Rill erosion processes on a constantly saturated slope

Rill erosion processes on saturated soil slopes are important for understanding erosion hydrodynamics and determining the parameters of rill erosion models. Saturated soil slopes were innovatively created to investigate the rill erosion processes. Rill erosion processes on saturated soil slopes were modelled by using the sediment concentrations determined by sediment transport capacities (STCs) measurement and the sediment concentrations at different rill lengths. Laboratory experiments were performed under varying slope gradients (5°, 10°, 15°, and 20°) and unit-width flow rates (0.33, 0.67, and 1.33 × 10⁻³ m³ s⁻¹ m⁻¹) to measure sediment concentrations at different rill lengths (1, 2, 4, and 8 m) on saturated soil slopes. The measured sediment concentrations along saturated rills ranged from 134.54 to 1,064.47 kg/m³, and also increased exponentially with rill length similar to non-saturated rills. The model of the rill erosion process in non-saturated soil rills was applicable to that in saturated soil rills. However, the sediment concentration of the rill flow increased much faster, with the increase in rill length, to considerably higher levels at STCs. The saturated soil rills produced 120–560% more sediments than the non-saturated ones. Moreover, the former eroded remarkably faster in the beginning section of the rills, as compared with that on the non-saturated soil slopes. This dataset serves as the basis for determining the erosion parameters in the process-based erosion models on saturated soil slopes.     

Use of fallout tracers 7Be, 210Pb and 137Cs to distinguish the form of sub‐surface soil erosion delivering sediment to rivers in large catchments

Fallout radionuclides (FRNs) ¹³⁷Cs and ²¹⁰Pb are well established as tracers of surface and sub‐surface soil erosion contributing sediment to river systems. However, without additional information, it has not been possible to distinguish sub‐surface soil erosion sources. Here, we use the FRN ⁷Be (half‐life 53 days) in combination with ¹³⁷Cs and excess ²¹⁰Pb to trace the form of erosion contributing sediment in three large river catchments in eastern Australia; the Logan River (area 3700 km²), Bowen River (9400 km²) and Mitchell River (4700 km²). We show that the combination of ¹³⁷Cs, excess ²¹⁰Pb and ⁷Be can discriminate horizontally aligned sub‐surface erosion sources (rilled and scalded hillslopes and the floors of incised drainage lines and gully ‘badland’ areas) from vertical erosion sources (channel banks and gully walls). Specifically, sub‐surface sources of sediment eroded during high rainfall and high river flow events have been distinguished by the ability of rainfall‐derived ⁷Be to label horizontal soil surfaces, but not vertical. Our results indicate that in the two northern catchments, erosion of horizontal sub‐surface soil sources contributed almost as much fine river sediment as vertical channel banks, and several times the contribution of hillslope topsoils. This result improves on source discrimination provided previously and indicates that in some areas erosion of hillslope soils may contribute significantly to sediment yield, but not as topsoil loss. We find that in north‐eastern Australia, scalded areas on hillslopes and incising drainage lines may be sediment sources of comparable importance to vertical channel banks. Previous studies have used the combination of ¹³⁷Cs, excess ²¹⁰Pb and ⁷Be to estimate soils losses at the hillslope scale. Here, we show that with timely and judicious sampling of soil and sediment during and immediately after high flow events ⁷Be measurements can augment fallout ¹³⁷Cs and ²¹⁰Pb to provide important erosion source information over large catchments. Copyright © 2013 John Wiley & Sons, Ltd.     

Use of fallout radionuclides as indicators of erosion processes

The different depth penetration characteristics of ¹³⁷Cs, ⁷Be and ²¹⁰Pb excess in undisturbed soils can be used to identify erosion processes by analysis of sediments derived from surface erosion. Caesium-137 concentrations (half-life 30 years) typically decrease to half the surface value at between 30 and 50 mm. Beryllium-7 (half-life 53 days) has half-penetration depths of between 0.7 and 10 mm, whereas ²¹⁰Pb excess (half-life 20.2 years) has half-penetration depths between 10 and 30 mm. Experiments designed to determine the applicability of these depth penetration characteristics to soil erosion studies are reported. Surface runoff was artificially generated at two locations in a grazed paddock using a rainfall simulator. Suspended sediment was extracted from runoff and analysed for natural and artificial gamma emitting radio-nuclides. Suspended sediment derived from sheet flow contained initially high values of ¹³⁷Cs, ⁷Be and ²¹⁰Pb excess. As the experiment continued ¹³⁷Cs concentrations remained high, but ⁷Be and ²¹⁰Pb excess value decreased with time. This is interpreted as indicating a change from sheet dominated erosion to rill dominated erosion. During a second experiment artificial rain was allowed to fall onto an eroded gully wall. The derived suspended sediment contained no detectable ¹³⁷Cs, ⁷Be or ²¹⁰Pb excess. Overland flow from above the gully wall was then allowed to run down the gully face and mix with the water falling directly onto the gully wall. There was no detectable change in the radionuclide signature, showing that the gully wall was the predominant source of sediment. This was tested independently by mass balance and ²²⁶Ra to ²³²Th ratios. The good correlation between ²¹⁰Pb excess and ⁷Be at this site suggests that the differential technique described here may be applicable over time-scales longer than are possible with ⁷Be. It may therefore be practical to examine catchment erosion history through analysis of ²¹⁰Pb excess and ¹³⁷Cs in sediment cores.     

Rill characteristics and sediment transport as a function of slope length during a storm event on loess soil

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.     

Fire effects on rangeland hydrology and erosion in a steep sagebrush‐dominated landscape

Post‐fire runoff and erosion from wildlands has been well researched, but few studies have researched the degree of control exerted by fire on rangeland hydrology and erosion processes. Furthermore, the spatial continuity and temporal persistence of wildfire impacts on rangeland hydrology and erosion are not well understood. Small‐plot rainfall and concentrated flow simulations were applied to unburned and severely burned hillslopes to determine the spatial continuity and persistence of fire‐induced impacts on runoff and erosion by interrill and rill processes on steep sagebrush‐dominated sites. Runoff and erosion were measured immediately following and each of 3 years post‐wildfire. Spatial and temporal variability in post‐fire hydrologic and erosional responses were compared with runoff and erosion measured under unburned conditions. Results from interrill simulations indicate fire‐induced impacts were predominantly on coppice microsites and that fire influenced interrill sediment yield more than runoff. Interrill runoff was nearly unchanged by burning, but 3‐year cumulative interrill sediment yield on burned hillslopes (50 g m^?2) was twice that of unburned hillslopes (25 g m^?2). The greatest impact of fire was on the dynamics of runoff once overland flow began. Reduced ground cover on burned hillslopes allowed overland flow to concentrate into rills. The 3‐year cumulative runoff from concentrated flow simulations on burned hillslopes (298 l) was nearly 20 times that measured on unburned hillslopes (16 l). The 3‐year cumulative sediment yield from concentrated flow on burned and unburned hillslopes was 20 400 g m^?2 and 6 g m^?2 respectively. Fire effects on runoff generation and sediment were greatly reduced, but remained, 3 years post‐fire. The results indicate that the impacts of fire on runoff and erosion from severely burned steep sagebrush landscapes vary significantly by microsite and process, exhibiting seasonal fluctuation in degree, and that fire‐induced increases in runoff and erosion may require more than 3 years to return to background levels. Published in 2008 by John Wiley & Sons, Ltd.     

Size characteristics of sediment in interrill overland flow on a semiarid hillslope,Southern Arizona

This study examines the size characteristics of sediment removed from a semiarid hillslope by interrill overland flow. Rainfall simulation experiments were conducted on a runoff plot 18 m wide and 35 m long established on a piedmont hillslope in southern Arizona. The top of the plot coincided with the hillslope divide, and its outlet was located within a shallow rill. Samples of runoff were obtained from two cross-sections located in the interrill portion of the plot upslope of the rill and from a calibrated flume through which was directed interrill overland flow reaching the bottom of the plot. Analyses of sediment contained in these samples showed that sediment in interrill flow is finer than the matrix soil. The fineness of the interrill sediment compared to the matrix soil appears to be due to the inability of interrill overland flow to transport the coarser fraction of the sediment supplied to it by raindrop detachment. This finding implies that the rate of soil erosion in interrill areas is not. as is commonly supposed, limited by the rate at which raindrops can detach sediment but by the rate at which they detach sediment of a size that the overland flow is competent to transport. The relative fineness of sediment eroded from this hillslope is consistent with other evidence for the recent evolution of shrub-covered hillslopes in southern Arizona.     

Short‐term erosion rates from a 7Be inventory balance

Detailed soil erosion studies bene?t from the ability to quantify the magnitude of erosion over time scales appropriate to the process. An inventory balance for ⁷Be was used to calculate sediment erosion in a 30·73 m² plot during a series of runoff‐producing thunderstorms occurring over three days at the Deep Loess Research Station in Treynor, Iowa, USA. The inventory balance included determination of the pre‐ and post‐storm ⁷Be inventories in the soil, the atmospheric in?ux of ⁷Be during the event, and pro?les of the ⁷Be activity in the soil following the atmospheric deposition. The erosion calculated in the plot using the ⁷Be inventory balance was 0·058 g cm^?2, which is 23 per cent of the annual average erosion determined using ¹³⁷Cs inventories. The calculated erosion from the mass balance is similar to the 0·059 g cm^?2 of erosion estimated from the amount of sediment collected at the outlet of the 6 ha ?eld during the study period and the delivery ratio (0·64). The inventory balance of ⁷Be provides a new means for evaluating soil erosion over the time period most relevant to quantifying the prediction of erosion from runoff. Copyright © 2003 John Wiley & Sons, Ltd.     

Concentrated flow erosion as a main source of sediments in Galicia,Spain

Knowledge of soil loss rates by water erosion under given climate, soil, topography, and management conditions is important for establishing soil conservation schemes. In Galicia, a region with Atlantic climatic conditions in Spain, field observations over the last decade indicate that interrill, rill and ephemeral gully erosion may be an important sediment source. The aim of this work was to assess concentrated erosion rates, describe types of rills and ephemeral gullies and determine their origin, evolution and importance as sediment sources. Soil surface state and concentrated flow erosion were surveyed on medium textured soils, developed over basic schists of the Ordenes Complex series (Coruña province, Spain) from 1997 to 2006. Soil surface state was characterized by crust development, tillage features and roughness degree. Soil erosion rate was directly measured in the field. Concentrated flow erosion took place mainly on seedbeds and recently tilled surfaces in late spring and by autumn or early winter. During the study period, erosion rates were highly variable and the following situations could be distinguished: (a) no incision or limited rill incision, i.e. below 2 Mg ha^?1 year^?1; (b) generalized rill and ephemeral gully incision in the class of mean values between 2·5 and 6·25 Mg ha^?1 year^?1, this was the most common erosion pattern; and (c) heavy erosion as observed during an extremely wet winter period, between October 2000 and February 2001, with erosion figures that may be about ten orders of magnitude higher, up to 55–60 Mg ha^?1 year^?1. Therefore, low values of soil losses are dominant, but also large values of rill and ephemeral gully erosion occurred during the study period. Copyright © 2009 John Wiley & Sons, Ltd.     

First‐year post‐fire erosion rates in Bitterroot National Forest,Montana

Accelerated runoff and erosion commonly occur following forest fires due to combustion of protective forest floor material, which results in bare soil being exposed to overland flow and raindrop impact, as well as water repellent soil conditions. After the 2000 Valley Complex Fires in the Bitterroot National Forest of west‐central Montana, four sets of six hillslope plots were established to measure first‐year post‐wildfire erosion rates on steep slopes (greater than 50%) that had burned with high severity. Silt fences were installed at the base of each plot to trap eroded sediment from a contributing area of 100 m². Rain gauges were installed to correlate rain event characteristics to the event sediment yield. After each sediment‐producing rain event, the collected sediment was removed from the silt fence and weighed on site, and a sub‐sample taken to determine dry weight, particle size distribution, organic matter content, and nutrient content of the eroded material. Rainfall intensity was the only significant factor in determining post‐fire erosion rates from individual storm events. Short duration, high intensity thunderstorms with a maximum 10‐min rainfall intensity of 75 mm h^?1 caused the highest erosion rates (greater than 20 t ha^?1). Long duration, low intensity rains produced little erosion (less than 0·01 t ha^?1). Total C and N in the collected sediment varied directly with the organic matter; because the collected sediment was mostly mineral soil, the C and N content was small. Minimal amounts of Mg, Ca, and K were detected in the eroded sediments. The mean annual erosion rate predicted by Disturbed WEPP (Water Erosion Prediction Project) was 15% less than the mean annual erosion rate measured, which is within the accuracy range of the model. Published in 2007 by John Wiley & Sons, Ltd.     

Assessing non-steady-state erosion processes using paired 10Be–26Al in southeastern Tibet

Quantifying erosion rates over various spatial and temporal scales across the Tibetan Plateau and its surrounding mountains is crucial to understanding the topographic evolution of the orogen. In this work, we report a new dataset of ¹⁰Be-derived basin-wide erosion rates from the main tributaries and streams draining the eastern Himalayan syntaxis. The 22 basin-wide erosion rates ranged from 78 ± 7 m Myear⁻¹ to 3,490 ± 612 m Myear⁻¹ across the study area. ²⁶Al was contemporarily measured to evaluate the impact of sediment storage and non-steady-state erosion processes in the syntaxis region. The paired study of ¹⁰Be and ²⁶Al reveals that several samples violated the steady-state erosion assumption and were compatible with the scenario of perturbation of reworked sediments or deeply sourced materials introduced by landslides. For most samples, deep-sourced materials with higher ²⁶Al/¹⁰Be ratios were no longer perturbing the ¹⁰Be signals in river sediments. It is possible that the deep-sourced materials had been wiped out of the basins before the collection of samples in this work. However, the perturbation of reworked sediments was observed over a range of basin scales, limiting the use of a single sediment sample as a representative erosion product for upstream basins. Compared with tectonically stable regions, the incorporation of reworked fluvial sediments, deeply sourced materials or sub-glacial eroded materials into sampled sediments led to the decoupling between basin-wide erosion rates and topographic or climatic indices. Caution should be taken when deriving erosion rates from rapidly eroding regions with old, deeply buried sediments such as the eastern Himalayan syntaxis, where calculated erosion rates may be highly overestimated.     

Topographic variation in soil erosion and accumulation determined with meteoric 10Be

Understanding natural soil redistribution processes is essential for measuring the anthropogenic impact on landscapes. Although meteoric beryllium-10 (¹⁰Be) has been used to determine erosion processes within the Pleistocene and Holocene, fewer studies have used the isotope to investigate the transport and accumulation of the resulting sediment. Here we use meteoric ¹⁰Be in hilltop and valley site soil profiles to determine sediment erosion and deposition processes in the Christina River Basin (Pennsylvania, USA). The data indicate natural erosion rates of 14 to 21 mm 10⁻³ yr and soil ages of 26 000 to 57 000 years in hilltop sites. Furthermore, valley sites indicate an alteration in sediment supply due to climate change (from the Pleistocene to the Holocene) within the last 60 000 years and sediment deposition of at least 0.5–2 m during the Wisconsinan glaciation. The change in soil erosion rate was most likely induced by changes in geomorphic processes; probably solifluction and slope wash during the cold period, when ice advanced into the mid latitudes of North America. This study shows the value of using meteoric ¹⁰Be to determine sediment accumulation within the Quaternary and quantifies major soil redistribution occurred under natural conditions in this region. © 2018 John Wiley & Sons, Ltd.     

MHYDAS‐Erosion: a distributed single‐storm water erosion model for agricultural catchments

In this paper, we present MHYDAS‐Erosion, a dynamic and distributed single‐storm water erosion model developed as a module of the existing hydrological MHYDAS model. As with many catchment erosion models, MHYDAS‐Erosion is able to simulate sediment transport, erosion and deposition by rill and interrill processes. Its originality stems from its capacity to integrate the impact of land management practices (LMP) as key elements controlling the sedimentological connectivity in agricultural catchments. To this end, the water‐sediment pathways are first determined by a specific process‐oriented procedure defined and controlled by the user, which makes the integration of LMP easier. The LMP dynamic behaviours are then integrated into the model as a time‐dependent function of hydrological variables and LMP characteristics. The first version of the model was implemented for vegetative filters and tested using water and sediment discharge measurements at three nested scales of a densely instrumented catchment (Roujan, OMERE Observatory, southern France). The results of discharge and soil loss for simulated rainfall events have been found to acceptably compare with available data. The average R² values for water and sediment discharge are 0·82 and 0·83, respectively. The sensitivity of the model to changes in the proportion of LMP was assessed for a single rain event by considering three scenarios of the Roujan catchment management with vegetative filters: 0% (Scenario 1), 18% (Scenario 2, real case) and 100% (Scenario 3). Compared to Scenario 2 (real case), soil losses decreased for Scenario 3 by 65% on the agricultural plot scale, 62% on the sub‐catchment scale and 45% at the outlet of the catchment and increased for Scenario 1 by 0% on the plot scale, 26% on the sub‐catchment scale and 18% at the outlet of the catchment. Copyright © 2010 John Wiley & Sons, Ltd.     

Dynamics of soil erosion rates and controlling factors in the Northern Ethiopian Highlands – towards a sediment budget

This paper analyses the factors that control rates and extent of soil erosion processes in the 199 ha May Zegzeg catchment near Hagere Selam in the Tigray Highlands (Northern Ethiopia). This catchment, characterized by high elevations (2100–2650 m a.s.l.) and a subhorizontal structural relief, is typical for the Northern Ethiopian Highlands. Soil loss rates due to various erosion processes, as well as sediment yield rates and rates of sediment deposition within the catchment (essentially induced by recent soil conservation activities), were measured using a range of geomorphological methods. The area‐weighted average rate of soil erosion by water in the catchment, measured over four years (1998–2001), is 14·8 t ha^?1 y^?1, which accounts for 98% of the change in potential energy of the landscape. Considering these soil loss rates by water, 28% is due to gully erosion. Other geomorphic processes, such as tillage erosion and rock fragment displacement by gravity and livestock trampling, are also important, either within certain land units, or for their impact on agricultural productivity. Estimated mean sediment deposition rate within the catchment equals 9·2 t ha^?1 y^?1. Calculated sediment yield (5·6 t ha^?1 y^?1) is similar to sediment yield measured in nearby catchments. Seventy‐four percent of total soil loss by sheet and rill erosion is trapped in exclosures and behind stone bunds. The anthropogenic factor is dominant in controlling present‐day erosion processes in the Northern Ethiopian Highlands. Human activities have led to an overall increase in erosion process intensities, but, through targeted interventions, rural society is now well on the way to control and reverse the degradation processes, as can be demonstrated through the sediment budget. Copyright © 2007 John Wiley & Sons, Ltd.     

Interrill erosion in the sloping lands of northern Laos subjected to shifting cultivation

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.     

Impact of rainfall pattern on interrill erosion process

The impact of rainfall pattern on the interrill erosion process is not fully understood despite its importance. Systematic rainfall simulation experiments involving various rainfall intensities, stages, intensity sequences, and surface cover conditions were conducted in this study to investigate their effects on the interrill erosion process. Five rainfall patterns designed with the same total kinetic energy/precipitation (increasing, decreasing, rising–falling, falling–rising and constant patterns) were randomly delivered to a pre‐wet clay loam soil surface at a 10° slope gradient. Significant differences in soil losses were observed among the different rainfall patterns and stages, but there was no obvious difference in runoff. Kinetic energy flux (KE_r) was a governing factor for interrill erosion, and constant rainfall pattern (CST) produced nine times greater soil loss than runs with no KE_r. Varied‐intensity patterns had a profound effect on raindrop‐induced sediment transport processes; path analysis results indicated that said effect was complex, interactive and intensity‐dependent. Low hydraulic parameter thresholds further indicated that KE_r was the dominant factor in detaching soil particles, while overland flow mainly contributed to transporting the pre‐detached particles. This study not only sheds light on the mechanism of interrill sediment transport capacity and detachability, but also may provide a useful database for developing event‐based interrill erosion prediction models. Copyright © 2017 John Wiley & Sons, Ltd.     

Erosion of the eastern United States observed with 10Be

The problem of identifying areas of accelerated erosion in a dynamic landscape is complicated. The limited history of sediment yield measurements makes this task difficult even if geomorphic evidence is available. Beryllium-10, a cosmogenic isotope produced by cosmic rays interacting with the earth's atmosphere and surface, has chemical and physical properties that make it useful as a tracer for erosion and sediment transport processes. The rarity of the stable isotope, ⁹Be, allows ¹⁰Be to be detected with accelerator mass spectrometry in natural materials at extremely low levels. Backgrounds for rocks and sediments below 10⁵ atom per g are now attainable, a value to be compared with an average deposition rate of 1.3 × 10⁶ atom cm^?2 yr^?1. The affinity of Be for the components of soil and sediment is sufficiently high that it is effectively immobilized on contact, thereby allowing ¹⁰Be to function as a tracer of sediment transport. To a good approximation all the ¹⁰Be transport out of a drainage basin is on the sediment leaving it. The number of ¹⁰Be atoms passing the gauging station can be determined by measuring the concentration of the isotope in the sediment, if the annual sediment load is known. The ratio of the ¹⁰Be carried from the basin by the sediment to that incident upon it, called the erosion index, has been determined for 48 drainage basins within the same physiographic province, which allows them to be reasonably compared, all of which have sediment yield data. Basins located in the Atlantic coastal plain have an average index of 0.3 with the maximum observed being 0.9. Basins located between the fall line and the mountains, a region called the Piedmont, have an average value of 2.2 with individual values ranging from 0.6 to 6.7; this marked difference is thought to result from two centuries of farming on land of moderate gradient. Basins in the highland regions reflect local conditions with low indices for those in grass and timber and high indices associated with destructive land use. The data allow an estimate of the erosion index for the pre-colonial Piedmont, which then allows the pre-colonial sediment yield to be calculated. A number of basins have also been examined world wide with similar conclusions derived. An important deviation from the rule is noted for rivers that erode large regions of loess, such as the Mississippi, Hwang Ho, and Yangtze. Large aeolian deposits were laid down during the ice age in these basins, deposits that brought inherited ¹⁰Be with them and that are easily eroded.     

Beryllium‐7 wet deposition variation with storm height,synoptic classification,and tree canopy state in the mid‐Atlantic USA

Short‐lived fallout isotopes, such as beryllium‐7 (⁷Be), are increasingly used as erosion and sediment tracers in watersheds. ⁷Be is produced in the atmosphere and delivered to the Earth's surface primarily in precipitation. However, relatively little has been published about the variation in ⁷Be wet deposition caused by storm type and vegetation cover. Our analysis of precipitation, throughfall, and sediments in two forested, headwater catchments in the mid‐Atlantic USA indicates significant variation in isotope deposition with storm type and storm height. Individual summer convective thunderstorms were associated with ⁷Be activity concentrations up to 5.0 Bq l^?1 in precipitation and 4.7 Bq l^?1 in throughfall, while single‐event wet depositional fluxes reached 168 Bq m^?2 in precipitation and 103 Bq m^?2 in throughfall. Storms originating from the continental USA were associated with lower ⁷Be activity concentrations and single‐event wet depositional fluxes for precipitation (0.7–1.2 Bq l^?1 and 15.8–65.0 Bq m^?2) and throughfall (0.1–0.3 Bq l^?1 and 13.5–98.9 Bq m^?2). Tropical systems had relatively low activity concentrations, 0.2–0.5 Bq l^?1 in precipitation and 0.2–1.0 Bq l^?1 in throughfall, but relatively high single‐event depositional fluxes due to large rainfall volumes, 32.8–67.6 Bq m^?2 in precipitation and 25.7–134 Bq m^?2 in throughfall. The largest sources of ⁷Be depositional variation were attributed to storm characteristics including precipitation amount and maximum storm height. ⁷Be activity associated with fluvial suspended sediments also exhibited the highest concentration and variability in summer (175–1450 Bq kg^?1). We conclude the dominant source of variation on event‐level ⁷Be deposition is storm type. Our results illustrate the complex relationships between ⁷Be deposition in precipitation and throughfall and demonstrate event‐scale relationships between the ⁷Be in precipitation and on suspended sediment. Copyright © 2015 John Wiley & Sons, Ltd.     

Plot‐scale measurement of soil erosion at the experimental area of Sparacia (southern Italy)

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, R_e ≥ 139 MJ mm ha^?1 h^?1), mean soil loss from the USLE plots was significantly correlated with R_e. 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.     

Modelling the process of soil detachment by rill flow on steep loessial hillslopes

Soil detachment by rill flow is a key process of rill erosion, modelling this process can help in understanding rill erosion mechanisms. However, many soil detachment models are established on conceptual assumptions rather than experimental data. The objectives of this study were to establish a model of soil detachment by rill flow based on flume experimental data and to quantitatively verify the model. We simulated the process of soil detachment by rill flow in flume experiments with a soil-feeding hopper using loessial soil on steep slopes. Seven flow discharges, six slopes and five sediment loads were combined. Soil detachment capacity, sediment transport capacity, and soil detachment rate by rill flow under different sediment loads were measured. The process of soil detachment by rill flow can be modelled by a dual power function based on soil detachment capacity and transport capacity deficit as variables. The established model exhibited high credibility (NSE=0.97; R²=0.97). The contributions of soil detachment capacity and transport capacity deficit to soil detachment rate by rill flow reached 60% and 36%, respectively. Soil detachment capacity exerted more influence on soil detachment rate than did transport capacity deficit. The performance of the WEPP rill erosion equation is also favourable (NSE=0.95; R²=0.97). The two power exponents in the model we established strengthen the role of soil detachment capacity in soil detachment rate and weaken that for transport capacity deficit. Soil detachment capacity and transport capacity deficit played important roles in the determination of soil detachment rate by rill flow. The results can be applied to implement the numerical modeling and prediction of rill erosion processes on steep loessial hillslopes. © 2019 John Wiley & Sons, Ltd.