Dreidimensionale Hydrostratigraphie eines Tal-Hang-Aquifers: Integration von Georadar, Geoelektrik, Bodenkunde und Sedimentologie am Beispiel des Seebachs, Nordschwarzwald

Filtering and storage of precipitation, runoff, and subsequent groundwater recharge is governed by the structure and properties of the shallow subsurface and the soils formed therein. Hence, detailed knowledge about the three-dimensional structure, thickness and composition of the shallow subsurface is essential to quantify these processes; special benefit can be derived in connection with the hydraulic and material-specific properties. Geobodies can be mapped by complementary, non-invasive, geophysical methods. Associated with lithofacies, geophysical and other properties these “geobodies” can be fingerprinted. A 3D model containing e.g. porosity, field capacity, permeability, grain size and soil chemistry can be build. Geoelectrical resistance tomography and three-dimensional (3D) ground-penetrating radar surveys have been carried out in the catchment of the “Seebach” (Forbach, Bunter, Black Forest, Southern Germany). A test field was established and investigated with respect to the sedimentological and pedological architecture of the shallow subsurface, going along with lithofacies mapping, granulometry, and permeability investigations. The synthesis of all data resulted in a three-dimensional quantitative subsurface model of the shallow subsurface architecture. Together with the associated hydrological characteristics, this can serve as input parameters for water budget and sorption models

Chemical denudation rates in the humid tropics of East Africa and comparison with 10Be-derived erosion rates

Based on 2 years of hydrochemical monitoring of 15 rivers in the western East African Rift, together with the geochemistry of soils, river sediments, and bedrocks, we calculated chemical denudation rates and tracked shifts of major cation ratios via chemical weathering. In contrast to previous studies emphasizing low chemical denudation rates in tropical cratonic areas, we also found high rates due to more easily soluble Quaternary volcanic tephras, and to a minor degree due to amphibolites. Quartz-derived 10Be erosion rates fail to predict these high rates because major sources of solutes are provided by tephras and mafic minerals. Although cosmogenic denudation rates significantly increase with increasing topography this is not reflected in chemical rates. Hence, the strong tectonic rejuvenation in this rift setting does not significantly accelerate chemical denudation. Cation ratios from rocks over soils, sediments to waters show enrichment in K and Ca with respect to Na and Mg for all rock types

Chemical denudation rates in the humid tropics of East Africa and comparison with 10Be-derived erosion rates

Based on 2 years of hydrochemical monitoring of 15 rivers in the western East African Rift, together with the geochemistry of soils, river sediments, and bedrocks, we calculated chemical denudation rates and tracked shifts of major cation ratios via chemical weathering. In contrast to previous studies emphasizing low chemical denudation rates in tropical cratonic areas, we also found high rates due to more easily soluble Quaternary volcanic tephras, and to a minor degree due to amphibolites. Quartz-derived 10Be erosion rates fail to predict these high rates because major sources of solutes are provided by tephras and mafic minerals. Although cosmogenic denudation rates significantly increase with increasing topography this is not reflected in chemical rates. Hence, the strong tectonic rejuvenation in this rift setting does not significantly accelerate chemical denudation. Cation ratios from rocks over soils, sediments to waters show enrichment in K and Ca with respect to Na and Mg for all rock types