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Draining peatlands for agriculture induces peat decomposition, subsidence, and carbon (C) and nitrogen (N) losses, thereby contributing to soil degradation and climate change. To sustain the agricultural productivity of these organic soils, coverage with mineral soil material has increasingly been used. To evaluate the effect of this practice on the N flows within the plant–soil system, we conducted a 15N tracer experiment on a drained peatland that was managed as an intensive meadow. This peatland was divided into two parts, either without (reference “Ref”) or with ~ 40 cm mineral soil cover (coverage “Cov”). We applied 15NH415NO3 on field plots to follow the fate of 15N in plant–soil system over 11 months. In addition, N mineralization was determined by laboratory incubation. The field experiment showed that Cov lost less 15N (p 15N uptake was similar at both sites. The lower net N loss from the Cov site was accompanied by higher soil 15N retention. The laboratory incubation revealed a ~ 3 times lower N mineralization at Cov than at Ref, whereas the N release per unit soil N was around two times higher at Cov than at Ref, suggesting a faster SOM turnover rate at Cov. Overall, the mineral soil cover increased the retention of fertilizer-N in the soil, thus reducing the system N losses. Our result indicates that agricultural production on drained peatland is less harmful to the environment with mineral soil coverage than using drained peatland directly.

Soil erosion (SE) and saturated hydraulic conductivity (Ksat) are the essential indicators for land degradation and soil nutrient loss. Both processes are linked with each other as one can enhance the other resulting in positive feedback loops. The increase in soil erosion might block the macropores and reduce Ksat. In contrast, the reduction in Ksat triggers the runoff and increases soil erosion. However, modelling and predicting soil erosion, hydraulic properties are usually not adequately considered. We tried to link soil erosion directly with Ksat on a global scale. For this, we used global soil erosion and saturated hydraulic conductivity maps to yield combined soil risk classes. SE and Ksat maps were obtained from Borrelli et al. (2017) and Gupta et al. (2021), respectively. Each map was classified into six classes based on the previous studies. Moreover, both maps' classes were combined by creating six merged classes to develop the modified soil risk map. The modified soil risk map highlights regions with low Ksat and high SE. Furthermore, the final map was validated using continental and/or national sediment yield (SY) datasets. SY classes were compared with final risk classes to validate the accuracy of the map. The modified soil risk map showed higher accuracy compared to the SE map when compared with SY classes. This study demonstrates the first attempt to link soil erosion to soil hydraulic properties on large scales.

Drainage for agriculture induces peatland decomposition, subsidence, and nitrogen (N) losess, thereby contributing to climate change. In order to maintain the productivity of agricultural managed peatland, and to counteract soil subsidence, mineral soil coverage is becoming an increasingly used practice in Switzerland and other European countries. Mineral soil coverage may change the N balance from the corronsponding organic soil. To explore the effect of this practice on the N flow within the plant – soil system and the N loss, we carried out a field experiment on a peatland in the Swiss Rhine Valley that was managed as an intensive meadow. The peatland was divided into two parts, either without (Ref) or with mineral soil coverage, thickness ~ 40 cm (Cov). In this experiment, 15NH415NO3 were applied on field plots to follow the recovery of 15N in grass, root, and soil over 11 months. The 15N that was not recovered was designated as lost via leaching or gaseous emissions. Soil N mineralization was measured in a laboratory incubation. And the gaseous N loss as N2O was determined by automatic time integrating chamber systems (ATIC) over two years. The experimental results showed that the total 15N loss from Cov was lower (p < 0.05) than from Ref, even though plant 15N uptake did not vary between the two sites. The lower net N loss from the Cov site was accompanied by higher soil 15N retention in the soil. The laboratory incubation revealed a ~2 times higher specific N release per unit soil N at Cov than at Ref, suggesting a faster SOM turnover rate at Cov. Regarding the N loss as N2O, emissions from Ref were at the upper end of previously measured fluxes in drained peatland. In contrast, N2O emissions from Cov were reduced by a factor of nine over two years. Overall, the mineral soil cover increased the retention of fertilizer-N in the soil, thus reducing the system N losses, especially N loss as N2O emissions. Our results indicate agricultural production on drained peatland is less harmful to the environment with mineral soil coverage than using drained peatland directly.

Soil loss by water erosion is one of the main threats to soil health and food production in intensively used agricultural areas. To assess its significance to the overall sediment production we applied the Water and Tillage Erosion Model/Sediment Delivery model (WaTEM/SEDEM) to the Luoyugou catchment, a sub-catchment of the Yellow River basin within the Chinese Loess plateau. WaTEM/SEDEM considers rill and inter-rill erosion and deposition rates, resulting in sediment yield rates leaving the catchment. Although terraces were established in the 1990s to reduce soil loss, no further soil erosion modeling has been published for this area. Applying 1000 Monte Carlo simulations of the WaTEM/SEDEM, modeled average soil loss by rill and inter-rill erosion for 2020 was 12.4 ± 11.8 t ha-1 yr-1, with sediment yield at the outlet of 52949 ± 11215 t yr-1. Terracing reduced erosion rates, while land cover changes, mainly conversion of forests and grassland partly counteracted the mitigation (combined effect: 50% reduction). Modeled sediment loads by rill and inter-rill erosion account for 17.1% of the total long-term sediment production recorded by flow discharge measurements. Other processes not considered by the model like landslides, gully erosion, riverbank erosion, and sediment production by construction seem to dominate overall sediment yield. Considering years with baseline sediment production only, measured and modeled sediment yield compared well, indicating that the latter processes contribute mainly during extreme events.

Soil mobilization has been investigated by means of fallout radionuclides (FRN) in a first-order catchment of the Eastern Alps. Caesium-137, 210Pbxs. (210Pb excess or unsupported fraction), and 241Am have been measured in soil samples collected from a pasture at about 2150 m above sea level. Combining pedological and radioactivity data, including mineral-related radionuclides (primordial 40K and nuclides belonging to the 232Th and 238U decay chains), the distribution of FRNs, their spatial variability, vertical distribution, and relationships with pedological and topographical variables were assessed. Because of low activity concentration, it was not possible to use artificial long-lived 241Am as a soil tracer, but preliminary results are encouraging. Inventories of 210Pbxs. and 137Cs have been converted into soil mobilization rates applying the MODERN model. Despite the gentle steepness and the absence of evident signs of erosion, the slopes of the considered catchment are affected by erosion at a rate up to 6 t ha−1 yr−1, likely related to grazing. A comparison between 210Pbxs. and 137Cs has revealed that at this site 137Cs, the most used FRN for estimating soil redistribution, is not suitable for this purpose, probably due to its irregular spatial distribution on snow-covered ground after the Chernobyl accident. Conversely, 210Pbxs., owing to its continuous input, has provided reliable estimates of soil redistribution rates, in accordance with local morphology. The latter has in fact been related to morphometric variables in a regression model to provide an overview of soil erosion/sedimentation across the entire catchment, confirming that 210Pbxs. is a viable alternative to trace soil erosion and deposition where the Chernobyl fallout occurred on snow-covered ground.

Quantifying soil redistribution rates is a global challenge addressed with direct sediment measurements (e.g. traps), models, and isotopic, geochemical, and radionuclide tracers. The isotope of plutonium, namely 239+240Pu, is a relatively new soil redistribution tracer in this challenge. Direct validation of 239+240Pu as a soil redistribution tracer is, however, still missing. We used a unique sediment yield time series in southern Italy, reaching back to the initial fallout of 239+240Pu to verify 239+240Pu as a soil redistribution tracer. Distributed soil samples (n=55) were collected in the catchment, and at undisturbed reference sites (n=22), 239+240Pu was extracted, measured with inductively coupled plasma mass spectrometry (ICP-MS), and converted to soil redistribution rates. Finally, we used a generalized additive model (GAM) to regionalize soil redistribution estimates for the catchment. For the catchment sites, mean 239+240Pu inventories were significantly reduced (16.8 ± 10.2 Bq m−2) compared to the reference inventory (40.5 ± 3.5 Bq m−2), indicating the dominance of erosion. Converting these inventory losses into soil erosion rates resulted in an average soil loss of 22.2 ± SD 7.2 t ha−1 yr−1. The uncertainties of the approach stemmed mainly from the high measurement uncertainties of some low-activity samples where samples have been bulked over depth. Therefore, we recommend taking incremental soil samples and extracting larger soil volumes (∼ 20 g). The geographic coordinates and the flow accumulation best described the spatial pattern of erosion rates in the GAM model. Using those predictors to upscale Pu-derived soil redistribution rates for the entire catchment resulted in an average on-site loss of 20.7 t ha−1 yr−1, which corresponds very well to the long-term average sediment yield of 18.7 t ha−1 yr−1 measured at the catchment outlet and to 137Cs-derived soil redistribution rates. Overall, this comparison of Pu-derived soil redistribution rates with measured sediment yield data validates 239+240Pu as a suitable retrospective soil redistribution tracer.

Peatlands store carbon in the form of dead organic residues. Climate change and human impact impose risks on the sustainability of the peatlands carbon balance due to increased peat decomposition. Here, we investigated molecular changes in the upper peat layers (0-40 cm), inferred from high-resolution vertical depth profiles, from a boreal peatland using two-dimensional H-1-C-13 nuclear magnetic resonance (NMR) spectroscopy, and comparison to delta C-13, delta N-15, and carbon and nitrogen content. Effects of hydrological conditions were investigated at respective sites: natural moist, drainage ditch, and natural dry. The molecular characterization revealed preferential degradation of specific side-chain linkages of xylan-type hemicelluloses within 0-14 cm at all sites, indicating organic matter losses up to 25%. In contrast, the xylan backbone, galactomannan-type hemicelluloses, and cellulose were more resistant to degradation and accumulated at the natural moist and drainage site. delta C-13, delta N-15, and carbon and nitrogen content did not correlate with specific hemicellulose structures but reflected changes in total carbohydrates. Our analysis provides novel insights into peat carbohydrate decomposition and indicates substantial organic matter losses in the acrotelm due to the degradation of specific hemicellulose structures. This suggests that variations in hemicellulose content and structure influence peat stability, which may have important implications with respect to climate change.

To evaluate the sustainability of biomass plantations, effects on soil organic carbon (SOC) need to be quantified. Miscanthus × giganteus is increasingly used as a bioenergy plant, and it has been hypothesized that, after conversion from cropland, Miscanthus cropping increases SOC storage, whereas conversion from grassland to Miscanthus provides, on average, no sequestration. All field studies hitherto were carried out on mineral soils with topsoil SOC contents of below 3.3%. Here, we analyze in the temperate zone of Switzerland five sites that have been cultivated with Miscanthus for 19–24 years and of which four sites are higher in topsoil SOC content (4.7%–16.2%) and storage (188–262 t SOC) than any previously studied Miscanthus plantation in Europe. We used the difference in carbon isotopic signature between C4 (Miscanthus) and neighboring plots with C3 vegetation (grassland) to quantify the accumulation of new SOC from Miscanthus down to 0.75 m. Annual C4‐C accumulation rates were 1.66 (standard error ± 0.14) t C4‐C ha−1 year−1 (range: 1.26–2.01) in the upper 0.3 m of soil and 1.96 (±0.18) t C4‐C ha−1 year−1 (1.40–2.38) in 0–0.75 m. Average rates for 0–0.3 m were higher than those of mineral soils (n = 37) published previously (0.96 [±0.10] t C4‐C ha−1 year−1). However, high rates of C4‐C accumulation were also reported previously for some mineral soils. Nevertheless, the one mineral soil in our study did not reveal a systematically different accumulation of Miscanthus‐derived carbon compared with the four carbon‐rich soils. We therefore conclude that soils rich in organic matter do not show a different C4‐C accumulation pattern as compared with mineral soils. However, their C4‐C accumulation rates are at the upper end of the data ensemble. Our results further underpin that conversion to Miscanthus, despite C4‐C accumulation, provides no means to increase soil carbon stocks relative to grassland management.

A small fraction of freezing cloud droplets probably initiates much of the precipitation above continents. Only a minute fraction of aerosol particles, so-called icenucleating particles (INPs), can trigger initial ice formation at 15 C, at which cloud-Top temperatures are frequently associated with snowfall. At a mountaintop site in the Swiss Alps, we found that concentrations of INPs active at 15 C can be parameterised by different functions of coarse (2 um) aerosol particle concentrations, depending on whether an air mass is (a) precipitating, (b) nonprecipitating, or (c) carrying a substantial fraction of dust particles while non-precipitating. Consequently, we suggest that a parameterisation at moderate supercooling should consider coarse particles in combination with air mass differentiation. © 2021 Mary Ann Liebert Inc.. All rights reserved., Atmospheric Chemistry and Physics, 21 (2), ISSN:1680-7375, ISSN:1680-7367

The exchange of gaseous elemental mercury, Hg(0), between the atmosphere and terrestrial surfaces remains poorly understood mainly due to difficulties in measuring net Hg(0) fluxes on the ecosystem scale. Emerging evidence suggests foliar uptake of atmospheric Hg(0) to be a major deposition pathway to terrestrial surfaces. Here, we present a bottom-up approach to calculate Hg(0) uptake fluxes to aboveground foliage by combining foliar Hg uptake rates normalized to leaf area with species-specific leaf area indices. This bottom-up approach incorporates systematic variations in crown height and needle age. We analyzed Hg content in 583 foliage samples from six tree species at 10 European forested research sites along a latitudinal gradient from Switzerland to northern Finland over the course of the 2018 growing season. Foliar Hg concentrations increased over time in all six tree species at all sites. We found that foliar Hg uptake rates normalized to leaf area were highest at the top of the tree crown. Foliar Hg uptake rates decreased with needle age of multiyear-old conifers (spruce and pine). Average species-specific foliar Hg uptake fluxes during the 2018 growing season were 18 ± 3 µg Hg m−2 for beech, 26 ± 5 µg Hg m−2 for oak, 4 ± 1 µg Hg m−2 for pine and 11 ± 1 µg Hg m−2 for spruce. For comparison, the average Hg(II) wet deposition flux measured at 5 of the 10 research sites during the same period was 2.3 ± 0.3 µg Hg m−2, which was 4 times lower than the site-averaged foliar uptake flux of 10 ± 3 µg Hg m−2. Scaling up site-specific foliar uptake rates to the forested area of Europe resulted in a total foliar Hg uptake flux of approximately 20 ± 3 Mg during the 2018 growing season. Considering that the same flux applies to the global land area of temperate forests, we estimate a foliar Hg uptake flux of 108 ± 18 Mg. Our data indicate that foliar Hg uptake is a major deposition pathway to terrestrial surfaces in Europe. The bottom-up approach provides a promising method to quantify foliar Hg uptake fluxes on an ecosystem scale.

Peatland degradation is tightly connected to hydrological changes and microbial metabolism. To better understand these metabolism processes, more information is needed on how microbial communities and substrate cycling are affected by changing hydrological regimes. These activities should be imprinted in stable isotope bulk values (δ

The prevention of the negative consequences induced by accelerated soil erosion depends on well thought out and economically viable mitigation policies that are founded on the accurate source apportionment of erosion hotspots. Typically, quantification of sediment source apportionment is difficult and requires the impractical and economically unfeasible solution of in-situ sampling at all possible erosion hotspots. An alternative and commonly applied technique is source and sediment fingerprinting with complimentary unmixing of the sediment fingerprint by mass balance equations, with a recent surge of Bayesian inference to incorporate uncertainty in sediment apportionment.The compound-specific isotope analysis of fatty acids are commonly used for land-use specific fingerprints. However, fingerprinting using isotopic tracers has shown limitations in multiple catchments in which δ13C of fatty acids plot in a 1-dimensional mixing line, resulting in the contribution of the central source being mis-classified as source contribution from either source located at the mixing line endpoints. In this study, we used δ15N as an additional land-use specific tracer to expand the fatty acid linear mixing line into a more suitable N-dimensional mixing polygon. We use an initial “brute force method” with virtual mixtures to explore all combinations and permutations of tracers and their model performance.Results show that increasing the number of fatty acid tracers had a detrimental effect on unmixing performance, suggesting that increasing the number of conservative tracers does not always produce an improved unmixing result as previously understood when using a Bayesian framework. Expanding on this, we hypothesised that if the relative source-source values are constant between different length fatty acids, the mixing space will also be constant, resulting in the application of additional δ13C of fatty acid tracers being comparable to applying repetitions of an identical tracer making additional fatty acid tracers potentially redundant. The performance of the unmixing models using δ13C fatty acid tracers can then be understood to depend on the model’s capacity to handle redundant tracers. The effect of tracer redundancy was quantified by adding identical duplicate tracers (repetitions of the same tracer, δ13C FA C26) or different fatty acid tracers (δ13C FA C24, C28, C30) to the δ15N and δ13C FA C26 tracer set in a three, four and five tracer set and unmixed using the Bayesian framework MixSIAR.Increasing the number of identical tracers in a tracer set decreased model performance resulting from the propagation of the source-based uncertainty outweighing any discrimination power gained. The latter contradicts the previous idea that MixSIAR handles non-informative tracers. The addition of fatty acids (C24, C28, C30) to C26 showed a lower but proportional decrease in model performance compared to additional identical tracers. This suggests that using multiple tracers which have the same relative mixing space are practically equivalent to applying identical tracer multiple times. We conclude that when using a Bayesian framework for unmixing models, it is beneficial to remove redundant tracers which display the same relative mixing space to improve model performance.

Quantifying soil erosion is a major research challenge due to erosion's episodic character and spatial variation. Fallout radionuclides as 239+240Pu and 137Cs are powerful tools to assess net soil losses integrated over long periods applicable to most regions of the world. The traditional approach of the FRN method is based on the comparison between an inventory (total radionuclide activity per unit area) at a given sampling site and that of an undisturbed reference site (e.g., located in a flat and well-vegetated area). Compared to reference, a decrease in the FRN inventory indicates erosion and an increase indicating deposition of sediments and associated FRN. So far, FRN based assessment was restricted to a regional/catchment scale as spatially distributed data of reference inventories was missing.In this study, we aim at upscaling the FRN approach to a central area of Europe covering France, North Italy, South Germany, and Belgium using the Land Use/Cover Area frame Survey – LUCAS soil sample bank. Both fallout sources left a specific radionuclide imprint in European soils. First, plutonium was used to quantify global versus Chernobyl fallout contributions to 137Cs found in European soils. Subsequently, spatial prediction models (general additive models) allowed reconstructing the global versus Chernobyl 137Cs fallout pattern across national boundaries. The definition of these 137Cs and the Pu baseline maps allows assessing soil redistribution rates at n=137 cropland sites with both FRNs across the study area. We selected barley, wheat, maize, and vineyard plots covering different slope angles as cropland sites. For both FRNs, differences between the reference and site-specific FRN inventory show an inventory and associated topsoil (0-20cm) loss of approximately 10% since 1963. Converting these inventory changes with a simple mass balance model to soil redistribution rates results in average soil erosion rates of 8.8 ± 6.3 t/ ha yr, assuming a tillage depth of 20 cm. Although the involved uncertainties are large, these net erosion rates exceed the expected magnitude.

Lake sediments can be used as great environmental archives, especially when they are varved due to anoxic conditions at the lake bottom. Such an annual resolution of these archives can give unique insights in past environmental and climate settings and changes. Here, we try to track back changes in the erosion dynamics and associated land-use and potentially climate changes at the catchment scale from seasonal to centennial scales at Lake Baldegg, Switzerland.Land-use changes and agricultural practices become nowadays a key factor of sediment dynamics by modifying the soils erosive risk and the catchment sediment connectivity. And while soil erosion is one of the biggest threats to soil fertility as well as to ecological health of freshwater systems, restoration and management plans of water bodies can only be efficient if the sediment sources and their respective contributions, i.e. the proportion attributable to different land uses and agricultural practices, are identified.For this we used a compound-specific stable isotope approach (δ13C of long-chain fatty acids (LC-FA)) combined with connectivity modelling to a 130-years old varved lake sediment core from a eutrophic Swiss lake. We were able to discriminate grassland, arable and forest soils using the LC-FAs C26:0 and C28:0. Between 1940 to 1960 forest soils were the main source of the terrestrial sediment origin (80-100%). After 1960 a clear change in sediment origin happened. The contribution of arable and grassland soils to lake sediments were increasing. However quantitative attribution and differentiation between grassland and arable land were difficult due to the linear distribution of the tracers between the sources.For sediments older than 1940 the isotopic signal could no longer be explained by today’s terrestrial sources. We hypothesized additional sources of the assumed terrestrial long-chain fatty acids like (1) historical peatlands and/or former reed grass areas and (2) in-situ LC-FA production by algae.Since the last presentation at EGU2019 we went back to Lake Baldegg to expand our potential source sample set to explain deviation of source signals from sediments. After consultation of historic maps and reports, we located sites where peatlands and reed grass existed before the 1940s and where reed gras is still growing. There we took plant as well as soil samples and peat/lake sediment cores from a historical pond, which was connected to the lake and where reed grass grows today.To investigate the potential in-situ production of LC-FAs by algae or other microorganisms in the water column, we did four sampling-trips on the lake between April 2021 and September 2021 to get algae and water samples from different depths and integrating over depth. These samples were filtered over glas fibre filters, extracted and analysed for FAs. In some samples we found LC-FAs in different concentrations. Especially for the algae samples this was surprising. Depending on their isotopic signature we can now differentiate between terrestrial or aquatic production.The proof of significant aquatic contribution of LC-FAs to lacustrine sediments in Swiss lakes would be an important finding also regarding the common use of assumed terrestrial biomarkers in lake sediments for climate reconstruction.

Despite the importance of vegetation uptake of atmospheric gaseous elemental mercury (Hg(0)) within the global Hg cycle, little knowledge exists on the physiological, climatic and geographic factors controlling stomatal uptake of atmospheric Hg(0) by tree foliage. We investigate controls on foliar stomatal Hg(0) uptake by combining Hg measurements of 3,569 foliage samples across Europe with data on tree species traits and environmental conditions. To account for foliar Hg accumulation over time, we normalized foliar Hg concentration over the foliar life period from the simulated start of the growing season to sample harvest. The most relevant parameter impacting daily foliar stomatal Hg uptake was tree functional group (deciduous versus coniferous trees). On average, we measured 3.2 times higher daily foliar stomatal Hg uptake rates in deciduous leaves than in coniferous needles of the same age. Across tree species, for foliage of beech and fir, and at two out of three forest plots with more than 20 samples, we found a significant (p

Taking advantage of the different histories of Hg deposition in Davos Seehornwald in E-Switzerland and Changbai Mountain in NE-China, the influence of atmospheric deposition on Hg soil dynamics in forest soil profiles was investigated. Today, Hg fluxes in bulk precipitation were similar, and soil profiles were generally sinks for atmospherically deposited Hg at both sites. Noticeably, a net release of 2.07 μg Hg m

During the last centuries major parts of European peatlands were degraded along with drainage and land use changes. Peatland biodiversity and essential ecosystem functions (e.g. flood prevention, groundwater purification and CO2 sink) were dramatically impaired. Moreover, climate change threatens peatlands in the near future. Increasing pressure to peatland ecosystems calls for a more cost-efficient method to indicate the current state of peatlands and the success of restoration effort. Metabolism processes in peatland soils are imprinted in stable isotope signatures due to differences in microorganism communities and their metabolic pathways. Therefore we hypothesize that depth profiles of nitrogen stable isotope values provide a promising opportunity to detect peatland decomposition or restoration. We studied five peatlands: Degero Stormyr (Northern Sweden), Lakkasuo (Central Finland) and three mires in the Black Forest (Southern Germany). At all locations cores were taken from adjacent drained (or rewetted) and natural sites to identify δ15N trends that could indicate changes due to drainage and restoration. At all drained (and rewetted) sites we found a distinct peak ( turning point ) of the δ15N values in the center of the drained horizon. To verify our interpretation δ13C, the C / N ratio and the bulk density were measured and a microscopic analysis of the macro residuals in the peat cores was made. In addition we did a phospholipid fatty acid (PLFAs) analysis to link our results to microbial community composition. We distinguished between fungal and bacterial-derived PLFAs. In accordance with other studies, our results suggest, that fungi dominate the microbial metabolism in the upper, aerobic peat horizon. This is reflected by depleted δ15N values. Downwards the drained horizon conditions slowly switch to oxygen limitation. In consequence fungal-derived PLFAs decreases whereas bacterial-derived PLFAs are rising. The highest diversity of microbial-derived PLFAs is indicated by the δ15N turning point. Below the δ15N turning point, oxygen is increasingly limited and concentrations of all microbial-derived PLFAs are decreasing down to the onset of the permanently waterlogged, anaerobic horizon. Peatland cores with restoration success show, above the formerly drainage-affected horizon, again no depth trend of the isotopic values. Hence, we conclude that δ15N stable isotope values reflect microbial community composition, which differ between drained and natural peatlands.

To gain a better understanding of the global application of soil erosion prediction models, we comprehensively reviewed relevant peer-reviewed research literature on soil-erosion modelling 1994-2017. Our aim was to identify (i) processes and models most frequently addressed in the literature, (ii) regions within which models are primarily applied, (iii) what regions remain unaddressed and why, and (iv) how frequently studies are conducted to validate/evaluate model outcomes relative to measured data. To perform this task, we merged the knowledge of a group of 66 soil-erosion scientists from 67 research institutions and 25 countries. The resulting database ‘Global Applications of Soil Erosion Modelling Tracker (GASEMT)’ includes 3,030 individual modelling records from 126 counties encompassing all continents (except Antarctica). Out of 8,471 articles identified as potentially relevant, we reviewed 1,697 articles and transferred relevant information from each into the database. For each record reported in the GASEMT database, 42 attributes were evaluated. The GASEMT database provides insights into the state-of-the-art of soil- erosion models and model applications worldwide. The database is also intended to support the upcoming country-based United Nations global soil-erosion assessment. This database may help inform soil erosion research priorities in that it builds a foundation for future targeted in-depth analyses. GASEMT is an open-source database that anyone can use to develop research, rectify errors, and expand.

The accelerated sediment supply from agricultural soils to riverine and lacustrine environments leads to negative off-site consequences. In particular, the sediment connectivity from agricultural land to surface waters is strongly affected by landscape patchiness and the linear structures that separate field parcels (e.g. roads, tracks, hedges, and grass buffer strips). Understanding the interactions between these structures and sediment transfer is therefore crucial for minimising off-site erosion impacts. Although soil erosion models can be used to understand lateral sediment transport patterns, model-based connectivity assessments are hindered by the uncertainty in model structures and input data. Specifically, the representation of linear landscape features in numerical soil redistribution models is often compromised by the spatial resolution of the input data and the quality of the process descriptions. Here we adapted the Water and Tillage Erosion Model and Sediment Delivery Model (WaTEM/SEDEM) using high-resolution spatial data (2 m × 2 m) to analyse the sediment connectivity in a very patchy mesoscale catchment (73 km2) of the Swiss Plateau. We used a global sensitivity analysis to explore model structural assumptions about how linear landscape features (dis)connect the sediment cascade, which allowed us to investigate the uncertainty in the model structure. Furthermore, we compared model simulations of hillslope sediment yields from five subcatchments to tributary sediment loads, which were calculated with long-term water discharge and suspended sediment measurements. The sensitivity analysis revealed that the assumptions about how the road network (dis)connects the sediment transfer from field blocks to water courses had a much higher impact on modelled sediment yields than the uncertainty in model parameters. Moreover, model simulations showed a higher agreement with tributary sediment loads when the road network was assumed to directly connect sediments from hillslopes to water courses. Our results ultimately illustrate how a high-density road network combined with an effective drainage system increases sediment connectivity from hillslopes to surface waters in agricultural landscapes. This further highlights the importance of considering linear landscape features and model structural uncertainty in soil erosion and sediment connectivity research.

Purpose: Natural rates of soil production or a target soil thickness that allows unrestricted land use can serve as a basis for defining tolerable soil erosion rates. Guidelines for tolerable soil erosion rates in alpine grasslands do not yet exist, partly due to the lack of information of soil formation and production rates. We (i) defined soil formation/production rates for alpine grasslands on siliceous lithology and compared them to measured and modelled soil erosion rates and resulting soil thickness with a special focus on the Urseren Valley (Central Swiss Alps) and (ii) discussed possible trends for alpine soils under global change. Materials and methods: Ranges of soil formation, production and erosion rates were determined using published and our own data for Alpine grasslands soils. Two definitions of tolerable erosion rate were used: when (i) current soil depth remains constant over time; and (ii) at least a minimum soil depth is maintained (minimum thicknesses for individual land uses still need to be defined). Results and discussion: Soil production and related tolerable erosion rates (i.e. 50-90% of the soil production rate) are a strong function of time. Average soil production rate in alpine areas for relatively old soils (>10-18kyr) is between 54 (±14) and 113 (±30) tkm−2year−1, for young soils (>1-10kyr) between 119 (±44) and 248 (±91) tkm−2year−1 and for very young soils (≤1kyr) between 415 (±242) and 881 (±520) tkm−2year−1. Measured recent soil erosion rates in alpine areas at intensively used slopes range from 600 to 3000tkm−2year−1. Average catchment values for the Urseren Valley using the model USLE plus soil loss due to landslides resulted in an overall loss of 180tkm−2year−1, which considerably exceeds production rates of the soils. Conclusions: The comparison of soil production and erosion rates indicated unsustainable management of grassland soils in the Urseren Valley. Other Alpine regions report similar or even higher erosion rates. Consequently, attention has to be paid to Alpine grasslands used for agricultural purposes because today's soil erosion rates often considerably exceed soil formation, thus resulting in very shallow soils. Future global change is likely to increase soil erosion rates even further.

Purpose: Global warming is expected to change the thermal and hydrological soil regime in permafrost ecosystems which might impact soil erosion processes. Erosion assessment using radionuclides can provide information on past and ongoing, i.e. time-split, processes. The focus of this work was to find out if permafrost soils in the Swiss Alps differ in their medium- and long-term erosion rates from non-permafrost soils and if rates have accelerated during the last few decades. Materials and methods: Using cosmogenic (meteoric 10Be) and anthropogenic radionuclides (137Cs, 239 + 240Pu), a time-split approach was achieved by determining erosion activities on the long (millennia; 10Be) and medium term (decades; 137Cs, 239 + 240Pu). Additionally, the stable isotope δ 13C signature in soil organic matter was used as a qualitative indicator for soil disturbance patterns. We compared soil erosion processes in permafrost soils and nearby unfrozen soils in the alpine (sites at 2,700m asl, alpine tundra) and the subalpine (sites 1,800m asl, natural forest) range of the Swiss Alps (Upper Engadine). 137Cs, 239 + 240Pu and δ 13C measurements were performed at the alpine sites only. Results and discussion: Depending on the calculation procedure (profile distribution model or inventory method), the 137Cs measurements revealed soil accumulation rates of 1-3t/km2/year in permafrost soils and 34-52t/km2/year in non-permafrost soils. However, due to snow cover and subsequent melt-water runoff during 137Cs deposition after the Chernobyl accident, caesium does not seem to be an appropriate soil erosion tracer on the investigated alpine sites. With 239 + 240Pu, more reliable results were achieved. 239 + 240Pu measurements provided erosion rates of 31-186t/km2/year in permafrost soils and accumulation rates of 87-218t/km2/year in non-permafrost soils. Erosion and accumulation were relatively low and related to the vegetation community. The long-term (10Be) soil redistribution rates (erosion rates up to 49t/km2/year and accumulation rates up to 4t/km2/year) were low with no significant differences between permafrost and non-permafrost sites. The δ 13C signature indicated soil disturbances in permafrost and non-permafrost soils compared to the reference site. Conclusions: Our results highlight that soil redistribution rates have increased during the last few decades. However, whether the higher medium-term erosion rates obtained for the last decades are the result of the ongoing climate warming and related accelerated soil erosion or if other factors (e.g. measurement uncertainties) have been responsible for such an increase could not fully be clarified.

The accelerated sediment supply from agricultural soils to riverine and lacustrine environments leads to negative off-site consequences. In particular, the sediment connectivity from agricultural land to surface waters is strongly affected by landscape patchiness and the linear structures that separate field parcels (e.g. roads, tracks, hedges, and grass-buffer-strips). Understanding the feedbacks between these structures and sediment transfer is therefore crucial for minimising off-site erosion impacts. Although soil erosion models can be used to understand lateral sediment transport patterns, model-based connectivity assessments are hindered by the uncertainty in model structures and input data. In particular, the representation of linear landscape features in numerical soil redistribution models is often compromised by the spatial resolution of the input data and the quality of the process descriptions. Here we adapted the WaTEM/SEDEM model using high resolution spatial data (2 m × 2 m) to analyse the sediment connectivity in a very patchy mesoscale catchment (73 km2) of the Swiss Plateau. Specifically, we used a global sensitivity analysis to explore model structural assumptions about how linear landscape features (dis)connect the sediment cascade. Furthermore, we compared model simulations of hillslope sediment yields from five sub-catchments to tributary sediment loads, which were calculated with long-term water discharge and suspended sediment measurements. Our results showed that roads were the main regulators of sediment connectivity in the catchment. In particular, the sensitivity analysis revealed that the assumptions about how the road network (dis)connects the sediment transfer from field-blocks to water courses had a much higher impact on modelled sediment yields than the uncertainty in model parameters. Moreover, model simulations showed a higher agreement with tributary sediment loads when the road network was assumed to directly connect sediments from hillslopes to water courses. Our results ultimately illustrate how a high-density road network combined with an effective drainage system increase sediment connectivity from hillslopes to surface waters in this representative catchment of the Swiss Plateau. This further highlights the importance of considering linear structures in soil erosion and sediment connectivity models.