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1.
Soil erosion by concentrated flow can cause serious environmental damage. Erosion‐control geotextiles have considerable potential for reducing concentrated flow erosion. However, limited data are available on the erosion‐reducing potential of geotextiles. In this study, the effectiveness of three biological geotextiles in reducing soil losses during concentrated flow is investigated. Hereto, runoff was simulated in a concentrated flow flume, filled with an erodible sandy loam on three slope gradients (13·5, 27·0 and 41·5%). Treatments included three biological geotextiles (borassus, buriti and bamboo) and one bare soil surface. Darcy–Weisbach friction coefficients ranged from 0·01 to 2·84. The highest values are observed for borassus covered soil surfaces, followed by buriti, bamboo and bare soil, respectively. The friction coefficients are linearly correlated with geotextile thickness. For the specific experimental conditions of this study, borassus geotextiles reduced soil detachment rate on average to 56%, buriti geotextiles to 59% and bamboo geotextiles to 66% of the soil detachment rate for bare soil surfaces. Total flow shear stress was the hydraulic parameter best predicting soil detachment rate for bare and geotextile covered surfaces (R2 = 0·75–0·84, p <0·001, n = 12–15). The highest resistance against soil detachment was observed for the borassus covered soil surfaces, followed by buriti, bamboo and bare soil surfaces, respectively. Overall, biological geotextiles are less effective in controlling concentrated flow erosion compared with interrill erosion. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
2.
Methods for predicting unit plot soil loss for the ‘Sparacia’ Sicilian (Southern Italy) site were developed using 316 simultaneous measurements of runoff and soil loss from individual bare plots varying in length from 11 to 44 m. The event unit plot soil loss was directly proportional to an erosivity index equal to (QREI30)1·47, being QREI30 the runoff ratio (QR) times the single storm erosion index (EI30). The developed relationship represents a modified version of the USLE‐M, and therefore it was named USLE‐MM. By the USLE‐MM, a constant erodibility coefficient was deduced for plots of different lengths, suggesting that in this case the calculated erodibility factor is representative of an intrinsic soil property. Testing the USLE‐M and USLE‐MM schemes for other soils and developing simple procedures for estimating the plot runoff ratio has practical importance to develop a simple method to predict soil loss from bare plots at the erosive event temporal scale. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
3.
Four techniques for soil erosion assessment were compared over two consecutive seasons for bare-fallow plots and a maize-cowpea sequence in 1985 at IITA, Ibadan, Nigeria. The techniques used were: tracer (aluminium paint), nails (16 and 25), the rill method, and the Universal Soil Loss Equation (USLE). Soil loss estimated by these techniques was compared with that determined using the runoff plot technique. There was significantly more soil loss (P < 0·01) in bare-fallow than in plots under maize (Zea mays) or cowpea (Vigna unguiculata). In the first season, soil loss from plots sown to maize was 40·2 Mg ha?1 compared with 153·3 Mg ha?1 from bare-fallow plots. In the second season, bare-fallow plots lost 87·5 Mg ha?1 against 39·4 Mg ha?1 lost from plots growing cowpea. The techniques used for assessing erosion had no influence on the magnitude of soil erosion and did not interfere with the processes of erosion. There was no significant difference (P < 0·05) between soil erosion determined by the nails and the runoff plot technique. Soil loss determined on six plots (three under maize, three bare-fallow) by the rill technique, at the end of the season, was significantly lower (P < 0·05) than that determined by the runoff plot technique. The soil loss estimated by the rill method was 143·2, 108·8 and 121·9 Mg ha?1 for 11, 11, and 8 per cent slopes respectively, in comparison with 201·5, 162·0, and 166·4 Mg ha?1 measured by the runoff plot method. Soil loss measured on three bare-fallow plots on 10 different dates by the rill technique was also significantly lower (P < 0·01) than that measured by the runoff plot. In the first season the USLE significantly underestimated soil loss. On 11, 11, and 8 per cent slopes, respectively, soil loss determined by the USLE was 77, 92, and 63 per cent of that measured by the runoff plot. However, in the second season there was no significant difference between soil loss determined by the USLE and that determined by the conventional runoff plot technique. 相似文献
4.
On the basis of detailed rill surveys carried out on bare plots of different lengths at slopes of 12 per cent, basic rill parameters were derived. Rill width and maximum depth increased with plot length, whereas rill amount and cross‐sectional area, expressed per unit length, remained similar. On smaller plots, all rills were connected in a continuous transport system reaching the plot outlet, whilst on larger plots (10 and 20 m long) part of the rills ended with a deposition areas inside the plots. Amounts of erosion, calculated from rill volume and soil bulk density, were compared with soil loss measured at the plot outlets. On plots 10 and 20 m long, erosion estimated from volume of all rills was larger than measured soil loss. The latter was larger than erosion estimated from volume of contributing rills. To identify contributing soil loss area on these plots, two methods were applied: (i) ratio of total soil loss to maximum soil loss per unit area, and (ii) partition of plot area according to the ratio of contributing to total rill volume. Both methods resulted in similar areas of 21·8–23·5 m2 for the plot 10 m long and 31·2 m2 for the plot 20 m long. Identification of contributing areas enabled rill (5·9 kg m?2) and interrill (2·6 kg m?2) erosion rate to be calculated, the latter being very close to the value predicted from the Universal Soil Loss Equation. Although rill and interrill rates seemed to be similar on all plots, their ratio increased slightly with plot length. Application of this ratio to compute slope length factor of the Revised Universal Soil Loss Equation resulted in similar values to those predicted with the model. The achieved balance of soil loss suggested that all the sediment measured at the plot outlet originated from contributing rills and associated contributing rill areas. The results confirmed the utility of different plot lengths as a research tool for analysing the dynamic response of soil to rainfall–runoff. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
5.
There is a growing opinion that poorly managed plantation forests in Japan are contributing to increased storm runoff and erosion. Here we present evidence to the contrary from runoff plots at two scales (hillslope and 0·5 × 2 m plots) for several forest conditions in the Mie and Nariki catchments. Runoff coefficients from small plots in untended hinoki forests were variable but typically higher than from better managed or deciduous forests during small storms at Nariki; at Mie, runoff during small events was highly variable from all small plots but runoff coefficients were similar for hinoki plots with and without understory vegetation, while the deciduous plot had lower runoff coefficients. Storm runoff was less at the hillslope scale than the plot scale in Mie; these results were more evident at sites with better ground cover. During the largest storms at both sites, differences in runoff due to forest condition were not evident regardless of scale. Dynamic soil moisture tension measurements at Nariki indicated that during a large storm, flow in the upper organic‐rich and root‐permeated soil horizons was 3·2 times higher than measured overland runoff from a small hinoki plot with poor ground cover and 8·3 times higher than runoff from a deciduous forest plot. On the basis of field observations during storms, at least a portion of the monitored ‘Hortonian overland flow’ was actually occurring in this near‐surface ‘biomat’. Therefore our field measurements in both small and large plots potentially included biomat flow in addition to short‐lived Hortonian runoff. Because overland flow decreased with increasing scale, rill erosion did not occur on hillslopes. Additionally, runoff coefficients were not significantly different among cover conditions during large storms; thus, the ‘degraded’ forest conditions appear not to greatly enhance peak flows or erosion potential at larger scales, especially when biomat flow is significant. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
6.
Obtaining good quality soil loss data from plots requires knowledge of the factors that affect natural and measurement data variability and of the erosion processes that occur on plots of different sizes. Data variability was investigated in southern Italy by collecting runoff and soil loss from four universal soil‐loss equation (USLE) plots of 176 m2, 20 ‘large’ microplots (0·16 m2) and 40 ‘small’ microplots (0·04 m2). For the four most erosive events (event erosivity index, Re ≥ 139 MJ mm ha?1 h?1), mean soil loss from the USLE plots was significantly correlated with Re. Variability of soil loss measurements from microplots was five to ten times greater than that of runoff measurements. Doubling the linear size of the microplots reduced mean runoff and soil loss measurements by a factor of 2·6–2·8 and increased data variability. Using sieved soil instead of natural soil increased runoff and soil loss by a factor of 1·3–1·5. Interrill erosion was a minor part (0·1–7·1%) of rill plus interrill erosion. The developed analysis showed that the USLE scheme was usable to predict mean soil loss at plot scale in Mediterranean areas. A microplot of 0·04 m2 could be used in practice to obtain field measurements of interrill soil erodibility in areas having steep slopes. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
7.
Studies of soil erosion on small plots present upscaling problems. The results in the literature on the effect of slope length (i.e. scale) on runoff and soil erosion are contradictory. Furthermore, most studies that examine scale effects measured through erosion plots have been conducted in Mediterranean environments. The objective of this study was to assess the effects of plot size on runoff and soil loss in a subtropical environment. Other measurements were taken to appraise the topsoil property changes inside the plots. The soil was ploughed twice, the surface was leveled with a hoe and it was kept bare during the experiment. Data were collected from 10 paired plots, five plots measuring 10 m × 1 m and five plots measuring 1 m × 1 m, installed in the same pedo‐geomorphologic unit. Measurements were carried out from November 2008 to November 2009. During this period, 97 natural storms were registered. The results indicate that the small plots tended to have higher runoff (30% higher) compared to larger plots, especially during periods of greater rainfall volume, duration and intensity. The soil loss was similar in both the 1 m2 plots (6·33 kg/m2) and the 10 m2 plots (6·26 kg/m2). Moreover, the dynamics of the soil loss during the experiment was relatively similar across both plot sizes. The large plots tended to have a greater internal complexity. In these plots, the steps retreat were higher, the overland flow scars were more frequent, and points of rill initiation and protochannels emerged in several parts of the plots. The results of the small plots were comparable to the results obtained on the large plots, especially in relation to soil loss. These plots were useful for short‐term assessments of soil erosion. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
8.
Shaozhong Kang Lu Zhang Xiaoyu Song Shuhan Zhang Xianzhao Liu Yinli Liang Shiqing Zheng 《水文研究》2001,15(6):977-988
Soil erosion is a severe problem hindering sustainable agriculture on the Loess Plateau of China. Plot experiments were conducted under the natural rainfall condition during 1995–1997 at Wangdongguo and Aobao catchments in this region to evaluate the effects of various land use, cropping systems, land slopes and rainfall on runoff and sediment losses, as well as the differences in catchment responses. The experiments included various surface conditions ranging from bare soil to vegetated surfaces (maize, wheat residue, Robinia pseudoacacia L., Amorpha fruticosa L., Stipa capillata L., buckwheat and Astragarus adsurgens L.). The measurements were carried out on hill slopes with different gradients (i.e. 0 ° to 36 °). These plots varied from 20 to 60 m in length. Results indicated that runoff and erosion in this region occurred mainly during summer storms. Summer runoff and sediment losses under cropping and other vegetation were significantly less than those from ploughed bare soil (i.e. without crop/plant or crop residue). There were fewer runoff and sediment losses with increasing canopy cover. Land slope had a major effect on runoff and sediment losses and this effect was markedly larger in the tillage plots than that in the natural grass and forest plots, although this effect was very small when the maximum rainfall intensity was larger than 58·8 mm/h or smaller than 2·4 mm/h. Sediment losses per unit area rose with increasing slope length for the same land slope and same land use. The effect of slope length on sediment losses was stronger on a bare soil plot than on a crop/plant plot. The runoff volume and sediment losses were both closely related to rainfall volume and maximum intensity, while runoff coefficient was mainly controlled by maximum rainfall intensity. Hortonian overland flow is the dominant runoff process in the region. The differences in runoff volume, runoff coefficient and sediment losses between the catchments are mainly controlled by the maximum rainfall intensity and infiltration characteristics. The Aobao catchment yielded much larger runoff volume, runoff coefficient and sediment than the Wangdongguo catchment. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献
9.
Frederick B. Pierson Corey A. Moffet C. Jason Williams Stuart P. Hardegree Patrick E. Clark 《地球表面变化过程与地形》2009,34(2):193-203
Changing fire regimes and prescribed‐fire use in invasive species management on rangelands require improved understanding of fire effects on runoff and erosion from steeply sloping sagebrush‐steppe. Small (0·5 m2) and large (32·5 m2) plot rainfall simulations (85 mm h–1, 1 h) and concentrated flow methodologies were employed immediately following burning and 1 and 2 years post‐fire to investigate infiltration, runoff and erosion from interrill (rainsplash, sheetwash) and rill (concentrated flow) processes on unburned and burned areas of a steeply sloped sagebrush site on coarse‐textured soils. Soil water repellency and vegetation were assessed to infer relationships in soil and vegetation factors that influence runoff and erosion. Runoff and erosion from rainfall simulations and concentrated flow experiments increased immediately following burning. Runoff returned to near pre‐burn levels and sediment yield was greatly reduced with ground cover recovery to 40 per cent 1 year post‐fire. Erosion remained above pre‐burn levels on large rainfall simulation and concentrated flow plots until ground cover reached 60 per cent two growing seasons post‐fire. The greatest impact of the fire was the threefold reduction of ground cover. Removal of vegetation and ground cover and the influence of pre‐existing strong soil‐water repellency increased the spatial continuity of overland flow, reduced runoff and sediment filtering effects of vegetation and ground cover, and facilitated increased velocity and transport capacity of overland flow. Small plot rainfall simulations suggest ground cover recovery to 40 per cent probably protected the site from low‐return‐interval storms, large plot rainfall and concentrated flow experiments indicate the site remained susceptible to elevated erosion rates during high‐intensity or long duration events until ground cover levels reached 60 per cent. The data demonstrate that the persistence of fire effects on steeply‐sloped, sandy sagebrush sites depends on the time period required for ground cover to recover to near 60 per cent and on the strength and persistence of ‘background’ or fire‐induced soil water repellency. Published in 2009 by John Wiley & Sons, Ltd. 相似文献
10.
Soil and water losses from new citrus orchards growing on sloped soils in the western Mediterranean basin 总被引：2，自引：0，他引：2
Ten representative research sites were selected in eastern Spain to assess soil erosion rates and processes in new citrus orchards on sloping soils. The experimental plots were located at representatives sites on limestone, in areas with 498 to 715 mm year?1 mean annual rainfall, north‐facing slopes, herbicide treated, and new (less than 3 years old) plantations. Ten rainfall simulation experiments (1 h at 55 mm h?1 on 0·25 m2 plots) were carried out at each of the 10 selected study sites to determine the interill soil erosion and runoff rates. The 100 rainfall simulation tests (10 × 10 m) showed that ponding and runoff occurred in all the plots, and quickly: 121 and 195 s, respectively, following rainfall initiation. Runoff discharge was one third of the rainfall, and sediment concentration reached 10·4 g L?1. The soil erosion rates were 2·4 Mg ha?1 h?1 under 5‐year return period rainfall thunderstorms. These are among the highest soil erosion rates measured in the western Mediterranean basin, similar to badland, mine spoil and road embankment land surfaces. The positive relationship between runoff discharge and sediment concentration (r2 = 0·83) shows that the sediment availability is very high. Soil erosion rates on new citrus orchards growing on sloped soils are neither tolerable nor sustainable. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
11.
John Wainwright Anthony J. Parsons Eva N. Müller Richard E. Brazier D. Mark Powell Bantigegne Fenti 《地球表面变化过程与地形》2008,33(7):1113-1128
In the two previous papers of this series, we demonstrated how a novel approach to erosion modelling (Mahleran – Model for Assessing Hillslope‐Landscape Erosion, Runoff And Nutrients) provided distinct advantages in terms of process representation and explicit scaling characteristics when compared with existing models. A first evaluation furthermore demonstrated the ability of the model to reproduce spatial and temporal patterns of erosion and their particle‐size characteristics on a large rainfall‐simulation plot. In this paper, we carry out a more detailed evaluation of the model using monitored erosion events on plots of different size. The evaluation uses four plots of 21·01, 115·94, 56·84 and 302·19 m2, with lengths of 4·12, 14·48, 18·95 and 27·78 m, respectively, on similar soils to the rainfall‐simulation plot, for which runoff and erosion were monitored under natural rainfall. Although the model produces the correct ranking of the magnitude of erosion events, it performs less well in reproducing the absolute values and particle‐size distributions of the eroded sediment. The implications of these results are evaluated in terms of requirements for process understanding and data for parameterization of improved soil‐erosion models. We suggest that there are major weaknesses in the current understanding and data underpinning existing models. Consequently, a more holistic re‐evaluation is required that produces functional relationships for different processes that are mutually consistent, and that have appropriate parameterization data to support their use in a wide range of environmental conditions. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
12.
Anthony J. Parsons Richard E. Brazier John Wainwright D. Mark Powell 《地球表面变化过程与地形》2006,31(11):1384-1393
Eight runoff plots, located within a small catchment within the Walnut Gulch Experimental Watershed, southern Arizona, were constructed to test the argument that sediment yield (kg m?2) decreases as plot length increases. The plots ranged in length from 2 m to 27·78 m. Runoff and sediment loss from these plots were obtained for ten natural storm events. The pattern of sediment yield from these plots conforms to the case in which sediment yield first increases as plot length increases, but then subsequently decreases. Data from the present experiment indicate that maximum sediment yield would occur from a plot 7 m long. Analysis of both runoff and sediment yield from the plots indicates that the relationship of sediment yield to plot length derives both from the limited travel distance of individual entrained particles and from a decline in runoff coefficient as plot length increases. Particle‐size analysis of eroded sediment confirms the role of travel distance in controlling sediment yield. Whether in response to the finite travel distance of entrained particles or the relationship of runoff coefficient to plot length, the experiment clearly demonstrates that the erosion rates for hillslopes and catchments cannot be simply extrapolated from plot measurements, and that alternative methods for estimating large‐area erosion rates are required. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
13.
Runoff and erosion processes can increase after wildfire and post-fire salvage logging, but little is known about the specific effects of soil compaction and surface cover after post-fire salvage logging activities on these processes. We carried out rainfall simulations after a high-severity wildfire and post-fire salvage logging to assess the effect of compaction (uncompacted or compacted by skid traffic during post-fire salvage logging) and surface cover (bare or covered with logging slash). Runoff after 71 mm of rainfall across two 30-min simulations was similar for the bare plots regardless of the compaction status (mean 33 mm). In comparison, runoff in the slash-covered plots averaged only 22 mm. Rainsplash in the downslope direction averaged 30 g for the bare plots across compaction levels and decreased significantly by 70% on the slash-covered plots. Sediment yield totalled 460 and 818 g m−2 for the uncompacted and compacted bare plots, respectively, and slash significantly reduced these amounts by an average rate of 71%. Our results showed that soil erosion was still high two years after the high severity burning and the effect of soil compaction nearly doubled soil erosion via nonsignificant increases in runoff and sediment concentration. Antecedent soil moisture (dry or wet) was the dominant factor controlling runoff, while surface cover was the dominant factor for rainsplash and sediment yield. Saturated hydraulic conductivity and interrill erodibility calculated from these rainfall simulations confirmed previous laboratory research and will support hydrologic and erosion modelling efforts related to wildfire and post-fire salvage logging. Covering the soil with slash mitigated runoff and significantly reduced soil erosion, demonstrating the potential of this practise to reduce sediment yield and soil degradation from burned and logged areas. 相似文献
14.
Orders of magnitude increase in soil erosion associated with land use change from native to cultivated vegetation in a Brazilian savannah environment 总被引：4，自引：0，他引：4 
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下载免费PDF全文 The Brazilian savanna (cerrado) is a large and important economic and environmental region that is experiencing significant loss of its natural landscapes due to pressures of food and energy production, which in turn has caused large increases in soil erosion. However the magnitude of the soil erosion increases in this region is not well understood, in part because scientific studies of surface runoff and soil erosion are scarce or nonexistent in the cerrado as well as in other savannahs of the world. To understand the effects of deforestation we assessed natural rainfall‐driven rates of runoff and soil erosion on an undisturbed tropical woodland classified as ‘cerrado sensu stricto denso’ and bare soil. Results were evaluated and quantified in the context of the cover and management factor (C‐factor) of the Universal Soil Loss Equation (USLE). Replicated data on precipitation, runoff, and soil loss on plots (5 × 20 m) under undisturbed cerrado and bare soil were collected for 77 erosive storms that occurred over 3 years (2012 through 2014). C‐factor was computed annually using values of rainfall erosivity and soil loss rate. We found an average runoff coefficient of ~20% for the plots under bare soil and less than 1% under undisturbed cerrado. The mean annual soil losses in the plots under bare soil and cerrado were 12.4 t ha‐1 yr‐1 and 0.1 t ha‐1 yr‐1, respectively. The erosivity‐weighted C‐factor for the undisturbed cerrado was 0.013. Surface runoff, soil loss and C‐factor were greatest in the summer and fall. Our results suggest that shifts in land use from the native to cultivated vegetation result in orders of magnitude increases in soil loss rates. These results provide benchmark values that will be useful to evaluate past and future land use changes using soil erosion models and have significance for undisturbed savanna regions worldwide. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
15.
Despite widespread bench‐terracing, stream sediment yields from agricultural hillsides in upland West Java remain high. We studied the causes of this lack of effect by combining measurements at different spatial scales using an erosion process model. Event runoff and sediment yield from two 4‐ha terraced hillside subcatchments were measured and field surveys of land use, bench‐terrace geometry and storage of sediment in the drainage network were conducted for two consecutive years. Runoff was 3·0–3·9% of rainfall and sediment yield was 11–30 t ha−1 yr−1 for different years, subcatchments and calculation techniques. Sediment storage changes in the subcatchment drainage network were less than 2 t ha−1, whereas an additional 0·3–1·5 t ha−1 was stored in the gully between the subcatchment flumes and the main stream. This suggests mean annual sediment delivery ratios of 86–125%, or 80–104% if this additional storage is included. The Terrace Erosion and Sediment Transport (TEST) model developed and validated for the studied environment was parameterized using erosion plot studies, land use surveys and digital terrain analysis to simulate runoff and sediment generation on the terraced hillsides. This resulted in over‐estimates of runoff and under‐estimates of runoff sediment concentration. Relatively poor model performance was attributed to sample bias in the six erosion plots used for model calibration and unaccounted covariance between important terrain attributes such as slope, infiltration capacity, soil conservation works and vegetation cover. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
16.
Causes and underlying processes of measurement variability in field erosion plots in Mediterranean conditions 总被引：1，自引：0，他引：1
C. Boix‐Fayos M. Martínez‐Mena A. Calvo‐Cases E. Arnau‐Rosalén J. Albaladejo V. Castillo 《地球表面变化过程与地形》2007,32(1):85-101
An understanding of the sources of variation in the use of erosion plots and of their feasibility to meet the objectives of each specific research project is key to improving future field designs, selecting data for modelling purposes and furthering knowledge of soil erosion processes. Our own field experiences from ongoing research on soil erosion processes since 1989, have allowed us to detect several methodological problems that cause measurement variability. Here several examples are presented concerning: (i) differences in long‐term soil erosion data between open and closed plots; (ii) differences in soil loss derived from replica soil erosion plots; and (iii) differences in soil loss data derived from plots at a range of spatial scales. Closed plots are not the most suitable method for long‐term monitoring of soil erosion rates due to the risk of exhaustion of available material within the plot. The difference in time after which exhaustion occurs depends on the surface soil characteristics, the climatological conditions and the size of the plots. We detected four and seven years as ‘time to exhaustion’. Different results are frequently obtained between pairs of replica plots. Differences up to a factor of nine have been detected in total soil loss between replica plots due to different spatial patterns of surface components. Different constraints appear depending on the spatial scale of measurement of soil loss. We obtained lower runoff percentages at coarser scales; however, larger sediment concentrations are observed at coarser scales (1·32 g l?1, catchment; 0·30 g l?1, 30 m2; 0·17 g l?1, 1 m2 scales). The smaller the plot, the larger the hydrological disconnection within the system, the lower the energy flows due to short distances and the quicker the response to runoff due to an artificial decrease of concentration times for continuous flow. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
17.
The degradation of grasslands is a common problem across semi‐arid areas worldwide. Over the last 150 years, much of the south‐western United States has experienced significant land degradation, with desert grasslands becoming dominated by shrubs and concurrent changes in runoff and erosion which are thought to propagate further the process of degradation. Plot‐based experiments to determine how spatio‐temporal characteristics of soil moisture, runoff and erosion change over a transition from grassland to shrubland were carried out at four sites over a transition from black grama (Bouteloua eriopoda) grassland to creosotebush (Larrea tridentata) shrubland at the Sevilleta NWR LTER site in New Mexico. Each site consisted of a 10 × 30 m bounded runoff plot and adjacent characterization plots with nested sampling points where soil moisture content was measured. Results show distinct spatio‐temporal variations in soil moisture content, which are due to the net effect of processes operating at multiple spatial and temporal scales, such as plant uptake of water at local scales versus the redistribution of water during runoff events at the hillslope scale. There is an overall increase in runoff and erosion over the transition from grassland to shrubland, which is likely to be associated with an increase in connectivity of bare, runoff‐generating areas, although these increases do not appear to follow a linear trajectory. Erosion rates increased over the transition from grassland to shrubland, likely related in part to changes in runoff characteristics and the increased capacity of the runoff to detach, entrain and transport sediment. Over all plots, fine material was preferentially eroded which has potential implications for nutrient cycling since nutrients tend to be associated with fine sediment. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
18.
The results of erosion studies carried out at three representative sites in the European Mediterranean basin are discussed. The objectives of the study are to clarify the underlying processes affecting soil erosion and to quantify erosion and runoff in the framework of mitigation of land degradation. The study was carried out at three instrumented field stations using similar layouts and experimental set-ups and harmonized field procedures. Runoff and sediment yield from bounded plots were measured for different types of land use for longer periods. The runoff and sediment values were found to be relatively low, and showed average annual values between 2·0 and 8·9 1 m−2 for runoff, and between 20·2 and 28·1 g m−2 for sediment yield. The results show that the individual plot response on an event basis shows no relationship between runoff and sediment yield for two of the three sites. On an annual average basis a significant relationship is found between the runoff and sediment yield. Significant differences were observed between different types of land use, especially between semi-natural vegetation, burned and abandoned field cover types on the one hand, and agricultural fields on the other hand. The runoff and erosion values were lowest for the semi-natural fields. It was found that in non-cultivated fields the bounded plots might suffer from depletion of available sediment. It can be concluded that erosion figures are very low for the sites studied, and that the maintenance of semi-natural vegetation may help in the prevention of runoff generation and erosion. It can be concluded that the use of bounded plots may not be as ideal as might be expected from its wide application. In some cases open plots, especially under semi-natural land use, may produce much better results, especially when measuring over longer periods. Copyright © 1999 John Wiley & Sons, Ltd. 相似文献
19.
Effects of patterned Artemisia capillaris on overland flow velocity under simulated rainfall 总被引：2，自引：0，他引：2
Vegetation cover is an important factor for erosion control. Laboratory‐simulated rainfall experiments were conducted to quantify the effectiveness of patchy distributed Artemisia capillaris in retarding overland flow velocity. Simulated storms (60, 90, 120, and 150 mm h?1) were applied on a bare plot (CK) and four different plant patterns, a banded pattern perpendicular to the slope direction (BP), a single long strip parallel to slope direction (LP), small patches distributed like a checkerboard (SP1), and small patches distributed like a letter “X” (SP2). All treatments had three replicates. Each plot underwent two sets of experiments, intact plant plots and root plots (the above‐ground parts were removed, only roots were reserved), respectively. Results showed that flow velocity increased with rainfall intensity, and the lower slope velocity (Vl) was higher than the upper slope velocity (Vu). The removal of grass shoots increased flow velocity. Compared with bare soil plot, intact plants reduced mean flow velocity by 14%–60%, whereas the reduction declined to <40% for the root plots. BP and both SP treatments performed more effectively than LP in retarding flow velocity, whereas no significant differences were identified between BP and SP. The contributions of A. capillaris shoots and roots to the reductions in flow velocity under different rainfall intensities were different. The shoots made greater contribution of 53%–97% at 60 and 90 mm h–1, and the roots contributed more (51%–81%) at 120 and 150 mm h–1. Runoff and sediment rate had significant (p < 0.05) linear correlations with mean flow velocity. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
20.
Seasonal evolution of runoff generation on agricultural land in the Belgian loess belt and implications for muddy flood triggering 总被引：1，自引：0，他引：1
Muddy floods due to agricultural runoff are a widespread and frequent phenomenon in the European loess belt, and particularly in central Belgium. These floods are triggered when high quantities of runoff are generated on cropland and cause severe erosion. Three soil surface characteristics are relevant to determine the runoff potential of cultivated soils: soil cover by crops and residues, soil surface crusting and roughness. These characteristics have been observed on 65 cultivated fields throughout 2005. A heavy rainfall event representative for events triggering muddy floods in the region (60 mm h?1 during 30 minutes) has been simulated using a 0·5 m2 simulator on fields with the 17 most observed combinations of soil surface characteristics in central Belgium. Runoff is not observed in the case of (ploughed) bare uncrusted soils, nor in the case of soils covered by crops showing a transitional crust and a moderate roughness (1–2 cm). In the cases where runoff has been observed, mean runoff coefficients ranged from 13% (wheat in July) to 58% (sugar beet or maize in May and June). Grassed buffer strips (GBSs) and grassed waterways (GWWs) show a higher runoff coefficient (62% for GBSs and 73% for GWWs) than most cultivated soils (13–58%). Furthermore, it is demonstrated that small plot measurements can be used to estimate runoff generation at the field scale. A classification of runoff generation risk based on the surveys of soil surface characteristics has been applied to common crops of central Belgium. February as well as the period between May and September are the most critical for runoff at the field scale. However, it appears from monitoring of a 16 ha catchment that the highest runoff volumes and peak discharges are recorded between May and August after heavy rainfall, explaining why 85% of muddy floods are recorded during this period in central Belgium. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献