Kristof Van Oost

Evaluating the effects of changes in landscape structure on soil erosion by water and tillage

Landscape structure, or the spatial organization of different land units, has an impact on erosion and sedimentation on agricultural land. However, current erosion models emphasize the temporal, and less the spatial, variability of relevant parameters so that the effects of changes in landscape structure have hitherto not been studied in detail. Therefore, a spatially distributed water and tillage erosion model that allows the incorporation of landscape structure is presented. The model is applied to three study sites in the Belgian Loam Belt where significant changes in landscape structure occurred over the last fifty years. Erosion rates were shown to change by up to 28% however, with decreases as well as increases occurring. These could be explained by the interaction of changes in land use with changes in the position of field boundaries. Thus, landscape structure is an important control when the effect of environmental change on erosion risk is to be assessed.

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.

Legacy of human-induced C erosion and burial on soil–atmosphere C exchange

Carbon exchange associated with accelerated erosion following land cover change is an important component of the global C cycle. In current assessments, however, this component is not accounted for. Here, we integrate the effects of accelerated C erosion across point, hillslope, and catchment scale for the 780-km2 Dijle River catchment over the period 4000 B.C. to A.D. 2000 to demonstrate that accelerated erosion results in a net C sink. We found this long-term C sink to be equivalent to 43% of the eroded C and to have offset 39% (17–66%) of the C emissions due to anthropogenic land cover change since the advent of agriculture. Nevertheless, the erosion-induced C sink strength is limited by a significant loss of buried C in terrestrial depositional stores, which lagged the burial. The time lag between burial and subsequent loss at this study site implies that the C buried in eroded terrestrial deposits during the agricultural expansion of the last 150 y cannot be assumed to be inert to further destabilization, and indeed might become a significant C source. Our analysis exemplifies that accounting for the non–steady-state C dynamics in geomorphic active systems is pertinent to understanding both past and future anthropogenic global change.

Integrating science, policy and farmers to reduce soil loss and sediment delivery in Flanders, Belgium

Abstract This paper describes the evolution of soil erosion perception with policy makers and farmers in Flanders, and how these changes have resulted in the emergence of a soil conservation policy. Until the mid 1990s, soil erosion and its related problems received little attention in the environmental debate. This has changed through increased interest in environmental issues in general, as well as an increasing number of scientific reports on soil erosion and sediment delivery. New legislation that made the sediment problem a big financial issue in 1995, however, was the main reason for the recognition of soil erosion as an environmental problem with the policy makers. Despite the lack of monitoring soil erosion, a soil conservation policy emerged recently, which is clearly represented in the 2001 “soil erosion decree” by the Flemish government. This policy provides important opportunities for soil conservation as it incorporates both scientists and farmers. The involvement of farmers in demonstration projects is crucial with this respect as they have to be convinced about the usefulness and applicability of soil conservation measures. Farmers also participate in the development of a management plan. However, the success of the new policy could be undermined by its rapid development. There is still a lack of data underpinning the status of the erosion problem, and, the goals of the policy are not clearly defined. Furthermore, the administrative organisation is currently not favourable for an optimal co-operation with the farmers.

An assessment of the global impact of 21st century land use change on soil erosion

Human activity and related land use change are the primary cause of accelerated soil erosion, which has substantial implications for nutrient and carbon cycling, land productivity and in turn, worldwide socio-economic conditions. Here we present an unprecedentedly high resolution (250 × 250 m) global potential soil erosion model, using a combination of remote sensing, GIS modelling and census data. We challenge the previous annual soil erosion reference values as our estimate, of 35.9 Pg yr−1 of soil eroded in 2012, is at least two times lower. Moreover, we estimate the spatial and temporal effects of land use change between 2001 and 2012 and the potential offset of the global application of conservation practices. Our findings indicate a potential overall increase in global soil erosion driven by cropland expansion. The greatest increases are predicted to occur in Sub-Saharan Africa, South America and Southeast Asia. The least developed economies have been found to experience the highest estimates of soil erosion rates.Human activity and related land use change are the primary cause of soil erosion. Here, the authors show the impacts of 21st century global land use change on soil erosion based on an unprecedentedly high resolution global model that provides insights into the mitigating effects of conservation agriculture.

Global rainfall erosivity assessment based on high-temporal resolution rainfall records

The exposure of the Earth’s surface to the energetic input of rainfall is one of the key factors controlling water erosion. While water erosion is identified as the most serious cause of soil degradation globally, global patterns of rainfall erosivity remain poorly quantified and estimates have large uncertainties. This hampers the implementation of effective soil degradation mitigation and restoration strategies. Quantifying rainfall erosivity is challenging as it requires high temporal resolution(<30 min) and high fidelity rainfall recordings. We present the results of an extensive global data collection effort whereby we estimated rainfall erosivity for 3,625 stations covering 63 countries. This first ever Global Rainfall Erosivity Database was used to develop a global erosivity map at 30 arc-seconds(~1 km) based on a Gaussian Process Regression(GPR). Globally, the mean rainfall erosivity was estimated to be 2,190 MJ mm ha−1 h−1 yr−1, with the highest values in South America and the Caribbean countries, Central east Africa and South east Asia. The lowest values are mainly found in Canada, the Russian Federation, Northern Europe, Northern Africa and the Middle East. The tropical climate zone has the highest mean rainfall erosivity followed by the temperate whereas the lowest mean was estimated in the cold climate zone.

Soil organic carbon mobilization by interrill erosion: Insights from size fractions

Sediments mobilized by interrill erosion are often highly enriched in soil organic carbon (SOC) in comparison to source soils. This selectivity may lead to the preferential mobilization of SOC with specific properties, e.g., SOC that is especially susceptible to decomposition. This may then have important implications with respect to the role of soil erosion in the global carbon cycle. We addressed this issue by investigating the behavior of different SOC components in field rainfall simulation experiments on arable fields in loess-derived soils. We characterized the mobilization of mineral-bound organic carbon (MOC) and particulate organic carbon (POC) by interrill erosion using size fractionation and we used the C:N ratio as a tracer variable to determine the composition of the SOC in eroded sediments. MOC was found to be preferentially mobilized by interrill erosion in comparison to POC. The enrichment ratio (i.e., the ratio of the concentration of a soil constituent in the eroded sediment to its concentration in the original soil) of MOC decreased with increasing sediment concentration. The enrichment ratio of POC displayed a similar pattern to that of MOC but enrichment was less pronounced. Furthermore, sediments were found to be enriched in fine POC while they were impoverished with respect to coarse POC. The selective MOC mobilization together with the dominance of MOC in the total SOC pool in the soil explained the dominance of MOC in interrill eroded sediment. The fact that it is mainly MOC that is mobilized by interrill erosion implies that the SOC in the interrill eroded sediments is on average at least as recalcitrant than that in the source soils which may have important implications for the fate of the mobilized SOC. In order to understand the role of soil erosion in C cycling, MOC and POC need to be considered separately not only because they are chemically different but also because of their different behaviors with respect to geomorphic processes.

Lateral transport of soil carbon and land−atmosphere CO2 flux induced by water erosion in China

Significance The role of soil erosion as a net sink or source of atmospheric CO2 remains highly debated. This work quantifies national-scale land−atmosphere CO2 fluxes induced by soil erosion. Severe water erosion in China has caused displacement of 180 ± 80 Mt C⋅y-1 of soil organic carbon during the last two decades, and the consequent land−atmosphere CO2 flux from water erosion is a net CO2 sink of 45 ± 25 Mt C⋅y-1, equivalent to 8–37% of the terrestrial carbon sink previously assessed in China. This closes an important gap concerning large-scale estimation of lateral and vertical CO2 fluxes from water erosion and highlights the importance of reducing uncertainty in assessing terrestrial carbon balance. Soil erosion by water impacts soil organic carbon stocks and alters CO2 fluxes exchanged with the atmosphere. The role of erosion as a net sink or source of atmospheric CO2 remains highly debated, and little information is available at scales larger than small catchments or regions. This study attempts to quantify the lateral transport of soil carbon and consequent land−atmosphere CO2 fluxes at the scale of China, where severe erosion has occurred for several decades. Based on the distribution of soil erosion rates derived from detailed national surveys and soil carbon inventories, here we show that water erosion in China displaced 180 ± 80 Mt C⋅y−1 of soil organic carbon during the last two decades, and this resulted a net land sink for atmospheric CO2 of 45 ± 25 Mt C⋅y−1, equivalent to 8–37% of the terrestrial carbon sink previously assessed in China. Interestingly, the “hotspots,” largely distributed in mountainous regions in the most intensive sink areas (>40 g C⋅m−2⋅y−1), occupy only 1.5% of the total area suffering water erosion, but contribute 19.3% to the national erosion-induced CO2 sink. The erosion-induced CO2 sink underwent a remarkable reduction of about 16% from the middle 1990s to the early 2010s, due to diminishing erosion after the implementation of large-scale soil conservation programs. These findings demonstrate the necessity of including erosion-induced CO2 in the terrestrial budget, hence reducing the level of uncertainty.