T. A. Quine

Patterns of rock fragment cover generated by tillage erosion

Abstract Intensively cultivated areas in the upper part of the Guadalentin catchment (southeast Spain) show a systematic spatial pattern of surface rock fragment cover (Rc). 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 km2 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 rare 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.

Landscape-scale modeling of carbon cycling under the impact of soil redistribution: The role of tillage erosion

Despite its global significance, soil-atmosphere carbon (C) exchange under the impact of soil redistribution remains an unquantified component of the global C budget. Here we use radionuclide and soil organic carbon (SOC) data for two agricultural fields in Europe to undertake a spatial analysis of sediment and SOC fate during erosion and deposition in agricultural uplands. C fluxes induced by soil redistribution are quantified by incorporating C dynamics in a spatially distributed model including both water- and tillage-induced soil redistribution (SPEROS-C). The SOC patterns predicted by SPEROS- C are in good agreement with field observations and show that in upland areas, tillage erosion and deposition exerts a large influence on SOC redistribution and soil profile evolution at a timescale of a few decades. The formation of new SOC at eroding sites and the burial of eroded SOC below plough depth provide an important mechanism for C sequestration on sloping arable land in the order of 3–10 g C m 2 yr 1 . Any attempt to manage agricultural land to maximize sequestration must fully account for erosion, burial and fate of eroded and buried SOC across the landscape and must also account for the correlation between tillage and erosion.

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

Tillage erosion has been identifed 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 tillage transport coeffcient, are very consistent and range in the order of 400–800 kg m-1yr-1 and 70–260 kg m-1yr-1 for mechanized and nonmechanized 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.

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

The leaching characteristics of air pollution control (APC) residues collected in Shanghai, China, were compared by performing three compliance leaching tests. These were the standard Chinese method for determining the leaching toxicity of solid waste (GB 5086.1-1997), the USEPAs Toxicity Characteristic Leaching Procedure (TCLP), and the new European shake test (EN 12457-3). In particular, behaviors of raw samples and samples that had been subjected to natural aging were compared. Both the leaching tests and natural aging substantially affected the leaching results concerning the APC residue samples. Most importantly, EN and GB tests classified the raw APC residues as hazardous, but the residues passed the TCLP test as nonhazardous. After it had been naturally aged for 720 h, however, the aged sample was classified as hazardous by the TCLP and EN tests, but as nonhazardous by the GB test. Metals that are thought to have been immobilized by carbonation were released at pH 6.3. Model calculations based on the geochemical thermodynamic equilibrium model MINTEQA2 revealed that the formation of metal carbonates did not correspond to the noted change in the leaching behaviors in the three leaching tests. Rather, the partial neutralization of alkaline ash by dissolved CO2 changing the final pH of the leachate dominated the leaching characteristics. The leaching results showed a change in leachate pH.

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 70 cm) was found on lower concavities where displaced soil was deposited. The spatial pattern of 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 ˇ2 , 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. All rights reserved.

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 (Cs-137) measurements would appear to offer a rapid means of assembling data relevant to the evaluation of tillage erosion and tillage translocation. However, use of Cs-137 data in this way requires an approach to the analysis of Cs-137 data which accounts for both tillage erosion and tillage translocation. The latter is particularly significant on short slopes, A method of analysing Cs-137 data has been developed, that employs a linear, multistore, mass-balance model of soil and Cs-137 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

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

1. 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. 2. 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. 3. 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. 4. 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. 5. 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.

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. Copyright

Modeling alluvial landform change in the absence of external environmental forcing

Alluvial fan evolution and morphology are often considered to respond primarily to external forcing (e.g., tectonics, climate, and base-level change). Here we present a numerical model of alluvial fan evolution that shows that dramatic and persistent fan entrenchment may occur in the absence of such forcing. This process is driven by positive autogenic feedbacks between flow width, sediment transport, and rate of fan aggradation. Entrenchment is initiated where sediment accommodation space limits continued fan growth. Our results highlight a need to rethink both the representation of fluvial width adjustment in landscape evolution models and the established framework for the interpretation of fluvial landforms as archives of environmental change.

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 15851 t km(-2) year(-1) respectively. Estimates of annual sediment yield from the study catchment based on analysis of sediment deposits year in the two sediment-trap reservoirs ranged between 4627 and 32472 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