The Contrasted Impact of Land Abandonment on Soil Erosion in Mediterranean Agriculture Fields

Abandonment of agricultural land results in on- and off-site consequences on soil system and there is a need to evaluate the impact on soil erosion to understand the ecosystem's changes. The aim of this research is to assess the impact of abandonment in four Mediterranean crops (vineyards, almonds, citrus and olives) on soil and water losses. To achieve this goal, 105 rainfall simulation experiments were conducted in agriculture fields (vineyards in Málaga, almonds in Murcia, and citrus and olive in Valencia) and on the paired abandoned plots. After abandonment, soil detachment decreased drastically in the olive and citrus orchards, meanwhile vineyards did not show any difference and almonds registered higher erosion rates after the abandonment. Terraced orchards of citrus and olives recovered a dense vegetation cover after the abandonment, meanwhile the sloping terrain of almonds and vineyards enhanced the development of crusts and rills and a negligible plant cover that resulted in high erosion rates. The contrasted response of the abandonment is discussed

Soil erosion in Mediterranean landscapes : Experimental investigation on crusted surfaces by means of the Portable Wind and Rainfall Simulator

The influence of wind on raindrops and subsequent processes of soil detachment and transport on natural soil surfaces is an essential gap of knowledge. The urgently required data about reactions, interactions and actual impact on soil erosion rates are generally produced under laboratory conditions on highly disturbed substrates, which cannot reflect natural system responses. The Portable Wind and Rainfall Simulator was applied on autochthonous soils in semi-arid Spain to investigate and quantify the relative impact of wind-driven rain on total erosion. On highly degraded crusted soils and freshly ploughed orchard soils in semi-arid Spain, total erosion measured during experiments (30 min; 96 mm h-1) were 28.8 - 150.4 g m-2 and 29.5 - 30.7 g m-2, respectively. Concerning the relative impact of wind-driven rain on total erosion, ambiguous results were obtained: the difference to erosion generated by windless rain ranged from +37.4 to -24.2%, to sediment concentration from +46.7 to -20.6% and to runoff coefficients from +18.8 to -7.4%.The study indicates a potentially very strong impact of wind-driven rain and underlines the paramount importance of experimental data derived on autochthonous soil surfaces for process understanding, realistic assessment of soil erosion rates and application in soil erosion models

A small portable rainfall simulator for reproducible experiments on soil erosion

The importance of distinguishing and discretely studying the subprocesses of runoff generation and erosion has led to the development of rainfall simulations on small plots. We methodically upgraded a small portable rainfall simulator with particular respect to (1) rainfall characteristics that include homogeneous spatial rainfall distribution and drop spectrum, (2) handling, and (3) control of test conditions. We measured simulator characteristics with rain gauges, calibration plate and Laser Precipitation Monitor by Thies (LPM). The upgraded small rainfall simulator, and measurements of the improved rainfall characteristics are presented in this paper.The upgraded configuration shows the desired improvements: regarding drop size distribution, a close relationship to natural rainfall (Marshall & Palmer Distribution) can be observed. Due to low fall heights, measured drop fall velocities are slow; maximum velocities range between 3.4 and 5 m s1. Mean kinetic energy expenditure, mean kinetic energy per unit area and unit depth of rainfall and mean momentum are 214 J m2 h1, 5.8 J m2 mm1 and 0.016 kg m s1, respectively. The spatial rainfall distribution of the upgraded simulator is homogenous with a Christiansen-Uniformity Coefficient of 91%. The measured variables show extremely low variation throughout all tests and should therefore be reproducible in field investigations at any time

The role of wind-driven rain for soil erosion – an experimental approach

Recent research has shown that wind can have a significant influence on velocity, impact angle and kinetic energy of raindrops, and subsequently increases soil erosion. The aims of this study were to 1) quantify the influence of wind on water erosion, 2) specifically observe the difference in processes between windless rain (WLR) and wind-driven rain (WDR) simulations and 3) test the device's and test sequence's practicability. The Portable Wind and Rainfall Simulator (PWRS), recently developed at Trier University for plot-scale in situ assessment of differences in soil erosion with and without the influence of wind on raindrops, was used. To facilitate extraction of the influences of WDR on soil erosion, to avoid systematic errors, and to reduce variability between test plots, a defined order of four consecutive test runs was established: 0) wind simulation, 1) WLR simulation on dry soil, 2) WLR simulation on moist soil, 3) WDR simulation. The tests were conducted on homogenous sandy substrate deposited on an area of 15.2 m x 60 m with uniform and smooth surface and low inclination (1 degrees) in the Willem Genet Tunnel of Wageningen University. The results show an increase of eroded sediment ranging from 113% up to 1108% for WDR simulations in comparison to WLR simulations. The increase in runoff was considerably lower (15% to 71%), resulting in an increase of sediment concentration between 56% and 894%. The results indicate an immense impact of WDR on soil erosion of sandy cohesionless substrate. The experimental setting and measurement proved reliable and reproducible and enables a clear process observation and quantification in the field

Comparative measurements with seven rainfall simulators on uniform bare fallow land

To assess the inflfl uence of rainfall simulator type and plot dimensions on runoff and erosion, seven small portable rainfall simulators from Freiberg, Tübingen, Trier (all Germany), Valencia, Zaragoza (both Spain), Basel (Switzerland) and Wageningen (the Netherlands) were compared on a prepared bare fallow fifi eld. The experiments were carried out during an international rainfall simulator workshop, organized at Trier University (Germany) from 30th of June to 1st of July 2011.The tested rainfall simulators differ in design, rainfall intensities, rain spectra, etc. and represent most of the devices which have been used over the last decade in Europe. The plots for the different rainfall simulators were selected as similar as possible concerning soil physical and chemical properties, aspect and inclination and were chosen to be placed side by side in horizontal direction. Test procedure was standardized in order to examine the inflfl uence of the rainfall simulator andplot dimension only. The results show a clear and consistent relationship in runoff, erosion and infifi ltration behaviour of the different used rainfall simulators. With all the devices total soil loss is measurable, but different plot sizes, intensities and kinetic energies of the simulated rainfall caused differences in soil loss and runoff quantities per unit of area. Regarding course characteristics over runs, similarities could be observed especially in runoff behaviour. The rainfall simulators (> 1 m² plot size) are able to reproduce infifi ltration and interrillerosion processes. With an increase of plot size (≥ 1 m²), rill-erosion will be also reflfl ected. Therefore it can be concluded that up to a certain plot size, the results of the different simulators are comparable and depend in their magnitude on the properties of the applied rainfall. The increase in process complexity with increasing plot size shows, that the scale of the simulation is one of the most important parameters to be taken intoaccount when comparing values of erosion and runoff

Quantitative comparison of initial soil erosion processes and runoff generation in Spanish and German vineyards

The aim of this study was to enable a quantitative comparison of initial soil erosion processes in European vineyards using the same methodology and equipment. The study was conducted in four viticultural areas with different characteristics (Valencia and M\ue1laga in Spain, Ruwer-Mosel valley and Saar-Mosel valley in Germany). Old and young vineyards, with conventional and ecological planting and management systems were compared. The same portable rainfall simulator with identical rainfall intensity (40mmh(-1)) and sampling intervals (30min of test duration, collecting the samples at 5-min-intervals) was used over a circular test plot with 0.28m(2). The results of 83 simulations have been analysed and correlation coefficients were calculated for each study area to identify the relationship between environmental plot characteristics, soil texture, soil erosion, runoff and infiltration. The results allow for identification of the main factors related to soil properties, topography and management, which control soil erosion processes in vineyards. The most important factors influencing soil erosion and runoff were the vegetation cover for the ecological German vineyards (with 97.6\ub18% infiltration coefficients) and stone cover, soil moisture and slope steepness for the conventional land uses

Qualitative comparison of soil erosion, runoff and infiltration coefficients using small portable rainfall simulators in Germany, Spain and France

EGU.European Geosciences Union General Assembly, Vienne, AUT, 17-/04/2016 - 22/04/201