Effects Of Microtopography Research Articles

Grazing intensity and micro-topographical effects on some nitrogen and carbon pools and fluxes in sheep-grazed hill country in New Zealand

A significant proportion of grazed land in New Zealand is in hill country and this area supports a large proportion of the national sheep and beef herd. Little is known about the effect of increased grazing intensity on nitrogen (N) and carbon (C) cycling and losses from these hill country grazing systems, nor of the effect of micro-topography on N and C pools and fluxes. A three year grazing trial was conducted to gather information on the effect of an increase in grazing intensity on soil chemistry and N and C leaching in three distinct micro-topographical classes.In this temperate environment, micro-topography was the dominant influence on annual net herbage accumulation, soil chemistry and N and C leaching. Net herbage accumulation was two- and five-fold greater on low (<13°) compared to medium (13–25°) and high (>25°) slopes (14.6, 7.8, and 2.9tDMha−1yr−1, respectively). Low slope soils had generally higher concentrations of phosphorus and N and C species compared to soils on medium and high slopes. Nitrogen leaching was greatest in low compared to medium slope areas: three-year mean estimates of annual leaching were 80 vs. 7kg inorganic Nha−1, and 40 vs. 8kg dissolved organic Nha−1, respectively. Per ha estimates of inorganic N leaching in this landscape (where low, medium and high slopes occupy 10, 60 and 30% of the land area) are 15kgNha−1 if we make the assumption that high slopes leach as much inorganic N as medium slopes, or 12kgNha−1 if it is assumed that high slopes do not leach at all. The significant effect of slope on parameters measured is a reflection of micro-topographical influences on livestock grazing, resting and excreting patterns. Estimates of annual dissolved organic C leaching were not significantly different between low and medium slopes (185 vs. 132kgCha−1, respectively). Grazing intensity, at the two contrasting grazing pressures employed (annual mean standing biomass of 1900 vs. 1475kgDMha−1), had no significant impact on the variables measured in this three year study, demonstrating the robust nature of these grazing systems in the short-term.Our study provides new and quantitative information on net herbage accumulation, soil characteristics and nutrient leaching in grazed hill country. This new information will enable the development and refinement of N and C models to inform sustainable farming practices for this nationally important land use.

Modeling micro-topographic controls on boreal peatland hydrology and methane fluxes

Abstract. Small-scale surface heterogeneities can influence land-atmosphere fluxes and therefore carbon, water and energy budgets on a larger scale. This effect is of particular relevance for high-latitude ecosystems, because of the great amount of carbon stored in their soils. We introduce a novel micro-topographic model, the Hummock-Hollow (HH) model, which explicitly represents small-scale surface elevation changes. By computing the water table at the small scale, and by coupling the model with a process-based model for soil methane processes, we are able to model the effects of micro-topography on hydrology and methane emissions in a typical boreal peatland. In order to assess the effect of micro-topography on water the balance and methane emissions of the peatland we compare two versions of the model, one with a representation of micro-topography and a classical single-bucket model version, and show that the temporal variability in the model version with micro-topography performs better if compared with local data. Accounting for micro-topography almost triples the cumulative methane flux over the simulated time-slice. We found that the single-bucket model underestimates methane emissions because of its poor performance in representing hydrological dynamics. The HH model with micro-topography captures the spatial dynamics of water and methane fluxes, being able to identify the hotspots for methane emissions. The model also identifies a critical scale (0.01 km2) which marks the minimal resolution for the explicit representation of micro-topography in larger-scale models.

The synergistic effect of micro-topography and biochemical culture environment to promote angiogenesis and osteogenic differentiation of human mesenchymal stem cells

Critical failures associated with current engineered bone grafts involve insufficient induction of osteogenesis of the implanted cells and lack of vascular integration between graft scaffold and host tissue. This study investigated the combined effects of surface microtextures and biochemical supplements to achieve osteogenic differentiation of human mesenchymal stem cells (hMSCs) and revascularization of the implants in vivo. Cells were cultured on 10μm micropost-textured polydimethylsiloxane (PDMS) substrates in either proliferative basal medium (BM) or osteogenic medium (OM). In vitro data revealed that cells on microtextured substrates in OM had dense coverage of extracellular matrix, whereas cells in BM displayed more cell spreading and branching. Cells on microtextured substrates in OM demonstrated a higher gene expression of osteoblast-specific markers, namely collagen I, alkaline phosphatase, bone sialoprotein, and osteocalcin, accompanied by substantial amount of bone matrix formation and mineralization. To further investigate the osteogenic capacity, hMSCs on microtextured substrates under different biochemical stimuli were implanted into subcutaneous pockets on the dorsal aspect of immunocompromised mice to study capacity for ectopic bone formation. In vivo data revealed greater expression of osteoblast-specific markers coupled with increased vascular invasion on microtextured substrates with hMSCs cultured in OM. Together, these data represent a novel regenerative strategy that incorporates defined surface microtextures and biochemical stimuli to direct combined osteogenesis and re-vascularization of engineered bone scaffolds for musculoskeletal repair and relevant bone tissue engineering applications.

Effects of microtopography on spatial point pattern of forest stands on the semi-arid Loess Plateau, China

Microtopography may affect the distribution of forests through its effect on rain redistribution and soil water distribution on the semi-arid Loess Plateau, China. In this study, we investigated the characteristics of microtopography on two shady slopes (slope A, 5 hm2, uniform slope; slope B, 5 hm2, microtopography slope) and surveyed the height, the diameter at breast height and the location (x, y coordinates) of all selected individual trees (Robinia pseudoacacia Linn., Pyrus betulifolia Bunge, Populus hopeiensis Hu & Chow, Armeniaca sibirica Lam., Populus simonii Carr. and Ulmus pumila Linn.) on slope A and slope B in the watersheds of Wuqi county, Shaanxi province. Subsequently, the effects of microtopography on the spatial pattern of forest stands were analyzed using Ripley’s K(r) function. The results showed that: (1) The maximal aggregation radiuses of the tree species on the uniform slope (slope A) were larger than 40 m, whereas those of the tree species on the microtopography slope (slope B) were smaller than 30 m. (2) On slope B, the spatial association of R. pseudoacacia with P. betulifolia, A. sibirica, P. simonii and U. pumila varied from being strongly negative to positive at microtopography scales. The spatial association of Populus hopeiensis Hu & Chow with U. pumila also varied from being strongly negative to positive at microtopography scales. However, there was no spatial association between P. betulifolia and P. hopeiensis, P. betulifolia and A. sibirica, P. betulifolia and P. simonii, P. betulifolia and U. pumila, P. hopeiensis and A. sibirica, P. hopeiensis and P. simonii, A. sibirica and P. simonii, A. sibirica and U. pumila, and P. simonii and U. pumila. On slope A, the spatial association between tree species were strongly negative. The results suggest that microtopography may shape tree distribution patterns on the semi-arid Loess Plateau.

둔촌동 습지에서 미지형이 식물 군락 구성에 미치는 영향

본 연구에서는 둔촌동 습지에서 미지형이 식물 군락 구성에 미치는 영향을 연구하기 위하여 2007~2008년에 걸쳐 지형에 따른 수위 변화와 식물 군락의 변화를 조사하였다. 조사 지역을 지대가 낮은 지형부터 높은 지형까지 4개 구역으로 구분하여 조사하였으며, 각각의 구역은 조사 지역 면적 대비 약 11%, 10%, 18%, 24%의 면적을 가지고 있었다. 조사 기간동안 수환경의 pH는 6.10(<TEX>${\pm}0.13$</TEX>), 전기전도도는 <TEX>$51.5({\pm}6.0){\mu}s/cm$</TEX>이었으며, <TEX>$PO_4$</TEX>-P, <TEX>$NO_3$</TEX>-N, <TEX>$NH_4$</TEX>-N은 각각 <TEX>$0.04({\pm}0.02)mg/L$</TEX>, <TEX>$0.14({\pm}0.07)mg/L$</TEX> 그리고 0.01mg/L 이하로 유지되었다. 2008년 3~4월 누적 강수량이 2007년 대비 약 56%로 적었던 것이 지대가 낮은 지형에서 수위 환경 차이를 유발하여 식물 군락 형성에 매우 큰 영향을 미쳤으며, 지형의 높이에 따라 해당 구역을 우점하는 식물 길드가 다르게 나타났다. 이러한 결과는 종자로부터 생활사가 시작되는 1년생 식물 종들이 조사 지역을 전체적으로 우점하였기 때문이며, 다양한 길드의 식물들이 혼재하기 위해서는 높이 구배가 있는 미지형이 조성되어야 한다는 것을 의미한다. The purpose of this study is to investigate the effect of micro-topography to vegetation pattern in Dunchon-dong wetland. To characterize the effect of micro-topography, changes in water level and vegetation pattern were monitored from 2007 to 2008. Depending on the relative elevation, the study site was divided into 4 sectors. The relative areas of sectors in ascending order were 11%, 10%, 18% and 24%, respectively. During investigation period, average water pH was 6.10 (<TEX>${\pm}0.13$</TEX>), electron conductivity was <TEX>$51.5({\pm}6.0){\mu}s/cm$</TEX>, <TEX>$PO_4$</TEX>-P, <TEX>$NO_3$</TEX>-N and <TEX>$NH_4$</TEX>-N concentration were <TEX>$0.04({\pm}0.02)mg/L$</TEX>, <TEX>$0.14({\pm}0.07)mg/L$</TEX>, and lower than 0.01mg/L, respectively. Water level was very changeable in low-water season because the area of lowest sector was small. This characteristic increased the effect of difference of accumulated precipitation from March to April in 2007 and 2008 to plant community composition in lower sectors. Different plant guilds dominated respective sectors and annual plants were major dominant species in the study site. This study suggested that the elevation gradients are necessary to create the habitats for various plant guilds in wetland.

Rough Surface and High-Forb Seed Mix Promote Ecological Restoration of Simulated Well Pads

AbstractBecause of disturbance and exotic plant invasions, ecological restoration is necessary for maintaining functional big sagebrush ecosystems in western North America. Downy brome control is often necessary in restoring this ecosystem type; however, many brome control measures hinder ecological restoration by limiting the types of plants which can be established. Microtopography manipulation may aid weed control by entrapping undesirable seeds. We undertook a field experiment at four sites in the Piceance Basin of western Colorado, USA to test the effects of microtopography (rough with brush mulch or flat with straw mulch), seed mix (high-forb or balanced), and herbicide (140 g ai ha−1imazapic ammonium salt or none) on downy brome control and perennial plant establishment following disturbance. Three years post-treatment, downy brome had become established at two of the four sites, one each with high (GVM) and low (MTN) downy brome seed rain. At GVM, the rough/brush treatment augmented the effectiveness of imazapic, reducing downy brome biomass six-fold. At MTN, the rough/brush surface reduced downy brome biomass 10-fold in the absence of imazapic. Across all four sites, forb and shrub biomass were higher with the high-forb mix, and there was no effect of seed mix on downy brome or annual forb biomass. Restoring a full complement of plant functional groups in big sagebrush ecosystems may be aided by increasing forbs in seed mixes, and manipulating soil microtopography.

Testing of corner’s rules across woody plants in Tiantong region, Zhejiang Province: effects of micro-topography

Testing of corner’s rules across woody plants in Tiantong region, Zhejiang Province: effects of micro-topography

Surface peat structure and chemistry in a tropical peat swamp forest

Background and Aims Tropical peat swamp forests (PSF) are great stores of terrestrial carbon and host unique biodiversity. Despite their importance for carbon accounting, the peat characteristics are sparsely studied, and the effect of microtopography on peat properties has not been reported before.

Representing effects of micro-topography on runoff generation and sub-surface flow patterns by using superficial rill/depression storage height variations

An adequate representation of micro-topography in spatially explicit, physically based models can be crucial in modeling runoff generation, surface/subsurface flow interactions or subsurface flow p...

Representing effects of micro-topography on runoff generation and sub-surface flow patterns by using superficial rill/depression storage height variations

An adequate representation of micro-topography in spatially explicit, physically based models can be crucial in modeling runoff generation, surface/subsurface flow interactions or subsurface flow patterns in hydrological systems with pronounced micro-topography. However, representation of micro-topography in numerical models usually requires high grid resolutions to capture relevant small scale variations in topography at the range of centimeters to meters. High grid resolutions usually result in longer simulation times, especially if fully integrated model approaches are used where the governing partial differential equations for surface and subsurface flow are solved simultaneously. This often restricts the implementation of micro-topography to plot scale models where the overall model domain is small to minimize computational cost resulting from a high grid resolution. In this study an approach is presented where a highly resolved digital elevation model (DEM) for a hummocky topography in a plot scale wetland model (10 m × 21 m × 2 m), is represented by spatially distributed rill/depression storage zones in a numerical model with a planar surface. By replacing the explicit micro-topography with spatially distributed rill/depression storage zones, important effects of micro-topography on surface flow generation and subsurface transport characteristics (e.g. residence time distributions) are being preserved, while at the same time the number of computational nodes is reduced significantly. We demonstrate that the rill/depression storage concept, which has been used for some time to represent time delays in the generation of surface runoff, can also be used to mimic subsurface flow patterns caused by micro-topography. Results further indicate that the rill/depression storage concept is an efficient tool to represent micro-topography in plot scale models because model computation times drop significantly. As important aspects of surface and subsurface flows induced by micro-topography can be mimicked adequately by applying the rill/depression storage concept on a coarser grid, it may also be a useful tool to represent micro-topography in numerical flow models beyond the plot scale.

The role of soil-surface sealing, microtopography, and vegetation patches in rainfall-runoff processes in semiarid areas

[1] The hydrological response of semiarid watersheds to short but intense rainfall events is complex due to feedbacks among water fluxes, vegetation patches, topography, and soil properties. This paper seeks to quantify the combined impact of soil-surface sealing, microtopography, and vegetation patches on surface hydrologic processes on a semiarid hillslope. A modeling approach using a two-layer conceptual infiltration model and two-dimensional surface runoff model was developed to study rainfall-runoff relationships. This combined model is applicable to heterogeneous areas with spatially varying soil properties, landscape, and land-cover characteristics. Data from a semiarid site in southern Israel was used to evaluate the model and analyze fundamental hydrologic mechanisms. Our results indicate that seal layer, microtopography, and vegetation play important roles in dry land runoff processes: seal layer controls runoff generation; vegetation patches affect overland flow by enhancing local infiltration rates; microtopography has a small impact on the total amount of runoff, but shapes the spatial pattern of overland flow. The presence of vegetation patches amplifies the effect of microtopography by increasing spatial variability of infiltration and runoff. Results also show that water resource allocation favors vegetation patches through surface runoff, with maximum local cumulative infiltration one order of magnitude higher than the amount of water available from rainfall. This suggests a sophisticated system of water resource distribution in semiarid ecosystems through complex interactions among environmental factors.

Effects of post‐windthrow salvage logging on microsites, plant composition and regeneration

AbstractQuestionsHow does windthrow influence plant diversity and composition as well as regeneration and microsite characteristics? What are the consequences of post‐windthrow salvage logging on these key attributes?LocationEastern black spruce–moss forest,Quebec,Canada.MethodsA total of 92 plots were sampled, each with a radius of 11.28 m; 49 of these plots were salvaged while 43 were unsalvaged. Regeneration density, plant diversity and seedbeds were characterized. We tested the effect of microtopography and windthrow severity on species richness and Shannon diversity index for salvaged and unsalvaged windthrows using a mixed model. Partial redundancy analysis (RDA) determined which environmental and stand characteristics were most important in explaining differences in plant species and forest floor types among the treatments. The effects of treatments (salvaged and unsalvaged windthrows), microtopography attributes, windthrow severity and regeneration species on seedling and sapling abundance were tested using a linear mixed model.ResultsSalvaged windthrow, with a large proportion of skid trails, dead mosses andSphagnum, had a lower degree of seedbed heterogeneity. Also, some understorey species present in the unsalvaged ecosystem were absent from the salvaged windthrow.Sphagnumand other moss species were clearly associated with the unsalvaged treatment. White birches were positively associated with mound microtopography in the unsalvaged windthrow.ConclusionFrom an ecosystem‐based forest management perspective, natural post‐windthrow understorey conditions and microsite heterogeneity can be in part maintained in salvaged cut blocks by incorporating retention patches that include downed and standing dead wood and living trees of diverse sizes. These steps should favour plant regeneration and augment diversity for salvage logging after wind disturbance.

Engineering the Microstructure of Electrospun Fibrous Scaffolds by Microtopography

Controlling the structure and organization of electrospun fibers is desirable for fabricating scaffolds and materials with defined microstructures. However, the effects of microtopography on the deposition and, in turn, the organization of the electrospun fibers are not well understood. In this study, conductive polydimethylsiloxane (PDMS) templates with different micropatterns were fabricated by combining photolithography, silicon wet etching, and PDMS molding techniques. The fiber organization was varied by fine-tuning the microtopography of the electrospinning collector. Fiber conformity and alignment were influenced by the depth and the slope of microtopography features, resulting in scaffolds comprising either an array of microdomains with different porosity and fiber alignment or an array of microwells. Microtopography affected the fiber organization for hundreds of micrometers below the scaffold surface, resulting in scaffolds with distinct surface properties on each side. In addition, the fiber diameter was also affected by the fiber conformity. The effects of the fiber arrangement in the scaffolds on the morphology, migration, and infiltration of cells were examined by in vitro and in vivo experiments. Cell morphology and organization were guided by the fibers in the microdomains, and cell migration was enhanced by the aligned fibers and the three-dimensional scaffold structure. Cell infiltration was correlated with the microdomain porosity. Microscale control of the fiber organization and the porosity at the surface and through the thickness of the fibrous scaffolds, as demonstrated by the results of this study, provides a powerful means of engineering the three-dimensional structure of electrospun fibrous scaffolds for cell and tissue engineering.

The fouling hydroid Ectopleura larynx: a lack of effect of next generation antifouling technologies

The hydroid Ectopleura larynx is one of the main fouling organisms on salmon aquaculture cages in Norway; this study investigated novel surface materials and microtopographies to deter its settlement. The settlement preferences of hydroid larvae for 12 materials with wettabilities ranging from hydrophobic (54°) to hydrophilic (112°) were tested in a no-choice bioassay. Although settlement differed between materials, with the highest average settlement on polytetrafluoroethylene (95%) and the lowest on untreated polyurethane (53%), no trend regarding the tested wettabilities could be found and none of the tested materials was able to reduce average settlement below 50%. Furthermore, nine high-density polyethylene (HDPE, 100–600 μm microtopographies) and seven polydimethylsiloxane (PDMS; 40–400 μm microtopographies) microtextured surfaces were tested. There was no systematic effect of microtopography on the settlement of E. larynx larvae. However, there was a preference for settlement in channels on PDMS microtopographies between 80 and 300 μm. Similarly, there were no preferences for any of the examined microtopographies in a 12-day field test using PDMS surfaces at a commercial fish farm. The study indicated that neither surface wettability (hydrophilicity–phobicity) nor microtopographies were effective at deterring the settlement of the hydroid E. larynx. The high plasticity of the aboral pole and the hydrorhiza of the hydroids may explain settlement even under unfavourable conditions, highlighting the successful colonisation traits of this dominant biofouling species.

Fine‐scale variability of topsoil moisture in a first‐order stream of a temperate forest

ABSTRACTThis work explains the effect of microtopography on the spatio‐temporal gradient of topsoil moisture in a first‐order stream in a forested mountainous area of northern Spain. This gradient was also related with the availability of suitable microsites for a forest riparian sedge (Carex remota).Topsoil moisture, presence of C. remota and height and distance from the stream edges were measured in 385 points along 35 transects perpendicular to the stream. Soil moisture measurements were repeated in three different dates.Topsoil moisture showed a sigmoid trend that defined the limits of a wet riparian zone at 1·25 m of distance from and 0·55 m in elevation above stream banks. Our riparian zone was narrower than other studies because of the steep slopes (25%) of the mountainous area studied. Elevation above stream banks was more influential than distance in defining the limits of the riparian zone.In the riparian zone, values of soil moisture were high and constant even at the end of a dry period due to the continuous water flow. In the adjacent upland forest, soil moisture varied according to rainfall. These high and constant soil moisture values defined the suitable microsites for C. remota. Copyright © 2013 John Wiley &amp; Sons, Ltd.

The Importance of Microtopography and Nurse Canopy for Successful Restoration Planting of the Slow-Growing Conifer Pilgerodendron uviferum

Recent studies have shown that, owing to a lack of seed trees, the natural rate of recovery of fire-disturbed bog forests previously dominated by the endemic and endangered conifer Pilgerodendron uviferum (D. Don) Florin is extremely slow. Hence, increasing the number of seed trees in the landscape through restoration planting could remove the principal biotic filter, limiting recovery of these forests. Here, we analyzed how the success of restoration plantings may be improved through the choice or manipulation of microsites in P. uviferum forests on Chiloé Island in North Patagonia. For this purpose, we manipulated microtopography in water-logged sites in bogs (mounds, flat terrain, mineral soil) and changed canopy conditions (gaps, semi-open, closed canopy) in upland sites with better drainage. In bogs, there was no significant effect of microtopography on growth and survival of P. uviferum plantings. However, fluorescence measurements indicated lower stress in seedlings established on mounds. Seedlings in upland areas established beneath a nurse canopy had lower mortality and higher relative shoot growth, foliar nutrients, photosynthetic light use efficiency and chlorophyll fluorescence values than those planted in the open. This indicates that seedlings of the slow growing P. uviferum can tolerate extremely wet conditions, yet suffer from stress when grown in the open. Here, the removal of canopy appeared to have also removed or reduced mycorrhizal networks for seedlings, leading to poorer nutrition and growth. Based on these results, recommendations for restoration plantings in highly degraded P. uviferum forests are presented.

Fate of fertilizer 15N in intensive ridge cultivation with plastic mulching under a monsoon climate

Reducing nitrogen (N) leaching to groundwater requires an improved understanding of the effect of microtopography on N fate. Because of the heterogeneity between positions, ridge tilled fields, frequently used in intensive agriculture, should be treated as two distinct management units. In this study, we measured N dynamics in plastic-mulched ridges and bare furrows with the goal of developing more sustainable agricultural practices with optimal gains, namely crop production versus limited impacts on water quality. We investigated: (1) biomass production; (2) crop N uptake; (3) N retention in soil; and (4) N leaching using 15N fertilizer in a radish crop. Broadcast mineral N fertilizer application prior to planting resulted in high total leaching losses (of up to 390 N kg ha−1). The application of plastic mulch in combination with local fertilizer management did not help to reduce N leaching. At all fertilizer N rates, the mean NO3 − concentrations in seepage water were found to be above the WHO drinking water standard of 50 mg NO3 − l−1. To reduce NO3 − leaching, we recommend: (1) decreasing the fertilizer N rates to a maximum of 150 kg N ha−1; (2) applying fertilizer N in 3–4 split applications according to the plant’s N needs; (3) applying fertilizer N to the ridges (after their formation) to avoid losses from the furrows; and (4) increasing the soil organic matter content to enhance the water and nutrient retention by covering the furrows with plant residues.

漫溢干扰过程中微地形对幼苗定居的影响

PDF HTML阅读 XML下载 导出引用 引用提醒 漫溢干扰过程中微地形对幼苗定居的影响 DOI: 10.5846/stxb201105170646 作者: 作者单位: 中国科学院 新疆生态与地理研究所,中国科学院 新疆生态与地理研究所,新疆师范大学地理科学与旅游学院,新疆师范大学地理科学与旅游学院,新疆师范大学地理科学与旅游学院,中国科学院 新疆生态与地理研究所 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金项目(30970549,40971284);自治区高校青年教师培育基金项目(XJEDU2008S41) Effects of the microhabitats on the seedling emergence during the flooding disturbance Author: Affiliation: Xinjiang Institute of Ecology and Geography,Chinese Academy of Sciences,Xinjiang Institute of Ecology and Geography,Chinese Academy of Sciences,Geography Science and Tourism Department of Xinjiang National University,Geography Science and Tourism Department of Xinjiang National University,Geography Science and Tourism Department of Xinjiang National University,Xinjiang Institute of Ecology and Geography,Chinese Academy of Sciences Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:通过对比漫溢干扰后边坡、坡中和坡底幼苗的物种组成、密度、幼苗周边的环境条件及土壤种子库的差异来分析漫溢干扰过程中,微地形对幼苗定居的影响。结果表明:(1)微地形对幼苗物种组成和生物多样性指数的影响很大。漫溢干扰后,位于边坡、坡中和坡底幼苗的Simpson多样性指数和Mcintosh均匀度指数在0.01的水平上差异极显著,Margalef丰富度指数在0.05的水平上差异显著。(2)微地形对土壤盐分含量影响很大。方差分析的结果表明,除HCO3-和K+外,边坡、坡中和坡底的pH值、CO32-、SO42-、Ca2+和Mg2+各指标在0.01的水平上差异极显著;全盐、总盐、Cl-和Na+各指标均在0.05的水平上差异显著。(3)微地形通过改变幼苗定居的环境条件,进而影响幼苗库的物种组成、密度和生物多样性指数。微地形中,幼苗库的各种生态指标均小于对应的土壤种子库的生态指标,从坡底到坡中到边坡,除单位面积上的植被密度外,土壤种子库和幼苗库的各项生态指标的变化趋势均不同。 Abstract:The Tarim River is the longest continental river in China and charactered by its fragile ecosystem in the word. The ecological processes of the Tarim River basin have undergone great changes due to the irrational human activities over the past 50 years, especially in the lower reaches of Tarim River. Therefore, the ecological water conveyance project(EWCP) has been implemented since 2000. The EWCP is an emergency plan for conserving the natural vegetation, controlling the desertification and improving the environment in the lower reaches of Tarim River. It transfers water from the Bosten Lake, to Daxihaizi Reservoir, and finally to Taitema Lake along the water channel. There have been 12 times of watering to the lower Tarim River during the period from 2000 to 2011. After the EWCP,the natural vegetation has obvious response to the water condition change. The studies on the soil seed bank in the region are very important to restoring the degraded ecosystem in lower reaches.Soil seed bank is the potential plant population or plant community. It plays an important role in occurrence, succession, and recovery process of vegetation. The germinated species and germinated seed number in soil seed bank determine the species composition and species number of seedlings in a certain degree. Meanwhile, the topography condition in the study areas is also an important factor on influencing germination ability of soil seed bank. Micro-topography impacts the seedling species composition and distribution pattern through the spatial differences in germination ability of soil seed bank, light, water and salt conditions. This paper takes the EWCP as a case study to analyze the effects of micro-topography on the seedling emergence during the flooding disturbance by the method of variance analysis. The species composition, seedling density, environmental condition and soil seed bank in three micro-topography type of the side slope, hillside and base of slope are compared after river flooding disturbance. The study results revealed that: (1) Species composition and diversity indices of the seedling were significantly influenced by different types of the micro-topography. After overflowing disturbance, Simpson index and Mcintosh index of seedling species in three types of micro-topography are aloes highly significant at the level of 0.01, and Margalef index is significantly different at the level of 0.05.(2) There is also a great effect on soil salt in the different micro-topography. The variance analysis showed that: except for the HCO3- and K+, the value of pH, CO32-, SO42-, Ca2+ and Mg2+ in three types of micro-topography are all significantly different at the level of 0.01, and the value to total salt, soluble salt, Cl- and Na+ are significantly different at the level of 0.05. (3) Micro-topography can affect the species composition, density and diversity indices of the seedling by changing the resided seedling's microhabitat. Under the condition of the micro-topography, the values of the ecological indicators in the seedling bank were less than those in the soil seed bank. From the base slope, hillside slope to side slope, the changing trends of the ecological indicators were different between the soil seed bank and seedling bank expect for the indicator of the vegetative density..The results can better reveal the impact mechanism of river flooding on compose and construction of the plant community, which has an important significance on the degraded ecosystem restoration. Furthermore, the results have a practical reference on protecting and recovering of the natural vegetation in the study region after river flooding interference. 参考文献 相似文献 引证文献

Modeling methane emissions from the Alaskan Yukon River basin, 1986–2005, by coupling a large‐scale hydrological model and a process‐based methane model

Much progress has been made in methane modeling for the Arctic. However, there is still large uncertainty in emissions estimates due to the spatial variability in water table depth resulting from complex topographic gradients, and due to variations in methane production and oxidation due to complex freezing and thawing processes. Here we extended an extant methane emission module within a biogeochemistry model, the Terrestrial Ecosystem Model (TEM), to include a large‐scale hydrology model, the variable infiltration capacity (VIC) model. The VIC model provides the required inputs, including freezing and thawing fronts, soil temperature and moisture, to the methane module. The effect of topography on the redistribution of soil moisture and water table depth was explicitly modeled using the TOPMODEL approach. The coupled modeling framework was applied to the Yukon River basin at a spatial resolution of 1 km from 1986 to 2005. The simulations show that the average annual net emissions of CH4 from the region are 4.01 Tg CH4 yr−1. El Niño phenomena usually lead to positive emission anomalies, while decreases in net CH4 emissions may be associated with strong La Niña events. Precipitation was found to be more closely related to CH4 dynamics than to soil temperature and active layer depth during the study period. This study suggests that the effects of soil freezing and thawing processes and the effects of microtopography on hydrology should be considered in the quantification of CH4 emissions.

Laboratory Experiments on the Effect of Microtopography on Soil-Water Movement: Spatial Variability in Wetting Front Movement

The effect of microtopography on soil-water movement is a topic of interest for a range of disciplines, with experimental studies investigating the relationship between the two lacking. Laboratory experiments were conducted by simulating rainfall across packed soil surfaces to investigate the effect of microtopography on wetting front movement within experimental soil profiles. In small soil box experiments, the observed wetting fronts for soil profiles showed considerably deeper movement beneath a smooth surface than depressions for 12–60 min rainfalls. For large soil box experiments, the wetting front reached moisture sensors installed at 5 and 10 cm depths and corresponding to various rough and smooth surface features at significantly different times, with movement being most rapid beneath the smooth surface. Wetting front movement was “quicker” beneath surface peaks than depressions for the rough surface as attributed to 2D/3D unsaturated flow. This study provides valuable experimentally based insight into the effect of microtopography on soil-water movement.