Soil erosion in the Alps
Land degradation and especially soil erosion are associated with the irretrievable loss of the basic soil resource and thus have a major impact on water and biogeochemical cycles, biodiversity and plant primary productivity. Mountainous Swiss areas are expected to be particularly affected by recurrent extreme events like droughts and/or heavy precipitation (snow/rainfall), which are the main triggering mechanisms of erosional events.
To efficiently mitigate and control soil losses by erosion and reduce their environmental impacts in Alpine grasslands, reliable and validated methods for comprehensive data generation on the magnitude and spatial extent of soil erosion are needed.
How to use Radionuclides to quantify Soil erosion
One approach to quantify erosion rates includes:
- Artificial radionuclides such as 137Cs and Pu isotopes which originated from thermonuclear weapon tests in the 1950s-1960s and nuclear power plant accidents (i.e. Chernobyl);
- Geogenic radioisotopes such as unsupported 210Pb;
- Cosmogenic radioisotopes such as short-lived 7Be.
The basic principles for their applications in soil erosion and sedimentation studies are similar: Radionuclides reach the land surface by dry and wet fallouts from the atmosphere. Because these radionuclides are rapidly and strongly adsorbed to fine soil particles, they accumulate in the top soil with limited migration and bioavailability. Documenting the subsequent redistribution of the radionuclides, which move across the landscape in association with soil/sediment particles primarily through physical processes, requires effective means of tracing rates and patterns of erosion and deposition within landscapes.
To this end, this project is divided in two main section:
- The 137Cs re-sampling approach;
- The use of Pu isotopes as tracer for soil erosion assessment.
1. The 137Cs re-sampling approach
Over the past decades, radioactive fallout 137Cs has been used as a tracer to provide information on soil erosion and sedimentation rates. However, the method may produce relatively large uncertainties in Alpine grasslands. The latter difficulties are caused by a combination of
- the heterogeneous distribution of atmospheric 137Cs Chernobyl fallout;
- the partly snow covered ground in Alpine areas during the fallout event in April 1986, which results in inhomogeneous 137Cs distribution during snow melt;
- uncertainties in finding undisturbed references sites in the geomorphological and anthropogenic highly active slopes of the Alps.
To avoid the uncertainties associated with the high variability of reference sites, we developed a new sampling concept, the 137Cs re-sampling approach.
The idea is to re-sample sites which have already been measured for 137Cs inventories in the past years, thus using temporal instead of spatial reference.
2. The use of Pu isotopes as tracer for soil erosion assessment
Recently, the artificial radioisotope soil and sediment tracer Plutonium (Pu) has been suggested to the research community as a new approach to determine soil erosion rates.
The use of this anthropogenic radioisotope could help to overcome the limitation of 137Cs in mountainous areas (i.e. the spatial heterogeneity of Chernobyl fallout combined with 137Cs deposition on snow covered Alpine ground) as:
- the fallout of 239+240Pu is mostly linked to the past nuclear bomb tests which mainly took place from 1954 to the mid-1960’s;
- it is deposited throughout the year not connected to one single deposition event on snow covered ground;
- the long half-life of Pu isotopes (i.e. 239Pu [half-life = 24110 years] and 240Pu [half-life = 6561 years]) ensures long-term availability to be used as tracers for environmental purposes