In the last decades, soils and their agricultural management have received great scientific and p... more In the last decades, soils and their agricultural management have received great scientific and political attention due to their potential to act as a sink of atmospheric carbon dioxide (CO 2). Agricultural management has strong potential to accelerate soil redistribution, and, therefore, it is questioned if soil redistribution processes affect this potential CO 2 sink function. Most studies analysing the effect of soil redistribution upon soil organic carbon (SOC) dynamics focus on water erosion and analyse only relatively small catchments and relatively short time spans of several years to decades. The aim of this study is to widen this perspective by including tillage erosion as another important driver of soil redistribution and by performing a model-based analysis in a 200 km 2 sized arable region of northeastern Germany for the period since the conversion from forest to arable land (approx. 1000 years ago). The spatially explicit soil redistribution and carbon (C) turnover model SPEROS-C was applied to simulate lateral soil and SOC redistribution and SOC turnover. The model parameterisation uncertainty was estimated by simulating different realisations of the development of agricultural management over the past millennium. The results indicate that, in young moraine areas, which are relatively dry but have been intensively used for agriculture for centuries, SOC patterns and dynamics are substantially affected by tillage-induced soil redistribution processes. To understand the landscape-scale effect of these redistribution processes on SOC dynamics, it is essential to account for long-term changes following land conversion as typical soil-erosioninduced processes, e.g. dynamic replacement, only take place after former forest soils reach a new equilibrium following conversion. Overall, it was estimated that, after 1000 years of arable land use, SOC redistribution by tillage and water results in a current-day landscape-scale C sink of up to 0.66 ‰ yr −1 of the current SOC stocks. The C input into the soil is modelled by assuming an exponential root density profile (Gerwitz and Page, 1974; Van Oost et al., 2005), while manure input is only assigned to the plough layer (or layers). The allocation of total root dry matter to each soil layer z (m) was calculated according to a reference soil depth z r = 0.25 m (Van Oost et al., 2005) and a constant c that determines the proportion of the roots per soil layer (p z ; Eq. 9).
Modellbasierte Forschung zu Mikroplastik in der Umwelt : Synthesepapier ; Im Rahmen des Forschungsschwerpunktes Plastik in der Umwelt, Quellen - Senken - Lösungsansätze
Soil carbon stocks in stable tropical landforms are dominated by geochemical controls and not by land use
Global Change Biology, Feb 27, 2023
Soil organic carbon (SOC) dynamics depend on soil properties derived from the geoclimatic conditi... more Soil organic carbon (SOC) dynamics depend on soil properties derived from the geoclimatic conditions under which soils develop and are in many cases modified by land conversion. However, SOC stabilization and the responses of SOC to land use change are not well constrained in deeply weathered tropical soils, which are dominated by less reactive minerals than those in temperate regions. Along a gradient of geochemically distinct soil parent materials, we investigated differences in SOC stocks and SOC (Δ14C) turnover time across soil profile depth between montane tropical forest and cropland situated on flat, non‐erosive plateau landforms. We show that SOC stocks and soil Δ14C patterns do not differ significantly with land use, but that differences in SOC can be explained by the physicochemical properties of soils. More specifically, labile organo‐mineral associations in combination with exchangeable base cations were identified as the dominating controls over soil C stocks and turnover. We argue that due to their long weathering history, the investigated tropical soils do not provide enough reactive minerals for the stabilization of C input in either high input (tropical forest) or low‐input (cropland) systems. Since these soils exceeded their maximum potential for the mineral related stabilization of SOC, potential positive effects of reforestation on tropical SOC storage are most likely limited to minor differences in topsoil without major impacts on subsoil C stocks. Hence, in deeply weathered soils, increasing C inputs may lead to the accumulation of a larger readily available SOC pool, but does not contribute to long‐term SOC stabilization.
Supplemented information on valley positions The following text represents the supplementary resu... more Supplemented information on valley positions The following text represents the supplementary results and short discussion on geochemical soil parameters, SOC stocks and stabilization assessed at valley positions of contrasting parent material geochemistry investigated in tropical rain mountain forest in the border region of the Congo and Nile basement. We show that, in valley positions, significant variation in the size of SOC stocks are related to changes in hydrological conditions and alluvial processes compared to non-valley positions. Geochemical differences in SOC stabilization mechanisms between regions remain in place, but are less prominent in valleys than at non-valley positions. SI 1 Supplementary results on valley positions 1.1 Pedogenic oxides For valley positions, pyrophosphate extractable oxide mass (0.02 to 0.66 mass%) and oxalate extractable oxide mass (0.03 to 4.29 mass%) were low compared to DCB extractable oxide mass (0.11 to 10.79 mass%) (Fig. S1). In general, valley positions showed a comparable picture compared to non-valley positions (Fig. 3, S1) with the exception that valley soils in the mixed sedimentary region had considerably lower amounts of pedogenic oxides at all soil depths (< 0.27 mass%) compared to valley soils in the mafic and felsic region.
From intentionally used plastic films to soil microplastic contamination
&lt;p&gt;In modern agriculture, plastic material is intentionally used for different purp... more &lt;p&gt;In modern agriculture, plastic material is intentionally used for different purposes. In 2020, it was estimated that about 7.1 10&lt;sup&gt;5&lt;/sup&gt; t of plastic was used in European agriculture, whereas most plastic was applied in form of plastic mulch films to improve growing conditions, e.g., via temperature regulation or reduction of evaporation. Most of this plastic films are made from Light Density Polyethene (LDPE) with different physical (e.g., thickness between 15 and 200 &amp;#181;m) and chemical properties (e.g., different types and amounts of additives for UV stabilization). Plasticulture improves productivity but a growing number of studies indicate soil contamination with macro-, meso- and microplastic particles originating from plastic mulching films. The aim of this study is to compare the changes in plastic film properties and stability as basis for the fragmentation into meso- to microplastic following different environmental stressors applied to plastic films used for different purposes. A series of lab experiments was set-up to mimic natural UV radiation as well as mechanical stress. Overall, six different agricultural films were tested (two black LDPE mulch films, thickness 20 &amp;#181;m; two transparent LDPE films of small tunnels, thickness 180 &amp;#181;m; and two black-white LDPE asparagus mulch films, thickness 100 and 150 &amp;#181;m). In a first step, different UV light exposures time were used (Q-SUN Xe-1-SE xenon test chamber, TUV (300-400 nm)) to simulate LDPE aging as exposed to sunlight at the soil surface, in second step mechanical stress was applied during an abrasion test (20 g of standard soil were mixed with the degraded samples at 4 rpm for 61 days). Both treatments and their combinations were then analyzed regarding changes in plastic properties. Therefore, we used a 3d laser scanner confocal microscope (LSM) to analyze changes in plastic surfaces, a Fourier-transform infrared-attenuated total reflectance spectrometer (FTIR-ATR) to determine changes in the chemical compounds, an optical contact angle (OCA) to determine changes in hydrophobicity and finally tested changes in mechanical stability with a universal nanomechanical tester (UNAT). First results indicate that UV alone can affect the stability of the films, which is increased by mechanical stress. The FTIR-ATR spectra, especially from the thin black film, presented variation at the carbonyl band (1800-1600 cm&lt;sup&gt;-1&lt;/sup&gt;) after the degradation test; LSM results for the degradation test didn&amp;#8217;t show any significant change, while preliminary results from the mechanical stress present changes on its surface; for OCA preliminary results the thin black film showed a variation from 85.7&lt;sup&gt;o&lt;/sup&gt; to 77.2&lt;sup&gt;o&lt;/sup&gt; after UV degradation. Overall, the tests indicate the importance of a combination of UV radiation and mechanical stress for LDPE film degradation, which especially in case of the thin, black mulch film leads to a change in plastic properties paving the way for plastic fragmentation within months of environmental exposure, while the thicker foils are less affected within such timeframe. Hence, thin plastic mulching foils might improve agricultural productivity but on the cost of increasing soil plastic contamination.&lt;/p&gt;
Due to the rapidly growing population in tropical Africa, a substantial rise in food demand is pr... more Due to the rapidly growing population in tropical Africa, a substantial rise in food demand is predicted in upcoming decades, which will result in higher pressure on soil resources. However, there is limited knowledge on soil redistribution dynamics following land conversion into arable land in tropical Africa that is partly caused by infrastructure limitations for long-term landscape-scale monitoring. In this study, fallout radionuclides 239+240 Pu are used to assess soil redistribution along topographic gradients at two cropland sites and at three nearby pristine forest sites located in the DR Congo, Uganda and Rwanda. In the study area, a 239+240 Pu baseline inventory is found that is higher than typically expected for tropical regions (mean forest inventory 41 Bq m −2). Pristine forests show no indication of soil redistribution based on 239+240 Pu along topographical gradients. In contrast, soil erosion and sedimentation on cropland reached up to 37 cm (81 Mg ha −1 yr −1) and 40 cm (87 Mg ha −1 yr −1) within the last 55 years, respectively. Cropland sites show high intra-slope variability with locations showing severe soil erosion located in direct proximity to sedimentation sites. This study shows the applicability of a valuable method to assess tropical soil redistribution and provides insight into soil degradation rates and patterns in one of the most socioeconomically and ecologically vulnerable regions of the world.
Connectivity has been embraced by the geosciences community as a useful concept to understand and... more Connectivity has been embraced by the geosciences community as a useful concept to understand and describe hydrological functioning and sediment movement through catchments. Mathematical modelling has been used for decades to quantify and predict erosion and transport of sediments, e.g. in scenarios of land use change or conservation measures. Being intrigued by both models and the connectivity concept, as a group of modellers we aimed at investigating what different models could tell us about connectivity. Therefore, we evaluated the response of contrasted spatially-distributed models to landscape connectivity features and explained the differences based on different model structures. A total of 53 scenarios were built with varying field sizes and orientations, as well as the implementation of soil conservation measures. These scenarios were simulated, for two rainfall intensities, with five event-and process-based water and soil erosion models-EROSION3D, FullSWOF_2D, LandSoil, OpenLISEM and Watersed. Results showed that rainfall amount plays the most important role in determining relative export and connected area of runoff and sediment in all models, indicating that functional aspects of connectivity were more important than structural connectivity. As for the role of structural landscape elements, there was no overall agreement between models regarding the effects of field sizes, crop allocation pattern, and conservation practices; agreement was also low on the spatial patterns of connectivity. This overall disagreement between models was unexpected. The results of this exercise suggest that the correct parameterization of runoff and sediment production and of routing patterns may be an important issue. Thus, incorporating connectivity functions based on routing would help modelling forward. Our results also suggest that structural connectivity indices may not suffice to represent connectivity in this type of catchment (relatively simple and monotonous land cover), and functional connectivity indices should be applied.
Soil erosion dynamics in the White Nile-Congo ridge region &#8211; two years of high frequency UAV monitoring
&lt;p&gt;Tropical Africa is globally one of the most sensitive regions for soil erosion a... more &lt;p&gt;Tropical Africa is globally one of the most sensitive regions for soil erosion and is characterised by an important yield gap. Rapid population growth is expected to triple food demands in Sub-Saharan Africa by 2050. These rising food demands need to be met by cropland that is highly prone to soil erosion. In particular, the White Nile-Congo ridge region between the DR Congo and Uganda is a hotspot for issues relating to food security linked to massive soil degradation due to steep terrain, highly erosive rainfall and low soil cover conditions. Despite its importance, most soil erosion studies in the region are based on plot or large-scale modelling studies. Both approaches lack information on inter-field connectivity processes, which are especially important in smallholder farming structures with an average field size of 0.1 ha. To address this, a UAV-based monitoring campaign was carried out over different cropland sites (two sites in the DR Congo and two in Uganda) at high spatial and temporal resolution. The campaign covered more than 500 individual fields which were monitored twice per month (for two years) using UAV-based aerial photography to get insights into event-based rill erosion processes and the role of landscape connectivity. The aerial photography data was classified according to its field condition: (i) vegetation covered, (ii) bare soil without signs of rill erosion, (iii) field with rill erosion. The results highlight the role of land cover patchiness due to smallholder farming structures on inter-field connectivity with rill erosion often discontinuing downslope across field boundaries. Therefore, rill development is highly localised and affects individual fields. We further conclude that rill erosion in the White Nile-Congo ridge region is not an episodic process but takes place regularly during the rainy season as a result of high frequency erosive rainfall (on average 20 erosive rainfall events per rain season) falling on bare soil in fields that are left fallow for individual cultivation periods. Rill erosion dynamics in the study area are complex and controlled by processes that are challenging to be represented in large scale predictions on soil degradation.&lt;/p&gt;
Suspended sediment is an integral part of riverine transport and functioning that has been strong... more Suspended sediment is an integral part of riverine transport and functioning that has been strongly altered during the Anthropocene due to the overwhelming human pressure on soils, sediments and the water cycle. Understanding the controls of changing suspended sediment in rivers is therefore vital for effective management strategies. Here we present results from a trend analysis of suspended sediments covering 62 monitoring stations along the German waterways with more than 440 000 water samples taken between 1990 and 2010. Based on daily monitoring of suspended sediment concentration (SSC), we found significant declines of mean annual SSC and annual suspended sediment loads at 49 of 62 monitoring stations between 1990 and 2010. On average SSC declines by-0.92 mg l-1 yr-1. At some stations decreases during the 20 years represent up to 50% of the long-term average SSC. Significant decreases of SSC are associated with declining SSL loads. The contemporary suspended sediment loads of the Rhine at the German-Dutch border approaches the natural base level of ~1 Mt yr-1 , which was achieved by the Rhine during the mid-Holocene when the suspended sediment load was adjusted to the Holocene climatic conditions and before the onset of increased loads due to human induced land use changes in the Rhine catchment. At this point we can only speculate regarding potential reasons for a decline in sediment supply to larger rivers. We argue that changes in soil erosion within the catchments and/or the sediment connectivity in upstream headwaters, e.g. due to the construction of small rainwater retention basins, are the major reason for declining SSC in the studied river channels.
A millennium of arable land use – the long-term impact of water and tillage erosion on landscape-scale carbon dynamics
. In the last decades, soils and their agricultural management have received great scientific and... more . In the last decades, soils and their agricultural management have received great scientific and political attention due to their associated potential to act as sink of atmospheric carbon dioxide (CO2). It is questioned if soil redistribution processes affect this potential CO2 sink function, as agricultural management has a strong potential to accelerate soil redistribution. Most studies analysing the effect of soil redistribution upon soil organic carbon (SOC) dynamics focus on water erosion, analyse only relatively small catchments and relatively short timespans of several years to decades. The aim of this study is to widen the perspective by including tillage erosion as another important driver of soil redistribution and performing a model-based analysis in a 200 km2-sized arable region of north-eastern Germany for the period since the conversion from forest to arable land (approx. 1000 years ago). Therefore, a modified version of the spatially explicit soil redistribution and carbon (C) turnover model SPEROS-C was applied to simulate lateral soil and SOC redistribution and SOC turnover (spatial resolution 5 m x 5 m). The model parameterisation uncertainty was estimated by simulating different realisations of the development of agricultural management over the past millennium. The results indicate that in young moraine areas, which are relatively dry but intensively used for agriculture for centuries, SOC patterns and SOC dynamics are substantially affected by tillage-induced soil redistribution processes. To understand the landscape scale effect of these redistribution processes on SOC dynamics it is essential to account for long-term changes following land conversion, as typical soil-erosion induced processes, e.g. dynamic replacement, only take place after former forest soils reach a new equilibrium following conversion. Overall, it was estimated that after 1000 years of arable land use SOC redistribution by tillage and water erosion results in a landscape scale C sink of up to 0.66 ‰ per year.
HS9.2/GM3.4/SSS2.10. Erosion and sediment delivery in agricultural landscapes: monitoring, modelling and management
The EGU General Assembly, 2011
Erosion and sediment delivery in agricultural landscapes: monitoring, modelling and management Ag... more Erosion and sediment delivery in agricultural landscapes: monitoring, modelling and management Agricultural landscapes are mainly composed by a mosaic of cultivated fields, uncultivated patches (woodlands, heath land, wetlands), and a network of mostly linear anthropogenic structures (hedgerows, embankments, drainage ditches, grass strips, terraces). In these environments, hydrological connectivity, sediment delivery into streams and at longer time soil cover geometry are closely linked to spatial and temporal dynamics in land use and management. Agricultural landscapes are exposed to fast changes in environmental conditions but agriculture itself dynamically reconfigures our landscapes via changes in land use and management. To understand, analyse and potentially manage future changes in water and sediment fluxes in these landscape it is essential to deal with these interrelationship between different driving forces. This session will present contributions addressing different aspe...
Soil erosion rates on arable land frequently exceed the pace at which new soil is formed. This im... more Soil erosion rates on arable land frequently exceed the pace at which new soil is formed. This imbalance leads to soil thinning (i.e. truncation), whereby subsoil horizons and their underlying parent material become progressively closer to the land surface. As soil erosion is a selective process and subsurface horizons often have contrasting properties to the original topsoil, truncation-induced changes to soil properties might affect erosion rates and runoff formation through a soil erosion feedback system. However, the potential interactions between soil erosion and soil truncation are poorly understood due to a lack of empirical data and the neglection of long-term erodibility dynamics in erosion simulation models. Here, we present a novel modelbased exploration of the soil erosion feedback system over a period of 500 years using measured soil properties from a diversified database of 265 agricultural soil profiles in the UK. For this, we adapted the Modified Morgan-Morgan-Finney model (MMMF) to perform a modelling experiment in which topography, climate, land cover, and crop management parameters were held constant throughout the simulation period. As selective soil erosion processes removed topsoil layers, the model gradually mixed subsurface soil horizons into a 0.2 m plough layer and updated soil properties using mass-balance mixing models. Further, we estimated the uncertainty in model simulations with a forward error assessment. We found that modelled erosion rates in 99 % of the soil profiles were sensitive to truncation-induced changes in soil properties. The soil losses in all except one of the truncation-sensitive profiles displayed a decelerating trend, which depicted an exponential decay in erosion rates over the simulation period. This was largely explained by decreasing silt contents in the soil surface due to selective removal of this more erodible particle size fraction and the presence of clayey or sandy substrata. Moreover, the soil profiles displayed an increased residual stone cover, which armoured the land surface and reduced soil detachment. Contrastingly, the soils with siltier subsurface horizons continuously replenished the plough layer with readily erodible material, which prevented the decline of soil loss rates over time. Although our results are limited by the edaphoclimatic conditions represented in our data, as by our modelling assumptions, we have demonstrated how modelled soil losses can be sensitive to erosion-induced changes in soil properties. These findings are likely to affect how we calculate soil lifespans and make long-term projections of land degradation.
Microplastic detection in arable soil using a 3D Laser Scanning Confocal Microscope coupled with a Machine-Learning Algorithm
In Europe, about 0.71 million tonnes of agricultural plastic were intentionally used in 2019. Mos... more In Europe, about 0.71 million tonnes of agricultural plastic were intentionally used in 2019. Most widely used were plastic films (about 75%), which are dominated by light density polyethylene (LDPE). Especially LDPE plastic films for mulching covers in direct contact arable soil to increase temperature and reduce evaporation. Thereby, microplastic is detached from the mulch film via mechanical and environmental weathering. Another microplastic pathway in arable soil is the application of sewage sludge. Depending on land use, a 4 to 23 times higher microplastic contamination in soils than in the sea is estimated. Obviously, microplastic input to soils is critically high, but an accurate quantification is still lacking. This is partly caused by challenges in detection and analysis of microplastic in soils. First, it is challenging to extract microplastic from a matrix of organic and inorganic particles of similar size. Second, the well-established spectroscopic methods (e.g., Raman a...
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