Multi-channel ground-penetrating radar to explore spatial variations in thaw depth and moisture content in the active layer of a permafrost site

Multi-channel ground-penetrating radar (GPR) was applied at a permafrost site on the Tibetan Plateau to investigate the influence of surface properties and soil texture on the late-summer thaw depth and average soil moisture content of the active layer. Measurements were conducted on an approximately 85 × 60 m<sup>2</sup> sized area with surface and soil textural properties that ranged from medium to coarse textured bare soil to finer textured, sparsely vegetated areas covered with fine, wind blown sand, and it included the bed of a gravel road. The survey allowed a clear differentiation of the various units. It showed (i) a shallow thaw depth and low average soil moisture content below the sand-covered, vegetated area, (ii) an intermediate thaw depth and high average soil moisture content along the gravel road, and (iii) an intermediate to deep thaw depth and low to intermediate average soil moisture content in the bare soil terrain. From our measurements, we found hypotheses for the permafrost processes at this site leading to the observed late-summer thaw depth and soil moisture conditions. The study clearly indicates the complicated interactions between surface and subsurface state variables and processes in this environment. Multi-channel GPR is an operational technology to efficiently study such a system at scales varying from a few meters to a few kilometers

Einfluss von Maßnahmen der Bodennutzung auf Bodenfunktionen

Eine wesentliche Voraussetzung für eine nachhaltige Bodennutzung ist die Beurteilung der Wirkung von Bodennutzungsmaßnahmen auf Bodenfunktionen. Als solche betrachten wirdie Produktion von Biomasse, die Speicherung von Wasser und Kohlenstoff, die Filterung von Wasser und die Funktion des Bodens als Lebensraum für Organismen. Um den Einfluss von Maßnahmen der Bodennutzung auf diese Funktionen vorhersagenzu können ist ein umfassendes Verständnis von Bodenprozessen unabdingbar. Unser Ansatz ist die dominierenden Komponenten (Prozesse und funktionellen Eigenschaften) in Böden und ihre Interaktionen zu identifizieren. Der Fokus liegt hierbei auf funktionellen Eigenschaften, die sich nur relativ langsam verändern und als Indikatoren für die zugrundeliegenden, wechselwirkenden Bodenprozessen interpretiert werden können. Die Identifizierung der wichtigsten Interaktionen basiert auf einer Analyse der vorhandenen Literatur. Diese soll als Suchmaschine der gesamten bodenwissenschaftlichen Gemeinschaft zur Verfügung gestellt werden. Darüber hinaus wird für spezifische Wechselwirkung auf bestehende Modellansätze zurückgegriffen. Ebenso werden bestehende Modelle genutzt um aus detaillierter Prozessmodellierung die langfristigen Bodenfunktionen abzuschätzen

Monitoring of active layer dynamics at a permafrost site on Svalbard using multi-channel ground-penetrating radar

Multi-channel ground-penetrating radar is used to investigate the late-summer evolution of the thaw depth and the average soil water content of the thawed active layer at a high-arctic continuous permafrost site on Svalbard, Norway. Between mid of August and mid of September 2008, five surveys have been conducted in gravelly soil over transect lengths of 130 and 175 m each. The maximum thaw depths range from 1.6 m to 2.0 m, so that they are among the deepest thaw depths recorded in sediments on Svalbard so far. The thaw depths increase by approximately 0.2 m between mid of August and beginning of September and subsequently remain constant until mid of September. The thaw rates are approximately constant over the entire length of the transects within the measurement accuracy of about 5 to 10 cm. The average volumetric soil water content of the thawed soil varies between 0.18 and 0.27 along the investigated transects. While the measurements do not show significant changes in soil water content over the first four weeks of the study, strong precipitation causes an increase in average soil water content of up to 0.04 during the last week. These values are in good agreement with evapotranspiration and precipitation rates measured in the vicinity of the the study site. While we cannot provide conclusive reasons for the detected spatial variability of the thaw depth at the study site, our measurements show that thaw depth and average soil water content are not directly correlated. <br><br> The study demonstrates the potential of multi-channel ground-penetrating radar for mapping thaw depth in permafrost areas. The novel non-invasive technique is particularly useful when the thaw depth exceeds 1.5 m, so that it is hardly accessible by manual probing. In addition, multi-channel ground-penetrating radar holds potential for mapping the latent heat content of the active layer and for estimating weekly to monthly averages of the ground heat flux during the thaw period