Effects of land cover change and land abandonment on sediment yield in semiarid mediterranean catchments using geochemical, gis and field techniques - SEDIMED
Erosion models often do not allow quantifying the impact of human activities and land use/-cover change on erosion rates, as they are generally calibrated for single erosion processes using short-term erosion data, which represent a combined signal of both natural and human-induced erosion. The use of geochemical techniques, such as in-situ produced cosmogenic nuclides, is seen as offering a means of overcoming some of these problems. This technique has proven to be remarkably accurate to provide long-term natural erosion rates and to analyze quantitatively the impact of human activity on the rate and spatial pattern of erosion processes.
Measurements of cosmogenic nuclides provide new insights into the ways and the rates at which sediment is generated, transported, and deposited over timescales ranging from 1.000 to 1.000.000 years. Sediment fluxes are known to be episodic, and conventional sediment-yield measurements can greatly underestimate or overestimate long-term average sediment flux rates. Cosmogenic nuclide-based denudation rates average out episodic fluctuations in sediment fluxes, and reflect long-term fluxes dominated by the natural preanthropogenic background.
Erosion rates can be inferred from the concentration of cosmogenic isotopes in modern and historical sediment deposits evaluating the differences in concentrations of Terrestrial Cosmogenic Nuclides (TCN's) that are isotopes produced in situ by the interaction between exposed secondary cosmic rays in target minerals. The concentration of TCN’s in a sample is dependent on three factors: the exposure time, the rate of erosion and production rate of the isotope at the sample location.
The Western Mediterranean region is the core region of this project, as it was identified by the United Nations as one of the regions mostly affected by desertification in Europe. The main objective is to provide quantitative data on the historical evolution of erosion processes in relation to past and present land use change.
Figure 1. Left. Melque dam (Visigothic era); Right. Moracanta dam (Roman era).
In this study, we will quantify the concentration of 10Be and 26Al at different depths in soil profiles, reservoir deposits and stream sediments to analyse changes in the rates of erosion. Several terraced dams built in Roman and Visigotic era have been sampled and their human occupation history was reconstructed from literature. These dams are located in small catchments (<10 km2)
Figure 2. DEM and contour lines maps for Melque DAM.
This research project is funded by the European Research Executive Agency. Program Marie Curie Intra European Fellowships: FP7-PEOPLE-IEF-2008. Proposal N° 236064.
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