下降的趋势.黄土高原HI具有显著的空间分异特征,即汾渭谷地、宁夏内蒙沿黄冲积平原等地堑凹陷区是HI低值区,而黄土丘陵沟壑区是HI的高值区;黄土高原丘陵沟壑区地貌发育处于幼年期、壮年期和老年期的面积分别占总面积的7.9%、83.4%和8.7%,整体来看处于地貌发育壮年期;黄土高原丘陵沟壑区侵蚀产沙强度和地貌发育过程关系密切,HI与输沙模数存在显著的正相关.当前,黄土高原强烈的侵蚀产沙是其地貌发育处于壮年期的自然表现,这将是一个非常漫长的自然过程.     

Wind tunnel simulation of the effects of freeze–thaw cycles on soil erosion in the Qinghai–Tibet Plateau

Intense freezing and thawing actions occur in the Qinghai–Tibet Plateau because of its high elevation and cold temperature. The plateau's unique environment makes it easy to generate wind erosion under dry, windy weather conditions, resulting in the emergence of desertification. As a major form of freeze–thaw erosion, freeze–thaw and wind erosion is displayed prominently on the Qinghai–Tibet Plateau. Therefore, in this study, soil samples were collected from the surface of the plateau to undergo freeze–thaw and wind erosion simulation experiments. Results show that wind erosion strength increases with an increasing number of freeze–thaw cycles, water content in the freezing–thawing process, and the difference in freeze–thaw temperatures. Therefore, in the conditions of water participation, the main reason for the freeze–thaw and wind erosion in the Qinghai–Tibet Plateau is the damage to the soil structure by repeated, fierce freeze–thaw actions, and the sand-bearing wind is the main driving force for this process. The research results have theoretical significance for exploring the formation mechanism of freeze–thaw and wind erosion in the Qinghai–Tibet Plateau, and provide a scientific basis for freeze–thaw desertification control in the plateau.     

The classification and assessment of freeze-thaw erosion in Tibet

Freeze-thaw erosion is the third largest soil erosion type after water erosion and wind erosion. Restricted by many factors, few researches on freeze-thaw erosion have so far been done at home and abroad, especially those on the assessment method of freeze-thaw erosion. Based on the comprehensive analysis of impact factors of free-thaw erosion, this paper chooses six indexes, including the annual temperature range, annual precipitation, slope, aspect, vegetation and soil, to build the model for relative classification of freeze-thaw erosion using weighted and additive methods, and realizes the relative classification of the freeze-thaw erosion in Tibet with the support of GIS software. Then a synthetic assessment of freeze-thaw erosion in Tibet has been carried out according to the relative classification result. The result shows that the distribution of freeze-thaw eroded area is very extensive in Tibet, accounting for 55.3% of the total local land area; the spatial differentiation of freeze-thaw erosion with different intensities is obvious; and the difference in distribution among different regions is also obvious.     

西藏冻融侵蚀的分级和评价

Freeze-thaw erosion is the third largest soil erosion type after water erosion and wind erosion. Restricted by many factors, few researches on freeze-thaw erosion have so far been done at home and abroad, especially those on the assessment method of freeze-thaw erosion. Based on the comprehensive analysis of impact factors of free-thaw erosion, this paper chooses six indexes, including the annual temperature range, annual precipitation, slope, aspect, vegetation and soil, to build the model for relative classification of freeze-thaw erosion using weighted and additive methods, and realizes the relative classification of the freeze-thaw erosion in Tibet with the support of GIS software. Then a synthetic assessment of freeze-thaw erosion in Tibet has been carried out according to the relative classification result. The result shows that the distribution of freeze-thaw eroded area is very extensive in Tibet, accounting for 55.3% of the total local land area; the spatial differentiation of freeze-thaw erosion with different intensities is obvious; and the difference in distribution among different regions is also obvious.     

西藏水土流失敏感性评价及其空间分异规律

Based on Universal Soil Loss Equation and methods of mathematics model and GIS analysis, this study classified influence of precipitation, soil, topography and vegetation upon sensitivity of soil erosion into five different degrees which are extreme sensitivity, quite sensitivity, sensitivity, less sensitivity and no sensitivity. Assessment map of each factor was generated separately. Integrated assessment map of sensitivity of soil erosion has also been drawn by overlapping function with Arcinfo. Furthermore, the study analyzed distribution characteristics and spatial difference of sensitivity of soil erosion under special plateau environment of Tibet. According to sensitivity degree, some important controlling regions was confirmed so that departments of water conservancy, traffic management and agriculture could make scientific and reasonable decisions for their respective subject planning.     

Assessment and spatial distribution of sensitivity of soil erosion in Tibet

Based on Universal Soil Loss Equation and methods of mathematics model and GIS analysis, this study classified influence of precipitation, soil, topography and vegetation upon sensitivity of soil erosion into five different degrees which are extreme sensitivity, quite sensitivity, sensitivity, less sensitivity and no sensitivity. Assessment map of each factor was generated separately. Integrated assessment map of sensitivity of soil erosion has also been drawn by overlapping function with Arcinfo. Furthermore, the study analyzed distribution characteristics and spatial difference of sensitivity of soil erosion under special plateau environment of Tibet. According to sensitivity degree, some important controlling regions was confirmed so that departments of water conservancy, traffic management and agriculture could make scientific and reasonable decisions for their respective subject planning.     

基于改进土壤冻融水循环的Biome-BGC模型估算青藏高原草地NPP

Biome-BGC模型被广泛用于估算植被净初级生产力（Net Primary Productivity, NPP）,但是该模型未考虑冻土区土壤冻融水循环过程对植被生长的影响。本文基于Biome-BGC模型,改进冻土区活动层土壤冻融水循环,估算了2000—2018年青藏高原高寒草地NPP。通过比较原模型和改进后的模型,并对NPP模拟结果的时空特征进行了分析,结果表明：① 增加冻融循环提高了NPP估算精度,青藏高原草地NPP均值由114.68 gC/(m²·a)提高到128.02 gC/(m²·a)。② 原模型和改进后NPP的空间分布差异较大,时间变化趋势差异不明显。③ 青藏高原草地NPP总量为253.83 TgC/a,呈东南向西北递减的空间格局,年均增速为0.21gC/(m²·a)（P=0.023）,显著增加的占17.85%,主要分布在羌塘高寒草原地带的大部分地区和藏南山地灌木草原地带的西部。④ 该冻融水循环改进方法简单可靠,具有在其他多年冻土区推广的价值。     

The impacts of urbanization on soil erosion in the Loess Plateau region

1 IntroductionThe Loess Plateau region covers an area of 62.4(104 km2 and lies in the center of northern China. Urbanization and economic development have been quickened in recent decades. Both the number of towns established and scale of cities have increased. Although the pace of urbanization has been accelerated, the eco-environmental control in urban areas still lags behind relatively. Moreover, the construction and development of cities damaged the already vulnerable eco-environment to …     

The impacts of urbanization on soil erosion in the Loess Plateau region

The accelerated urbanization has resulted in new soil erosion in the Loess Plateau region since the 1980s. A concept of urban erosion and its impacts on environment are discussed. The experimental studies and field investigations show that those loose silt and earth piles formed by urban construction can be eroded seriously: Under stormy rain, the amount of sediment from steep man-dumped slope is 10.8–12.2 times that of from uncovered slope land; the result of experiments with the wind tunnel also shows that the damage to the surface structure of dry loess can cause serious soil erosion by wind in some cities of the region. Even if in the urban built-up area, there are many loose sandy soil, mud and silt, which are washed into rivers by city’s ground flow in the rainy season. So, anthropogenically induced soil erosion has made soil erosion more serious around the urban areas. And the urban eroded environment has several characteristics such as fragility, complexity, seasonality and quick variability. Urban areas witness a quick economic growth and have more construction projects than rural areas, which brings more intensive changes of environments during a short period of time or adds some new elements to the erosion system. Therefore erosion has experienced more intensive impact by human activities. So, the possible impact of urbanization on erosion environment must be taken into consideration when designing or planning to exploit natural resources or to develop urban areas in the Loess Plateau.     

The impacts of urbanization on soil erosion in the Loess Plateau region

The accelerated urbanization has resulted in new soil erosion in the Loess Plateau region since the 1980s. A concept of urban erosion and its impacts on environment are discussed. The experimental studies and field investigations show that those loose silt and earth piles formed by urban construction can be eroded seriously: Under stormy rain, the amount of sediment from steep man-dumped slope is 10.8-12.2 times that of from uncovered slope land; the result of experiments with the wind tunnel also shows that the damage to the surface structure of dry loess can cause serious soil erosion by wind in some cities of the region. Even if in the urban built-up area, there are many loose sandy soil, mud and silt, which are washed into rivers by city’s ground flow in the rainy season. So, anthropogenically induced soil erosion has made soil erosion more serious around the urban areas. And the urban eroded environment has several characteristics such as fragility, complexity, seasonality and quick variability. Urban areas witness a quick economic growth and have more construction projects than rural areas, which brings more intensive changes of environments during a short period of time or adds some new elements to the erosion system. Therefore erosion has experienced more intensive impact by human activities. So, the possible impact of urbanization on erosion environment must be taken into consideration when designing or planning to exploit natural resources or to develop urban areas in the Loess Plateau.     

Remote-sensing data reveals the response of soil erosion intensity to land use change in Loess Plateau,China

Developing an effective approach to rapidly assess the effects of restoration projects on soil erosion intensity and their extensive spatial and temporal dynamics is important for regional ecosystem management and the development of soil conservation strategies in the future. This study applied a model that was developed at the pixel scale using water soil erosion indicators (land use, vegetation coverage and slope) to assess the soil erosion intensity in the Loess Plateau, China. Landsat TM/ETM+ images in 2000, 2005 and 2010 were used to produce land use maps based on the object-oriented classification method. The MODIS product MOD13Q1 was adopted to derive the vegetation coverage maps. The slope gradient maps were calculated based on data from the digital elevation model. The area of water soil-eroded land was classified into six grades by integrating slope gradients, land use and vegetation coverage. Results show that the Grain-To-Green Project in the Loess Plateau worked based on the land use changes from 2000 to 2010 and enhanced vegetation restoration and ecological conservation. These projects effectively prevented soil erosion. During this period, lands with moderate, severe, more severe and extremely severe soil erosion intensities significantly decreased and changed into less severe levels, respectively. Lands with slight and light soil erosion intensities increased. However, the total soil-eroded area in the Loess Plateau was reduced. The contributions of the seven provinces to the total soil-eroded area in the Loess Plateau and the composition of the soil erosion intensity level in each province are different. Lands with severe, more severe and extremely severe soil erosion intensities are mainly distributed in Qinghai, Ningxia, Gansu and Inner Mongolia. These areas, although relatively small, must be prioritised and preferentially treated.