Monika Schaub

Stable carbon isotopes as an indicator for soil degradation in an alpine environment (Urseren Valley, Switzerland)

Analyses of soil organic carbon (SOC) content and stable carbon isotope signatures (delta(13)C) of soils were assessed for their suitability to detect early stage soil erosion. We investigated the soils in the alpine Urseren Valley (southern central Switzerland) which are highly impacted by soil erosion. Hill slope transects from uplands (cambisols) to adjacent wetlands (histosols and histic to mollic gleysols) differing in their intensity of visible soil erosion, and reference wetlands without erosion influence were sampled. Carbon isotopic signature and SOC content of soil depth profiles were determined. A close correlation of delta(13)C and carbon content (r > 0.80) is found for upland soils not affected by soil erosion, indicating that depth profiles of delta(13)C of these upland soils mainly reflect decomposition of SOC. Long-term disturbance of an upland soil is indicated by decreasing correlation of delta(13)C and SOC (r </= 0.80) which goes in parallel with increasing (visible) damage at the site. Early stage soil erosion in hill slope transects from uplands to adjacent wetlands is documented as an intermediate delta(13)C value (-27.5 per thousand) for affected wetland soil horizons (0-12 cm) between upland (aerobic metabolism, relatively heavier delta(13)C of -26.6 per thousand) and wetland isotopic signatures (anaerobic metabolism, relatively lighter delta(13)C of -28.6 per thousand). Carbon isotopic signature and SOC content are found to be sensitive indicators of short- and long-term soil erosion processes.

Application of in-situ measurement to determine 137Cs in the Swiss Alps.

Establishment of (137)Cs inventories is often used to gain information on soil stability. The latter is crucial in mountain systems, where ecosystem stability is tightly connected to soil stability. In-situ measurements of (137)Cs in steep alpine environments are scarce. Most studies have been carried out in arable lands and with Germanium (Ge) detectors. Sodium Iodide (NaI) detector system is an inexpensive and easy to handle field instrument, but its validity on steep alpine environments has not been tested yet. In this study, a comparison of laboratory measurements with GeLi detector and in-situ measurements with NaI detector of (137)Cs gamma soil radiation has been done in an alpine catchment with high (137)Cs concentration (Urseren Valley, Switzerland). The aim of this study was to calibrate the in-situ NaI detector system for application on steep alpine slopes. Replicate samples from an altitudinal transect through the Urseren Valley, measured in the laboratory with a GeLi detector, showed a large variability in (137)Cs activities at a meter scale. This small-scale heterogeneity determined with the GeLi detector is smoothed out by uncollimated in-situ measurements with the NaI detector, which provides integrated estimates of (137)Cs within the field of view (3.1 m(2)) of each measurement. There was no dependency of (137)Cs on pH, clay content and carbon content, but a close relationship was determined between measured (137)Cs activities and soil moisture. Thus, in-situ data must be corrected for soil moisture. Close correlation (R(2) = 0.86, p < 0.0001) was found for (137)Cs activities (in Bq kg(-1)) estimated with in-situ (NaI detector) and laboratory (GeLi detector) methods. We thus concluded that the NaI detector system is a suitable tool for in-situ measurements in alpine environments. This paper describes the calibration of the NaI detector system for field application under elevated (137)Cs activities originating from Chernobyl fallout.

Determination of δ18O in soils: measuring conditions and a potential application

The stable oxygen isotope signature (delta(18)O) of soil is expected to be the result of a mixture of components within the soil with varying delta(18)O signatures. Thus, the delta(18)O of soils should provide information about the soils substrate, especially about the relative contribution of organic matter versus minerals. As there is no standard method available for measuring soil delta(18)O, the method for the measurement of single components using a high-temperature conversion elemental analyser (TC/EA) was adapted. We measured delta(18)O in standard materials (IAEA 601, IAEA 602, Merck cellulose) and soils (organic and mineral soils) in order to determine a suitable pyrolysis temperature for soil analysis. We consider a pyrolysis temperature suitable when the yield of signal intensity (intensity of mass 28 per 100 microg) is at a maximum and the acquired raw delta(18)O signature is constant for the standard materials used and when the quartz signal from the soil is still negligible. After testing several substances within the temperature range of 1075 to 1375 degrees C we decided to use a pyrolysis temperature of 1325 degrees C for further measurements. For the Urseren Valley we have found a sequence of increasing delta(18)O signatures from phyllosilicates to upland soils, wetland soils and vegetation. Our measurements show that the delta(18)O values of upland soil samples differ significantly from wetland soil samples. The latter can be related to the changing mixing ratio of the mineral and organic constituents of the soil. For wetlands affected by soil erosion, we have found intermediate delta(18)O signatures which lie between typical signatures for upland and wetland sites and give evidence for the input of upland soil material through erosion.