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

Algebraic quantization of the closed bosonic string

The gauge invariant observables of the closed bosonic string are quantized without anomalies in four space-time dimensions by constructing their quantum algebra in a manifestly covariant approach. The quantum algebra is the kernel of a derivation on the universal envelopping algebra of an infinite-dimensional Lie algebra. The search for Hilbert space representations of this algebra is separated from its construction, and postponed.Comment: 22 pages. Revised: minor changes as in the published version (CMP

The invariant charges of the Nambu-Goto String and Canonical Quantization

It is shown that the algebra of diffeomorphism-invariant charges of the Nambu-Goto string cannot be quantized in the framework of canonical quantization. The argument is shown to be independent of the dimension of the underlying Minkowski space.Comment: v2: reference adde

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

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

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

Tracing of particulate organic C sources across the terrestrial-aquatic continuum, a case study at the catchment scale (Carminowe Creek, southwest England)

Soils deliver crucial ecosystem services, such as climate regulation through carbon (C) storage and food security, both of which are threatened by climate and land use change. While soils are important stores of terrestrial C, anthropogenic impact on the lateral fluxes of C from land to water remains poorly quantified and not well represented in Earth system models. In this study, we tested a novel framework for tracing and quantifying lateral C fluxes from the terrestrial to the aquatic environment at a catchment scale. The combined use of conservative plant-derived geochemical biomarkers n-alkanes and bulk stable δ13C and δ15N isotopes of soils and sediments allowed us to distinguish between particulate organic C sources from different land uses (i.e. arable and temporary grassland vs. permanent grassland vs. riparian woodland vs. river bed sediments) (p < 0.001), showing an enhanced ability to distinguish between land use sources as compared to using just n-alkanes alone. The terrestrial-aquatic proxy (TAR) ratio derived from n-alkane signatures indicated an increased input of terrestrial-derived organic matter (OM) to lake sediments over the past 60 years, with an increasing contribution of woody vegetation shown by the C27/C31 ratio. This may be related to agricultural intensification, leading to enhanced soil erosion, but also an increase in riparian woodland that may disconnect OM inputs from arable land uses in the upper parts of the study catchment. Spatial variability of geochemical proxies showed a close coupling between OM provenance and riparian land use, supporting the new conceptualization of river corridors (active river channel and riparian zone) as critical zones linking the terrestrial and aquatic C fluxes. Further testing of this novel tracing technique shows promise in terms of quantification of lateral C fluxes as well as targeting of effective land management measures to reduce soil erosion and promote OM conservation in river catchments

Canonical quantization of non-commutative holonomies in 2+1 loop quantum gravity

In this work we investigate the canonical quantization of 2+1 gravity with cosmological constant $\Lambda>0$ in the canonical framework of loop quantum gravity. The unconstrained phase space of gravity in 2+1 dimensions is coordinatized by an SU(2) connection $A$ and the canonically conjugate triad field $e$. A natural regularization of the constraints of 2+1 gravity can be defined in terms of the holonomies of $A+=A + \sqrt\Lambda e$. As a first step towards the quantization of these constraints we study the canonical quantization of the holonomy of the connection $A_{\lambda}=A+\lambda e$ on the kinematical Hilbert space of loop quantum gravity. The holonomy operator associated to a given path acts non trivially on spin network links that are transversal to the path (a crossing). We provide an explicit construction of the quantum holonomy operator. In particular, we exhibit a close relationship between the action of the quantum holonomy at a crossing and Kauffman's q-deformed crossing identity. The crucial difference is that (being an operator acting on the kinematical Hilbert space of LQG) the result is completely described in terms of standard SU(2) spin network states (in contrast to q-deformed spin networks in Kauffman's identity). We discuss the possible implications of our result.Comment: 19 pages, references added. Published versio