科尔沁沙地小叶锦鸡儿群落固沙作用的研究

建立人工植被是科尔沁沙地退化生态系统恢复与重建的基础，也是土地沙漠化防治的有效措施。本文以科尔沁沙地典型固沙灌木植物种——小叶锦鸡儿(Caragana microphylla)为研究对象，采用空间序列代替时间序列的方法，比较系统地研究了小叶锦鸡儿生长发育特征、更新途径，以及小叶锦鸡儿群落的固沙作用，并从水量平衡角度探讨了小叶锦鸡儿固沙植被的土壤水分状况和蒸散量变化。 研究结果表明：(1) 在生长季，小叶锦鸡儿的生物量在7月份达到最大值，且其生长发育速度与降水量相关；人工平茬和自然萌孽是小叶锦鸡儿主要且有效的更新途径。(2) 小叶锦鸡儿群落对近地表风速具有显著的阻滞作用，群落内总输沙量及各层输沙量均明显低于流动沙丘，小气候得到明显改善。(3) 6年生、11年生和22年生小叶锦鸡儿群落对土壤理化性质均有明显的改善作用。土壤中微沙(0.05～0.1 mm)和粘粒(<0.05 mm)含量增加，表层(0～10 cm)土壤容重减小，孔隙度和饱和含水率增大，土壤持水能力提高；土壤有机碳、全氮、碱解氮、全磷、有效磷和有效钾含量均有不同程度增加，尤以表层增加幅度最大，并且灌丛对养分有明显的富集效应。(4) 与天然小叶锦鸡儿群落的土壤含水量相比，人工小叶锦鸡儿群落内土壤含水量较低，且呈现出随植被生长发育年限增加而不断减少的趋势；在生长季，人工植被区绝大部分的降雨量都通过蒸散作用丧失，各试验样地蒸散量呈现单峰型曲线模式。

科尔沁沙地东南部地区主要植物叶片性状研究

以科尔沁沙地44种主要植物为研究对象，分别测定了叶片厚度、面积、体积、比叶面积、叶干物质含量、叶氮含量（单位重量的和单位面积的）、叶磷含量（单位重量的和单位面积的）、叶钾含量（单位重量的和单位面积的）、单位重量叶氮再吸收效率、单位重量叶磷再吸收效率和单位重量叶钾在吸收效率16种叶性因子，分别从叶片光合作用，水分生理及养分再吸收方面探讨不同植物对生境的适应能力，为当地生态环境恢复中植物选择与配置提供理论依据。结果表明： 不同生长型植物在叶片形态性状和叶片养分再吸收效率上没有显著差异，这说明不同生长型植物在光合作用、养分保存能力上对环境的适应机制存在较大重叠。不同生长型植物在叶片功能性状上差异显著，乔木主要是通过减弱光合作用，减缓生长速度，延长养分从衰老叶片的转移时间来适应贫瘠生境；草本植物主要是通过增强光合作用，加速叶片养分和干物质周转，提高对衰老叶片养分的再吸收速度来适应生境；灌木的生存策略介于乔木和草本之间。 豆科植物对土壤氮贫瘠的适应能力和对水分的利用效率显著高于非豆科植物；而非豆科植物对氮的保持能力和对干旱胁迫的适应能力显著强于豆科植物；禾本科草本植物的叶氮含量显著高于非禾本科草本植物；非禾本科草本植物对钾再吸收效率显著大于禾本科草本植物，说明非禾本科草本植物表现出对钾营养高度的保存能力，对钾胁迫的适应力强于禾本科草本植物。以上结果表明不同功能型植物具有不同的适应对策。 对4种典型生境中主要植物的叶片性状比较发现，除农田外，其它3种生境中植物叶片性状均未出现显著的差异。而农田植物仅在叶片形态性状上显著高于其它生境，造成这种现象的原因：一方面可能是相对其它叶片性状来说，植物叶片形态易受生境要素的影响，另一方面可能是由于该生境中物种种类较少。但从整体来看，土壤特征以及植被差异对叶片性状的影响不大。 植物对叶氮、磷和钾的再吸收效率之间呈显著的正相关，这与某些学者的研究结论是相矛盾的，以后可在更广泛的范围内进行验证。另外，植物对氮和磷的再吸收效率显著大于对钾的再吸收效率。这一方面说明了植物对氮、磷和钾的再吸收效率机制不同，另一方面可能是由于研究区土壤氮和磷营养缺乏，植物为了满足自身养分需求而采取的一种生存对策。根据植物对氮、磷和钾再吸收效率平均值大小顺序，可推测3种养分对植物生长的限制作用顺序是氮＞磷＞钾，氮可能是影响科尔沁沙地植物生长最强的营养元素。

科尔沁沙地樟子松人工林土壤呼吸对水分变化的响应

土壤是陆地生态系统最大的碳库，其碳储量是大气碳储量的两倍。土壤呼吸是土壤碳库的最大输出途径。在干旱半干旱区降雨格局以及土壤水分条件的变化对土壤呼吸的影响具有重要意义。本研究以半干旱区科尔沁沙地东部樟子松人工林为研究对象，通过室内培养模拟研究、野外降雨量控制研究和降雨频率模拟及干湿交替模拟试验，研究了科尔沁沙地半干旱人工林生态系统土壤呼吸对水分变化的响应趋势，探讨了降雨格局变化对土壤呼吸的影响，结果表明： （1）土壤呼吸速率随温度和土壤含水量的升高分别呈指数和线性增长；温度和土壤含水量分别影响着土壤呼吸对土壤水分和温度的敏感性； （2）降雨量变化影响土壤呼吸日动态变化，降水量增加30%，土壤24h释放CO2量升高了35.9%，当降水量减少30%时，土壤24h释放的CO2量降低了59.6%，而且干旱降低了土壤呼吸日动态变化的幅度； （3）降雨量变化对土壤呼吸月季动态具有一定影响。降雨量增加30%，8~10月土壤总呼吸CO2释放速率升高40.7%~166.4%，土壤异养呼吸CO2释放速率升高40.5%~194.3%；降雨量降低30%使降雨较频繁的8月份土壤总呼吸CO2释放速率降低34.0%~70.0%，土壤异养呼吸CO2释放速率下降20.9%~ 64.0%，而在降雨较少的9~10月份降雨量的减少对土壤呼吸则没有显著影响； （4）降雨量的变化对土壤总呼吸和异养呼吸温度敏感性有一定影响。当降雨量减少30%时，土壤总呼吸的Q10值由5.4下降到2.22，土壤异养呼吸的Q10值由4.84下降到1.81； （5）用温湿度耦合作用经验模型Rt = 0.307e0.0064（W·T）来描述三个降雨处理样地土壤呼吸速率与土壤温度及土壤含水量的关系，可以解释土壤呼吸速率变异的80.2%； （6）在较高的温度条件下，降雨频率增加一倍时，土壤呼吸速率将升高约24%；当温度较低时，降雨频率对土壤呼吸速率的影响不显著； （7）土壤呼吸随着干旱程度的增加而逐渐下降，但当进行降水模拟后，土壤呼吸值迅速升高，可升高降水前的41.0% ~ 128%，而后又迅速下降，呈现明显的脉动（pulse）效应。

封育措施对科尔沁沙地植被恢复的影响

过度放牧是科尔沁地区土地沙化的主要原因之一。围栏封育可以有效的抑制牲畜对植被的破坏，促进沙地植被恢复，从而改善区域的生态环境。本文以科尔沁沙地主要固沙植被——小叶锦鸡儿群落为研究对象，采用空间序列代替时间序列的方法，对比分析了不同封育年限和自然放牧条件下小叶锦鸡儿群落的土壤种子库特征、植被群落结构及空间异质性、土壤理化性质和土壤水分动态，较系统地探讨了封育措施对沙地植被恢复的影响。 研究结果表明：(1) 封育措施促使固沙植被区土壤种子库密度显著增加，自然放牧的小叶锦鸡儿群落封育2年、6年和12年后土壤种子库密度分别提高了15.7%、482.5%和728.1%；土壤种子库的物种多样性和均匀度随着封育时间的增加而降低；封育和放牧条件下小叶锦鸡儿群落土壤种子库均为聚集分布，封育措施降低了土壤种子库的空间异质性。(2) 封育措施对沙地植被恢复具有显著的促进作用，封育6年和12年后总植株密度分别提高了108.0%和239.3%，草本植物盖度分别提高了261.6%和271.6%；封育2年后群落的物种多样性增加，封育6年后群落的物种多样性和均匀度随着封育时间的增加而降低；放牧条件下小叶锦鸡儿群落植株密度具有强烈的空间自相关性，封育后空间自相关性降低。(3) 封育措施显著改善了土壤的养分状况，放牧地封育后土壤表层(0~10cm)的有机质、全氮、碱解氮、全磷、速效磷和速效钾含量均有不同程度的增加；封育区土壤含水量在0~10cm及40~60cm深度高于放牧区，在10~40cm及60~120cm深度低于放牧区；土壤含水量随着封育时间的增加而逐渐减少，但封育措施对土壤含水量的影响并不显著。

科尔沁沙地丘间低地植物种间关联研究

丘间低地植物种间关联研究有助于阐述丘间低地植物种间替代的机制。丘间低地面积对植物种间关联关系的影响、沙丘固定对丘间低地植物种间关联关系的影响研究对沙区植被恢复和植物多样性保护具有重要意义。但是，目前还未发现相关研究报道。 作者以科尔沁沙地为研究对象，选择流动沙丘区和固定沙丘区丘间低地面积系列，通过将植物划分为沙生植物、沼泽-草甸植物和草原植物三种生态组群，运用χ2检验和AC关联系数对植物的种间关联关系进行了分析。在流动沙丘区，随丘间低地面积的增大，沙生植物之间的关联性从正关联转变为负关联。当丘间低地面积小于0.5ha时，所有沙生植物之间都呈正关联；当丘间低地面积大于2ha时，所有沙生植物都呈负关联。大部分沙生植物与沼泽-草甸植物之间呈强烈的负关联。在固定沙丘区，随丘间低地面积的增大，草原植物之间种间关联表现为关联性从正关联转变为负关联；或始终呈正关联，但关联强度逐渐减小。大部分草原植物与沼泽-草甸植物之间呈强烈的负关联。不管在流动沙丘区还是在固定沙丘区，随丘间低地面积的增大，|AC| ≤ 0.3的种对数占所有种对数的百分比增大，|AC| ≥ 0.7的种对数占所有种对数的百分比减小。当丘间低地面积相同时，固定沙丘区丘间低地中|AC| ≤ 0.3的种对数占所有种对数的百分比小于流动沙丘区，|AC|≥ 0.7的种对数占所有总对数的百分比大于流动沙丘区。 本研究表明：1）丘间低地面积增大导致种间关系松散；2）沙丘固定导致丘间低地植物种间关系更加紧密。

我国北方沙质沉积物气候代用指标对比研究

In this study we examined samples of sandy sediments along the north-south transects crossing the Taklimakan Desert, the Badain Jaran Desert and the Hunshandake Sandy Land respectively. The grain size was measured via dry sieving, and the carbonate content by means of an Eijkelkamp instrument. The analyses of grain size and carbonate contents show: (1) The sand grains of the Badain Jaran Desert are coarsest and best sorted, this should be associated with the strongest usual wind among these three regions. (2) The different desert have its special wind condition in their own regions. The Badain Jaran Desert and the Taklimakan Desert both show that the wind is getting weaker from north towards south, but the Hunshandake Sandy Land have the similar wind stress from north towards south. (3) The frequency curves of the sandy sediments from the Badain Jaran Desert show a kind of distinct double peaks, presumably associated with the alternative transportations of summer and winter monsoons in the north boundaries of the summer monsoon. (4) There are great differences of the carbonate contents among these three regions, this maybe associated with the humidity, the humidity of Hunshandake Sandy Land is the best, and the one of the Taklimakan Desert would be the worst among them. Analyses of The three profiles about grain size and carbonate contents show: (1) From 8ka BP, the winter-monsoon was getting weaker, and the summer-monsoon accordingly became stronger, and about 1 ka later, the winter-monsoon was getting stronger again. (2) In the stage of the profiles, there maybe show two circles of dry and wet climate, and the climate changes in those three regions show the similar trend.

浑善达克沙地与河北沽源地区土地沙漠化研究

The Otindag sandy land and the Guyuan region of Hebei Province lie in the agro-pastoral zone, where sandy desertification is serious. So they are typical for us to study on. In this paper, detail investigation were made on the Remote Sensing, Hydrochemistry, Chronology, grain size analyzing of research region to monitor sandy desertification and environmental background. The main conclusions are presented as following: 1. According to the diverse natural condition, the research area is divided into three types as sandy land desertification, cultivated land desertification and desertification reflected by lake change. The monitoring result of the first type shows that the main performance way of the sandy desertification in Otindag sandy land is that (1) the expansion of both the shifting dune and the half fixed sandy dune, (2) the reduce of the fixed sandy dune. While the result of the second type shows (1) the desertification land in the Guyuan region has first increasing then reducing change for about 30 years. (2) The sand mainly concentrates west of the research area and small part of wind-drift sand distributes northeast the research area with the spot shape. (3) The meadow area increases obviously. As far as the third type, the Dalai Nur lake area occurs first expanding then reducing change and the wind-drift sand around the lake first reduces then increases. 2. The land cover of the different types change with the same law. It is worth notice that the lake area changes oppositely with that of the wind-drift sand. 3. For about 5,000 a B.P. -2800 a B.P., the well developed palaeosols emerged. After that, three layer palaeosols were founded in the profile of Otindag sandy land. The analyses of grain size show that the sand grains of the south were coarser than that of the north. The sand in the north and middle were well sorted, while the south poor sorted. 4. Both the natural and human impact on the process of sandy desertification. On this research result, different regions have different influences. So the measures to improve sandy desertification should be choosed respectively.

Experiments on interaction between current-induced vibration and scour of submarine pipelines on sandy bottom

In order to understand the dynamic behavior of submarine pipelines exposed to current and the mechanism of the interaction between current-induced vibration and scour of pipelines on a sandy bottom, an experimental investigation is conducted with a small scale model A test model which can be tested in the flume is set up by taking into account the typical working conditions of the pipelines and by applying the similarity theory. The interactions between the shape of the scour hole and the behavior of the pipeline as well as the flow patterns of the current are detailed, and the interaction mechanism outlined. The effect of vibration of the pipeline on the development of dynamic scour at different stages is found out. The proposed experimental method and test results provide an effective means for design of marine pipelines against scouring.

Improved Analysis Method for Wave-Induced Pipeline Stability on Sandy Seabed

The existing Det Norske Veritas DNV Recommended Practice RP E305 for pipeline on-bottom stability is mainly based on the pipe–soil interaction model reported by Wagner et al. in 1987, and the wake model reported by Lambrakos et al. in 1987, to calculate the soil resistance and the hydrodynamic forces upon pipeline, respectively. Unlike the methods in the DNV Practice, in this paper, an improved analysis method is proposed for the on-bottom stability of a submarine pipeline, which is based on the relationships between Um/ gD 0.5 and Ws / D2 for various restraint conditions obtained by the hydrodynamic loading experiments, taking into account the coupling effects between wave, pipeline, and sandy seabed. The analysis procedure is illustrated with a detailed flow chart. A comparison is made between the submerged weights of pipeline predicted with the DNV Practice and those with the new method. The proposed analysis method may provide a helpful tool for the engineering practice of pipeline on-bottom stability design.

Experimental Study Of Vortex-Induced Vibrations Of A Pipeline Near An Erodible Sandy Seabed

Based on similarity analyses, a series of experiments have been conducted with a newly established hydro-elastic facility to investigate the transverse vortex-induced vibrations (VIVs) of a submarine pipeline near an erodible sandy seabed under the influence of ocean currents. Typical characteristics of coupling processes between pipe vibration and soil scour in the currents have been summarized for Case 1: pipe is laid above seabed and Case 11: pipe is partially embedded in seabed on the basis of the experimental observations. Pipe vibration and the corresponding local scour are usually two coupled physical processes leading to an equilibrium state. The influence of initial gap-to-diameter ratio (e(0)/D) on the interaction between pipe vibration and local scour has been studied. Experimental results show that the critical values of V-r for the initiation of VIVs of the pipe near an erodible sand bed get bigger with decreasing initial gap-to-diameter ratio within the examined range of e(0)/D (-0.25 < e(0)/D < 0.75). The comparison of the pipe vibrations near an erodible soil with those near a rigid boundary and under wall-free conditions indicates that the vibration amplitudes of the pipe near an erodible sand bed are close to the curve fit under wall-free conditions; nevertheless, for the same stability parameter, the maximum amplitudes for the VIV coupled with local scour increase with the increase of initial gap-to-diameter ratio. (c) 2007 Elsevier Ltd. All rights reserved.

Ocean currents-induced pipeline lateral stability on sandy seabed

Unlike previous mechanical actuator loading methods, in this study, a hydrodynamic loading method was employed in a flow flume for simulating ocean currents induced submarine pipeline stability on a sandy seabed. It has been observed that, in the process of pipeline losing lateral stability in currents, there usually exist three characteristic times: (1) onset of sand scour; (2) slight lateral displacement of pipeline; and (3) breakout of pipeline. An empirical linear relationship is established between the dimensionless submerged weight of pipeline and Froude number for describing pipeline lateral stability in currents, in which the current-pipe-soil coupling effects are reflected. Scale effects are examined with the method of "modeling of models," and the sand particle size effects on pipeline stability are also discussed. Moreover, the pipeline stability in currents is compared with that in waves, which indicates that the pipeline laid directly upon the sandy seabed is more laterally stable in currents than in waves.

Oscillatory Flow Induced Hydrodynamic Forces upon a Pipeline near Erosive Sandy Seabed

An experimental study of the properties of hydrodynamic forces upon a marine pipeline is presented in this paper, in the equilibrium scour conditions for various Keulegan-Carpenter numbers and various initial relative gaps between pipeline and the erosive sandy seabed. The tests are conducted in a U-shaped oscillatory water tunnel with a sand box located at the bottom of the test section. According to the experimental results, the maximum horizontal forces on the pipelines with an initial gap to seabed will decrease to some extent due to scouring process. For engineering appliances, it seems safer to estimate wave induced forces on pipelines under the assumption that seabed is plane. However, it should be noticed that great changes would be brought to the frequency properties of lift forces because of the sandy scour beneath the pipeline, which occurs for certain KC numbers.

Experimental Study of Pipeline Stability on Sandy Seabed under the Influence of Ocean Currents

Ocean-current-induced pipeline stability on sandy seabed was simulated physically in a flow flume. The process of pipeline losing onbottom stability in currents was recorded and analyzed. Experimental data show that, for a pipeline directly laid on sandy seabed, there exists a linear relationship between the dimensionless submerged weight of pipeline and Froude number, in which the current-pipe-soil coupling effects are reflected. The sand-particle size effects on pipeline onbottom stability are further discussed. The new established empirical relationship may provide a guide for the engineering practice of current-induced on-bottom stability design of a submarine pipeline.