Impacts of anthropogenic and environmental factors on the occurrence of shallow landslides in an alpine catchment (Urseren Valley, Switzerland)

Changes in climate and land use pose a risk to stability of alpine soils, but the direction and magnitude of the impact is still discussed controversially with respect to the various alpine regions. In this study, we explicitly consider the influence of dynamic human-induced changes on the occurrence of landslides in addition to natural factors. Our hypothesis was that if changes in land use and climate have a significant influence on the occurrence of landslides we would see a trend in the incidence of landslides over time. We chose the Urseren Valley in the Central Swiss Alps as investigation site because the valley is dramatically affected by landslides and the land use history is well documented. Maps of several environmental factors were used to analyse the spatial landslide pattern. In order to explain the causation of the temporal variation, time-series (45 years) of precipitation characteristics, cattle stocking and pasture maps were compared to a series of seven landslide investigation maps between 1959 and 2004. We found that the area affected by landslides increased by 92% from 1959 to 2004. Even though catchment characteristics like geology and slope largely explain the spatial variation in landslide susceptibility (68%), this cannot explain the temporal trend in landslide activity. The increase in stocking numbers and the increased intensity of torrential rain events had most likely an influence on landslide incidence. In addition, our data and interviews with farmers pointed to the importance of management practice

Total bacterial number concentration in free tropospheric air above the Alps

Over a period from June to October 2010, we carried out four short campaigns on the northern alpine ridge (High Altitude Research Station Jungfraujoch, 3,450m above sea level) to determine bacterial number concentrations by collecting aerosol with liquid impingers, followed by filtration, fluorescent staining and counting with a microscope. Impinger liquid was also subjected to drop freeze tests to determine the number of ice nucleators. Parallel measurements of 222Rn enabled us to distinguish air masses with no, or little, recent land surface contact (free troposphere, 222Rn≤0.50Bqm−3) from air masses influenced by recent contact with land surface (222Rn>0.50Bqm−3). In free tropospheric air, concentration of total bacteria was on average 3.4×104cellsm−3 (SD=0.8×104cellsm−3). When wind conditions preceding sampling were calm, or when the station was in clouds during sampling, there was no detectable difference in bacterial number concentrations between free tropospheric air and air influenced by recent land surface contact. One campaign was preceded by a storm. Here, recent land surface contact had enriched the air in bacterial cells (up to 7.5×104cellsm−3). Very few of these bacteria may act as ice nucleators in clouds. The median ratio of ice nucleators to the number of bacterial cells in our study was 1.0×10−5. We conclude that injection of bacterial cells into the free troposphere is an intermittent process. Conditions controlling the release of bacteria into near surface air are probably more of a limiting factor than vertical transport and mixing of near surface air into the free tropospher

Soil loss by wind (SoLoWind): a new GIS-based model to identify risk areas

The focus of wind erosion studies in Germany is located in the Northern and Eastern parts of the country, where wind erosion is a major soil threat and environmental concern. One of the most susceptible regions not only within Germany, but also within Europe (1, 2) is Western Saxony even though no high resolution erosion risk map exists for that region yet. A new wind erosion model for modeling soil loss by wind called SoLoWind was developed and tested for Western Saxony (3). SoLoWind extends the existing DIN model (DIN standard 19706) applied by the public authorities in Germany to a multidirectional model with new causal factors. The new factors are combined by fuzzy logic with the original DIN factors into four modules. The “Natural Wind Erosions Susceptibility” (SUS) module determines the regional soil erodibility with respect to soil texture, soil organic content, soil moisture and wind speeds. A “Soil Cover” (COV) module distinguishes between bare soil and covered soil in satellite images. Furthermore, the modules “Mean Field Length” (MFL) and “Mean Protection Zones” (MPZ) are parameters for the wind erosions avalanching effect and sheltering of windbreaks. Both modules are weighted according to the frequency of wind directions. The application showed that about one-third of all arable land in Western Saxony have either high (26.9%) or very high soil erosion risk (3.6%) by wind. As such, wind erosion is a serious land degradation threat for the region as it is in the adjacent federal states. According to the modeled off-site effects of wind erosion, a potential danger of reduced visibility by windblown dust to sections of the highway A72 could clearly be identified which calls for immediate protection measures. The transparency, adaptability, and user-friendliness of the model suggest that SoLoWind might serve as a planning tool for soil conservation strategies not merely in Western Saxony, but also in other regions

239 + 240Pu from “contaminant” to soil erosion tracer: Where do we stand?

As soil erosion is the major threat to one of the most essential resources of humankind, methods to quantify soil redistribution are crucial for agro-environmental assessment as well as for optimisation of soil conservation practices. The use of fallout radionuclides (FRN) as soil redistribution tracers is, next to modelling, currently the most promising approach for assessing soil erosion. This review aims to evaluate the suitability of Plutonium (Pu) in general and the 239+240Pu isotopes in particular as soil redistribution tracers. It provides information on its origin, distribution and behaviour in soils and in the environment. Analytical methods, their recent advances as well as limitations, are discussed. To establish the current state of knowledge and to deepen our understanding, particular attention is given to the main existing achievements and findings based on using 239+240Pu as soil erosion tracer in agroecosystems. We further discuss similarities and differences to other more mature FRN techniques such as the 137Cs based approach which has been until now the most widely used method. We conclude that 239+240Pu has the potential to become the next generation of soil redistribution tracer compared to the more mature FRN techniques mostly due to (i) its long half-life guaranteeing its long-term availability in the environment, (ii) its analytical advantage in terms of measurement precision and measurement time and (iii) its greater homogeneity at reference sites due to its main origin from past atmospheric nuclear weapon tests. In identifying some key future research opportunities and needs, we hope to refine the efficiency of this promising agro-environmental tracer for effective soil redistribution studies under future climate and land use change

Biological residues define the ice nucleation properties of soil dust

Soil dust is a major driver of ice nucleation in clouds leading to precipitation. It consists largely of mineral particles with a small fraction of organic matter constituted mainly of remains of micro-organisms that participated in degrading plant debris before their own decay. Some micro-organisms have been shown to be much better ice nuclei than the most efficient soil mineral. Yet, current aerosol schemes in global climate models do not consider a difference between soil dust and mineral dust in terms of ice nucleation activity. Here, we show that particles from the clay and silt size fraction of four different soils naturally associated with 0.7 to 11.8 % organic carbon (w/w) can have up to four orders of magnitude more ice nucleation sites per unit mass active in the immersion freezing mode at −12 °C than montmorillonite, the nucleation properties of which are often used to represent those of mineral dusts in modelling studies. Most of this activity was lost after heat treatment. Removal of biological residues reduced ice nucleation activity to, or below that of montmorillonite. Desert soils, inherently low in organic content, are a large natural source of dust in the atmosphere. In contrast, agricultural land use is concentrated on fertile soils with much larger organic matter contents than found in deserts. It is currently estimated that the contribution of agricultural soils to the global dust burden is less than 20 %. Yet, these disturbed soils can contribute ice nuclei to the atmosphere of a very different and much more potent kind than mineral dusts

Stable carbon isotopes as indicators for micro-geomorphic changes in palsa peats

Palsa peats are unique northern ecosystems formed under an arctic climate and characterized by a high biodiversity and sensitive ecology. The stability of the palsas are seriously threatened by climate warming which will change the permafrost dynamic and induce a degradation of the mires. We used stable carbon isotope depth profiles in two palsa mires of Northern Sweden to track environmental change during the formation of the mires. Soils dominated by aerobic degradation can be expected to have a clear increase of carbon isotopes (δ13C) with depth, due to preferential release of 12C during aerobic mineralization. In soils with suppressed degradation due to anoxic conditions, stable carbon isotope depth profiles are either more or less uniform indicating no or very low degradation or depth profiles turn to lighter values due to an enrichment of recalcitrant organic substances during anaerobic mineralisation which are depleted in 13C. The isotope depth profile of the peat in the water saturated depressions (hollows) at the yet undisturbed mire Storflaket indicated very low to no degradation but increased rates of anaerobic degradation at the Stordalen site. The latter might be induced by degradation of the permafrost cores in the uplifted areas (hummocks) and subsequent breaking and submerging of the hummock peat into the hollows due to climate warming. Carbon isotope depth profiles of hummocks indicated a turn from aerobic mineralisation to anaerobic degradation at a peat depth between 4 and 25 cm. The age of these turning points was 14C dated between 150 and 670 yr and could thus not be caused by anthropogenically induced climate change. We found the uplifting of the hummocks due to permafrost heave the most likely explanation for our findings. We thus concluded that differences in carbon isotope profiles of the hollows might point to the disturbance of the mires due to climate warming or due to differences in hydrology. The characteristic profiles of the hummocks are indicators for micro-geomorphic change during permafrost up heaving

Mercury evasion from a boreal peatland determined with advanced REA and chamber methods

Gasförmiges, elementares Quecksilber (Hg^0) ist die dominierende Form von Hg in der Atmosphäre und steht in ständigem Austausch mit Böden und Wasseroberflächen. In borealen Mooren ist dieser Land-Atmosphären-Austausch von Hg^0 von besonderer Relevanz. - in solch anoxischen Ökosystem bildet sich das hochtoxische Methylquecksilber (MeHg) - , da sich verändernde Depositions- und Emissionsraten den Hg-Pool im Boden beeinflussen. Um natürliche influssfaktoren zu bestimmen, welche die Reduktion von Hg(II) zu Hg^0 und damit die Ausgasung fördern, haben wir dynamische Durchflusskammern (DFCs) verwendet. Der Effekt von erhöhter Schwefel- und Stickstoffdeposition sowie veränderten Temperatur- und Feuchtebedingungen auf den Hg^0-Fluss wurden untersucht und typische Flussraten für unser Untersuchungsgebiet quantifiziert. Das boreale Moor liegt etwa 10 Kilometer westlich von Vindeln, in der Provinz Västerbotten in Schweden. Um den ganzjährigen In- und Output von Hg^0 über die Atmosphäre zu quantifizieren, entwickelten wir ein neues Relaxed Eddy Accumulation (REA) System mit zwei Lufteinlässen, nur einem Detektor und einem ausgefeilten, automatischen Kalibrationsmodul. Während den Hg-Messungen wurden meteorologische Parameter, im Wasser gelöstes Hg^0(DGM) und die Gesamtdeposition von Hg gemessen. Letztere während der Vegetationsperiode 2014. Das Gesamt-Hg im Boden und im Abflussbereich des Moores wurde vorgängig bestimmt und trägt zum besseren Verständnis des Hg-Kreislaufs bei. Hohe Schwefeldepositionen, wie sie in den 80er-Jahren in Schweden üblich waren, führten zu einer Hemmung von Hg-Emissionen. Dies ist mit einer initialen Ausgasung von Hg zu Beginn des Versuches oder mit dem Binden von Hg an Schwefelgruppen und anschliessendem Abtransport im Oberflächenwasser zu erklären. DFC-Messungen im Juli 2014 wurden während Strahlungstagen durchgeführt und zeigten einen deutlichen Tagesgang und eine starke lineare Abhängigkeit von der Temperatur innerhalb und ausserhalb der Kammern. Erste Auswertungen der REA-Daten zeigten eine Spannweite der Monatsmittelwerte zwischen -6 ng m^-2 h^-1 im November 2013 und 15 ng m^-2 h^-1 im Juni 2014. Hg^0-Emissionen dominierten während des Sommers und Hg^0-Deposition von Spätherbst bis Frühling. Als erste Forschungsgruppe gelang es uns, den Hg^0-Fluss über einem borealen Moor während eines ganzen Jahres zu messen und dabei REA erfolgreich anzuwenden. Des Weiteren konnten wir mit DFC-Messungen Faktoren identifizieren, welche Hg^0-Emissionen hemmen oder begünstigen. Die Ausgasung von Hg^0 in die Atmosphäre scheint die Menge im Abfluss deutlich zu übersteigen und deutet darauf hin, dass das boreale Moor heute nicht nur eine Quelle für MeHg, sondern auch für Gesamt-Hg ist

Soil erosion in an avalanche release site (Valle d'Aosta: Italy): towards a winter factor for RUSLE in the Alps

Soil erosion in Alpine areas is mainly related to extreme topographic and weather conditions. Although different methods of assessing soil erosion exist, the knowledge of erosive forces of the snow cover needs more investigation in order to allow soil erosion modeling in areas where the snow lays on the ground for several months. This study aims to assess whether the RUSLE (Revised Universal Soil Loss Equation) empirical prediction model, which gives an estimation of water erosion in t ha yr⁻¹ obtained from a combination of five factors (rainfall erosivity, soil erodibility, topography, soil cover, protection practices) can be applied to mountain areas by introducing a winter factor (<i>W</i>), which should account for the soil erosion occurring in winter time by the snow cover. The <i>W</i> factor is calculated from the ratio of Ceasium-137 (¹³⁷Cs) to RUSLE erosion rates. Ceasium-137 is another possible way of assessing soil erosion rates in the field. In contrast to RUSLE, it not only provides water-induced erosion but integrates all erosion agents involved. Thus, we hypothesize that in mountain areas the difference between the two approaches is related to the soil erosion by snow. In this study we compared ¹³⁷Cs-based measurement of soil redistribution and soil loss estimated with RUSLE in a mountain slope affected by avalanches, in order to assess the relative importance of winter erosion processes such as snow gliding and full-depth avalanches. Three subareas were considered: DS, avalanche defense structures, RA, release area, and TA, track area, characterized by different prevalent winter processes. The RUSLE estimates and the ¹³⁷Cs redistribution gave significantly different results. The resulting ranges of <i>W</i> evidenced relevant differences in the role of winter erosion in the considered subareas, and the application of an avalanche simulation model corroborated these findings. Thus, the higher rates obtained with the ¹³⁷Cs method confirmed the relevant role of winter soil erosion. Despite the limited sample size (11 points), the inclusion of a <i>W</i> factor in RUSLE seems promising for the improvement of soil erosion estimates in Alpine environments affected by snow movements

Comparative study of elemental mercury flux measurement techniques over a Fennoscandian boreal peatland

Quantitative estimates of the land-atmosphere exchange of gaseous elemental mercury (GEM) are biased by the measurement technique employed, because no standard method or scale in space and time are agreed upon. Here we present concurrent GEM exchange measurements over a boreal peatland using a novel relaxed eddy accumulation (REA) system, a rectangular Teflon (R) dynamic flux chamber (DFC) and a DFC designed according to aerodynamic considerations (Aero-DFC). During four consecutive days the DFCs were placed alternately on two measurement plots in every cardinal direction around the REA sampling mast. Spatial heterogeneity in peat surface characteristics (0-34 cm) was identified by measuring total mercury in eight peat cores (57 +/- 8 ng g(-1), average SE), vascular plant coverage (32-52%), water table level (4.5-14.1 cm) and dissolved gaseous elemental mercury concentrations (28-51 pg L-1) in the peat water. The GEM fluxes measured by the DFCs showed a distinct diel pattern, but no spatial difference in the average fluxes was detected (ANOVA, alpha = 0.05). Even though the correlation between the Teflon DFC and Aero-DFC was significant (r = 0.76, p &lt; 0.05) the cumulative flux of the Aero-DFC was a factor of three larger. The average flux of the Aero-DFC (1.9 ng m(-2) h(-1)) and REA (2 ng m(-2) h(-1)) were in good agreement. The results indicate that the novel REA design is in agreement for cumulative flux estimates with the Aero-DFC, which incorporates the effect of atmospheric turbulence. The comparison was performed over a fetch with spatially rather homogenous GEM flux dynamics under fairly consistent weather conditions, minimizing the effect of weather influence on the data from the three measurement systems. However, in complex biomes with heterogeneous surface characteristics where there can be large spatial variability in GEM gas exchange, the small footprint of chambers ( &lt; 0.2 m(2)) makes for large coefficients of variation. Thus many chamber measurement replications are needed to establish a credible biome GEM flux estimate, even for a single point in time. Dynamic flux chambers will, however, be able to resolve systematic differences between small scale features, such as experimentally manipulated plots or small scale spatial heterogeneity

Plants or bacteria? 130 years of mixed imprints in Lake Baldegg sediments (Switzerland), as revealed by compound-specific isotope analysis (CSIA) and biomarker analysis

Soil erosion and associated sediment transfer are among the major causes of aquatic ecosystem and surface water quality impairment. Through land use and agricultural practices, human activities modify the soil erosive risk and the catchment connectivity, becoming a key factor of sediment dynamics. Hence, restoration and management plans of water bodies can only be efficient if the sediment sources and the proportion attributable to different land uses are identified. According to this aim, we applied two approaches, namely compound-specific isotope analysis (CSIA) of long-chain fatty acids (FAs) and triterpenoid biomarker analysis, to a eutrophic lake, Lake Baldegg, and its agriculturally used catchment (Switzerland). Soils reflecting the five main land uses of the catchment (arable lands, temporary and permanent grasslands, mixed forests, orchards) were subjected to CSIA. The compound-specific stable isotope δ13C signatures clearly discriminate between potential grasslands (permanent and temporary) and forest sources. Signatures of agricultural land and orchards fall in between. The soil signal was compared to the isotopic signature of a lake sediment sequence covering ca. 130 years (before 1885 to 2009). The recent lake samples (1940 to 2009, with the exception of 1964 to 1972) fall into the soil isotopic signature polygon and indicate an important contribution of the forests, which might be explained by (1) the location of the forests on steep slopes, resulting in a higher connectivity of the forests to the lake, and/or (2) potential direct inputs of trees and shrubs growing along the rivers feeding the lake and around the lake. However, the lake sediment samples older than 1940 lie outside the source soils' polygon, as a result of FA contribution from a not yet identified source, most likely produced by an in situ aquatic source, either algae, bacteria or other microorganisms or an ex-site historic source from wetland soils and plants (e.g. Sphagnum species). Despite the overprint of the yet unknown source on the historic isotopic signal of the lake sediments, land use and catchment history are clearly reflected in the CSIA results, with isotopic shifts being synchronous with changes in the catchment, land use and eutrophication history. The investigated highly specific biomarkers were not detected in the lake sediment, even though they were present in the soils. However, two trimethyltetrahydrochrysenes (TTHCs), natural diagenetic products of pentacyclic triterpenoids, were found in the lake sediments. Their origin is attributed to the in situ microbial degradation of some of the triterpenoids. While the need to apportion sediment sources is especially crucial in eutrophic systems, our study stresses the importance of exercising caution with CSIA and triterpenoid biomarkers in such environments, where the active metabolism of bacteria might mask the original terrestrial isotopic signals.</p