47 research outputs found
Glacier − Permafrost Interaction at a Thrust Moraine Complex in the Glacier Forefield Muragl, Swiss Alps
No full textThe internal structures of a moraine complex mostly provide information about the manner in which they develop and thus they can transmit details about several processes long after they have taken place. While the occurrence of glacier–permafrost interactions during the formation of large thrust moraine complexes at polar and subpolar glaciers as well as at marginal positions of former ice sheets has been well understood, their role in the formation of moraines on comparatively small alpine glaciers is still very poorly investigated. Therefore, the question arises as to whether evidence of former glacier–permafrost interactions can still be found in glacier forefields of small alpine glaciers and to what extent these differ from the processes in finer materials at larger polar or subpolar glaciers. To investigate this, electrical resistivity tomography (ERT) and ground-penetrating radar (GPR) surveys were carried out in the area of a presumed alpine thrust moraine complex in order to investigate internal moraine structures. The ERT data confirmed the presence of a massive ice core within the central and proximal parts of the moraine complex. Using GPR, linear internal structures were detected, which were interpreted as internal shear planes due to their extent and orientation. These shear planes lead to the assumption that the moraine complex is of glaciotectonic origin. Based on the detected internal structures and the high electrical resistivity values, it must also be assumed that the massive ice core is of sedimentary or polygenetic origin. The combined approach of the two methods enabled the authors of this study to detect different internal structures and to deduce a conceptual model of the thrust moraine formation
Geophysical and Sedimentological Investigations of Peatlands for the Assessment of Lithology and Subsurface Water Pathways
No full textPeatlands located on slopes (herein called slope bogs) are typical landscape units in the Hunsrueck, a low mountain range in Southwestern Germany. The pathways of the water feeding the slope bogs have not yet been documented and analyzed. The identification of the different mechanisms allowing these peatlands to originate and survive requires a better understanding of the subsurface lithology and hydrogeology. Hence, we applied a multi-method approach to two case study sites in order to characterize the subsurface lithology and to image the variable spatio-temporal hydrological conditions. The combination of Electrical Resistivity Tomography (ERT) and an ERT-Monitoring and Ground Penetrating Radar (GPR), in conjunction with direct methods and data (borehole drilling and meteorological data), allowed us to gain deeper insights into the subsurface characteristics and dynamics of the peatlands and their catchment area. The precipitation influences the hydrology of the peatlands as well as the interflow in the subsurface. Especially, the geoelectrical monitoring data, in combination with the precipitation and temperature data, indicate that there are several forces driving the hydrology and hydrogeology of the peatlands. While the water content of the uppermost layers changes with the weather conditions, the bottom layer seems to be more stable and changes to a lesser extent. At the selected case study sites, small differences in subsurface properties can have a huge impact on the subsurface hydrogeology and the water paths. Based on the collected data, conceptual models have been deduced for the two case study sites
Three‐dimensional investigation of an open‐ and a closed‐system Pingo in northwestern Canada
No full textThe present study presents three-dimensional investigations of a hydrostatic pingo in the Mackenzie Delta region and a hydraulic pingo in the Ogilvie Mountains and contributes to a better understanding about the internal structures of the two pingo types. A combined approach using quasi-three-dimensional electrical resistivity tomography, ground-penetrating radar and frost probing allowed a clear delineation of frozen and unfrozen areas in the subsurface. At the hydrostatic pingo a massive ice core as well as a surrounding talik could be detected, but the location of the ice core and the talik differs from previous published assumptions. In contrast to acknowledged theory, at our site the massive ice core is not located in the center of the pingo but at the western edge, whereas the eastern flank is underlain by a talik, which surrounds the massive ice core. At the hydraulic pingo, the expected internal structure could be confirmed and the pathway of upwelling water could also be detected. The combined approach of the applied methods represents the first known three-dimensional geoelectrical investigation of pingos and provides new insights into the internal structure and architecture of the two different pingo types. The chosen approach allows further conclusions on the formation of these permafrost-affected landforms
Permafrost and Glaciers: Perspectives for the Earth and Planetary Sciences—Another Step Forward
No full text"Permafrost and glaciers are the most important components of the cryosphere. Their
mutual relationship has only recently become the subject of interdisciplinary research. The
fact that most of the permafrost and glacial studies have been carried out separately is an
obstacle to further consistent progress within this scientific field. Moreover, the progressive
specialization of research in Earth sciences has led to increasing difficulties with the holistic
view of the cryosphere in general." [...] (fragm.
Multi-method soil moisture monitoring at two temperate forest stands in Germany
No full textMany forests suffer increased drought stress due to climate change, particularly impacting Central Europe. However, our understanding considering drought stress and resulting tree mortality remains incomplete. For addressing this issue, fine-scale water balance assessment as well as robust and spatially integrating measures on large scales are necessary for forest ecosystem monitoring. The latter is particularly important to provide reliable data sets for verifying remote sensing and hydrological modelling products. Various traditional in-situ methods exist for assessing the water balance in forest ecosystems as for instance measuring the water content or matric potential. However, the spatial limitations of these methods have led to an increased importance of Cosmic Ray Neutron Sensing (CRNS) in the last two decades whose measuring signal is integrated over a larger area. We equipped two forest monitoring plots with ECH2O probes, Tensiomark soil systems, and installed a CRNS station at one site to measure soil water content and matric potential at different soil depths and distances to trees from November 2020 till November 2023. The results indicate distinct temporal and spatial variations influenced by meteorological conditions and soil properties, but also forest characteristics. The year 2022 is identified as exceptionally dry, causing high drought stress at one of the forest sites. The comparison between CRNS and traditional methods reveals a strong correlation, highlighting CRNS' potential in forest monitoring as a promising tool for an area wide assessment of water availability in forest ecosystems. Our study further advocates for the need of tree species-specific thresholds to assess matric potential in relation to drought stress in order to better assess the impact of climate change on our forest ecosystems
Stadtwald und Stadtbiotope die teils naturnahen Wälder und Fluren in und um Würzburg erfüllen wesentliche ökologische und gesellschaftliche Funktionen für Stadt und Umland. Die systematische Kartierung von ökologisch wertvollen Flächen in den Würzburger Gemarkungen bildet die Grundlage für integrale Schutz- und Pflegekonzepte sowie für die Bauplanung
No full textMonitoring spatiotemporal soil moisture variability in the unsaturated zone of a mixed forest using electrical resistivity tomography
No full textEuropean forests are suffering considerably from the consequences of the droughts of recent years, and the exact reasons and influencing factors for this are still not fully understood. This study was conducted to characterize the changes and dynamics of soil moisture in a mixed forest in northern Bavaria within 1 year. Since electrical resistivity correlates well with soil water content, we used two‐dimensional electrical resistivity tomography (ERT) monitoring and time‐lapse analyses to supplement punctual measurements by sensors and soil analyses to show soil moisture changes throughout a whole year (2020–2021). While the topsoil dries out significantly from summer to autumn down to a depth of about 3 m, a clear increase in soil water content and a decrease in resistivity below 3 m can be observed during winter period. Anomalies in the topsoil (0–1 m) showing lower resistivities than the surrounding substrate could be related to tree positions by additional terrestrial laser scans. A significant relationship could be found between tree crown projection area and resistivity in 1–2 m depth. We found a trend that mean resistivity below pine is lower as below beech. ERT data were also used to estimate the soil water content via Archie's law and the results correlate strongly with the measured values, but the degree of correlation varies depending on the depth level. ERT as a noninvasive method, in combination with additional data, for example, on the vitality status of individual trees, could help to better understand root water uptake and water supply to trees, especially during periods of drought
Combined 2D- and 3D ERT monitoring as a geophysical tool for investigating spatial and temporal soil moisture fluctuations in a pine-beech forest
No full textAs climate change continues, forests are increasingly suffering from drought stress, which is leading to widespread forest dieback, but also to increased mortality of individual trees. In this regard, the impact of small-scale differences in water availability on individual trees has not yet been sufficiently studied to determine possible responses of different tree species to future droughts. Since conventional soil moisture monitoring and sampling methods only consider single points or small volumes, Electrical Resistivity Tomography (ERT) is becoming increasingly important to cover a larger survey area and to detect small-scale heterogeneities with regard to soil properties and soil moisture.
The current study describes the application of a combined two- and three-dimensional geoelectrical monitoring approach with daily measurements over two years (May 2021 – April 2023) in a forest ecosystem in Lower Franconia (northwestern Bavaria, Germany), which is strongly affected by climate change. Soil water content, soil matric potential, throughfall, and stem flow are also measured at the forest site as well as precipitation at an adjacent forest clearing.
The seasonally (long-term) and precipitation-driven (short-term) temporal change of soil resistivity is correlated strongly with the measured soil water content and matric potential. The applied 3D-ERT approach also allowed a first three-dimensional monitoring of the subsurface below a European beech located in the middle of the measuring grid with a daily resolution. The corresponding results also provide first indications that besides soil moisture changes also chemical processes in the subsurface may influence temporal resistivity changes in the soil of forest sites.
The results of this study show that daily 3D-ERT is very suitable for investigating small-scale as well as short- and long-term variations in soil moisture, which is becoming increasingly important for understanding the causal relationships considering tree mortality and the subsurface
Monitoring of thermal conditions and snow dynamics at periglacial block accumulations in a low mountain range in central Germany
No full textThe Rhoen Mountains, a relict periglacial landscape in central Germany, feature a wide range of openwork block accumulations. Although located in a temperate climate, those have characteristics comparable with cold regions of higher altitude or latitude such as arctic‐alpine species, longer lasting snow patches or the discussed existence of summer or even year‐round ice lenses in one of the largest of these landforms in the Central German Uplands. This study aims for a characterization of the microclimatic conditions of two neighbouring block accumulations. Therefore, temperatures were registered by data loggers along profiles, and snow dynamics were monitored using time‐lapse cameras and terrestrial laser scans. These observations are finally compared with geophysical measurements to address the question of potential isolated low‐altitude permafrost occurrences. Mean ground surface temperatures show an inverse thermal gradient along the Schafstein block accumulation. Furrows were identified as the cold spots in winter, whereas snow melt holes are signs of a chimney effect. In summer, cold air flows out at ventilation holes along the front causing temperatures of up to 25°C below air temperatures, although no clear signs of permafrost were detected. Temperature correlations reveal periods indicative of a recurring internal summer air circulation. Coarse blocky substrate also favours ground cooling of the smaller Mathesberg block accumulation compared with its surroundings. Winter temperatures are influenced by a persistent snowbank forming due to drifting and blowing snow at the leeward edge of a plateau as little amounts of snow are sufficient to be redistributed by westerlies. The prolonged melt of the snowbank might have had or still has a local hydrological and geomorphological impact. Uncertainties remain regarding the behaviour of the microclimate of block accumulations in a warming climate. Being ‘cold spots’ of high ecological value further investigations are suggested
