Slope Gullies Research Articles

Soil erodibility affected by vegetation restoration on steep gully slopes on the Loess Plateau of China

Vegetation restoration influences near soil-surface characteristics and thus likely affects soil erodibility. This study was performed to quantify the effects of vegetation restoration on soil erodibility on steep gully slopes, and to identify the potential influencing factors on the Loess Plateau. Three shrub and four grass types distributed on different gully slopes were selected, and six erodibility indicators and an integrated erodibility index (IEI) were applied to indirectly evaluate the effects of vegetation restoration on soil erodibility. The former included the soil erodibility K factor, aggregate stability (the mean weight diameter, MWD, and the mean number of drop impacts, MND), saturated hydraulic conductivity (Ks), cohesion (Coh), and penetration resistance (PR), and the latter was calculated using these indicators and a weighted integration method. The results showed that vegetation restoration on steep gully slopes was effective in reducing soil erodibility on the Loess Plateau, and grasses seemed more effective than shrubs. Compared with the control, the K of vegetation-restored gully slopes decreased by 4.1–24.0%, and MWD, MND, Ks, Coh, and PR increased by 64.0–284.3, 51.4–269.5, 100.5–417.4, 10.1–172.2, and 63.3–278.9% respectively. Consequently, the IEI of the vegetation-restored gully slopes declined by 33.1–81.9%, and the mean reduction percentage of the four grasses was 1.5 times that of the three shrubs. The variation in soil erodibility was closely related to the changes in the soil organic matter content and root mass density with vegetation restoration. The results will help in understanding the soil conservation mechanisms of vegetation restoration on steep gully slopes.

A novel topographic parameterization scheme indicates that martian gullies display the signature of liquid water

Martian gullies resemble gullies carved by water on Earth, yet are thought to have formed in an extremely cold (<−50°C) and dry (humidity <100 precipitable micrometers) surface environment (cf. Mellon et al., 2004). Despite more than a decade of observations, no consensus has emerged as to whether liquid water is required to form martian gullies, with some recent studies favouring dry CO2-driven processes. That this argument persists demonstrates the limitations of morphological interpretations made from 2D images, especially when similar-looking landforms can form by very different processes. To overcome this we have devised a parameterization scheme, based on statistical discriminant analysis and hydrological terrain analysis of meter-scale digital topography data, which can distinguish between dry and wet surface processes acting on a landscape. Applying this approach to new meter-scale topographic datasets of Earth, the Moon and Mars, we demonstrate that martian gullied slopes are dissimilar to dry, gullied slopes on Earth and the Moon, but are similar to both terrestrial debris flows and fluvial gullies. We conclude that liquid water was integral to the process by which martian gullies formed. Finally, our work shows that quantitative 3D analyses of landscape have great potential as a tool in planetary science, enabling remote assessment of processes acting on planetary surfaces.

Relationships between plant colonization and soil characteristics in the natural recovery of an earthquake-triggered debris flow gully in the Wanglang National Nature Reserve, China

Fragmentation and loss of habitats due to natural disasters, like earthquakes and earthquake- triggered debris flows are existing threats to the long-term survival of the giant panda (Ailuropoda melanoleuca). To better understand natural recovery processes of the damaged habitat, field investigation and laboratory analysis were used to analyze relationships between plant colonization and soil characteristics in an over 30-year natural recovery of a damaged giant panda habitat in a debris flow gully after the 1976 Songpan-Pingwu earthquake in Sichuan Province, China. Four different damaged sites were selected that located at the center of the gully (center), on a flat alluvial fan (fan), in a side slope of the gully (slope), and at the ecotone between the gully and native forest (ecotone). Vegetation characteristics, soil physicochemical properties, and microbial biomass in the different sites and soil depths were measured. After the natural recovery, the soil fertility, water retention, and microbial biomass were highest at ecotone, followed by fan, slope, and center. Only a few perennial herbs colonized at center; shrubs started to invade at fan and slope, and the native trees dominated the community of ecotone. Furthermore, Fargesia spathacea(food for the giant panda)started to be re-established at ecotone, and the community characteristic of ecotone recovered similarly to the native habitat. These results suggested that improving the soil fertility, water retaining capacity and microbial biomass is fundamental to the plant colonization, particular for F. spathacea’s re-establishment in a damaged giant panda habitat.

Submarine gullies on the southern Weddell Sea slope, Antarctica

Submarine gullies are small-scale, confined channels on the order of tens of metres depth that form one of the most common morphological features of high-latitude continental slopes. Gully morphology varies in width, incision depth, length, sinuosity, branching order, shelf-incision, cross-sectional shape and gully spacing, with six distinct gully signatures recognized on high-latitude continental slopes (Gales et al. 2013 a , b ). Here we analyse the morphology of slope gullies off Halley and Filchner troughs in the southern Weddell Sea (Fig. 1a–f). Fig. 1. Multibeam bathymetry and along-slope profiles of gullies on the southern Weddell Sea continental margin. ( a ) Multibeam data showing V-shaped gullies at the mouth of Halley Trough. Acquisition system Kongsberg EM122. Frequency 12 kHz. Grid-cell size 30 m. ( b ) Sub-bottom profile of U-shaped gullies. VE×20. Location in (e). Acquisition system Kongsberg TOPAS PS 018. Frequency 18 kHz. Secondary beam frequency 1300–5000 Hz. ( c ) Along-slope profile through V-shaped gullies. Location in (a). VE×55. ( d ) Location of the study area (red boxes; map from IBCSO v. 3.0). FT, Filchner Trough; HT, Halley Trough. ( e ) Multibeam data showing U-shaped gullies at the mouth of Filchner Trough. Acquisition system Kongsberg EM120. Frequency 12 kHz. Grid-cell size 30 m. ( f ) Sub-bottom profile of U-shaped gullies. Location in (e). Acquisition …

Slope gradient and lithology as controls on the initiation of submarine slope gullies; Insights from the North Carnarvon Basin, Offshore NW Australia

Slope-confined submarine gullies are present on many continental margins, yet the controls on their initiation and demise are poorly understood because modern or recently active systems are rarely if ever monitored, and exhumed systems, typically formed in very fine-grained successions, are poorly preserved at outcrop. We use 3D seismic reflection and borehole data from offshore NW Australia to investigate long-term (~40Myr) variations in the geomorphology of Eocene-to-Miocene gullies that developed in mixed carbonate–clastic clinothems. Through time, clinoform slope gradient increases from 1.6° to 3.2°, with gullies forming when the clinoform slope exceeds 2.5°. After their inception, gullies increase in width (from 350m to 770m) and depth (from 37m to 60m). Slope steepening appears to coincide with a change from poorly cemented, fine-grained carbonate to better-cemented, coarse-grained carbonate, implying a secondary, lithological control on slope dip and, ultimately, gully formation.

Interplay between an axial channel belt, slope gullies and overbank deposition in the Puchkirchen Formation in the Molasse Basin, Austria

AbstractDeep‐water sediments in the Molasse Basin, Austria, were deposited in a narrow foreland basin dominated by a large channel belt located between the steep Alpine fold and thrust belt to the south and the gentler northern slope off the Bohemian Massif. Several gas fields occur outside the channel belt, along the outer bend of a large meander. Accumulation of these overbank sediments reflects a complicated interplay between slope accommodation and debris‐flow and turbidity‐flow interaction within the channel. The tectonically oversteepened northern slope of the basin (ca 2 to 3°) developed a regionally important erosional surface, the Northern Slope Unconformity, which can be traced seismically for &gt;100 km in an east–west direction and &gt;20 km from the channel to the north. The slope preserves numerous gullies sourced from the north that eroded into the channel belt. These gullies were ca 20 km long, &lt;1 km wide and ca 200 m deep. As the channel aggraded, largely inactive and empty gullies served as entry points into the overbank area for turbidity currents within the axial channel. Subsequently, debris‐flow mounds, 7 km wide and &gt;15 km long, plugged and forced the main channel to step abruptly ca 7 km to the south. This resulted in development of an abrupt turn in the channel pathway that propagated to the east and probably played a role in forming a sinuous channel later. As debris‐flow topography was healed, flows spread out onto narrow area between the main channel and northern slope forming a broad fine‐grained apron that serves as the main gas reservoir in this area. This model of the overbank splay formation and the resulting stratigraphic architecture within the confined basin could be applied in modern and ancient systems or for subsurface hydrocarbon reservoirs where three‐dimensional seismic‐reflection data is limited. This study elucidates the geomorphology of the oversteepened slope of the under‐riding plate and its effects on the sedimentation.

EARTH-FLOW LANDSCAPES OF THE NIZHNY NOVGOROD DECLIVITY (THE OKA AND VOLGA RIVERS SLOPE)

Earth-flow landscapes of the erosion right-bank slope of the Oka and Volga Rivers differ significantly both from the landscapes of the erosion-denudation flat interfluves of the right bank and from the low terraced accumulative left bank. We distinguish head-on and slopes - with active undercutting and side ones without undercutting. There are active landslides on the head-on slopes of the Oka and Volga rivers, and less active landslides on the slopes of gullies and balkas. Characteristic features of earth-flow landscapes depend on the history of relief development, geomorphological situation, lithology, and river lateral erosion. The four landscape-geomorphic regions are distinguished on the base of earth-flow landscape types.

黄土丘陵沟壑区主要草种枯落物的持水能力与养分潜在归还能力

Because of the serious soil erosion,the soil moisture and nutrients deficiency,the slowly recovery and scarcity of natural vegetation in the hill-gully Loess Plateau,the ecological effects of litter layer are particularly important for litter layer effective reduction on surface runoff and mitigate soil erosion. Thus,in this study,the litter accumulation ofcommunities and main herb species in different site conditions was investigated in the hill-gully Loess Plateau,water holding capacity of litter of main herb species was measured by the immersion method,potential nutrient return capacity of litter of main herb species was analyzed by measuring the nutrients content,lignin and cellulose content,then the effects of main species litter on soil fertility improvement was discussed. It' s important to understand the mechanism and efficacy of the resistance of plants to soil erosion. The main results were as follows: 1) the accumulation of community litter was between 73.74—175.26 g / m2,and was significantly different in slope-gully sites( P0. 05),ordered as shady gully slope hilltop sunny gully slope shady hilly slope sunny hilly slope. While in micro-sites ordered as under vegetation ephemeral gully fish-scale pit bare land on the sunny slope,ephemeral gully fish-scale pit under vegetation bare land on the shady slope and under vegetation bare land on the hilltop. 2) The maximal water holding capacity of litter of main species was up to 1.22—4.34 times of its dry mass,and it was extremely significantly different among species( P 0. 01),ordered as the defoliation of Bothriochloa ischaemun the defoliation of Artemisia gmelinii the deadwood of Bothriochloa ischaemun the defoliation of Lespedeza davurica the litter of Stipa bungeanaon the deadwood of Lespedeza davurica the deadwood of Artemisia gmelinii. 3) The organic carbon content( 7. 35% —40. 33%) and total nitrogen content( 0. 61%—1. 60%) of species were extremely significant different among species( P 0. 01),but they were not significantly different in slope-gully sites. 4) Indicators that influenced litter decomposition( such as lignin content,cellulose content,lignin / N ratio,C / N ratio) were extremely significant different among species( P 0. 01). The lignin content( 1.00%—8.20%) and cellulose content( 3. 16%—14. 06%) and lignin / N ratio( 0. 78—12. 48) were extremely significantly different in slope-gully sites( P 0. 05),while C / N ratio( 5.61—57.41) was not significantly different. 5)The potential nutrient return capacity of Artemisia gmelinii defoliation was the highest,followed by the litter of Lespedeza davurica and Bothriochloa ischaemun,and the litter of Stipa bungeanaon was the lowest. In conclusion,the water holding capacity and the potential nutrient return capacity of Bothriochloa ischaemun litter on the sunny slope and the defoliation of Artemisia gmelinii and Lespedeza davurica on the hilltop and shady slope were the highest among species in slope-gully sites,they could effectively improve the soil fertility. While,the litter of Stipa bungeanaon water holding capacity and the potential nutrient return capacity both were the lowest among species in slope-gully sites. The soil fertility effects of different species should be considered when the vegetation was used to control soil erosion. The species should be chosen which not only could control soil erosion but also significantly improve soil fertility,and then the soil quality could be slowly improved.Therefore,Bothriochloa ischaemun,Artemisia gmelinii and Lespedeza davurica were the good choice to control soil erosion on the slopes.

Anatomy of falling‐stage deltas in the Turonian Ferron Sandstone of the western Henry Mountains Syncline, Utah: Growth faults, slope failures and mass transport complexes

AbstractFalling‐stage deltas are predicted by sequence stratigraphic models, yet few reliable criteria are available to diagnose falling‐stage deltaic systems in surface exposures. Recent work on the Upper Cretaceous (Turonian) Ferron Sandstone in the western Henry Mountains Syncline of south‐central Utah has established its environment of deposition as a series of modest‐sized (5 to 20 km wide), probably asymmetrical, mixed‐influence deltas (‘Ferron Notom Delta’) that dispersed sediment eastwards from the rising Sevier orogenic hinterland into the Western Cordilleran Foreland Basin. Analysis of sandstone body stacking patterns in a 67 km long, depositional strike‐parallel (north–south) transect indicates that the growth of successive deltas was strongly forced by synsedimentary growth of a long wavelength (ca 100 km), 50 m amplitude fold structure. Herein, two discrete areas within this transect, superbly exposed in three dimensions, are documented in order to determine the details of stratal stacking patterns in the depositional dip direction, and thereby to assess the stratigraphic context of the Ferron Notom Delta. In the two study areas, dip transects expose facies representing river mouth bar to distal delta front environments over distances of 2 to 4 km. Key stratal packages are clinothems that offlap, downlap, and describe descending regressive trajectories with respective to basal and top datums; they are interpreted as the product of relative sea‐level fall. The vertical extent of clinoforms suggests that deltas prograded into &lt;30 m of water. Furthermore, these deltaic successions preserve abundant evidence of delta front slope failure, growth faulting, and incision and filling of deep (&lt;15 m) slope gullies. Gully fills are composed of chaotic intraformational breccia and/or massive sandstone, and constitute linear, ‘shoestring’ sandbodies in the distal portions of individual palaeodelta systems. They are interpreted to have been cut and filled during the late falling‐stage and lowstand of relative sea‐level cycles. The north–south distribution of the stratal style described above seems to be focused on the flanks of the growth anticline, and so the numerous falling‐stage systems tracts preserved within the Ferron Notom Delta probably owe their origin to synsedimentary structural growth, and the unstable fluid pressure regime that this growth imposed on the sea floor and shallow subsurface.

Vegetation cover in an ancient agricultural landscape: the Proszowice Plateau (southern Poland) as a case-study

The investigations on vegetation cover in the Proszowice Plateau (Małopolska Upland, southern Poland) in 1997-1999 were carried out. This vast area (770 sq. km), hitherto not in this respect investigated, is covered with arable fields in 80%. This area has been used for agriculture since the Neolithic age. The aim of the paper is to show the present state of the vegetation and flora in face of the growing man's impact upon living biotas and their environment. The Braun-Blanquet phytosociological method was used, yielding 1030 relevés. In effect, a total of 48 plant associations and communities were found. Plateaux and gently slopes are covered with arable fields. In the cereal communities &lt;em&gt;Vicietum tetraspermae&lt;/em&gt; and in the root crops &lt;em&gt;Echinochloo-Setarietum&lt;/em&gt; are mostly found. In the wide and shallow stream valleys moist and wet meadows (&lt;em&gt;Calthion&lt;/em&gt;, &lt;em&gt;Magnocaricion&lt;/em&gt;) predominate, and the stands of the xerothermic grassland (&lt;em&gt;Festuco-Brometea&lt;/em&gt;) occur in places not used for agriculture: on steep escarp-ments between fields and on steep slopes of hills, gullies and stream banks. Small and scarce forests (&lt;em&gt;Querco-Fagetea&lt;/em&gt;) are preserved on plateaux and on gently slopes. In the stream banks they consist of willow thickets (Salicion) and fragments of riverside carr (&lt;em&gt;Alno-Padion&lt;/em&gt;). Basing on the relevé material and floristic checklists a total of 860 vascular plant species was recorded, in this 19.2% of rare and endangered. The flora is of lowland character; c. 80% are native species. The characteristic feature of the Proszowice Plateau is the occurrence of the xerothermic grassland and wet meadows, in which species rare in other regions of the country flourish.

Debris-Flow Treatment: The Integration of Botanical and Geotechnical Methods

Due to special topographical, geological and meteorological conditions, debris flows occur frequently and result in heavy losses of lives and properties in mountainous areas, which become a great threaten to the sustainable development of regional economy and society in western China. At present, debris-flow prevention has performed well in many mountainous countries and has made headway in early warning, disaster mitigation by structural engineering methods, and risk analysis and management. In this paper, debris-flow prevention techniques have been introduced from the aspects of botanical methods, geotechnical engineering methods, and synthetic prevention system based on the above two methods. In addition, the treatment system of multilevel runoff and unconsolidated soil in the catchment with a chain of “slope–gully–valley” is set up in consideration of sediment load of main rivers, incorporation of slope improvement and gully retention, as well as micro-site factors for matching species with the site. Furthermore, attentions should be paid to the mechanism and technical details of vegetation measures for debris-flow prevention, as well as effective incorporation between botanical method and geotechnical method.

The role of tectonics and mass-transport complex emplacement on upper slope stratigraphic evolution: A 3D seismic case study from offshore Angola

Three dimensional seismic-reflection data of the mid-Pliocene-to-Holocene upper slope succession, offshore Angola, provide an opportunity to constrain the stratigraphic context, distribution, external morphology and internal strain within mass-transport deposits (MTDs). These data also allow an assessment of the impact that erosion and relief associated with MTDs have on upper slope stratigraphy and depositional patterns, and the role that MTDs play in achieving ‘grade’ on submarine slopes. The study area is dissected by a series of NW-SE-striking, thin-skinned, salt-detached normal faults, which bound a slope-perpendicular, intra-slope horst that divides the study area into two depocentres. Three main seismic packages and their six constituent units have been mapped across the study area and reveal that, during the initial stages of deposition, a series of MTDs were emplaced, the thickness and distribution of which are controlled by the intra-slope horst. Substantial volumes of substrate were removed and entrained into the parent flow, and significant and irregular relief (150 m) was developed along MTDs upper surface. This MTD-richpackage is interpreted to document a time when the slope was above grade, degradational processes dominated and sediment was trapped on the upper slope due to tectonic accommodation. Subsequent deposition was from either turbidity currents or and suspension fallout, at a time when the slope had begun to achieve ‘grade’ and depositional processes dominated. The associated depositional units display only minimal thickness variations with respect to the intra-slope horst, which had been ‘healed’ by this time; however, the unit displays pronounced and abrupt changes in thickness due to infilling of relief at the top of the preceding MTDs. The uppermost strata document a time when the slope was at grade and constructional process (i.e. aggradation and progradation) dominated. Deposition at this time was characterised by progradation of a mudstone-dominated, gullied slope system. This study highlights the role that tectonically- and mass transport-driven changes in bathymetry can have on upper slope accommodation and sediment dispersal. From a hydrocarbon exploration perspective this is critical, because tectonic and depositional accommodation provide a mechanism for capturing and trapping clastic sediments in an upper slope setting, which is otherwise typically associated with coarse-grained sediment bypass.

U-shaped slope gully systems and sediment waves on the passive margin of Gabon (West Africa)

3-D seismic reflection data has enabled the documentation of a system of remarkable modern and buried u-shaped gullies which intimately co-exist with upslope migrating sediment waves along 80 km of the Gabon continental slope. The modern gullies occur on a silty mud-dominated slope in water depths of 150–1500 m on an ~ 50 km wide slope with a gradient of 4.5° decreasing to 1.5°. The gully sets persist laterally for distances of at least 40 km and extend downslope for distances of up to 60 km. The gullies are u-shaped in cross-section, with a relief of 5–30 m, and widths of 50–400 m. Intriguingly, the gullies become narrower and shallower with distance down the slope, as well as increasing in number down slope. The majority of the gullies appear to be erosional but some appear to have resulted from simultaneous aggradation along inter-gully ridges and non-deposition along the adjacent gully floor. Hence, these gullies are interpreted to have formed mainly in response to spatially-variable deposition, rather than erosion. Upslope migrating sediment waves occur in close proximity to the gullies. Gullies cross fields of sediment waves and waves are observed to migrate up-slope locally within both the erosional and aggradational gullies. Evidence is lacking for any slumping or headward erosion in the headwall region of the gullies, which discounts formation by very local sediment gravity flows originating from shelf-edge collapse, as has been observed in other v-shaped gully systems. Based on our new data, and supported by theoretical studies on the mechanics of turbidity currents, we propose that the gullies and related sediment waves were formed by diffuse, sheet-like, mud-rich turbidity currents that presumably originated on the shelf. Instabilities in the turbidity currents generated a wave-shaped perturbation in a cross-flow direction leading to regularly spaced regions of faster and slower flow. For the non-aggradational and erosional gullies it is inferred that gully axes experienced flow velocities that mainly exceeded the settling velocity of the sediment in suspension, and thus no deposition occurred. In contrast, the aggradational gullies indicate lower flow velocities with sediment deposition both within the gully axes and on the gully flanks. Mixed mode gullies are also found which indicate that successive flows can experience variations in flow properties leading to interspersed erosional and depositional events. ► U-shaped slope gullies associated with sediment waves are discovered offshore Gabon. ► The gullies display both aggradational and erosional morphologies. ► Gullies occur at the modern seabed and buried in Pleistocene–Holocene sediments. ► Sheet-like, fine-grained turbidity currents can form both gullies and sediment waves. ► Perturbation in cross-flow direction of wide turbidity currents may form gullies.

Miocene shelf‐edge deltas and their impact on deepwater slope progradation and morphology, Northwest Shelf of Australia

AbstractLate‐middle Miocene to Pliocene siliciclastics in the Northern Carnarvon Basin, Northwest Shelf of Australia, are interpreted as having been deposited by deltas. Some delta lobes deposited sediments near and at the shelf break (shelf‐edge deltas), whereas other lobes did not reach the coeval shelf break before retreating landward or being abandoned. Shelf‐margin mapview morphology changes from linear to convex‐outward in the northern part of the study area where shelf‐edge deltas were focused. Location and character of shelf‐edge deltas also had significant impact on along‐strike variability of margin progradation and shelf‐edge trajectory. Total late‐middle and late Miocene margin progradation is ca. 13 km in the south, where there were no shelf‐edge deltas, vs. ca. 34 km in the north where shelf‐edge deltas were concentrated. In the central area, the deltas were arrested and accumulated a few kilometres landward of the shelf break, resulting in an aggradational shelf‐edge trajectory, in contrast to the more progradational trajectory farther north. This illustrates a potential limitation of shelf‐edge trajectory analysis: only where shelf‐edge deltas occur, there is sufficient sediment available for the shelf‐edge trajectory to record relative sea‐level fluctuations reliably. Small‐scale (ca. 400 m wide) incisions were already conspicuous on the coeval slope even before deltas reached the shelf break. However, slope gullies immediately downdip from active shelf‐edge deltas display greater erosion of underlying strata and are wider and deeper (&gt;1 km wide, ca. 100 m deep) than coeval incisions that are laterally offset from the deltaic depocenter (ca. 0.7 km wide, ca. 25 m deep). We interpret this change in slope‐gully dimensions as the result of greater erosion by sediment gravity flows sourced from the immediately adjacent shelf‐edge deltas. Similarly, gullies also incised further (up to 6 km) into the outer shelf in the region of active shelf‐edge deltas.

Sediment yield from irregularly shaped gullies located on the Fortuna lithologic formation in semi-arid area of Tunisia

The Fortuna geological formation dated from the late Oligocene to early Miocene is mainly composed of friable sandstone. Gully erosion on this substratum is developing complex shaped gullies where bank processes are as important as head advance by cutting and bed deepening by vertical incision. For irregularly shaped gullies quantitative information on gully erosion rates as related to gully head extension are scarce because bank active sides take many forms presumably depending on topography, climate and lithology. Our field cross section measurements of 4 gullies developed in the Fortuna Formation, (2 located on a steep slope area (> 15%) and the other two on a gentle slope (< 9%)), have shown that the geometry of these gullies is far from a conical gully shape. These field measurements were used to calculate gully reaches geometry and volume variation. No direct relationships between gully volume and length could be established for these gullies in the Fortuna formation. Nevertheless, since both gully top view area and maximum top width are increasing, as the gully reach length increases, relationships could be established between maximum top width and their equivalent width defined as the ratio between gully reach top view area and its length. Then, gully volume–length relationships could be established for each of the 5 maximum bank-full widths studied on the two gentle and two steep slope gullies. For any maximum top width, the gully volume–length relationship was found to be not unique but the volume is increasing linearly up to the 15 m and 45 m distance from the gully head and then logarithmically for steep and gentle slope gullies, respectively. The linear and logarithmic equations' coefficients were also found to be a function of gully maximum top width. These equations were then used to quantify gully sediment yields related to gully shape evolution for eight gullies tributaries of As Sahsafa wadis. For this purpose the top view areas and lengths of these eight gullies were digitized and monitored on rectified air photographs of 1962, 1974 and 2000 using a Geographic Information System (Arc View). Half of these gullies were located in an area with a gentle slope gradient and the other half with steep slope gradient. The average gullies length variation for the whole study period (1962–2000) were 11.74% and 10.32% whereas the average top view areas variation was 23.57% and 29.4% for gentle and steep slope gullies, respectively. Gullies volume changes during the periods 1962–1974 and 1974–2000 were then derived from the variation of gullies length and top view areas photo-measurements on these 8 tributaries using the relationships established from the four measured gullies. On gentle slopes, the average gully sediment yields during 1962–1974 and 1974–2000 periods were 3.98 and 2.28 m3 ha− 1 year− 1, respectively. On steep slopes, these values are 4.82 and 2.47 m3 ha− 1 year− 1.

水土流失治理措施对小流域土壤有机碳和全氮的影响

PDF HTML阅读 XML下载 导出引用 引用提醒 水土流失治理措施对小流域土壤有机碳和全氮的影响 DOI: 10.5846/stxb201108121182 作者: 作者单位: 西北农林科技大学资源环境学院,陕西杨凌,西北农林科技大学资源环境学院,中科院水利部水土保持与生态研究中心，陕西杨凌,西北农林科技大学资源环境学院,陕西杨凌,西北农林科技大学资源环境学院,陕西杨凌 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金资助(40771125) Effects of soil erosion control measures on soil organic carbon and total nitrogen in a small watershed Author: Affiliation: College of Resource and Environment,College of Resource and Environment,College of Resource and Environment,College of Resource and Environment 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:明确综合治理条件下小流域土壤有机碳(Soil organic carbon, SOC)和全氮(Total nitrogen, TN) 的空间分布特征及其影响因素,对科学评价水土流失区土壤固碳潜力具有重要意义。以黄土高原丘陵沟壑区典型小流域(砖窑沟流域)为对象,基于流域内3种典型地貌类型(梁峁坡、沟坡、沟谷)和3种典型水土流失治理措施(水平梯田、林地和草地措施,坡耕地为对照),采集土壤样品737个,研究地貌类型和水土流失治理措施对小流域SOC和TN变化的影响。结果表明,同一地貌类型上,水平梯田、林地和草地措施的SOC和TN(0-10 cm土层)含量均显著高于坡耕地(P<0.1)。梁峁坡上,水平梯田、林地和草地措施条件下的 SOC和TN含量较坡耕地依次提高了18%和24%、70%和59%、25%和21%;沟坡上,林地和草地措施的SOC和TN较坡耕地依次提高了76%和54%、25%和27%。同一治理措施在不同地貌类型间对0-10 cm土层SOC和TN的影响存在显著差异(P<0.1)。水平梯田条件下,沟谷的SOC和TN含量比峁坡提高了46%和43%;林地措施条件下,沟坡的SOC和TN含量比峁坡提高了18% 和6%;草地措施条件下,沟坡的SOC和TN含量比峁坡提高了14% 和18%。0-100 cm土层的SOC或TN在不同地貌类型或不同治理措施间的差异与土壤水分含量(Soil moisture, SM)的变化趋势基本一致,并且SOC或TN与SM呈指数关系y= aebx (y为SOC或TN,x为SM)。 Abstract:It is significance of assessing soil organic carbon (SOC) and total nitrogen (TN) sequestration potential to understand dynamics of soil organic carbon (SOC) and total nitrogen (TN) at a small watershed with comprehensive measures in the loess region of China. Based on three topographic positions (Ridge slope, Gully slope, Valley bottom) and three control measures for soil erosion (Level terrace,Woodland measures,Grassland measures), 737 soil samples were collected to investigate effects of topographic positions and soil erosion control measures on soil organic carbon and total nitrogen at Zhuan Yaogou watershed in the hilly region of Loess Plateau. Under the similar topographic positions, SOC and TN (0-10 cm soil layer) in level terrace, woodland and grassland were significantly higher than those in cropland on sloping land (P<0.1). For the ridge slope, SOC and TN in level terrace, woodland and grassland were 18% and 24%, 70% and 59%, and 25% and 21% higher than that in cropland on sloping land, respectively; For the gully slope, SOC and TN in woodland and grassland were 76% and 54%, and 25% and 27% higher than that in cropland on sloping land, respectively. The similar control measures for soil erosion produced significant differences among topographic positions (P<0.1). In the 0-10 cm soil layer, For the level terrace measure, SOC and TN in valley bottom were 46% and 43% higher than those in the ridge slope; For the woodland measures, SOC and TN in the gully slope were 18% and 6% higher than those in the ridge slope; For the grassland measures, SOC and TN in the gully slope were 14% and 18% higher than those in the ridge slope. In the 0-100 cm soil depth, SOC or TN had the similar change characteristics with soil moisture among the topographic positions and the soil erosion control measures. An exponential relationships of y= aebx (y is SOC or TN and x is soil moisture) were developed between SOC (TN) and soil moisture at the small watershed. 参考文献 相似文献 引证文献

Submarine gullies on Italian upper slopes and their relationship with volcanic activity revisited 20 years after Bill Normark’s pioneering work

Multibeam bathymetry and high-resolution seismic profiles depict in detail the characteristics of submarine gullies present in the upper continental slope offshore of the mouths of the Tiber and Volturno Rivers in the Tyrrhenian Sea and the Simeto River in the Ionian Sea. Upper slope gullies are interpreted as depositional features, growing because of faster aggradation on intergully areas with respect to their axes. The dispersal of river-flood sediment through plunging of hyperpycnal flows has been interpreted to be the limiting factor in sedimentation in gully axes. However, the generation of hyperpycnal flows requires a sediment concentration of several tens of kilograms per cubic meter in the river flows to overcome the higher density of seawater. This threshold is difficult to reach in medium-sized rivers (i.e., catchment basin of 500–5000 km 2 ), such as the Tiber and Volturno. Two alternative scenarios of enhanced sediment availability for these rivers have been proposed. The first scenario is related to sea-level fall and lowstand stages, when the climate conditions may have been different and a huge amount of unconsolidated, fine-grained sediment deposited during the previous highstand stage may have been eroded from the river valleys, coastal plain valleys and shelf delta, as suggested in pioneering work of one of the authors (Chiocci) and Bill Normark. This scenario might explain the formation of some of the gullies offshore of the Tiber River mouth, which developed during the last glacial maximum; however, it is unable to explain the gullies within deposits related to transgressive and highstand system tracts, such as offshore of the Simeto and Volturno River mouths. An alternative scenario is thus proposed on the basis of the relationship observed between the studied rivers and the presence of large volcanic edifices in their catchment basins. Explosive volcanic activity could have drastically modified their catchment basins and caused a sudden and large supply of loose tephras, increasing the sediment load in watercourses and consequently favoring the development of gully-forming hyperpycnal flows. The timing of volcanic activity on the three study areas matches, in fact, the presence or absence of gullies in upper slope depositional sequences.

Measuring medium-term sheet erosion in gullies from trees: A case study using dendrogeomorphological analysis of exposed pine roots in central Iberia

The assessment of gully erosion poses a great challenge because of the complexity and connectivity of the geomorphic processes involved. This study focuses on the quantification of sheet erosion rates in a set of slope gullies located on the northern piedmont of the Guadarrama Mountains (Spanish Central System). In order to delineate accurately the gully areas in which sheet erosion was predominant, the Hydrologic/Erosion Response Unit (HRU/ERU) approach was used and a dendrogeomorphological analysis of exposed tree roots was carried out to quantify sheet erosion rates in one selected HRU/ERU. Identification of the first year of exposure by erosion from anatomical criteria was therefore critical. The 29 samples taken were prepared for anatomical analysis and cross-dated. Anatomical analysis of the samples showed a reduction in the lumen area of earlywood tracheids following root exposure and also, in most cases, a slight increase in growth rings. Moreover, at the end of the ring, latewood tissue and visible annual borders were very clearly defined by several rows of thick-walled tracheids. A non-parametric test was used on the findings derived from this qualitative analysis to objectify determination of the first year of exposure. Estimates of sheet erosion were obtained by dividing the height of eroded soil by the number of years that each root was exposed. The mean value of soil erosion for the entire study site was then determined from statistical inference. Using this procedure, a range of sheet erosion rates between 6.2 and 8.8 mm y −1 (125.2 and 177.8 t ha −1 year −1) was obtained for the dominant HRU/ERU of these gullies in central Iberia. These estimates of eroded soil thickness were adjusted based on the recent finding that root anatomical changes occur prior to their exposure by erosion.

Role of topography in the behavior of the matric suction of unsaturated fill slopes

This paper presents the result of a field study on the influence of topography on the distribution of the matric suction of the soil in unsaturated slopes subjected to rainfall. The matric suction was measured in the lower, middle and upper parts of planar, ridge-like and gullied slopes before and after two significant rainfall events. Jet-filled tensiometers were used for depths of >1.2 m and the filter paper method at depths of <0.9 m. It was found that in the dry season the matric suction of the soil at a shallow depth in the gullied slope is significantly less than that in the planar and ridge-like slopes while following a rainfall event the decrease in the matric suction is smallest in the gullied slope and greatest in the ridge-like slope, irrespective of the amount of the accumulated precipitation.

Seabed morphology and shallow sedimentary structure of the Storfjorden and Kveithola trough-mouth fans (North West Barents Sea)

This study aims to present an overview of the seafloor morphology and shallow sedimentary structure of the Storfjorden and Kveithola Trough Mouth Fans (TMFs) on the northwestern Barents Sea continental margin. Data have been compiled from two International Polar Year (IPY) cruises (SVAIS, of the BIO Hespérides and EGLACOM of the R/V OGS-Explora) that yielded 15,340 km 2 of multi-beam bathymetry and 9500 km of sub-bottom seismic profiles. In this area, the continental shelf edge defines three wide and subdued sedimentary lobes forming Storfjorden TMF, one single lobe on Kveithola TMF, and three inter-TMF areas on the continental slope. The two northernmost lobes of Storfjorden TMF (Lobes I and II) are composed by thick (up to 50 m) sequences of glacially derived debris flow deposits interbedded with thin a few metres de-glacial and interglacial deposits. A network of upper slope gullies incises these debris flow deposits as a consequence of subglacial meltwater release at or near the shelf break. Gullies evolve into channels whose morphologic evidence disappears midslope, leaving place to a subdued chevron-like morphological pattern inherited by the preceeding glacial maximum debris flow deposits. A drastic change occurs on the continental slope of Storfjorden TMF Lobe III and Kveithola TMF, where are several translational submarine landslides mostly originated in the upper slope, the majority of which detach at the contact between Middle Weishelian glacigenic debris flows and the overlying acoustically laminated plumites. Dendritic canyon systems only develop in inter-TMF areas. The data suggest that TMF continental slope progradation depends on short-lived episodes of extreme sedimentation during glacial maxima and during the early deglaciation phase, and that an important controlling factor is the mechanism of ice stream retreat from the continental shelf edge. We suggest that the two northern Storfjorden sub-ice streams were composed of thicker and perhaps faster ice progressively draining a distal and larger ice source mainly located on Svalbard. Conversely, the southernmost Storfjorden sub-ice stream and the Kveithola ice stream were fed by a local, smaller marine-based ice dome grounded on Spitsbergenbanken. The ice dome persisted after the LGM, maintaining a local ice drainage system close to the shelf edge whose sedimentary evidence can be found on the continental slope of the southern lobe of Storfjorden TMF and Kveithola TMF. The high degree of lateral variability in the style of sedimentation on TMF slopes suggests that ice stream dynamics may vary considerably within the same glacial trough, and that such variability affects the long-term development of the architecture of TMFs.