Professor Timothy Quine
Deputy Vice-Chancellor (Education) / Professor of Earth System Science

Abstract:
Future C loss in mid-latitude mineral soils: climate change exceeds land use mitigation potential in France.

Many studies have highlighted significant interactions between soil C reservoir dynamics and global climate and environmental change. However, in order to estimate the future soil organic carbon sequestration potential and related ecosystem services well, more spatially detailed predictions are needed. The present study made detailed predictions of future spatial evolution (at 250 m resolution) of topsoil SOC driven by climate change and land use change for France up to the year 2100 by taking interactions between climate, land use and soil type into account. We conclude that climate change will have a much bigger influence on future SOC losses in mid-latitude mineral soils than land use change dynamics. Hence, reducing CO2 emissions will be crucial to prevent further loss of carbon from our soils.

Abstract:
Soil microbial populations in deep floodplain soils are adapted to infrequent but regular carbon substrate addition

© 2018 Floodplain soils provide an important link in the land-ocean aquatic continuum. Understanding microbial activity in these soils, which can be many metres deep, is a key component in our understanding of the role of floodplains in the carbon (C) cycle. We sampled the mineral soil profile to 3 m depth from two floodplain sites under long-term pasture adjacent to the river Culm in SW England, UK. Soil chemistry (C, nitrogen (N), phosphorus (P), soil microbial biomass (SMB), moisture content) and soil solution (pH, dissolved organic C (DOC) and N, nitrate, ammonium, water extractable P) were analysed over the 3 m depth in 6 increments: 0.0–0.2, 0.2–0.7, 1.0–1.5, 1.5–2.0, 2.0–2.5, and 2.5–3.0 m. 14 C-glucose was added to the soil and the evolution of 14 CO 2 measured during a 29 d incubation. From soil properties and 14 C-glucose mineralisation, three depth groups emerged, with distinct turnover times extrapolated from initial k 1 mineralisation rate constants of 2 h (topsoil 0.0–0.2 m), 4 h (subsoil 0.2–0.7 m), and 11 h (deep subsoil 1.0–3.0 m). However, when normalised by SMB, k 1 rate constants had no significant differences across all depths. Deep subsoil had a 2 h lag to reach maximal 14 CO 2 production whereas the topsoil and subsoil (0.2–0.7 m) achieved maximum mineralisation rates immediately. SMB decreased with depth, but only to half of the surface population, with the proportion of SMB-C to total C increasing from 1% in topsoil to 15% in deep subsoil ( > 1.0 m). The relatively large SMB concentration and rapid mineralisation of 14 C-glucose suggests that DOC turnover in deep soil horizons in floodplains is limited by access to biologically available C and not the size of the microbial population.

Abstract:
Tracing of particulate organic C sources across the terrestrial-aquatic continuum, a case study at the catchment scale (Carminowe Creek, southwest England)

© 2017 Elsevier B.V. Soils deliver crucial ecosystem services, such as climate regulation through carbon (C) storage and food security, both of which are threatened by climate and land use change. While soils are important stores of terrestrial C, anthropogenic impact on the lateral fluxes of C from land to water remains poorly quantified and not well represented in Earth system models. In this study, we tested a novel framework for tracing and quantifying lateral C fluxes from the terrestrial to the aquatic environment at a catchment scale. The combined use of conservative plant-derived geochemical biomarkers n-alkanes and bulk stable δ 13 C and δ 15 N isotopes of soils and sediments allowed us to distinguish between particulate organic C sources from different land uses (i.e. arable and temporary grassland vs. permanent grassland vs. riparian woodland vs. river bed sediments) (p. <. 0.001), showing an enhanced ability to distinguish between land use sources as compared to using just n-alkanes alone. The terrestrial-aquatic proxy (TAR) ratio derived from n-alkane signatures indicated an increased input of terrestrial-derived organic matter (OM) to lake sediments over the past 60 years, with an increasing contribution of woody vegetation shown by the C 27 /C 31 ratio. This may be related to agricultural intensification, leading to enhanced soil erosion, but also an increase in riparian woodland that may disconnect OM inputs from arable land uses in the upper parts of the study catchment. Spatial variability of geochemical proxies showed a close coupling between OM provenance and riparian land use, supporting the new conceptualization of river corridors (active river channel and riparian zone) as critical zones linking the terrestrial and aquatic C fluxes. Further testing of this novel tracing technique shows promise in terms of quantification of lateral C fluxes as well as targeting of effective land management measures to reduce soil erosion and promote OM conservation in river catchments.

Abstract:
An evaluation of the hysteresis in chemical concentration–discharge (C–Q) relationships from drained, intensively managed grasslands in southwest England

© 2017 IAHS. This study examined the hysteresis exhibited in concentration–discharge (C–Q) relationships in the runoff from four hydrologically separated fields (catchments) at an intensively managed grassland. The objectives were to examine C–Q relationships constructed from high-resolution time series of flow, temperature, pH, conductivity, nitrate and turbidity, and their implications for hydrological processes. High-resolution datasets from the quality assured records of the Rothamsted Research North Wyke Farm Platform in the UK were examined using a graphical method and cross-correlation statistics. The study found that storm events based C–Q hysteresis reflects the cross-correlation that is generally hidden in time series analysis of large datasets, and that although Q and water quality variables can be effectively influenced by catchment size, the C–Q relationship is less significantly influenced. The dominant C–Q relationships of the water variables in the study area reflect that saturated overland flow was prevalent during the study period in the catchments, while the CCF results indicate coupled transfer of sediments and solute in the area at lag ≥ 0. EDITOR D. Koutsoyiannis ASSOCIATE EDITOR M. D. Fidelibus.

Abstract:
Analysis of fundamental physical factors influencing channel bank erosion: results for contrasting catchments in England and Wales

© 2017, the Author(s). Channel bank erosion processes are controlled by numerous factors and as such are both temporally and spatially variable. The significance of channel bank erosion to the sediment budget is difficult to quantify without extensive fieldwork/data analysis. In this study, the importance of key physical factors controlling channel bank erosion, including channel slope, upstream catchment area, channel confinement, and sinuosity, was explored using regression analysis. The resulting analysis can be used in practical studies to provide a first approximation of bank erosion rates (in catchments similar to those investigated). A data set of channel bank erosion rates covering eight contrasting river catchments across England and Wales, over a time period of up to 150 years, was created using a modified GIS methodology. The best predictors were found to be upstream area, channel confinement, and sinuosity with respect to dimensionless width-averaged retreat rates (m m −1  yr −1 ). Notwithstanding these relationships, the results highlight the variability of the magnitude of sediment production by channel bank erosion both within and between catchments.

Abstract:
Ecosystem service delivery in Karst landscapes: anthropogenic perturbation and recovery

© 2017, the Author(s). Covering extensive parts of China, Karst landscapes are exceptional because rapid and intensive land use change has caused severe ecosystem degradation within only the last 50 years. The twentieth century intensification in food production through agriculture has led to a rapid deterioration of soil quality, evidenced in reduced crop production and rapid loss of soil. In many areas, a tipping point appears to have been passed as basement rock is exposed and ‘rocky desertification’ dominates. Through the establishment of the “Soil processes and ecological services in the karst critical zone of SW China” (SPECTRA) Critical Zone Observatory (CZO) we will endevaour to understand the fundmental processes involved in soil production and erosion, and investigate the integrated geophysical-geochemical-ecological responses of the CZ to perturbations. The CZ spans a gradient from undisturbed natural vegetation through human perturbed landscapes. We seek to understand the importance of heterogeneity in surface and below-ground morphology and flow pathways in determining the spatial distribution of key stocks (soil, C, vegetation, etc.) and their control on ecosystem service delivery. We will assess the extent to which the highly heterogeneous critical zone resources can be restored to enable sustainable delivery of ecosystem services. This paper presents the CZO design and initial assessment of soil and soil organic carbon stocks and evidence for their stability based on caesium-137 ( 137 Cs) data.

Abstract:
Nitrogen loss from karst area in China in recent 50 years: An in-situ simulated rainfall experiment's assessment

© 2017 the Authors. Ecology and Evolution published by John Wiley. &. Sons Ltd. Karst topography covers more than 1/3 of the People's Republic of China in area. The porous, fissured, and soluble nature of the underlying karst bedrock (primarily dolomite and limestone) leads to the formation of underground drainage systems. Karst conduit networks dominate this system, and rainfall takes a crucial role on water cycle at China karst area. Nitrogen loss from the karst system is of particular concern, with regard to nutrient use efficiency as well as water quality, as much of the karst system, including steeply sloping terrain, is used for intensive agriculture. We use simulated rainfall experiments to determine the relationship between rainfall and nitrogen loss at typical karst slope land and then estimate nitrogen loss from the karst soil. The results show that both surface runoff and subsurface runoff have a significant linear correlation with rainfall at all studied sites. Subsurface runoff is larger than surface runoff at two karst sites, while the opposite is true at the non-karst site. Exponential function satisfactorily described the correlation between rainfall and nitrogen concentrations in runoff. Nitrates accounted for 60%–95% of the dissolved nitrogen loss (DN, an index of N-loss in this rese arch). The estimated annual N-loss load varies between 1.05 and 1.67 Tg N/year in the whole karst regions of China from 1961 to 2014. Approximately, 90% of the N-loss load occurred during the wet season, and 90% of that passed through the subsurface. Understanding the processes and estimating N-loss is highly valuable in determining long-term soil security and sustainability in karst regions.

Abstract:
Relating Intensity of Soil Redistribution to Land Use Changes in Abandoned Pyrenean Fields Using Fallout Caesium-137

Copyright © 2017 John Wiley. &. Sons, Ltd. Fallout caesium-137 has been used to trace soil redistribution in abandoned fields located in the Central Spanish Pyrenees. A total of 28 fields with different lengths, slope angles and time since abandonment were selected on a representative south-facing slope of the Estarrún valley. The local reference inventory and the magnitude and spatial distribution of 137 Cs inventories within these fields were documented and used as a basis for assessing patterns of soil redistribution. The local reference inventory was estimated to be 4,500 Bqm −2. Within the fields, the average 137 Cs inventory at the top of the slope was 3,920 Bqm −2 , and accumulation of soil at the bottom of the slopes was demonstrated by an average 137 Cs inventory of 5,320 Bqm −2. Deviations from the reference inventory were highest for fields with the longest slopes that had been abandoned for less than 30 years. Here, increases in the 137 Cs inventory, relative to the reference inventory, in excess of 20% were found at the bottom of the slopes. Considering all the fields and all geomorphic positions within the fields, the greatest 137 Cs losses and gains were found in the fields with the longest duration of abandonment, indicating more intense soil redistribution. Irrespective of the timing of abandonment, the ranges of 137 Cs inventories in the fields were found to be proportional to the water erosion index. The 137 Cs technique demonstrated that patterns of sediment redistribution were closely related to the topographic and physiographic characteristics of the slopes. Copyright © 2017 John Wiley. &. Sons, Ltd.

Abstract:
Investigating the controls on soil organic matter decomposition in tussock tundra soil and permafrost after fire

© 2016 Elsevier Ltd. Rapid warming in Arctic ecosystems is resulting in increased frequency of disturbances such as fires, changes in the distribution and productivity of different plant communities, increasing thaw depths in permafrost soils and greater nutrient availability, especially nitrogen. Individually and collectively, these factors have the potential to strongly affect soil C decomposition rates, with implications for the globally significant stores of carbon in this region. However, considerable uncertainty remains regarding how C decomposition rates are controlled in Arctic soils. In this study we investigated how temperature, nitrogen availability and labile C addition affected rates of CO 2 production in short (10-day for labile C) and long-term (1.5 year for temperature and N) incubations of samples collected from burned and unburned sites in the Anaktuvuk river burn on the North Slope of Alaska from different depths (organic horizon, mineral horizon and upper permafrost). The fire in this region resulted in the loss of several cms of the organic horizon and also increased active layer depth allowing the impacts of four years of thaw on deeper soil layers to be investigated. Respiration rates did not decline substantially during the long-term incubation, although decomposition rates per unit organic matter were greater in the organic horizon. In the mineral and upper permafrost soil horizons, CO 2 production was more temperature sensitive, while N addition inhibited respiration in the mineral and upper permafrost layers, especially at low temperatures. In the short-term incubations, labile C additions promoted the decomposition of soil organic matter in the mineral and upper permafrost samples, but not in the organic samples, with this effect being lost following N addition in the deeper layers. These results highlight that (i) there are substantial amounts of labile organic matter in these soils (ii), the organic matter stored in mineral and upper. permafrost in the tussock tundra is less readily decomposable than in the organic horizon, but that (iii) its decomposition is more sensitive to changes in temperature and that (iv) microbial activity in deeper soil layers is limited by labile C availability rather than N. Collectively, these results indicate that in addition to the loss of C by combustion of organic matter, increasing fire frequency also has the potential to indirectly promote the release of soil C to the atmosphere in the years following the disturbance.

Abstract:
Mapping mean total annual precipitation in Belgium, by investigating the scale of topographic control at the regional scale

© 2016 Elsevier B.V. Accurate precipitation maps are essential for ecological, environmental, element cycle and hydrological models that have a spatial output component. It is well known that topography has a major influence on the spatial distribution of precipitation and that increasing topographical complexity is associated with increased spatial heterogeneity in precipitation. This means that when mapping precipitation using classical interpolation techniques (e.g. regression, kriging, spline, inverse distance weighting, etc.), a climate measuring network with higher spatial density is needed in mountainous areas in order to obtain the same level of accuracy as compared to flatter regions. In this study, we present a mean total annual precipitation mapping technique that combines topographical information (i.e. elevation and slope orientation) with average total annual rain gauge data in order to overcome this problem. A unique feature of this paper is the identification of the scale at which topography influences the precipitation pattern as well as the direction of the dominant weather circulation. This method was applied for Belgium and surroundings and shows that the identification of the appropriate scale at which topographical obstacles impact precipitation is crucial in order to obtain reliable mean total annual precipitation maps. The dominant weather circulation is determined at 260°. Hence, this approach allows accurate mapping of mean annual precipitation patterns in regions characterized by rather high topographical complexity using a climate data network with a relatively low density and/or when more advanced precipitation measurement tec hniques, such as radar, aren't available, for example in the case of historical data.

Abstract:
Sustained high magnitude erosional forcing generates an organic carbon sink: Test and implications in the Loess Plateau, China

© 2014 Elsevier B.V. Humans are now the most important geomorphic agent on the planet and accelerated erosion in agricultural landscapes results in high magnitude lateral organic carbon (OC) fluxes and significant perturbation of the land-ocean carbon flux. Nevertheless, the net effect of these lateral carbon fluxes on the C cycle is poorly constrained and there is no consensus as to whether they drive a net source or net sink of atmospheric CO2. Here, we test the hypothesis that, under sustained erosional forcing, soil carbon stocks on hillslopes reach a new equilibrium state in which all carbon exported with erosion is replaced; and, therefore, erosion results in a net sink for atmospheric CO2 at the scale of eroding hillslopes. The evidence from our study site, in the Loess Plateau of China, is consistent with this hypothesis. Despite net export of OC equivalent to ca. 10% NPP, we found that all of the eroded OC was replaced and, therefore, that the sink strength was equal to the C export rate. This sets the upper limit of the erosion-induced sink term at the scale of whole watershed. The fate of the exported carbon in reservoirs, floodplains, riverbeds and the ocean ultimately controls the watershed-scale sink strength. Nevertheless, the full replacement observed here suggests that erosion does not induce a C source, irrespective of the fate of the exported carbon, at least for high-input agricultural systems. Finally, we propose that assessment of the C cycle perturbation associated with erosion-induced lateral C fluxes must be made an integral part of accounting mechanisms for climate change mitigation strategies that are based on land use change and C sequestration in terrestrial environments.

Abstract:
The fate of buried organic carbon in colluvial soils: a long-term perspective

Colluvial soils are enriched in soil organic carbon (SOC) in comparison to the soils of upslope areas due to the deposition and progressive burial of SOC. This burial of SOC has important implications for the global carbon cycle, but the long-term dynamics of buried SOC remain poorly constrained. We addressed this issue by determining the SOC burial efficiency (i.e. the fraction of originally deposited SOC that is preserved in colluvial deposits) of buried SOC as well as the SOC stability in colluvial soils. We quantified the turnover rate of deposited SOC by establishing sediment and SOC burial chronologies. The SOC stability was derived from soil incubation experiments and the δ13C values of SOC. The C burial efficiency was found to decrease with time, reaching a constant ratio of approximately 17% by about 1000-1500 yr post-burial. This decrease is attributed to the increasing recalcitrance of the remaining buried SOC with time and a less favourable environment for SOC decomposition with increasing depth. Buried SOC in colluvial profiles was found to be more stable and degraded in comparison to SOC sampled at the same depth at a stable reference location. This is due to the preferential mineralisation of the labile fraction of the deposited SOC. Our study shows that SOC responds to burial over a centennial timescale; however, more insight into the factors controlling this response is required to fully understand how this timescale may vary, depending on specific conditions such as climate and depositional environment. © Author(s) 2014. CC Attribution 3.0 License.

Abstract:
Using caesium-134 and cobalt-60 as tracers to assess the remobilization of recently-deposited overbank-derived sediment on river floodplains during subsequent inundation events

River floodplains act as sinks for fine-sediment and sediment-associated contaminants. Increasing recognition of their environmental importance has necessitated a need for an improved understanding of the fate and residence times of overbank sediment deposits over a broad range of timescales. Most existing investigations have focused on medium-term accretion rates, which represents net deposition from multiple flood events over several decades. In contrast, the fate of recently-deposited sediment during subsequent overbank events has received only limited attention. This paper presents a novel tracing-technique for documenting the remobilization of recent overbank sediment on river floodplains during subsequent inundation events, using the artificial radionuclides, caesium-134 ( 134 Cs) and cobalt-60 ( 60 Co). The investigation was conducted within floodplains of the Rivers Taw and Culm in Devon, UK. Small quantities of fine-sediment ( <. 63μm dia.), pre-labelled with known activities of either 134 Cs or 60 Co, were deposited at 15 locations across each floodplain. Surface inventories, measured before and after three consecutive flood events, were used to estimate sediment loss (in g m -2 ). Significant reductions provided evidence of the remobilization of the labelled sediment by inundating floodwaters. Spatial variations in remobilization were related to localized topography. Sediment remobilized during the first two events for the River Taw floodplain were equivalent to 63·8% and 11·9%, respectively, of the original mass. Equivalent values for the River Culm floodplain were 49·6% and 12·5%, respectively, of the original mass. Sediment loss during the third event proved too small to be attributed to remobilization by overbank floodwaters. After the third event, a mean of 22·5% and 35·2% of the original mass remained on the Taw and Culm floodplains, respectively. These results provide evidence of the storage of the remaining sediment. The findings highlight the importance of remobilization of recently-deposited sediment on river floodplains during subsequent overbank events and demonstrate the potential of the tracing-technique. © 2013 John Wiley. &. Sons, Ltd.

Abstract:
Estimation of Soil Carbon Input in France: an Inverse Modelling Approach

Development of a quantitative understanding of soil organic carbon (SOC) dynamics is vital for management of soil to sequester carbon (C) and maintain fertility, thereby contributing to food security and climate change mitigation. There are well-established process-based models that can be used to simulate SOC stock evolution; however, there are few plant residue C input values and those that exist represent a limited range of environments. This limitation in a fundamental model component (i.e. C input) constrains the reliability of current SOC stock simulations. This study aimed to estimate crop-specific and environment-specific plant-derived soil C input values for agricultural sites in France based on data from 700 sites selected from a recently established French soil monitoring network (the RMQS database). Measured SOC stock values from this large scale soil database were used to constrain an inverse RothC modelling approach to derive estimated C input values consistent with the stocks. This approach allowed us to estimate significant crop-specific C input values (P. <. 0.05) for 14 out of 17 crop types in the range from 1.84 ± 0.69 t C ha -1 year -1 (silage corn) to 5.15 ± 0.12 t C ha -1 year -1 (grassland/pasture). Furthermore, the incorporation of climate variables improved the predictions. C input of 4 crop types could be predicted as a function of temperature and 8 as a function of precipitation. This study offered an approach to meet the urgent need for crop-specific and environment-specific C input values in order to improve the reliability of SOC stock prediction. © 2013 Soil Science Society of China.

Abstract:
REVIEW: the role of ecosystems and their management in regulating climate, and soil, water and air quality

Ecosystems have a critical role in regulating climate, and soil, water and air quality, but management to change an ecosystem process in support of one regulating ecosystem service can either provide co-benefits to other services or can result in trade-offs. We examine the role of ecosystems in delivering these regulating ecosystem services, using the UK as our case study region. We identify some of the main co-benefits and trade-offs of ecosystem management within, and across, the regulating services of climate regulation, and soil, water and air quality regulation, and where relevant, we also describe interactions with other ecosystem services. Our analysis clearly identifies the many important linkages between these different ecosystem services. However, soil, water and air quality regulation are often governed by different legislation or are under the jurisdiction of different regulators, which can make optimal management difficult to identify and to implement. Policies and legislation addressing air, water and soil are sometimes disconnected, with no integrated overview of how these policies interact. This can lead to conflicting messages regarding the use and management of soil, water and air. Similarly, climate change legislation is separate from that aiming to protect and enhance soil, water and air quality, leading to further potential for policy conflict. All regulating services, even if they are synergistic, may trade off against other ecosystem services. At a policy level, this may well be the biggest conflict. The fact that even individual regulating services comprise multiple and contrasting indicators (e.g. the various components of water quality such as nutrient levels, acidity, pathogens and sediments), adds to the complexity of the challenge. Synthesis and applications. We conclude that although there are some good examples of integrated ecosystem management, some aspects of ecosystem management could be better coordinated to deliver multiple ecosystem services, and that an ecosystem services framework to assess co-benefits and trade-offs would help regulators, policy-makers and ecosystem managers to deliver more coherent ecosystem management strategies. In this way, an ecosystem services framework may improve the regulation of climate, and soil, water and air quality, even in the absence of economic valuation of the individual services. We conclude that although there are some good examples of integrated ecosystem management, some aspects of ecosystem management could be better coordinated to deliver multiple ecosystem services, and that an ecosystem services framework to assess co-benefits and trade-offs would help regulators, policy-makers and ecosystem managers to deliver more coherent ecosystem management strategies. In this way, an ecosystem services framework may improve the regulation of climate, and soil, water and air quality, even in the absence of economic valuation of the individual services. © 2012 British Ecological Society.

Abstract:
Spatial variability and change in soil organic carbon stocks in response to recovery following land abandonment and erosion in mountainous drylands

This research investigates the impact of human activities on carbon (C) dynamics in a mountainous and semi-arid environment. Despite the low C status of drylands, soil organic carbon (SOC) is the largest C pool in these systems and therefore may offer significant C sequestration potential in systems recovering from degradation. Nevertheless, quantification of this potential is limited by lack of knowledge concerning the magnitude of and controls on regional SOC stocks. Therefore, this study aimed to (i) investigate the variability of soil organic carbon in relation to recovery period and key soil and topographical variables, and (ii) quantify the effects of recovery period following abandonment on SOC stocks. Soil profiles were sampled in the Sierra de los Filabres (southeast Spain) in different land units along geomorphic and degradation gradients. SOC contents were modelled using recovery period and soil and topographical variables. Sample depth, topographic position, altitude, recovery period and stone content were identified as the main factors for predicting SOC concentrations. SOC stocks in 1 m depth of soil varied between 3.16 and 76.44 t/ha. Recovery period (years since abandonment), topographic position and altitude were used to predict and map SOC stocks in the top 0.2 m. The results show that C accumulates rapidly during the first 10-50 yr following abandonment; thereafter, the stocks evolve towards a steady-state level. The erosion zones in the study area demonstrate greater potential to increase their SOC stocks when abandoned. Deposition zones have greater SOC values, although their C accumulation rate is lower compared with erosional landscapes in the first 10-50 yr following abandonment. Therefore, full understanding of the C sequestration potential of land use change in areas of complex topography requires knowledge of spatial variability in soil properties and in particular SOC. © 2012 the Authors. Journal compilation © 2012 British Society of Soil Science.

Abstract:
Spatially-explicit regional-scale prediction of soil organic carbon stocks in cropland using environmental variables and mixed model approaches

The effects of soil redistribution on the carbon (C) cycle and the need for spatially and depth-explicit C estimates at large scales have recently been receiving growing attention. In eroding agricultural landscapes, C gets transported from erosional to depositional landscape elements forming a heterogeneous pattern in quantity and quality of the distributed carbon. At present, methods and research to characterize this horizontal and vertical variability are either limited to local slope scales or, if applied to larger scales, to surface soil horizons with large uncertainties when extrapolated to deeper layers. In this study, we used soil profile data collected in two zones of differing soil texture (loam and clay-rich soils) in Luxembourg, to calibrate a linear mixed-effect model to predict the 3D soil C stock distribution on a regional scale for cropping systems using a set of spatially-explicit hydrologic, climatic, pedologic and geomorphologic variables. We demonstrate that due to a high spatial variability of C stocks it is mandatory to consider various environmental processes to predict C accurately on a regional scale, especially in deeper soil layers, and to avoid simple depth extrapolation of topsoil C data as has been done earlier in flat landscapes. Using estimates of topsoil C contents derived from hyperspectral remote sensing, we predict spatial patterns of C stocks for cropland on a regional scale and provide new insights into the spatial heterogeneity of soil C storage covering a large area. The variability of C stocks in the two texture zones expressed as values larger or smaller than the mean±standard deviation is hereby lower in the loam zone (26.2%) than in the clay zone (38.7%). We estimate a mean C stock (to 100cm soil depth) of 9.4±3.1kg/m 2 for the clay-rich soils and 11.3±2.4kg/m 2 for loamy soils. This represents the first regional estimate for C stocks for the research area using continuous spatial explicit datasets. © 2013.

Abstract:
Cellular modelling as a tool for interpreting historic braided river evolution

Results are presented from a new cellular model of braided river dynamics that simulates flow, sediment transport, morphological change and the effects of braidplain vegetation. This model is used to investigate the effect of changes in upstream sediment supply on braided river systems over simulation periods of 200 years. Modelled changes in channel morphology, associated with both aggradation and degradation, were seen to be consistent with those reported in the literature. In addition, simulation results allowed the identification of diagnostic characteristics of aggrading and degrading reaches, in the form of relationships between the age, extent and relative elevation of fluvial surfaces. Interpretation of spatial patterns of valley floor surface characteristics in the Avoca River, New Zealand, on the basis of these relationships, allowed the identification of channel reaches that appear to be experiencing either aggradation or degradation. These inferences are shown to be consistent with independent evidence of spatial patterns of sediment supply to the main valley floor, derived from aerial photographs and an existing sediment source inventory. These results illustrate the potential for using cellular models to develop an improved understanding of natural river behaviour. © 2007 Elsevier B.V. All rights reserved.

Abstract:
Variability in (CS)-C-137 inventories and potential climatic and lithological controls in the central Ebro valley, Spain

The extent of soil erosion in some Spanish semiarid regions has caused great concern regarding the sustainability of soil resources. Accelerated soil erosion, particularly in some Mediterranean areas, is likely to be one of the main environmental problems associated with climate change. Fallout Cs-137 has been shown to provide a reliable basis for assessing soil erosion rates in different environments around the world. However, existing information concerning the spatial variation of Cs-137 inventories at reference sites has identified a need for further investigation of the factors affecting their spatial variability in semiarid environments, where stony and skeletal soils are predominant. Reference sites at three locations in the central Ebro valley were selected to investigate the Cs-137 content of several grain size fractions. Each site included both natural vegetated conditions and cultivated land and the three sites were characterized by different values of mean annual rainfall. The results obtained demonstrate the influence of lithology, land use and climate on the spatial variability of Cs-137 inventories that increase from 1190, to 1500 and 1710 Bq center dot m(-2) with increasing annual rainfall values from 300 to 500 mm at the study sites. The soils on marls at the Valare (n) over tildea site had the highest proportion of Cs-137 in the coarse fractions of cultivated soils (12%) in comparison with soils developed on limestones at Loma Negra (5%), whereas no Cs-137 content was found in the coarse fractions of soils on glacis-terrace materials at Pe (n) over tilde aflor. The Cs-137 reference inventories are higher in soils on marls and sands at cultivated locations at Valare (n) over tildea and Pe (n) over tilde aflor, but have similar values in soils at cultivated and uncultivated locations on limestones at Loma Negra. Therefore, in absence of level undisturbed soils with natural vegetation cover, cultivated flat soils on hard rocks could provide reliable reference inventories.

Abstract:
Tillage erosion: a review of controlling factors and implications for soil quality

Tillage erosion has been identified as an important global soil degradation process that has to be accounted for when assessing the erosional impacts on soil productivity, environmental quality or landscape evolution. In this paper, we present a summary of available data describing tillage erosion. This provides insights in the controlling factors determining soil redistribution rates and patterns by tillage for various implements used in both mechanized and non-mechanized agriculture. Variations in tillage depth and tillage direction cause the largest variations in soil redistribution rates, although other factors, such as tillage speed and implement characteristics, also play an important role. In general, decreasing tillage depth and ploughing along the contour lines substantially reduce tillage erosion rates and can be considered as effective soil conservation strategies. Implement erosivities reported in literature, characterized by the til lage transport coefficient, are very consistent and range in the order of 400-800 kg m -1 yr -1 and 70-260 kg m -1 yr -1 for mechanized and non-mechanized agriculture, respectively. Comparison of tillage erosion rates with water erosion rates using a global data set indicates that tillage erosion rates are at least in the same order of magnitude or higher than water erosion rates, in almost all cases. Finally, we discuss how tillage erosion increases the spatial variability of soil properties and affects soil nutrient cycling. Considering the widespread use of tillage practices, the high redistribution rates associated with the process and its direct effect on soil properties, it is clear that tillage erosion should be considered in soil landscape studies. © 2006 SAGE Publications.

Abstract:
From water to tillage erosion dominated landform evolution

While water and wind erosion are still considered to be the dominant soil erosion processes on agricultural land, there is growing recognition that tillage erosion plays an important role in the redistribution of soil on agricultural land. In this study, we examined soil redistribution rates and patterns for an agricultural field in the Belgian loess belt. 137 Cs derived soil erosion rates have been confronted with historical patterns of soil erosion based on soil profile truncation. This allowed an assessment of historical and contemporary landform evolution on agricultural land and its interpretation in relation to the dominant geomorphic process. The results clearly show that an important shift in the relative contribution of tillage and water erosion to total soil redistribution on agricultural land has occurred during recent decades. Historical soil redistribution is dominated by high losses on steep midslope positions and concavities as a result of water erosion, leading to landscape incision and steepening of the topography. In contrast, contemporary soil redistribution is dominated by high losses on convex upperslopes and infilling of slope and valley concavities as a result of tillage, resulting in topographic flattening. This shift must be attributed to the increased mechanization of agriculture during recent decades. This study shows that the typical topographical dependency of soil redistribution processes and their spatial interactions must be accounted for when assessing landform and soil profile evolution. © 2005 Published by Elsevier B.V.

Abstract:
Tillage erosion and its effect on soil properties and crop yield in Denmark.

Tillage erosion had been identified as a major process of soil redistribution on sloping arable land. The objectives of our study were to investigate the extent of tillage erosion and its effect on soil quality and productivity under Danish conditions. Soil samples were collected to a 0.45-m depth on a regular grid from a 1.9-ha site and analyzed for 137Cs inventories, as a measure of soil redistribution, soil texture, soil organic carbon (SOC) contents, and phosphorus (P) contents. Grain yield was determined at the same sampling points. Substantial soil redistribution had occurred during the past decades, mainly due to tillage. Average tillage erosion rates of 2.7 kg m(-2) yr(-1) occurred on the shoulderslopes, while deposition amounted to 1.2 kg m(-2) yr(-1) on foot- and toeslopes. The pattern of soil redistribution could not be explained by water erosion. Soil organic carbon and P contents in soil profiles increased from the shoulder- toward the toeslopes. Tillage translocation rates were strongly correlated with SOC contents, A-horizon depth, and P contents. Thus, tillage erosion had led to truncated soils on shoulderslopes and deep, colluvial soils on the foot- and toeslopes, substantially affecting within-field variability of soil properties. We concluded that tillage erosion has important implications for SOC dynamics on hummocky land and increases the risk for nutrient losses by overland flow and leaching. Despite the occurrence of deep soils across the study area, evidence suggested that crop productivity was affected by tillage-induced soil redistribution. However, tillage erosion effects on crop yield were confounded by topography-yield relationships.

Abstract:
Re-defining tillage erosion: Quantifying intensity-direction relationships for complex terrain. 2. Revised mouldboard erosion model

Current tillage erosion models account for the influence of tillage direction in the magnitude of the soil transport coefficient. It is argued that a re-modelling of tillage erosion is preferable in which the influence of tillage direction is separated from the soil transport coefficient, which is a measure of tillage intensity. This has been achieved here by developing a two-dimensional tillage erosion model that incorporates tillage direction in the measure of slope and uses soil transport coefficients that are independent of tillage direction and based on relationships between transport and the slope in the direction that bisects tillage direction and the overturning direction. Mean tillage erosion, associated with a single pair of opposing tillage directions and pair of overturning directions, can be described by a two-dimensional diffusion-type equation if the dimensions are defined as the tillage direction and the direction perpendicular to tillage. Application of the model to a real-world case allows quantification of the potential soil conservation benefits associated with optimization of tillage direction. The scope for amelioration is related to the ratio between the coefficients for transport in the direction of tillage and perpendicular to tillage. As this ratio approaches unity, the potential for amelioration reduces towards zero. For the study site investigated, use of the experimentally derived ratio of 0.66 indicated that a 12% reduction in tillage erosion could be obtained by ploughing across the dominant field slope as compared to ploughing up and down the dominant slope. For an implement with a coefficient ratio of 0.2 the reduction in tillage erosion intensity, associated with optimizing the tillage direction, reaches 28%. Nevertheless, such benefits must be considered in the context of other management considerations. The tillage direction that minimizes erosion is associated with lateral slopes of 10°, or more, over 20% of the field. To the land-user this disadvantage may outweigh the soil conservation benefits.

Abstract:
Simulation of the redistribution of soil by tillage on complex topographies

Tillage redistributes soil and contributes significantly to the within-field soil variation, especially on topographically complex terrain. Although the basic principles of the redistribution are well understood, models for simulating the redistribution are poor predictors. This paper presents a modelling structure that allows a simulation of the redistribution of soil constituents on complex topographies for various tillage implements. The model simulates the redistribution of soil constituents by convoluting the probability distribution of the tillage displacement with the spatial distribution of the soil constituents. The probability distributions in two dimensions are derived from a series of tillage experiments conducted with a mouldboard plough at various positions in the landscape. Furthermore, the effects of topography and tillage direction on the probability distributions were characterized and implemented in the model. A first application showed that the direction of tillage significantly affects the long-term redistribution of soil constituents. The inclusion of other implements in the model was explored, and we found that data in the literature could be used for simulating the long-term effects of tillage.

Abstract:
Tillage erosion intensity in the South Canterbury Downlands, New Zealand

Growing awareness of the pressure on land resources emphasises the need to understand the full range of processes operating in human-impacted agroecosystems. In such systems one of the greatest threats to long-term sustainability is the erosion and depauperation of soil, which, until recently, was attributed almost entirely to water erosion. This study builds on recent awareness of the significance of tillage erosion and presents the results of an experimental investigation of tillage erosion due to mouldboard ploughing. Aluminium cubes were used to trace soil translocation as a result of a single pass of the plough perpendicular to the contour in downslope and upslope directions. In common with others studies, translocation was found to be directly proportional to slope tangent for downslope tillage and unrelated to slope for upslope tillage. The influence of non-topographic variables on the relationship between translocation distance and slope was partially filtered out by using the ratio of translocation distances in the tillage direction and perpendicular to tillage. Shallow plough depths of 0.17 m produced tillage detachment of only 230 kg/m 2 ; however, a high tillage translocation coefficient of 1.16 m/pass resulted in a soil flux coefficient of 265 kg/m.pass. The high tillage translocation coefficient is probably partly due to the loose nature of the regularly cultivated loessic soil, however, on the basis of comparison with other published studies, it is suggested that the high tillage speed of 7 km/h is the principal control on the magnitude of the coefficient. Analysis of the available data suggests that a 30% reduction in tillage erosion intensity could be obtained by reduction of the tillage speed to 4 km/h; nevertheless, more experimental work is needed to test this suggestion. On the transect studied, a pair of opposing passes of the mouldboard plough would produce erosion rates as high as 5.1 kg/m 2. year (51 t/ha.year) from shoulder slope elements and as high as 1.9 kg/m 2. year (19 t/ha.year) over half of the slope length. This pattern matched closely the distribution of. 137 Cs-derived erosion rates documented previously for a nearby field, suggesting that for this environment, as for many mechanised agricultural systems, tillage erosion is the dominant soil redistribution process and the greatest threat to long-term sustained on-site productivity. Reduction of tillage erosion should, therefore, be seen as a priority in the development of sustainable land management strategies.

Abstract:
Comparison of methods used to calculate tillage translocation using plot-tracers

Tillage translocation is measured in the studies of soil dispersion and soil erosion. The translocation of soil by tillage is normally measured with a tracer. Using plots, a volume of soil is labelled and then tilled. There are two methods of calculating translocation using plot-tracers. For the more common method, translocation is calculated directly from the distributions of tracer before and after tillage (Distribution-Curve Method). For the less common method, a summation curve is generated from the distribution of tracer after tillage by employing convolution, and translocation is calculated from this curve (Summation-Curve Method). In this paper, the two methods are described and compared using hypothetical and experimental data. Both methods provide accurate measures of gross translocation. The Summation-Curve Method provides a measure of error associated with gross translocation and a more thorough characterization of the dispersion of translocated soil; therefore, it was considered to be the superior of the two methods.

Abstract:
The effects of tillage displaced soil on soil properties and wheat biomass

Tillage operations transport large amounts of soil from convex slopes and deposit on concavities in hilly cultivated areas. Field experiment was conducted to assess tillage induced soil displacement and its effects on soil properties and wheat (Triticum aestivum L.) biomass production. The study was done on 3.5 ha fertilized and wheat seeded hillslope (14-21% slope) located 100 km north of Athens, Greece. Numbered aluminum cylinders (700), each 10 mm diameter by 10 mm height, were buried in soil as soil movement tracers (SMTs) to estimate soil displacement as a function of moldboard plowing with two depths in up-slope and down-slope directions. Furthermore, clay, organic matter, rock fragment content, phosphorus and 137 Cs were determined on 81 soil bulk cores to estimate soil redistribution rates along the study hillslope. Soil depth. and soil water storage were measured in 81 soil sites and related to the wheat biomass production. The mean SMT displacement distance due to 25-cm plow depth on 21% slope was 42 cm for down-slope tillage and 16 cm for up-slope tillage. Comparable values were 31 cm for down-slope and 14 cm for up-slope tillage on 14% slope gradient. The SMT distance for both tillage directions on 21% slope was about 60% less for 18-cm plow depth compared with 25-cm plow depth. Shallow soil (depth. < 25 cm) was observed on convex slope with greater percentages of sand, rock fragments, organic matter and lower percentages of clay and available water. In contrast, deeper soil (depth. > 70 cm) was found on lower concavities where displaced soil was deposited. The spatial pattern or 137 Cs inventories suggests that tillage erosion is a major erosion process in the study area. The maximum leaf area index of wheat was 2.8 for convex slope and 3.6 for concave slope. Wheat biomass, ranging from 0.2 to 1.2 kg m -2 , increased logarithmically with increased soil depth. Moldboard plowing displaced large amounts of soil from convex slope which changed soil properties to less favorable for wheat production. Application of the obtained empirical functions showed that under the existing climatic conditions and management practices, the unprofitably productive area will increase from 4.1 to 6.8% in a period of 7 years. © 2001 Elsevier Science B.V.

Abstract:
A study of soil erosion on a steep cultivated slope in the Mt. Gongga region near Luding, Sichuan, China, using the ¹³⁷Cs technique

This paper reports the results of an investigation of soil erosion on a steep cultivated slope in the Mt Gongga region of the Upper Yangtze River Basin, Southwest China, using the. 137 Cs technique. The effective. 137 Cs reference inventory for the study field, estimated from the bottom layer of a. 137 Cs depth profile at the deposition zones, is 2373.9 Bq/m 2 , accounting for 65.8% the local. 137 Cs reference inventory of 3607.7 Bq/m 2. It strongly indicates that a considerable amount of. 137 Cs input was lost prior to incorporation into the ploughing layer from the study field during the nuclear weapons testing period because of 1 37 Cs surface enrichment. The average erosion rate is estimated to be 4914 t/km 2 yr for a typical cultivated steep slope with an angle of 34° at the subtropical zone in the Mt Gongga region. It can reach to 22856 t/km 2 yr for a failure slope under cultivation.

Abstract:
Modeling translocation and dispersion of soil constituents by tillage on sloping land

Recent studies clearly indicated that soil tillage is a major factor affecting soil redistribution on arable land. However, existing modeling studies of the redistribution of soil constituents by tillage are largely theoretical in nature due to the lack of sufficient experimental data. This paper describes the results of field experiments carried out with a moldboard plow on different slope gradients showing that an important net downslope translocation and dispersion of soil constituents is associated with soil tillage. Both translocation and dispersion are strongly affected by slope gradient. Available experimental evidence suggests that redistribution of soil constituents can be modeled by convoluting the displacement probability distribution with the spatial distribution of the soil constituent. The convolution model presented here was found to be superior to existing models because it accounts for dispersion, directionality of tillage, and topography. A comparison of soil property data with model simulations indicated that soil tillage is a major factor when assessing the effect of erosion processes on the variability of soil properties.

Abstract:
Fine-earth translocation by tillage in stony soils in the Guadalentin, south-east Spain: an investigation using caesium-134

Tillage erosion is increasingly recognised as an important soil erosion process on agricultural land. In view of its potential significance, there is a clear need to broaden the experimental database for the magnitude of tillage erosion to include a range of tillage implements and agricultural environments. The study discussed in this paper sought to address the need for such data by examining tillage erosion by a duckfoot chisel plough in stony soils on steep slopes in a semi-arid environment. Results of the investigation of coarse fraction (rock fragment) translocation by tillage in this environment have been presented elsewhere and the paper focuses on tillage translocation and erosion of the fine earth. Tillage translocation was measured at 10 sites, representing both upslope and downslope tillage by a duckfoot chisel plough on five different slopes, with tangents ranging from 0.02 to 0.41. A fine-earth tracer, comprising fine earth labelled with 134 Cs, was introduced into the plough layer before tillage. After a single pass of the plough, incremental samples of plough soil were excavated and sieved to separate the fine earth from the rock fragments. Translocation of the fine-earth tracer was established by analysing the 134 Cs content of the samples of fine earth. These data were used to establish translocation distances for each combination of slope and tillage direction. Translocation distances of the fine earth were not significantly different from translocation distances of the coarse fraction. For all sites, except uphill on the 0.41 slope, translocation distances were found to be linearly related to slope tangent. The soil flux due to tillage for each site was calculated using the translocation distance and the mass per unit area of the plough layer. For slopes with tangents. < 0.25, the relationship between soil flux and tangent was linear and the soil flux coefficient derived was 520-660 kg m -1 per pass. This is much larger than the coefficients found in other studies and this high magnitude is attributed to the non-cohesive nature and high rock fragment content of the soil in this investigation. A second contrast with previous studies was found in non-linearity in the relationship between soil flux and tangent when steeper slopes were included. This was a product of variation in plough depth between the steepest slopes and the remainder of the study area. On the basis of the study it is suggested that an improved understanding of tillage erosion may be obtained by considering the dual processes of tillage detachment (mass per unit area of soil subject to tillage) and tillage displacement (equivalent to translocation distance per pass) in assessing, comparing and modelling tillage translocation. An improved model is proposed that recognises the complexity of soil redistribution by tillage, provides a framework for process-based investigation of the controls on tillage fluxes, and allows identification of potential self-limiting conditions for tillage erosion.

Abstract:
Rates and patterns of tillage and water erosion on terraces and contour strips: Evidence from caesium-137 measurements

Despite the widespread use of contour-strips and terraces for soil conservation little is known concerning the impact of such measures on rates and patterns of tillage erosion and tillage translocation. Caesium-137 ( 137 Cs) measurements would appear to offer a rapid means of assembling data relevant to the evaluation of tillage erosion and tillage translocation. However, use of 137 Cs data in this way requires an approach to the analysis of 137 Cs data which accounts for both tillage erosion and tillage translocation. The latter is particularly significant on short slopes. A method of analysing 137 Cs data has been developed, that employs a linear, multistore, mass-balance model of soil and 137 Cs redistribution to permit estimation of the contributions to erosion from both water and tillage erosion. This method is outlined and results from its application are discussed using case studies from Yanting, in Sichuan Province, China; Ha Sofonia, in Lesotho; and, Chinamora, in Zimbabwe. These case studies confirm the viability of the approach and provide valuable evidence for the importance of tillage erosion and translocation on terraces and contour-strips subject to cultivation by animal traction. Gross rates of tillage erosion were found to be of comparable or greater magnitude than gross rates of water erosion on the fields examined. It is, therefore, suggested that any evaluation of on-site impacts of erosion must take account of tillage erosion. Relationships between annual soil fluxes due to tillage and slope tangent were found to be very similar to the relationships established for a single pass of equivalent tillage equipment with mechanical traction. Furthermore, because tillage by animal traction necessitates downslope turning of the soil on every occasion, net downslope fluxes of soil associated with animal traction may exceed the levels associated with tillage by mechanised traction, in which the soil is typically turned in opposing directions on successive occasions.

Abstract:
Sediment transport by overland flow over an area of net deposition

Flume studies were conducted in order to evaluate the influence of slope, sediment size, discharge and inflow sediment concentration on sediment deposition by overland flow. Additionally, experiments were carried out to measure transport capacity of overland flow at low slopes, using a wide range of discharges. The experimental data show that the hydraulic conditions where net deposition occurs can be divided into two domains. The first domain is characterized by hydraulic conditions where transport capacity is not significant. In the second domain net deposition still occurs but transport capacity is significant. The size of the latter domain is dependent on the sediment size distribution, on the hydraulic roughness and on the inflow sediment concentration. The experiments clearly indicate the necessity of incorporating a threshold value in any deposition equation. These experiments demonstrate that shear stress is a valuable threshold for deposition modelling.

Abstract:
Tillage erosion, water erosion and soil quality on cultivated terraces near Xifeng in the Loess Plateau, China

This study sought to contribute to the understanding of soil redistribution by tillage on terraces and the extent and causes of within-field variation in soil properties by examining the spatial distributions of soil redistribution rates, derived using caesium-137, and of total nitrogen and total phosphorus concentrations, within a ribbon and a shoulder terrace in a yuan area of the Loess Plateau of China. Additional water erosion rate data were obtained for nine other terraces. Water erosion rates on the ribbon terraces were low ( < 1 kg m -2. yr -1 ), unless slope tangents exceeded 0.1. However, despite the use of animal traction, high rates of tillage erosion were observed (mean 5.5 kg m -2. yr -1 ). Soil nitrogen concentrations were related to rates of soil redistribution by tillage on the ribbon terrace examined in detail. In general, higher rates of water erosion (0.5-2.9 kg m -2. yr -1 ) and lower rates of tillage erosion (mean 1.4 kg m -2. yr -1 ) were evident on the longer shoulder terraces. On the shoulder terrace examined in detail, soil phosphorus concentrations were related to net rates of soil redistribution. A statistically significant regression relationship between water erosion rates and the USLE length and slope factor was used in conjunction with the simulation of tillage erosion rates to evaluate a range of terrace designs. It is suggested that off-site impacts of erosion could be further reduced by ensuring that the slope tangents are kept below 0.06 and lengths below 30 m, especially on the shoulder terraces. Tillage erosion and the systematic redistribution of soil nutrients could be reduced by modification of the contour-cultivation technique to turn soil in opposing directions in alternate years.

Abstract:
Use of caesium-137 data for validation of spatially distributed erosion models: the implications of tillage erosion

Validation of spatially distributed models using spatially distributed data represents a vital element in the development process; however, it is rarely undertaken. To a large extent, this reflects the problems associated with assembling erosion rate data, at appropriate temporal and spatial scales and with a suitable spatial resolution, for comparison with model results. The caesium-137 ( 137 Cs) technique would appear to offer considerable potential for meeting this need for data, at least for longer timescales. Nevertheless, initial attempts to use 137 Cs for model validation did not prove successful. This lack of success may be explained by the important role of tillage erosion in redistributing soil within agricultural fields and, therefore, contributing to the 137 Cs-derived soil redistribution rates. This paper examines the implications of tillage erosion for the use of 137 Cs in erosion model validation and presents an outline methodology for the use of 137 Cs in model validation. This methodology acknowledges and addresses the constraints imposed by the need to: (1) separate water and tillage erosion contributions to total soil redistribution as represented in 137 Cs derived rates; (2) account for lateral mixing of 13 67Cs within fields as a result of tillage translocation; (3) simulate long-term water erosion rates using the model under evaluation if 137 Cs-derived water erosion rates are to be used in model validation. The methodology is dependent on accurate simulation of tillage erosion and tillage translocation. Therefore, as greater understanding of tillage erosion is obtained, the potential for the use of 137 Cs in water erosion model validation will increase. Caesium-137 measurements remain one of the few sources of spatially distributed erosion information and, therefore, their potential value should be exploited to the full.

Abstract:
Soil erosion rates on sloping cultivated land on the Loess Plateau near Ansai, Shaanxi Province, China: an investigation using ¹³⁷Cs and rill measurements

Sediment yields from the rolling hills area of the Loess Plateau in northern China (10 000-25 000 t km -2. yr -1 ) are amongst the highest in the world. The sediment is believed to derive from both the deep gullies that dissect the rolling plateau and the steep cultivated fields on the slopes of the mounds between the gullies. However, there are few reliable data for erosion rates on the cultivated fields and it is suspected that current estimates (10 000-16 000 t km -2. yr -1 ) based on empirical relationships (derived from erosion plot studies) exceed the true values. This study sought to address the need for more information concerning erosion of the cultivated fields through derivation of erosion rates from measurements of rill volume and caesium-137 ( 137 Cs) inventories for typical fields near the village of Ansai, Shaanxi Province. The derived erosion rates are discussed and compared with estimates based on empirical relationships derived from erosion plot data. Where erosion rate estimates based on both rill volume data and. 137 Cs inventories are available, they show good agreement in the pattern of downslope variation. Both show a sharp decline in erosion rates at a slope length of c. 50 m. This is tentatively attributed to a change from transport-limited to detachment-limited conditions, where rill incision reaches the undisturbed loess at the base of the plough layer. No such decline is visible in the predictions based on empirical relationships derived from erosion plot data. Further evidence is presented that supports the suggestion that these empirical relationships overestimate erosion rates at slope lengths in excess of c. 50 m. It is tentatively suggested that the rates of soil erosion from sloping cultivated fields in the rolling hills area are more likely to lie in the range 8000-10000 t km -2. yr -1. than in the higher range suggested by the empirical relationships. © 1998 John Wiley Sons, Ltd.

Abstract:
Erosion processes and landform evolution on agricultural land - New perspectives from caesium-137 measurements and topographic-based erosion modelling

Despite growing interest in soil erosion on agricultural land, relatively little attention has been paid to the influence of erosion processes on the pattern of contemporary landform evolution. This in part reflects the problems associated with up-scaling the results of short-term process studies to temporal and spatial scales relevant to the study of landform evolution. This paper presents a new approach to examining the influence of erosion processes on landform evolution on agricultural land which employs: caesium-137 (. 137 Cs) measurements to provide medium-term (c.40 years) estimates of rates of landform change; experimental data and a topographic-based model to simulate soil redistribution by tillage; a mass-balance model of. 137 Cs redistribution to separate the water erosion and tillage components of the. 137 Cs 'signatures'; and field observations of water erosion for validation. This approach is used to examine the relative importance of water erosion and tillage processes for contemporary landform evolution at contrasting sites near Leuven, in Belgium, and near Yanan, in Shaanxi Province, China. This application of the approach provides good agreement between the derived water erosion rates and field observations, and hitherto unobtainable insights into medium-term patterns and rates of contemporary landform evolution. At Huldenberg in Belgium, despite rill incision of slope concavities and ephemeral gully incision of the valley floor, contemporary landform evolution is dominated by infilling of slope and valley concavities (rates. > 0·5 mm a. -1 ) and gradual lowering of slope angles as a result of tillage. In contrast, at Ansai (near Yanan) the slope is characterized by increase in slope angle over most of the length, recession of the steepest section at a rate. > 5mm a. -1. and by increasing planform curvature. At this site, contemporary landform evolution is dominated by water erosion. The constraints on the approach are examined, with particular attention being given to limitations on extrapolation of the results and to the sensitivity of the models to. parameter variation. © 1997 by John Wiley. &. Sons, Ltd.

Abstract:
Patterns of rock fragment cover generated by tillage erosion

Intensively cultivated areas in the upper part of the Guadalentin catchment (southeast Spain) show a systematic spatial pattern of surface rock fragment cover (R c ). The objective of this paper is to quantify and to explain this spatial rock fragment cover pattern. Therefore, a map of an intensively cultivated area of 5 km 2 was digitised, and for each pixel total topographic curvature was calculated. Next, rock fragment cover was determined photographically at 35 sites with a range of total slope curvatures. A linear relation between total curvature and rock fragment cover was found, except for narrow concavities. It was hypothesised that this pattern can be explained by a significant net downslope movement of rock fragments and fine earth by tillage. The displacement distances of rock fragments by tillage with a duckfoot chisel were measured by monitoring the displacement of tracers (painted rock fragments and aluminium cubes) on 5 sites having different slopes. The rate of tillage erosion for one tillage. pass with a duckfoot chisel, expressed by the diffusion constant (k), equals 282 kg/m for up and downslope tillage and only 139 kg/m for contour tillage. Nomograms indicate that mean denudation rates in almond groves due to tillage erosion (3 to 5 tillage passes per year) can easily amount to 1.5-2.6 mm/year for contour tillage and up to 3.6-5.9 mm/year for up- and downslope tillage for a field, 50 m long and having a slope of 20%. These figures are at least one order of magnitude larger than reported denudation rates caused by water erosion in similar environments. Hence tillage erosion contributes significantly to land degradation. The downslope soil flux induced by tillage not only causes considerable denudation on topographic convexities (hill tops and spurs) and upper field boundaries but also an important sediment accumulation in topographic concavities (hollows and valley bottoms) and at lower field boundaries. Kinetic sieving (i.e. the upward migration of rock fragments) by the tines of the duckfoot chisel also concentrates the largest rock fragments in the topsoil in such a way that a rock fragment mulch develops in narrow valleys and at the foot of the slopes. These results clearly indicate that tillage erosion is the main process responsible for the observed rock fragment cover pattern in the study area. Since the study area is representative for many parts of southern Spain where almond groves have expanded since 1970, the results have a wider application. They show to what extent intensive tillage of steep slopes has contributed to the increase in soil degradation, to changes in hillslope morphology (i.e. strong denudation of convexities, development of lynchets and rapid infilling of narrow valley bottoms) and to the development of rock fragment cover patterns which control the spatial variability of the hydrological and water erosion response within such landscapes.

Abstract:
Use of reservoir deposits and caesium-137 measurements to investigate the erosional response of a small drainage basin in the rolling loess plateau region of China

This paper reports the results of an investigation of the erosional response of the 3.86 km 2. Zhaojia Gully catchment in the rolling loess plateau region of Zichan County, Shaanxi Province, China. In the absence of direct measurements, information derived from reservoir deposits and from caesium-137 measurements on both the catchment soils and reservoir deposits was used to obtain a retrospective assessment of the longer-term (ca. 30 year) erosional response of the catchment and of the relative contributions of the rolling plateau surface and the gully areas to the sediment output from the basin. Net erosion rates on cultivated land occupying the gentle crest slopes and steeper lower slopes of the rolling plateau and the steep gully slopes were estimated to be 4500 t km -2. year -1 , 8584 t km -2. year -1. and 15 851 t km -2. year -1 , respectively. Estimates of annual sediment yield from the study catchment based on analysis of sediment deposits in the two sediment-trap reservoirs ranged between 4627 and 32 472 t km -2. year -1. Almost all the sediment transported from the catchment was contributed by 2-4 large floods each year. Measurements of the caesium-137 content of recent sediment deposits in a sediment-trap reservoir allowed the relative contributions of the total sediment yield derived from the rolling plateau and gully areas of the catchment to be estimated at 23 and 77 per cent, respectively. Analysis of the sediment deposits dating from 1973-1977 in another sediment trap reservoir allowed individual flood event couplets to be identified and indicated that the sediment associated with the first one or two floods in a season, when the soils of the plateau area were relatively dry, was derived primarily from the gully areas. The cultivated soils of the rolling plateau contributed an increased proportion of the total sediment yield during the latter stages of the flood season when the soils were wetter, and surface runoff and erosion were more widespread. Based on analysis of the caesium-137 content of the sediment deposited in this sediment-trap reservoir, the relative contributions of sediment from the rolling plateau and gully areas over the period 1973-1977 were estimated to be 21 and 79 per cent, respectively. The results obtained demonstrate the potential for using caesium-137 measurements and analysis of reservoir deposits to document the erosional response of a drainage basin. © 1997 by John Wiley. &. Sons, Ltd.

Abstract:
Use of fallout radionuclide measurements in sediment budget investigations

The sediment budget concept has been widely accepted as a valuable tool for documenting and interpreting the contemporary processes of erosion and deposition operating within a drainage basin. However, it is often difficult to assemble the information which is required to establish a reliable sediment budget. Fallout radionuclides offer the geomorphologist considerable potential for this purpose, by affording a means of assembling retrospective information on average medium-term (ie 35-150 years) rates of erosion and deposition within the landscape on the basis of present-day sample collection. Examples of the application of both fallout radionuclides in the investigation of soil redistribution on slopes and floodplain sedimentation rates are presented.

Abstract:
Use of caesium-137 and lead-210 as tracers in soil erosion investigations

There are two important limitations to the general application of the approach. These involve the complications introduced by inputs of Chernobyl-derived radiocaesium in many areas of Europe and the relatively low caesium-137 inventories encountered in some parts of the globe where fallout rates were low. Unsupported lead-210, a natural fallout radionuclide, can offer a viable alternative to caesium-137 as a sediment tracer in many environments. In addition, when used in combination with caesium-137, it offers potential as a complementary tracer, which can provide additional information on the erosional history of a site. The results of a study of soil redistribution within a small cultivated field at Butsford Barton, Colebrooke, Devon, UK are presented. -from Authors

Abstract:
Application of the caesium-137 technique in a study of soil erosion on gully slopes in a yuan area of the Loess Plateau near Xifeng, Gansu Province, China

The patterns shown by caesium-137 inventories were used to interpret the dominant erosion processes operating on cultivated and uncultivated land. These patterns demonstrate the importance of tillage redistribution and water erosion on cultivated terraces and suggest that both wind and water erosion processes operate on grassland areas. Rates of erosion previously derived for the sites on uncultivated land may be a serious underestimate, although the data do confirm the importance of full vegetation cover in controlling erosion. The erosion rates derived for terraced cultivated sites are in line with published estimates. Two terrace types were characterized by widely divergent net erosion rated indicating that narrow-strip terraces cultivated parallel to the contour should be used where possible, because these offer a clear soil conservation benefit. -from Authors

Abstract:
Soil erosion and redistribution on cultivated and uncultivated land near las bardenas in the central Ebro river Basin, Spain

The semiarid regions of Spain, including the central part of the Ebro River basin, are under threat due to desertification. Severe erosion, as a result of poor land management, has led to degradation of the soil resource, and there is a clear need for quantitative erosion rate data to evaluate the problem. This study aimed to examine the potential for using caesium‐137 to identify the patterns and rates of soil erosion and redistribution within this semiarid environment. Samples for the determination of caesium‐137 were collected from uncultivated slopes and cultivated valley floor sites near the head and outlet of a small representative basin in the Las Bardenas area. The measured patterns of caesium‐137 mobilization, redistribution and export provide a semiquantitative indication of the variation in erosion within the study site. Calibration of the caesium‐137 measurements, taking account of the differing behaviour of radiocaesium on cultivated and uncultivated land, allows estimation of the actual rates of erosion and deposition involved. The results show (1) the erosion rates on the cultivated land (1.6–2.5 kg m −2. yr −1 ) are typically more than five times those seen on the uncultivated land (0.2–0.4 kg m −2. yr −1 ), and (2) erosion on the uncultivated land is significantly less severe at the head of the basin than at the outlet. Study of the vegetation cover suggests that lower growing shrubs and grasses may be more effective in reducing erosion in this environment than trees. Copyright © 1994 Verlag Chemie, GmbH

Abstract:
Use of caesium-137 measurements to investigate relationships between erosion rates and topography

The costs associated with both the on-site and off-site impacts of soil loss from agricultural land highlight the imporance of the identification of landscape sensitivity to erosion. Sensitivity of the landscape to erosion at the micro-scale has been addressed in the present study by assessment of topographic controls upon the processes of erosion and deposition. The caesium-137( 137 Cs) technique is particulary suited to this task because of the point-specific nature of the long-term erosion rate estimates obtained and the high degree of spatial resolution that is achievable. In this study the pattern of 137 Cs-derived soil redistribution rates has been compared with the site topography for five arable fields on a range of soil types from southern UK. Topographic attributes (elevation, slope angle, profile curvature, planform curvature, upslope distance and upslope area) for individual sampling points were extracted from a digital terrain model of each site. The results of the regression analysis were used to identify topographically-defined sensitive areas on the soil types studied. -from Authors

Abstract:
Using chernobyl-derived fallout radionuclides to investigate the role of downstream conveyance losses in the suspended sediment budget of the river severn, United Kingdom

The sediment budget concept offers a valuable tool for interpreting the processes of erosion and sediment yield operating in a drainage basin. However, it is often difficult to assemble the information necessary to establish a reliable sediment budget. Fallout radionuclides offer considerable potential for this purpose. This contribution describes how measurements of the fate of Chernobyl-derived 134 Cs have been used to investigate the role of downstream conveyance losses associated with channel and floodplain storage in the suspended sediment budget of the 6850 km 2 basin of the River Severn above Upton on Severn. The results relate to a 3-year period, 1986–1989, and indicate that conveyance losses associated with floodplain and channel storage respectively accounted for 23% and 2% of the total suspended sediment load passing through the main channel system. © 1993 Taylor. &. Francis Group, LLC.

Abstract:
An evaluation of micromorphology as an aid to archaeological interpretation

The detailed description, analysis, and interpretation of field stratigraphy is fundamental to archaeological site interpretation. Investigation of morphology at the macro level can be supplemented by examination under the microscope of soil thin sections prepared from undisturbed samples. Until recently the main emphasis in micromorphological research associated with archaeology has been to assist with paleoenvironmental interpretation. This article reports experience gained from the routine investigation of soil thin sections collected from many archaeological sites throughout Scotland. Greater emphasis is now being given to the investigation of sediment type, anthropogenic features, and nature of disturbance during occupation and post‐depositional processes. Examples from known contexts such as hearths, byres, floors, and anthropogenic soils are given to illustrate the extent to which site formation processes can be elucidated from micromorphological characteristics. It is concluded that the accumulation of data from thin section description of known functional areas will ensure that micromorphology becomes a key research technique in geoarchaeology. Copyright © 1992 Wiley Periodicals, Inc. a Wiley Company

Abstract:
Fluvial transport and redistribution of Chernobyl fallout radionuclides

Fallout of Chernobyl-derived radionuclides over the UK evidenced marked spatial variation. Relatively high levels were recorded in central Wales, but they declined rapidly to the east and southeast. As a result, the headwaters of the River Severn received substantial inputs of fallout, whereas only low levels were recorded over the middle and lower reaches of its drainage basin. This situation afforded a valuable opportunity to investigate the sediment-associated transport of Chernobyl-derived radiocaesium through the 10 000 km 2. drainage basin and its redistribution by fluvial processes. Information on the fallout inputs of radiocaesium has been obtained from the sampling of soil inventories across the basin. Measurements of the radiocaesium content of suspended sediment have been made at several sites on the main river over a period extending from before the Chernobyl disaster through to 1988. Concentrations of caesium-137 in the suspended sediment increased by two orders of magnitude immediately after the accident up to 1450 mBq g. -1 , declined rapidly subsequently, but remained almost an order of magnitude greater than the pre-Chernobyl levels throughout the remainder of the period (1986-1988). Downstream redistribution of radiocaesium has occurred as a result of deposition of sediment-associated radiocaesium in channel and floodplain sinks. It is estimated that 0.6% of the total fallout input of Chernobyl-derived caesium-134 has been transported out of the basin during the period 1986-1990. Estimates of channel and floodplain storage of sediment-associated caesium-134 at the time of sampling in 1988 and 1989 account for 0.01% and 0.2% of the total fallout input to the basin respectively. © 1992 Kluwer Academic Publishers.

Abstract:
Investigating contemporary rates of floodplain sedimentation

Uses Cs-127 to estimate rates of sedimentation of floodplains. There are case studies of a 250m stretch of the River Culm floodplain near Exeter, a small part of the floodplain of the River Severn near Tewkesbury just above the junction with the Mill Avon (otherwise known as the Tewkesbury Ham), and the more rapidly accreting floodplain of the River Leira, 25 km NE of Oslo, Norway. -K.Clayton

Abstract:
Investigation of soil erosion on terraced fields near Yanting, Sichuan Province, China, using caesium-137

Much of the agricultural land in the Central Hills area of the Sichuan Basin is at risk from soil erosion by water. An investigation of rates and patterns of soil erosion on agricultural land near Yanting was undertaken using the caesium-137 technique. Erosion of the upper parts of sloping fields was found to be severe, with rates of the order of 20 to 50tha -1 yr -1. However, infield deposition and sediment retrieval from field ditches has led to low net soil loss from the fields with rates of the order of 1 to 6tha -1 yr -1. These data suggest that traditional soil conservation strategies are providing effective protection of much of the cultivated land, but the high potential for soil erosion must be recognized if any change is made in land use or management. -Authors

Abstract:
Fluvial redistribution of Chernobyl radionuclides

Most direct deposition of 134 Cs and 137 Cs in the Severn basin was in the upper headwaters in Wales so that the appearance of caesium in river sediments downstream records fluvial transport of eroded soil. There was also a flush with high values of caesium immediately after the event, no doubt with some in solution and some in suspension. The data therefore throw light on channel storage, flood plain storage and the catchment sediment budget. -K.Clayton

Abstract:
Rates of soil erosion on arable fields in Britain: quantitative data from caesium‐137 measurements

Abstract. Despite a growing awareness that erosion on arable land in Britain is a potential hazard to long‐term productivity, there is still only limited information on the rates involved, particularly long‐term values. Use of the caesium‐137 ( 137 Cs) technique to study soil erosion within arable fields on various soil types at 13 locations in southern Britain has yielded retrospective measurements of the long‐term (c. 30 years) rates of soil loss and the patterns of soil redistribution within the study fields. The range of long‐term rates of net soil loss extends from 0.61 per hectare per year on clay soils in Bedfordshire to 10.5 t per hectare per year on brown sands in Nottinghamshire. The measured rates are compared with other published data for similar soil types and land use, and the implications for long‐term productivity and potential environmental impacts are considered. Copyright © 1991, Wiley Blackwell. All rights reserved

Abstract:
Recent rates of soil loss from areas of arable cultivation in the UK

Soil erosion problems have traditionally received little attention in the UK. However, recent intensification of farming practices has led to increased erosion risk in many areas of arable cultivation. Faced with a lack of quantitative data on rates of soil loss in such areas over the past few decades, the authors have employed the 137 Cs technique to estimate recent rates of soil loss from arable fields on a variety of soil types. The results obtained from the 13 sites investigated point to gross erosion rates ranging between 2.2 and 12.2 t ha -1 year -1 and net erosion rates in the range 0.6-10.5 t ha -1 year -1. It is estimated that rates of soil loss during the past 30-35 years in areas with significant erosion risk may have increased by an order of magnitude or more. -from Authors

Abstract:
Recent rates of soil loss from areas of arable cultivation in the UK

Soil erosion problems have traditionally received little attention in the UK. However, recent intensification of farming practices has led to increased erosion risk in many areas of arable cultivation. Faced with a lack of quantitative data on rates of soil loss in such areas over the past few decades, the "SUP 137" Cesium technique has been applied to estimate recent rates of soil loss from arable fields on a variety of soil types. The results obtained from the 13 sites investigated point to gross erosion rates ranging between 2.2 and 12.2t ha "SUP -1" yr "SUP -1" and net erosion rates in the range 0.6-10.5t ha "SUP -1" yr "SUP -1". It is estimated that rates of soil loss during the past 30-35yr in areas with significant erosion risk may have increased by an order of magnitude or more. Such increases have important implications for long-term crop productivity and increased sediment yields downstream. It is suggested that suspended sediment yields are likely to have doubled in many areas experiencing increased rates of soil loss. (A)

Abstract:
Recent rates of soil loss from areas of arable cultivation in the UK

Soil erosion problems have traditionally received little attention in the UK. However, recent intensification of farming practices has led to increased erosion risk in many areas of arable cultivation. Faced with a lack of quantitative data on rates of soil loss in such areas over the past few decades, the "SUP 137" Cesium technique has been applied to estimate recent rates of soil loss from arable fields on a variety of soil types. The results obtained from the 13 sites investigated point to gross erosion rates ranging between 2.2 and 12.2t ha "SUP -1" yr "SUP -1" and net erosion rates in the range 0.6-10.5t ha "SUP -1" yr "SUP -1". It is estimated that rates of soil loss during the past 30-35yr in areas with significant erosion risk may have increased by an order of magnitude or more. Such increases have important implications for long-term crop productivity and increased sediment yields downstream. It is suggested that suspended sediment yields are likely to have doubled in many areas experiencing increased rates of soil loss. (A)

Abstract:
Use of ¹³⁷Cs measurements to investigate soil erosion on arable fields in the UK: potential applications and limitations

Recent awareness of the potential hazard of soil erosion on arable land in the UK has highlighted the lack of reliable data concerning actual rates of soil loss. This lack of information reflects both a low level of interest, and the lack of a simple and generally applicable method of documenting long‐term rates of soil loss. Existing methods involving the use of hazard classification procedures and direct measurement techniques, including erosion plots and field surveys, all possess significant limitations. The use of. 137 Cs measurements to provide information on rates of soil loss and deposition averaged over the past 30 years would appear to offer considerable potential. The results of applying this approach to three arable fields on contrasting soil types in Britain are reported. These results confirm the viability of the technique and its potential for providing information on patterns and rates of erosion and deposition within individual fields and their overall sediment budgets. Limitations include the restricted size of the areas that can be investigated and the need to take account of additional inputs of. 137 Cs derived from the Chernobyl accident. Copyright © 1991, Wiley Blackwell. All rights reserved