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1.
Testate amoebae that inhabit peat are sensitive indicators of water table position. In this study, we used testate amoebae in sediments from a mire in the western Alps (Lac du Thyl) to: (1) reconstruct the hydrology of the site over the last 7,000 years, (2) determine how hydrological changes affected testate amoebae diversity and (3) infer past trophic state shifts. The study site is located in one of the driest valleys of the Alps and is thus very sensitive to hydrological changes. Our study revealed that the water table depth increased (dry conditions) between 5,800 and 4,000 cal year BP. This triggered establishment of a Sphagnum-type peat and acidic conditions from 5,700 to 4,000 cal year BP. These processes were independent of ongoing transformations of the terrestrial vegetation and soil in the catchment area. After 1,690 cal year BP, the depth to the water table decreased (wetter conditions) and a minerotrophic fen developed. At the same time, the diversity of testate amoebae increased, probably as a result of deforestation that supported the expansion of grassland. Climate and land use were apparently more important factors controlling the lake hydrology than were changes in vegetation and soil in the catchment. Testate amoebae diversity was linked to land cover. Changes in pH were controlled indirectly by external forcing (climate), but more directly by fluctuations in the level of the water table (internal forcing) and autogenous expansion of Sphagnum.  相似文献   

2.
Hydraulic redistribution is the process of passive water movement from deeper moist soil to shallower dry soil layers using plant roots as conduits. Results from this study indicate that this phenomenon exists among two shrub species (Guiera senegalensis and Piliostigma reticulatum) that co-exist with annual food crops in Sahelian agro-ecosystems. Real-time measurements were conducted for soil water content, soil water potential and microclimate variables notably; air temperature, relative humidity, wind speed, precipitation and solar irradiance. Additionally, sap flow measurements were conducted in shrub roots using the thermal dissipation technique on intact and coppiced shrubs. Monthly predawn leaf water potential was measured using a portable pressure chamber. Soil water potential (Ψs) at the 20 cm depth declined significantly during the dry season with diel changes in Ψs of −0.6 to −1.1 MPa. These variations were attributed to passive water release from shrub roots resulting in overnight rewetting of drier upper soil layers. Sap flow measurements on tap and lateral shrub roots indicated daily reversals in the direction of flow. During the peak of the dry season, both positive (toward shrub) and negative (toward soil) flows were observed in lateral shrub roots with sap flow in the lateral roots frequently negative at night and rapidly becoming positive soon after sunrise. The negative sap flow at night in superficial lateral roots and the periodic positive flow in the descending tap roots were indicative of hydraulic redistribution. Hydraulic redistribution may be an important mechanism for drought stress avoidance while maintaining plant physiological functions in both shrubs and neighboring annuals in water-limited environments.  相似文献   

3.
Diversity theory predicts that species numbers should be highest at intermediate levels of both disturbance and environmental stress. We examined woody and herbaceous plant species richness and cover in the San Pedro River flood plain, along lateral gradients of water availability (ground-water depth), flood disturbance (inundation frequency), and distance from and elevation above the channel, and along longitudinal gradients of water availability (ground-water depth, surface flow permanence, and rainfall) and flood disturbance (total stream power). Herbaceous species were recorded during four sampling periods, and spatial patterns for this group were time-dependent, reflecting temporal variation in limiting factors. During the summer dry season of a dry year, when overall richness was low, richness and cover of herbaceous species declined laterally from the stream channel with increasing ground-water depth, consistent with the idea that low resource levels can limit species richness. Following the summer monsoon rains and floods, when water was less limiting and annuals were seasonally abundant, lateral patterns shifted such that herbaceous species richness and cover increased with increasing plot location above or from the channel. The relationship of herbaceous species richness with tree canopy cover also varied seasonally, shifting from positive (greater richness under canopy) in dry seasons to negative (lesser richness under canopy) in wet seasons. Longitudinally, herbaceous species richness and cover were limited primarily by stream flow and/or ground-water availability during the summer dry season of a dry year. Following the summer monsoon rains and floods, patterns were weighted by the seasonally abundant annuals, and richness increased among sites primarily with distance upstream (and related rainfall gradients). Richness and cover patterns also varied between years with different flood conditions. During the two sampling seasons in the year following a large flood, herbaceous species richness increased with flood disturbance intensity but declined at the few most intensely disturbed sites, consistent with intermediate disturbance theory.For woody species, richness within plant functional groups varied in opposing ways along the lateral gradients: hydromesic pioneer species decreased and hydromesic and xeric competitors increased with distance from or above the channel, with no overall change in species richness. Among sites, woody species richness patterns were related to water availability, but not to flood disturbance. However, richness of woody hydromesic pioneer species increased with both increasing site moisture and flood disturbance. Woody and herbaceous species richness both increased among sites as a function of increasing flood-plain width, likely due to species–area effects. Overall, results indicate that flood disturbance and water availability both influence species richness of riparian plants in the flood plain of this semi-arid region river, with the relative influence of each factor varying among plant groups and over time.  相似文献   

4.
沙质土壤水分运动参数研究   总被引：8，自引：3，他引：5  
苏培玺 《中国沙漠》2000,20(3):329-332
利用土壤水动力学原理,在室内测定了沙质土壤水分特征曲线、饱和导水率和非饱和导水率。在沙地葡萄园,建立观测场,埋设中子管和负压计,观测水分和吸力变化,基质吸力随土层加深而减小,10 cm处全年最大为126 cm水柱(12.4k Pa),30 cm处全年最大为116 cm水柱(11.4k Pa)。4月份吸力最大,土壤最干燥,7月份吸力最小,土壤最湿润。  相似文献   

5.
Liu  Muxing  Wang  Qiuyue  Guo  Li  Yi  Jun  Lin  Henry  Zhu  Qing  Fan  Bihang  Zhang  Hailin 《地理学报(英文版)》2020,30(6):949-968
Rainfall provides essential water resource for vegetation growth and acts as driving force for hydrologic process, bedrock weathering and nutrient cycle in the steep hilly catchment. But the effects of rainfall features, vegetation types, topography, and also their interactions on soil water movement and soil moisture dynamics are inadequately quantified. During the coupled wet and dry periods of the year 2018 to 2019, time-series soil moisture was monitored with 5-min interval resolution in a hilly catchment of the Three Gorges Reservoir Area in China. Three hillslopes covered with evergreen forest(EG), secondary deciduous forest mixed with shrubs(SDFS) and deforested pasture(DP) were selected, and two monitoring sites with five detected depths were established at upslope and downslope position, respectively. Several parameters expressing soil moisture response to rainfall event were evaluated, including wetting depth, cumulative rainfall amount and lag time before initial response, maximum increase of soil water storage, and transform ratio of rainwater to soil water. The results indicated that rainfall amount is the dominant rainfall variable controlling soil moisture response to rainfall event. No soil moisture response occurred when rainfall amounts was 8 mm, and all the deepest monitoring sensors detected soil moisture increase when total rainfall amounts was 30 mm. In the wet period, the cumulative rainfall amount to trigger surface soil moisture response in EG-up site was significantly higher than in other five sites. However, no significant difference in cumulative rainfall amount to trigger soil moisture response was observed among all study sites in dry period. Vegetation canopy interception reduced the transform ratio of rainwater to soil water, with a higher reduction in vegetation growth period than in other period. Also, interception of vegetation canopy resulted in a largeraccumulated rainfall amount and a longer lag time for initiating soil moisture response to rainfall. Generally, average cumulative rainfall amount for initiating soil moisture response during dry period of all sites(3.5–5.6 mm) were less than during wet period(5.7–19.7 mm). Forests captured more infiltration water compared with deforested pasture, showing the larger increments of both soil water storage for the whole soil profile and volumetric soil water content at 10 cm depth on two forest slopes. Topography dominated soil subsurface flow, proven by the evidences that less rainfall amount and less time was needed to trigger soil moisture response and also larger accumulated soil water storage increment in downslope site than in corresponding upslope site during heavy rainfall events.  相似文献   

6.
苏莹  赵明宪  王国平 《湿地科学》2006,4(4):292-297
通过对长白山圆池4个泥炭剖面样品的分析,揭示了其氮元素分布规律。在圆池选取4个具有代表性的采样点,利用泥炭采样器采取新鲜泥炭样品。分析结果表明,4个泥炭剖面氮元素含量在0.014%~3.353%之间;剖面间相比较,其中贫营养泥炭整体含氮量较低;4个泥炭剖面的氮元素分布呈现明显规律,受泥炭上层不同植物、泥炭水分和有机质含量等因素的影响,泥炭剖面中氮元素累积峰可能出现在剖面的表层(0~5cm)或中间层(10~20cm);泥炭剖面氮元素与有机质呈极显著的正相关;泥炭剖面C/N比值变化在9.51~66.98之间,部分剖面层位C/N比值异常高,表明该层位碳的累积速度显著高于氮元素。  相似文献   

7.
研究了潜水埋深(40、80、120、180、220cm)处理对一年生疏叶骆驼刺(Alhagi sparsifoli)幼苗生长和叶片形态的影响。结果表明:随着潜水埋深的增加,疏叶骆驼刺幼苗叶片厚度逐渐增加,叶片厚度在220cm埋深下最大,长度和宽度在120cm埋深下最大,且叶片长度呈优先减小的趋势;潜水埋深变化对疏叶骆驼刺株高生长影响不大,但对冠幅和分枝数的生长影响显著(p0.05);除40cm埋深处理中根系以平均1.24cm·d-1的速率扎入地下水层外,其他4个处理根系生长速率随潜水埋深的增加而增加,且180cm和220cm埋深下根系生长速率明显高于其他3个处理;根系到达220cm潜水埋深的时间为123d;幼苗生物量积累随着潜水埋深变化先增加后减小,茎叶生物量在120cm埋深处理中达到最大值,而根系生物量在180cm埋深下最大。潜水埋深变化对疏叶骆驼刺地上部分和根系生长的影响不同,潜水埋深增加有利于根系生长和根系生物量增加;以120cm为拐点,潜水埋深过浅或过深都会抑制地上部分生长;220cm潜水埋深条件下,疏叶骆驼刺生长缓慢且生物量的累积最小,表明若潜水埋深大于220cm则对幼苗生长不利。  相似文献   

8.
本文研究地下水浅埋深条件下,水位降深为0-40cm、0-55cm、0-70cm、0-85cm、0-100cm时给水度的变化规律。利用室内风积砂的排水实验获得实测给水度,分析实测给水度与经验公式计算的给水度和水位降深的关系。结果表明,当水位降深小于毛细上升高度时,给水度较小,并随着水位降深的增加而增大。当水位埋深大于毛细上升高度时,给水度由毛细上升高度段及毛细上升高度以上段组成。毛细上升高度段,给水度随着水位降深的增加而增大,给水度较小。而毛细上升高度以上段,给水度较大,并随着水位降深的增加趋于定值。雷志栋公式计算的给水度与实测给水度最相近。而Nachabe和Duke公式在进气值高度上计算的给水度都比实测给水度大。这些成果为浅埋深情况下地下水位波动的准确估计提供依据。  相似文献   

9.
Clean sweeping (i.e., frequent and shallow tillage in orchards) is a common practice in semi-arid areas. A potential drawback in dry areas is that the tree roots cannot access the water in the plough layer. Our objective was to quantify the loss of water by evaporation and the loss or gain by overland flow in almond (Prunus dulcis Mill.) orchards on loamy soils in southeast Spain. The evaporation from a 15 cm plough layer equals 70–104% of annual precipitation, taking into account losses or gains by overland flow. The large evaporation explains the low canopy cover observed, which averaged 3.2%. The runoff coefficient of the test sites is 1–6%. There is no drainage below 15 cm during dry years, except for an area that receives a net influx of overland flow. The trunk basal area in this depression is 12% larger compared to the rest of the field. The options for increasing the water intake of the trees are to reduce the tillage depth or to switch from clean sweeping to no-tillage combined with chemical weeding.  相似文献   

10.
The environmental controls on modern peatland testate amoebae (Protozoa: Rhizopoda) in the North of Ireland were investigated to assess the potential for Holocene palaeoclimate research within this region. Canonical Correspondence Analysis (CCA) revealed that hydrological factors (water table depth and moisture content) are the most important abiotic controls on organism distribution. A series of partial CCAs showed that water table depth explains 15.8% and moisture content explains 5.5% of the total variance. Monte-Carlo permutation tests showed that the results are highly significant (p < 0.002; p < 0.040 respectively). Transfer functions were generated for water table depth using weighted averaging tolerance downweighted (WA-Tol) regression and for moisture content using weighted averaging partial least squares regression (WA-PLS). The performance of the models was assessed using leave-one-out cross-validation (jacknifing). After removal of outlier samples, the improved transfer functions were found to perform well with an r jack2 and root mean square error of predictionjack of 0.83, 4.99 cm for water table depth and 0.76, 4.60% for moisture content respectively. The water table transfer function was applied to a fossil peat sequence from this region and reconstruction errors were generated by 1,000 bootstrap cycles. The water table reconstruction was also carried out using an established pan-European transfer function and was found to be similar to that based on the North of Ireland dataset. This demonstrates the persistent and comparable control of hydrological variables on the distribution of testate amoebae taxa across Europe and implies that regional training sets can suffice as long as no-analogue situations are not encountered.
G. T. SwindlesEmail:
  相似文献   

11.
土壤水分及土壤-大气界面对麦田水热传输的作用   总被引：13，自引：2，他引：11  
文章根据1996年在中国栾城农业生态试验站观测的田间试验资料,分析了土壤水分和土壤-大气界面对麦田水热传输的抑制和加速作用。对于显热和潜热输送,土壤水分起决定作用,土壤水分越小,显热通量越大,潜热通量越小,反之亦然。只在土壤水分较小时界面厚度对显热和潜热输送作用较大。对于土壤热输送,界面厚度起决定作用,界面厚度越大土壤热通量越小。分析还发现60cm深处土壤水势与叶水势和大气水势的相关系数较其它深度处的土壤水势大。0～60cm土层是确定土壤水分运动对界面水热传输影响的一个良好的指示层。  相似文献   

12.
利用稳定同位素技术测定降水、土壤水、植物茎干水的同位素组成,结合多元线性混合模型(IsoSource)确定科尔沁沙地东南部樟子松人工林内樟子松的根系吸水范围以及各水源的水分贡献率。通过连续观测强降水事件前后樟子松水分来源的变化,探究降水对樟子松水分利用的影响。结果表明樟子松茎干水与20cm以下土层的土壤水同位素组成最为接近,樟子松的水分吸收主要集中在这一层(最大取样深度80cm)。IsoSource模拟结果与观测结果一致,土壤水分条件较好时,大约60%以上的水分来自于20-80cm土层;当这一深度土壤含水量降低时,樟子松将会更多地依赖更深层的土壤水分。樟子松根系分布的最大深度远小于地下水位,因此很难利用到地下水。2009年7月13日14.4mm的降水前后,樟子松茎干水同位素组成的变化表明,降水结束后36小时樟子松可以感应到降水对表层20cm土壤水分的补充,这一土层的水分贡献率在接下来的24小时内迅速降低。不同水分条件下水分来源的多样性表明樟子松能较好地适应沙地生境。  相似文献   

13.
Peatland testate amoebae are sensitive indicators of local hydrology and have been used as proxies for surface moisture conditions in fossil studies. However, few regional calibration datasets exist in North America, and knowledge of testate amoeba ecology and distribution patterns are limited. The objectives of this study were to (1) investigate the relationship between testate amoebae, environment, and Sphagnum species in Michigan peatlands; (2) generate transfer functions from this dataset that can be applied to fossil data; and (3) describe vertical variation of testate amoebae inhabiting Sphagnum moss. Testate amoeba assemblages from 139 microsites within 11 peatlands in Michigan were compared to assess variability between and within peatlands. Most peatlands contained similar testate amoeba assemblages, although within individual peatlands the amount of assemblage variability is correlated to the amount of environmental heterogeneity. Of the measured environmental variables, depth to water table showed the strongest relationship with testate amoebae. Depth to water table can be reconstructed from fossil data with a mean error of ±7.5 cm, although predictive ability deteriorates in extremely dry environments (>30 cm water table depth). Vertical variation in testate amoeba assemblages was investigated at 89 Sphagnum-dominated microsites by directly comparing amoeba assemblages and the abundance and frequency of common taxa in upper and lower portions of the Sphagnum stem. Except for extremely dry microsites, considerable vertical variation in assemblage composition exists. Many agglutinate taxa are more abundant on lower portions of the Sphagnum stem, and taxa containing symbiotic zoochlorellae are more abundant on upper portions. Refinements in sampling procedures and analysis may improve the predictive ability of transfer functions.  相似文献   

14.
A dendrochronological study was made on fossil tree trunks of Scots pine, Pinus sylvestris , preserved in a peat bog at Hanvedsmossen, 50 km SW of Stockholm, Sweden. Of 56 sampled pines, 48 were assembled in a 204-year long floating chro-nology. The chronology spans 1686-1483 BC ± 23 years. The trunks are found at the very bottom of the peat accumulation. Because the roots stand in underlying clay, the tree stand germinated before or simultaneously with bog growth and provides maximum age for bog vegetation development which started c . 1480 BC. The pine growth steadily decreased during the last 30 years of the chronology and most trees died during the same period. It is proposed that the drainage outlets from Hanvedsmossen overgrew with brushwood simultaneously with the succession of pines, resulting in a higher sensitivity of tree growth to small changes in water levels. The preservation of the logs is suggested to be a result of a raised water table providing anaerobic conditions and later the logs were enveloped by peat growth. It is suggested that this period was the initial phase of the ensuing climate deterioration. The climate shifted to wetter conditions, i.e. higher amounts of precipitation, lower temperature or both. This resulted in lower evaporation giving additional peat bog growth and a locally raised water table.  相似文献   

15.
层状土壤中砂层层位对潜水蒸发的影响   总被引：7，自引：2，他引：7  
通过室内一维土柱实验,研究了夹砂层土体构型中砂层层位对潜水蒸发的影响,分析了其影响机理,进一步讨论了砂层位置和水分蒸发的定量关系。结果表明,砂层对于水分的蒸发既有促进也有抑制作用,在地下水埋深为50cm时,5cm厚的底砂层可使水分的蒸发强度增加10％-20％；砂层距水位的距离大于5cm时,砂层可抑制水分的蒸发,且当距离增加到35cm左右,其抑制率可达70％-80％；当砂层距水位的距离继续增大时,水分的蒸发强度基本保持不变。这主要是由砂层自身的导水率变化以及砂层与同剖面中其它土质导水率的相对大小发生变化而引起。累积蒸发量与砂层层位以及蒸发历时之间定量关系的建立为预测砂层对潜水蒸发的影响以及估算特定历时蒸发损失量最小的砂层层位提供了依据。  相似文献   

16.
Peatlands offer the potential for high resolution records of water balance over Holocene timescales, yet this potential is under-exploited in many areas of the world. Within Europe, peatlands are mostly confined to areas north of 55° N, but several areas of southern and eastern Europe contain small peatlands which may be suitable for palaeoclimatic reconstruction. In this paper we test the potential of peatlands in the Carpathian region for deriving quantified estimates of water table changes using testate amoebae analysis. A training set for palaeohydrological reconstruction from testate amoebae assemblages was obtained by collecting surface samples from 13 peatlands, including 9 from Hungary and 4 from Transylvania (Romania). Using a simple measure of mean annual water tables estimated from staining of PVC tape, we found that some peatlands were heavily influenced by runoff and groundwater, and were therefore not suitable as modern analogues of ombrotrophic climatically sensitive sites. The relationship between the testate amoebae assemblages in the modern samples and the environmental variables was explored using CCA. The CCA biplot showed that the most important variables are depth to water table and moisture content, confirming that hydrology is a key control on taxon distribution. pH was a secondary gradient. A transfer function for % moisture and depth to water table was established and applied to fossil assemblages from a sequence from Fenyves-tető, Transylvania, Romania. The reconstructed water table shows a number of variations which have parallels with other palaeoclimatic records from Europe and the North Atlantic prominent phases of higher water tables are associated with the periods 8000–8300 cal BP, 3000–2500 cal BP and after 600 cal BP. We suggest that these were periods of particular intensification of westerly airflow which affected eastern Europe as well as western and central Europe.  相似文献   

17.
用波谱分析法的研究结果表明,当地旱雨季土壤含水量差异较大:旱季土壤含水量<凋萎湿度,土壤水分严重亏缺。因受降水量的影响,土壤含水量呈周期为1a的波动变化。用谐波分析法还计算了各层次土壤含水量的谐波展开式,由此可预报土壤含水量变化趋势。  相似文献   

18.
皖江自然湿地土壤碳密度及其开垦为农田后的变化   总被引：7，自引：1，他引：6  
于2005年分别采集了安徽沿江4个淡水湖泊的自然湿地及其周边围垦农田的代表性土壤剖面样品,测定了总有机碳含量,讨论了天然淡水湿地有机碳密度与深度分布特征及其开垦为农田后的变化。结果显示,湿地表层（0～30cm）和全剖面（0～100cm）中的碳密度分别为42．5～57．4t／hm^2和81．5～91．6t／hm^2;而农田则分别为22．4～48．4t／hm^2和41．4～76．5t／hm^2。湿地开垦为农田后,土壤表层和全剖面的土壤有机碳含量明显降低,且有机碳含量的变异性增大。表明湿地开垦为农田后,其碳库失去稳定性。但是,开垦的旱地土壤的有机碳含量和碳密度显著低于开垦的稻田,故湿地开垦为旱地更不利于湿地碳库保护。因而,将湿地垦殖为水田是相对较有利于湿地碳库保护的人为土地利用方式。湿地开垦的碳库损失可能是土壤的大气CO2源效应的主要途径。  相似文献   

19.
克里雅河尾闾绿洲浅层地下水位埋深变化特征研究   总被引：2，自引：0，他引：2  
地下水位埋深的动态变化极大程度上控制着荒漠植被。达理雅博依位于克里雅河尾闾,是塔克拉玛干沙漠腹地现存面积最大的一处由荒漠河岸林构成的天然绿洲,在这里对地下水位埋深动态变化的监测有助于研究其对地表植被的影响,从而进一步揭示天然绿洲形成与维系的机理。由于复杂的地理环境和闭塞的交通,尚未有学者在该绿洲获得连续的地下水位埋深监测数据。于2012年10月在尾闾绿洲腹地设立了观测井,获取了2012-2018年间地下水位埋深数据,从地下水位埋深的日极值分布特征、日极差分布特征、年内和年际波动特征4个方面分析了该井近6 a来水位埋深的动态变化过程,并结合胡杨的生长习性探讨了尾闾绿洲地下水位埋深变化对生态系统的可能影响。对该绿洲地下水位埋深数据观测结果的初步分析表明:(1)测井每日水位埋深最小值多出现在16:00、20:00与04:00;每日水位埋深最大值多出现在16:00,分布于4-10月,尤以9月为多。(2)地下水位埋深日极差波动范围为0~0.5 m。大于0.1 m的日极差主要分布于7-8月,并以2017年最为显著。(3)地下水位埋深基本在1.0~3.0 m波动,月峰值主要出现在2-3月与8-9月。(4)地下水位埋深多年平均值为2.0 m,水位埋深总体呈缓慢上升,约0.08 m·a^-1。(5)各年水位埋深在1.0~2.0 m的总天数呈增加趋势,利于胡杨种子萌发与植株扎根;在2.0~4.0 m的总天数呈减少趋势,青壮胡杨生长可能受限。  相似文献   

20.
本文论述了北威尔士北美云杉林〔Ｐｉｃｅａｓｉｔｃｈｅｎｓｉｓ（Ｂｏｎｇ）Ｃａｒｒ〕土壤非饱和水在土壤剖面上的垂直和水平方向的时空变化过程及规律。结果表明，表层至１０ｃｍ深和３５～５０ｃｍ深的土壤层内非饱和水含量始终高于１０～２０ｃｍ和２０～３５ｃｍ深两层的非饱和水含量。土壤非饱和水有从上向下和从下向上补给中间层的规律。受水势梯度的影响，犁沟内非饱和水可以侧向补给相邻畦埂的土壤。在监测期，土壤中没有饱和水和过饱和水运动过程出现  相似文献   

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