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1.
Hydraulic thresholds for erosion of fourteen upland mineral and organic soils were determined in a hydraulic flume. These soils are from areas to be afforested in the United Kingdom. Some of the group are erosion resistant but others are susceptible to erosion once denuded of vegetation; for example, by preafforestation ploughing. These threshold data were required to calibrate a hydraulic model for effective design of preafforestation drainage networks on a variety of soils. However, simple field measures of soil properties indicative of erosion potential would be of value to the forestry industry for management purposes. Consequently, hydraulic threshold data were related by linear regression methods to basic soil properties, including organic content, grain size, bulk density, compression strength and penetration resistance. The investigation concluded that four peat soils are not eroded by clear water velocities up to 5·7 m s−1, although a mineral bedload might induce erosion at lesser current speeds. Penetration resistance is a good field indicator of the degree of humification of the peat soils. Although selected physical parameters contribute resistance to water erosion, an increased organic content is pre-eminent in reducing erosion susceptibility in both organic and mineral soils. Although compressive strength was not indicative of soil erodibility, field measurements of penetration resistance on a variety of soils could be related to hydraulic thresholds of erosion; albeit through the construction of discriminant functions interpolated by eye. Consequently, organic content (laboratory) or penetration resistance (field) might form the basis of classifying upland soils in terms of erodibility. Mineral soils differ widely in terms of their erodibility, so that subject to further consideration, the use of ploughing for forestry cultivation might be appropriate in wider circumstances than presently recommended by the Forests and Water Guidelines. Ploughing should be acceptable on deep peat providing the underlying mineral soil is not exposed in the bottom of the furrow, and furrows are not led from mineral soils on to deep peat. © 1997 John Wiley & Sons, Ltd.  相似文献   

2.
In agricultural basins of the southeastern coastal plain there are typically large disparities between upland soil erosion and sediment delivered to streams. This suggests that colluvial storage and redistribution of eroded soil within croplands is occurring, and/or that processes other than fluvial erosion are at work. This study used soil morphology and stratigraphy as an indicator of erosion and deposition processes in a watershed at Littlefield, North Carolina. Soil stratigraphy and morphology reflect the ways in which mass fluxes associated with cultivation transform the local soils. Fluvial, aeolian and tillage processes were all found to be active in the redistribution of soil. The soil transformations are of five general types. First, erosion and compaction in the cultivated area as a whole result in the thinning of Arenic and Grossarenic Paleudults and Paleaquults to form Arenic, Typic and Aquic Paleudults and Paleaquults. Second, redistribution of surficial material within the fields results in transitions between Arenic and Typic or Aquic subgroups as loamy sand A and E horizons are truncated or accreted. Third, aeolian deposition at forested field boundaries leads to the formation of compound soils with podzolized features. Fourth, sandy rill fan deposits at slope bases create cumulic soils distinct from the loamy sands of the source area or the darker, finer terrace soils buried by the fan deposits. Finally, tillage and fluvial deposition in upland depressions results in the gradual burial of Rains (poorly drained Typic Paleaquults) soils. Results confirm the importance of upland sediment storage and redistribution, and the role of tillage and aeolian processes as well as fluvial processes in the region. Copyright © 1999 John Wiley & Sons, Ltd.  相似文献   

3.
Strong winds are a characteristic feature of UK upland areas. Despite this, understanding of aeolian processes in upland environments of the UK is limited. This paper presents direct measurements and observations of blanket peat erosion by wind action during a two week period of desiccation in the North Pennines, Northern England. A circular configuration of mass flux sediment samplers was used to collect peat eroded by wind action from 16 cardinal compass directions. Meteorological conditions (wind speed, wind direction, precipitation and temperature) were recorded by an automatic weather station set up adjacent to the site. Surface desiccation led to peat crust erosion and dust deflation. During short (≤1 hour) periods of precipitation, wind‐driven rainfall also caused erosion. Typically, dust flux rates were up to two orders of magnitude lower than recorded during periods of sustained wet weather. Measurements demonstrate the hitherto unreported rapid switch in process regime between wind‐driven rainfall and dry blow deflation in blanket peat environments. Dry blow processes of blanket peat erosion may become more important in UK upland areas if climate change promotes more frequent surface desiccation. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

4.
A sediment budget was developed for the 1.7 km2 Maluna Creek drainage basin located in the Hunter Valley, New South Wales, Australia, for the period 1971-86. the impact of viticulture, which commenced at Maluna in 1971, was studied using erosion plots, with caesium-137 as an indicator of both soil erosion and sedimentation. Two methods were used to estimate vineyard soil losses from caesium-137 measurements. Sediment output from the catchment was measured for three years, and extrapolated from readings taken at a nearby long-term stream flow gauging station for the remaining 13 years. Relative amounts of soil loss from forest (60 per cent basin area), grazing land (30 per cent) and vineyards (10 per cent) were calculated. Soil losses by rain splash detachment were ten times greater from bare/cultivated sufaces than from the forest. Erosion plots of area 2 m2 showed no significant differences in soil loss between forest and grassland but, under bare soil, losses were 100 times greater. the 137Cs method was employed to calculate net soil loss from all vineyard blocks using both a previously established calibration curve and a proportional model. the latter method gave estimates of soil loss which were 3-9 times greater than by the calibration curve, and indicated that average soil losses from the vineyard were equivalent to 62 t ha?1 y?1 (1971-86). It was estimated that the forest contributed 1-8 per cent, the grazing land 1.6 per cent, and the vineyard 96.6 per cent of the total soil loss during that period. Sediment storages within the fluvial system adjacent to the vineyard ws 9460 t for the period, whereas sediment output was equivalent to 215 t km?1 y?1. Independent measurements of soil erosion, storage, and output showed that 56 per cent of the eroded sediment remained in the catchment, and 34 per cent was transported out by Maluna Creek. the budget was able to be balanced to within 10 per cent.  相似文献   

5.
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6.
The objective of this study is to explore in a critical way the potential of high-altitude (stereo) aerial photographs for the assessment of ephemeral gully erosion rates. On 28 May 1995, an intensive rainfall event (30 mm h−1 during 30 min, return period = 3 years) occurred in central Belgium. Ephemeral gullies formed within an area of 218 ha (study area 1) were mapped and measured both in the field and by high-altitude aerial photos taken at the same time. Comparison of these two methods shows that if only one of the two surveying techniques had been used, only 75 per cent of the total ephemeral gully length would have been detected, so that the combination of aerial and field data leads, in fact, to the best possible determination of total gully length within the selected area. A correction factor (C) is proposed, so that the results of an ephemeral gully erosion survey based on high-altitude (stereo) aerial photos can be adjusted for the undetected gullies. Next, a sequential series of high-altitude stereo aerial photographs, taken in six different years, was analysed in order to determine ephemeral gully erosion rates in three selected study areas (study areas 2, 3 and 4). Selection criteria were chosen so that these three areas were similar to study area 1 and representative for the cultivated areas in central Belgium where intense soil erosion regularly occurs. Ephemeral gullies were mapped and their total length was measured from the aerial photos. Using a mean gully cross-section of 0·2635 m2 (determined in study area 1), the average eroded volume is 1·89 m3 ha−1 in six months for study area 1, 0·86 m3 ha−1 in six months for area 2, 1·44 m3 ha−1 in six months for area 3, and 2·37 m3 ha−1 in six months for area 4. According to the correction factor (C), these mean ephemeral gully erosion volumes have to be increased by 44 per cent. The ephemeral gully erosion rates based on high-altitude stereo aerial photos, correspond well with the results of other surveys carried out in the Belgian loess belt. Copyright © 1999 John Wiley & Sons, Ltd.  相似文献   

7.
In this paper we quantitatively test the hypothesis that soil freeze–thaw (FT) processes significantly increase the potential for upland hillslope erosion during run‐off events that follow thaw. We selected a highly frost‐susceptible silt to obtain an upper bound on FT effects, and completed three series of six experiments each to quantify differences in soil erosion and rill development in a bare soil following a single FT cycle. Each series represented a specific soil moisture range: 16–18 per cent, 27–30 per cent and 37–40 per cent by volume, with nominal flow rates of 0·4, 1·2 and 2·4 L/min and slopes of 8° and 15°. Each experiment used two identical soil bins: one a control (C) that remained unfrozen, and another that was frozen and thawed once. Standard soil characterization tests did not detect significant differences between the FT and C bins. We measured cross‐sectional geometry of an imposed straight rectangular rill before each experiment, sediment load during and rill cross‐sections after. Changes in cross section provided detailed measures of erosion at specific locations, while sediment load from time series run‐off samples integrated the rill erosion. Several parameters, including average maximum rill width, average maximum rill depth, rill cross‐section depth measures and sediment load, all followed similar trends. Each was greater in the FT than in the C, with values that generally increased with slope and flow. However, soil moisture was the only parameter that affected the FT/C ratios. Average sediment load grouped by soil moisture provided FT/C ratios of 2·4, 3·0 and 5·0 for low, mid and high moisture, respectively. In contrast, a ‘dry’ experiment at 4–5 per cent soil moisture had FT/C of 1·02 for sediment load. These results show a dramatic increase with soil moisture in the rate and quantity of bare soil eroded due to the FT cycle. As both FT and C results were highly sensitive to initial conditions, minimum differences in soil weight, bulk density and soil moisture through each series of experiments were required to achieve consistent results, indicating that rill erosion may be chaotic. Published in 2005 by John Wiley & Sons, Ltd.  相似文献   

8.
Winter wheat–summer fallow is the conventional cropping system employed on >1·5 million ha within the Columbia Plateau of eastern Washington and northern Oregon. Wind erosion contributes to poor air quality in the region, yet little is known concerning the magnitude of soil and PM10 (particulate matter of ≤10 µm in aerodynamic diameter) loss from agricultural lands. Therefore, loss of soil and PM10 was assessed from a silt loam in eastern Washington during 2003 and 2004. Field sites were maintained in fallow using conventional tillage practices in 2003 (9 ha field) and 2004 (16 ha field) and instrumented to assess horizontal soil flux and PM10 concentrations at the windward and leeward positions in the field during high‐wind events. Soil flux was measured using creep and airborne sediment collectors while PM10 concentrations were measured using high‐volume PM10 samplers. Aggregate size distribution of parent soil and eroded sediment was characterized by rotary and sonic sieving. Six high‐wind events occurred over the two year period, with soil loss ranging from 43 kg ha?1 for the 12–22 September 2003 event to 2320 kg ha?1 for the 27–29 October 2003 event. Suspension‐sized particulates (<100 µm in diameter) comprised ≥90 per cent of the eroded sediment, indicating that direct suspension may be an important process by which the silt loam eroded. The corresponding loss of PM10 for these two events ranged from 5 to 210 kg ha?1. Loss of PM10 comprised 9–12 per cent of the total soil loss for the six events. This study suggests that the relatively small loss of PM10 from eroding agricultural fields maintained in summer fallow can affect air quality in the Columbia Plateau. Therefore, alternative tillage practices or cropping systems are needed for minimizing PM10 emissions and improving air quality in the region. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

9.
The areally weighted surface erosion for Niwot Ridge, an alpine interfluve in the Colorado Front Range, is 10−1 mm/y. This may be subdivided into rates for three generalized cover types: tundra meadow, 10−2 mm/y; dry tundra, 10−1 mm/y; late-lying snow patches, 10° mm/y. Tundra meadow (about 50 per cent of the interfluve area) yields about 5 per cent of the eroded material; dry tundra (35 per cent of the area) contributes slightly less than 50 per cent of the eroded material; while nivation hollows occupied by late-lying snow patches occupy only about 3 per cent of the area they contribute 50 per cent of the eroded material. The bulk of the surficial erosion is accomplished between June and September, primarily by rainsplash, except where snowmelt is important. The overall estimated surface lowering rate presented here is substantially higher than those reported previously.  相似文献   

10.
Soil loss rates due to piping erosion   总被引：1，自引：0，他引：1  
Compared with surface soil erosion by water, subsurface erosion (piping) is generally less studied and harder to quantify. However, wherever piping occurs, it is often a significant or even the main sediment source. In this study, the significance of soil loss due to piping is demonstrated through an estimation of soil volume lost from pipes and pipe collapses (n = 560) in 137 parcels under pasture on loess‐derived soils in a temperate humid climate (Belgium). Assuming a period of 5 to 10 years for pipe collapse to occur, mean soil loss rates of 2.3 and 4.6 t ha?1 yr?1 are obtained, which are at least one order of magnitude higher than surface erosion rates (0.01–0.29 t ha?1 yr?1) by sheet and rill erosion under a similar land use. The results obtained for the study area in the Flemish Ardennes correspond well to other measurements in temperate environments; they are, however, considerably smaller than soil loss rates due to subsurface erosion in semi‐arid environments. Although local slope gradient and drainage area largely control the location of collapsed pipes in the study area, these topographic parameters do not explain differences in eroded volumes by piping. Hence, incorporation of subsurface erosion in erosion models is not straightforward. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

11.
In gully erosion, the detached soil can be transported over long distances along the landscape. The eroded material can be redistributed and/or deposited on the soil surface along the landscape and then eventually be buried by newly eroded and deposited sediment. There can be significant variability of the soil conditions (e.g., texture and moisture content) over which the eroded material travels. The eroded material can be detected through the use of magnetic tracers attached to or mixed with the eroded soil. In this study we evaluated the degree to which the magnetic signal of the magnetite is conditioned by (i) burial depth of tracer, (ii) condition of soil covering the tracer and (iii) tracer concentration. In the laboratory containers were filled with a specific soil. In the filling process, a 0.5-cm layer of a soil–magnetite mixture was interspersed in the soil profile at a certain depth. Experiments encompassed three different soil–tracer concentrations (1000:1, 200:1, 100:1), four burial depths of tracer (0 cm, 3 cm, 5 cm and 10 cm from soil surface), and two different soils. In each case, the magnetic susceptibility was measured with a susceptometer. Experiments were repeated with different soil moisture contents. If the tracer is located under the soil surface, a minimum soil–tracer concentration of 200:1 is required for its correct detection. The intensity of the magnetic signal decreases dramatically with the vertical distance of the tracer from the soil surface. The maximum detection depth for the tracer's magnetic signal is strongly dependent on the natural magnetic susceptibility of the soil, which masks the tracer's signal. Variation in soil moisture content does not significantly affect the magnetic signal. For extensive field studies, the soil–tracer volume to be handled would be very high and therefore, it is necessary to explore new tracer application techniques.  相似文献   

12.
Peatlands are an important store of soil carbon, and play a vital role in global carbon cycling, and when located in close proximity to urban and industrial areas, can also act as sinks of atmospherically deposited heavy metals. Large areas of the UK's blanket peat are significantly degraded and actively eroding which negatively impacts carbon and pollutant storage. The restoration of eroding UK peatlands is a major conservation concern, and over the last decade measures have been taken to try to control erosion and restore large areas of degraded peat. This study utilizes a sediment source fingerprinting approach to assess the effect of restoration practices on sediment production, and carbon and pollutant export in the Peak District National Park, southern Pennines (UK). Suspended sediment was collected using time integrated mass flux samplers (TIMS), deployed across three field areas which represent the surface conditions exhibited through an erosion–restoration cycle: (i) intact; (ii) actively eroding; and (iii) recently re‐vegetated. Anthropogenic pollutants stored near the peat's surface have allowed material mobilized by sheet erosion to be distinguished from sediment eroded from gully walls. Re‐vegetation of eroding gully systems is most effective at stabilizing interfluve surfaces, switching the locus of sediment production from contaminated surface peat to relatively ‘clean’ gully walls. The stabilization of eroding surfaces reduces particulate organic carbon (POC) and lead (Pb) fluxes by two orders of magnitude, to levels comparable with those of an intact peatland, thus maintaining this important carbon and pollutant store. The re‐vegetation of gully floors also plays a key role in decoupling eroding surfaces from the fluvial system, and further reducing the flux of material. These findings indicate that the restoration practices have been effective over a relatively short timescale, and will help target and refine future restoration initiatives. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

13.
Field studies of rainsplash erosion   总被引：1，自引：0，他引：1  
Studies on sandy soils of the Cottenham Series in mid-Bedfordshire confirm in the field the relationships between splash erosion, rainfall energy and ground slope obtained in the laboratory experiments of other workers. Only 0·06 per cent of the rainfall energy contributes to splash erosion and rates are low, attaining a maximum of 0·082 kg m?2 y?1 on a slope of 11°. The major role of splash action is in the detachment of soil particles prior to their removal by overland flow.  相似文献   

14.
The wide range of studies describing the role of bank erosion in fluvial sediment supply have mostly lumped amounts of bank erosion into coarse temporal units, such as years. This paper investigates sediment yields from individual bank erosion events within the upper River Severn, UK (basin area 380 km2). Manual erosion pins and photo-electronic erosion pins were used to estimate bank erosion, and turbidity meters were used to determine suspended sediment transport. At the annual time-scale, the silt-clay fraction of bank-derived sediment accounted for an equivalent of 17 per cent of the suspended load, increasing to an average of 38 per cent at the monthly timescale, and then to an average of 64 per cent at the event timescale. This research highlighted that for an upland catchment, bank erosion was an important supply of suspended sediment, and that for some flood events bank erosion can supply more sediment than is transported. © 1997 John Wiley & Sons, Ltd.  相似文献   

15.
In this study our main objective was to quantify water interrill erosion in the sloping lands of Southeast Asia, one of the most bio‐geochemically active regions of the world. Investigations were performed on a typical hillslope of Northern Laos subjected to slash and burn agriculture practiced as shifting cultivation. Situations with different periods of the shifting cultivation cycle (secondary forest, upland rice cultivation following a four‐year fallow period and three‐year continuous upland rice cultivation) and soil orders (Ultisols, Alfisols, Inceptisols) were selected. One metre square micro‐plots were installed to quantify the soil material removed by either detachment of entire soil aggregate or aggregate destruction, and the detached material transported by thin sheet flow, the main mechanisms of interrill erosion. In addition, laboratory tests were carried out to quantify the aggregate destruction in the process of water erosion by slaking, dispersion and mechanical breakdown. The average runoff coefficient (R) evaluated throughout the 2002 rainy season was 30·1 per cent and the interrill erosion was 1413 g m?2 yr?1 for sediments and 68 g C m?2 yr?1 for soil organic carbon, which was relatively high. Among the mechanisms of interrill water erosion, aggregate destruction was low and mostly caused by mechanical breakdown due to raindrops, thus leading to the conclusion that detachment and further transport by the shallow runoff of macro‐aggregates predominates. R ranged from 23·1 to 35·8 per cent. It decreased with the proportion of mosses on the soil surface and soil surface coverage, and increased with increasing proportion of structural crust, thus confirming previous results. Water erosion varied from 621 to 2433 g m?2 yr?1 for sediments and from 31 to 146 g C m?2 yr?1 for soil organic carbon, and significantly increased with increasing clay content of the surface horizon, probably due to the formation of easily detachable and transportable sand‐size aggregates, and proportion of macro‐aggregates not embedded in the soil matrix and prone to transport. In addition, water erosion decreased with increasing proportion of structural crusts, probably due to their higher hardness, and when cultivation follows a fallow period rather than after a long period of cultivation due to the greater occurrence of algae on the soil surface, which affords physical protection and greater aggregate stability through binding and gluing. This study based on simultaneous field and laboratory investigations allowed successful identification and quantification of the main erosion mechanisms and controlling factors of interrill erosion, which will give arguments to further set up optimal strategies for sustainable use of the sloping lands of Southeast Asia. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

16.
Active gully systems developed on highly weathered or loose parent material are an important source of runoff and sediment production in degraded areas. However, a decrease of land pressure may lead to a return of a partial vegetation cover, whereby gully beds are preferred recolonization spots. Although the current knowledge on the role of vegetation on reducing sediment production on slopes is well developed, few studies exist on the significance of restoring sediment transport pathways on the total sediment budget of degraded mountainous catchments. This study in the Ecuadorian Andes evaluates the potential of vegetation to stabilize active gully systems by trapping and retaining eroded sediment in the gully bed, and analyses the significance of vegetation restoration in the gully bed in reducing sediment export from degraded catchments. Field measurements on 138 gully segments located in 13 ephemeral steep gullies with different ground vegetation cover indicate that gully bed vegetation is the most important factor in promoting short‐term (1–15 years) sediment deposition and gully stabilization. In well‐vegetated gully systems ( ≥ 30% of ground vegetation cover), 0.035 m3 m–1 of sediment is deposited yearly in the gully bed. Almost 50 per cent of the observed variance in sediment deposition volumes can be explained by the mean ground vegetation cover of the gully bed. The presence of vegetation in gully beds gives rise to the formation of vegetated buffer zones, which enhance short‐term sediment trapping even in active gully systems in mountainous environments. Vegetation buffer zones are shown to modify the connectivity of sediment fluxes, as they reduce the transport efficiency of gully systems. First calculations on data on sediment deposition patterns in our study area show that gully bed deposition in response to gully bed revegetation can represent more than 25 per cent of the volume of sediment generated within the catchment. Our findings indicate that relatively small changes in landscape connectivity have the potential to create strong (positive) feedback loops between erosion and vegetation dynamics. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

17.
A portable field wind tunnel was used to assess the sediment flux rates of loam and sand textured soils in the Mallee region of southeastern Australia. Three levels of crust disturbance (nil, moderate and severe) simulating stock trampling were investigated. The results demonstrated the importance of cryptogamic crusts in binding the soil surface and providing roughness after the soil was moderately disturbed. On the loamy soil, the crust helped maintain sediment flux rates below the erosion control target to 5 g m−1 s−1 for a 65 km h−1 wind measured at 10 m height. Once the crust was severely disturbed, sediment fluxes increased to 1·6 times the erosion target. On the sandy soil, even with no crust disturbance the sediment flux was 1·6 times the erosion control target. Disturbing the crust increased sediment fluxes to a maximum of 6·7 times the erosion control target. Removal of the crust also decreased the threshold wind velocity that resulted in an increase to the risk of erosion from <5 per cent to 20 per cent. © 1998 John Wiley & Sons, Ltd.  相似文献   

18.
1 INTRODUCTION Erosion caused by ephemeral flows is a frequent phenomenon in nature and contributes to the shape of the landscape. This type of erosion may cause great soil losses in agricultural areas, which are quickly transferred to the watershed outlets through the rill and gully network (Bennett et al., 2000; Poesen et al., 2003). Concentrated flow erosion is controlled by the erodibility of surface materials, climate, soil use and management, and watershed topography. Several metho…  相似文献   

19.
Riverbank erosion is a major contributor to catchment sediment budgets. At large spatial scales data is often restricted to planform channel change, with little information on process distributions and their sediment contribution. This study demonstrates how multi‐temporal LiDAR and high resolution aerial imagery can be used to determine processes and volumes of riverbank erosion at a catchment scale. Remotely sensed data captured before and after an extreme flood event, enabled a digital elevation model of difference (DoD) to be constructed for the channel and floodplain. This meant that: the spatial area that could be assessed was extensive; three‐dimensional forms of bank failures could be mapped at a resolution that enabled process inference; and the volume and rates of different bank erosion processes over time could be assessed. A classification of riverbank mass failures, integrating form and process, identified a total of 437 mass failure polygons throughout the study area. These were interpreted as wet flow mass failures based on the presence of a well defined scarp wall and the absence of failed blocks on the failure floor. The failures appeared to be the result of: bank exfiltration, antecedent moisture conditions preceding the event, and the historic development of the channel. Using one‐dimensional hydraulic modelling to delineate geomorphic features within the main boundary of the macrochannel, an estimated 1 466 322 m2 of erosion was interpreted as fluvial entrainment, occurring across catchment areas from 30 to 1668 km2. Only 8% of the whole riverbank planform area was occupied by mass failures, whilst fluvial entrainment covered 33%. A third of the volume of material eroded came from mass failures, even though they occupied 19% of the eroded bank area. The availability of repeat LiDAR surveys, combined with high‐resolution aerial photography, was very effective in erosion process determination and quantification at a large spatial scale. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

20.
The rate of blanket peat erosion was measured at an upland site in central Wales during the 1983-1984 drought years. Erosion pins, a peat surface sediment trap, and sediment sampling in the effluent stream, were used to estimate the rate of peat surface recession and the rate of organic sediment loss from the catchment. An overall rate of surface recession of 16 mm y?1 on exposed peat faces was recorded; this differed between faces of different aspects, with the greatest recession on southwest faces. Eroding peat surfaces exhibited maximum recession during the summer, but the peat surface sediment trap indicated that the highest rates of sediment loss from peat faces due to rain wash occurred during the autumn and early winter. Stream sediment sampling showed that the yield of organic sediment from the catchment was 34·4 t km?2 yr?1, with greatest losses also during the autumn and early winter. The evidence suggested that the surface recession, as measured on erosion pins, included a ‘wastage’ or shrinkage component, which possibly accounted for as much as 80 per cent of the apparent loss. Direct and circumstantial evidence suggested that peat wastage during the summer months was the most important agent of surface recession in the study period, which encompassed the two dry summers. Desiccation provided available sediment during the autumn, but organic sediment supply became limited as the winter progressed, despite the occurrence of frost heave.  相似文献   

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