Final Report Summary - SEDIMED (Effects of Land Cover Change and Land Abandonment on Sediment Yield in Semiarid Mediterranean Catchments Using Remote Sensing, GIS and Field Techniques)
Project aims and objectives
The main objective of the SEDIMED project is to quantify the effect of human activity on land degradation, based on a reconstruction of erosion rates and land use changes by an interdisciplinary approach that integrates techniques and methods from a variety of disciplines within the earth sciences, such as geomorphology, geo-archaeology, remote sensing and geochemistry. We selected the Tajo and Guadiana basin in central Spain for our analysis, as human land pressure is well documented for the last 1500 years. Specifically, we selected several catchments where water and sediment fluxes are controlled by historic reservoirs from the Roman era. In table 1 there is a description of the historic reservoirs surveyed. The catchment areas are generally small because limited construction techniques in the past made it impossible to hold big water volumes in the reservoirs.
In this project, we worked at two different spatial scales. First, we analysed temporal changes in erosion rates at 10, 100 and 10 000 years for the four sites that are described in table 1:
(A) The long-term integrated erosion rates were quantified based on concentrations of in-situ produced 10Be cosmogenic nuclides. River-borne sediments were taken at the outlets of the catchment, and samples were prepared for cosmogenic nuclide analyses. New data on long-term erosion rates (i.e. 10 000 years) were obtained.
(B) Medium-term erosion rates (i.e. 100 years) were reconstructed based on sediment accumulation rates in historical sites. Historical dam sites were the principal objects of this study, as their sedimentation history allows reconstructing catchment-wide erosion rates through historical time.
(C) Modern erosion rates (i.e. last 10 years) were derived from the literature. Existing erosion measurements on experimental plots were used to constrain modern erosion rates.
(D) Modern, medium-term and long-term erosion rates were compared for these four archaeological sites. Our data show that modern erosion rates are not significantly different from medium-term and long-term erosion rates, with the only exception of the modern erosion rates that are measured in irrigated croplands.
In a second step, we focused on the medieval Christian complex of Santa Maria de Melque (Toledo, Spain) because it has been widely studied from different perspectives. This complex, delimited by a perimetral fence, included a monastic church, Christian and Muslim villages and several reservoirs. Until now, studies have focused on the archaeological excavation of the surroundings of the church, collecting samples for 14C dating, anthracological, palynological and paleocarpological studies. We carried on new studies in this area that are described below:
(A) Mineralogy and elemental analyses of samples of bedrocks, soils and sediments retained in the reservoirs. The samples were analysed at the facilities of the soil department of the Université Catholique de Louvain (UCL), Belgium.
(B) Study in situ produced 10Be cosmogenic nuclide concentrations in soils and sediments retained in man-made reservoirs. Cleaning, pre-treatment and purification of the samples have been done at the geochemical laboratory at the host institution (UCL). Ratios of 10Be/9Be were measured in BeO targets at the ETH Zurich (Switzerland) accelerator mass spectrometer.
(C) Dating of soils, sediments and man-made constructions based on optically stimulated luminescence (OSL) dating techniques. Samples were taken in collaboration with J. Sanjurjo Sanchez and were sent to the Geological institute 'Isidro Parga Pondal' (La Coruna, Spain) for determination.
(D) Geophysical investigation of the sediment accumulation in man-made reservoir. A refined 3D model of accumulation of sediments was developed with data from seismic refraction equipment provided by International Geophysical Technology, S.L. (IGT Ltd.), Spain.
About the results, we can stress that, on one hand, long term erosion rates derived from 10Be cosmogenic nuclide ranged between 9.36 and 115.54 m/My (mean = 32.5 ± 3.7). On the other hand, the values for medium term erosion rates deduced from the sediments in reservoirs varied between 0.84 and 25.22 m/My. Our data suggest that there are no substantial differences between long and medium term erosion rates for the study sites.
Using the OSL dating technique in Melque, Spain, we reconstructed the time during which the reservoirs were operative. We concluded that the first of the dikes (M3: 650 750 a.D) must be coetaneous to the monastic building. During the Muslim occupation, a village was set and after the Christian conquest, two new reservoirs were built (M1; 968 1187 a.D; and M4; 1096 1265 a.D). Finally, in the XIII-XIV century, a new dike (M2; 1252 1476 a.D) was constructed.
The minerals identified are typical of metamorphic granitic eroded areas: feldspars (albite, anhortite, microcline, orthoclase), quartz, carbonates (calcite, dolomite, aragonite), oxides (rutile, hematite, goethite), micas (muscovite and biotite) and clay minerals (kaolinite, montmorillonite, muscovite, vermiculite).
From our results, we concluded that in Central and Western Spain, past land use and agriculture practices were sustainable in terms of soil conservation. Our data suggest that natural vegetation rapidly restores the vegetation cover in abandoned agricultural areas, thereby drastically reducing erosion rates. In Melque, the results show that there are no statistical differences between long and medium term erosion rates and the dating of sediments and dikes show a long time of exploitation of the complex, which changed the previous conception of human occupation in the area.
The new data that were collected during this project allow reconsideration of the interaction between humans and their environment. Modern erosion rates can be placed in their correct context when a long-term perspective is added. About the diffusion of the research project, apart from publications, there is a website (see links below) hosted at the Centre de recherche sur la terre et le climat Georges Lemaître - TECLIM:
http://www.climate.be/modx/index.php?id=165(öffnet in neuem Fenster)
http://www.astr.ucl.ac.be/modx/index.php?id=163(öffnet in neuem Fenster).
The main objective of the SEDIMED project is to quantify the effect of human activity on land degradation, based on a reconstruction of erosion rates and land use changes by an interdisciplinary approach that integrates techniques and methods from a variety of disciplines within the earth sciences, such as geomorphology, geo-archaeology, remote sensing and geochemistry. We selected the Tajo and Guadiana basin in central Spain for our analysis, as human land pressure is well documented for the last 1500 years. Specifically, we selected several catchments where water and sediment fluxes are controlled by historic reservoirs from the Roman era. In table 1 there is a description of the historic reservoirs surveyed. The catchment areas are generally small because limited construction techniques in the past made it impossible to hold big water volumes in the reservoirs.
In this project, we worked at two different spatial scales. First, we analysed temporal changes in erosion rates at 10, 100 and 10 000 years for the four sites that are described in table 1:
(A) The long-term integrated erosion rates were quantified based on concentrations of in-situ produced 10Be cosmogenic nuclides. River-borne sediments were taken at the outlets of the catchment, and samples were prepared for cosmogenic nuclide analyses. New data on long-term erosion rates (i.e. 10 000 years) were obtained.
(B) Medium-term erosion rates (i.e. 100 years) were reconstructed based on sediment accumulation rates in historical sites. Historical dam sites were the principal objects of this study, as their sedimentation history allows reconstructing catchment-wide erosion rates through historical time.
(C) Modern erosion rates (i.e. last 10 years) were derived from the literature. Existing erosion measurements on experimental plots were used to constrain modern erosion rates.
(D) Modern, medium-term and long-term erosion rates were compared for these four archaeological sites. Our data show that modern erosion rates are not significantly different from medium-term and long-term erosion rates, with the only exception of the modern erosion rates that are measured in irrigated croplands.
In a second step, we focused on the medieval Christian complex of Santa Maria de Melque (Toledo, Spain) because it has been widely studied from different perspectives. This complex, delimited by a perimetral fence, included a monastic church, Christian and Muslim villages and several reservoirs. Until now, studies have focused on the archaeological excavation of the surroundings of the church, collecting samples for 14C dating, anthracological, palynological and paleocarpological studies. We carried on new studies in this area that are described below:
(A) Mineralogy and elemental analyses of samples of bedrocks, soils and sediments retained in the reservoirs. The samples were analysed at the facilities of the soil department of the Université Catholique de Louvain (UCL), Belgium.
(B) Study in situ produced 10Be cosmogenic nuclide concentrations in soils and sediments retained in man-made reservoirs. Cleaning, pre-treatment and purification of the samples have been done at the geochemical laboratory at the host institution (UCL). Ratios of 10Be/9Be were measured in BeO targets at the ETH Zurich (Switzerland) accelerator mass spectrometer.
(C) Dating of soils, sediments and man-made constructions based on optically stimulated luminescence (OSL) dating techniques. Samples were taken in collaboration with J. Sanjurjo Sanchez and were sent to the Geological institute 'Isidro Parga Pondal' (La Coruna, Spain) for determination.
(D) Geophysical investigation of the sediment accumulation in man-made reservoir. A refined 3D model of accumulation of sediments was developed with data from seismic refraction equipment provided by International Geophysical Technology, S.L. (IGT Ltd.), Spain.
About the results, we can stress that, on one hand, long term erosion rates derived from 10Be cosmogenic nuclide ranged between 9.36 and 115.54 m/My (mean = 32.5 ± 3.7). On the other hand, the values for medium term erosion rates deduced from the sediments in reservoirs varied between 0.84 and 25.22 m/My. Our data suggest that there are no substantial differences between long and medium term erosion rates for the study sites.
Using the OSL dating technique in Melque, Spain, we reconstructed the time during which the reservoirs were operative. We concluded that the first of the dikes (M3: 650 750 a.D) must be coetaneous to the monastic building. During the Muslim occupation, a village was set and after the Christian conquest, two new reservoirs were built (M1; 968 1187 a.D; and M4; 1096 1265 a.D). Finally, in the XIII-XIV century, a new dike (M2; 1252 1476 a.D) was constructed.
The minerals identified are typical of metamorphic granitic eroded areas: feldspars (albite, anhortite, microcline, orthoclase), quartz, carbonates (calcite, dolomite, aragonite), oxides (rutile, hematite, goethite), micas (muscovite and biotite) and clay minerals (kaolinite, montmorillonite, muscovite, vermiculite).
From our results, we concluded that in Central and Western Spain, past land use and agriculture practices were sustainable in terms of soil conservation. Our data suggest that natural vegetation rapidly restores the vegetation cover in abandoned agricultural areas, thereby drastically reducing erosion rates. In Melque, the results show that there are no statistical differences between long and medium term erosion rates and the dating of sediments and dikes show a long time of exploitation of the complex, which changed the previous conception of human occupation in the area.
The new data that were collected during this project allow reconsideration of the interaction between humans and their environment. Modern erosion rates can be placed in their correct context when a long-term perspective is added. About the diffusion of the research project, apart from publications, there is a website (see links below) hosted at the Centre de recherche sur la terre et le climat Georges Lemaître - TECLIM:
http://www.climate.be/modx/index.php?id=165(öffnet in neuem Fenster)
http://www.astr.ucl.ac.be/modx/index.php?id=163(öffnet in neuem Fenster).