Hydrochemical Groundwater Evolution in the Bunter Sandstone Sequence of the Odenwald Mountain Range, Germany: A Laboratory and Field Study
Source: Aquatic Geochemistry, Volume 17, Number 2, March 2011 , pp. 165-193(29)
Abstract:Field and laboratory investigations were performed to identify the principal mechanisms of the hydrochemical groundwater evolution among low mineralised groundwater in the Triassic Bunter sandstone aquifer of the Odenwald low mountain range, central Germany. Hydrochemical composition comprises low pH, SO4-rich shallow groundwaters issued by springs (Ca-Mg-SO4-type) grading to SO4-poor deep groundwaters with near-neutral pH (Ca-HCO3-type). Batch experiments of the original rock were run to determine primary mineral alteration reactions and the origin of dissolved ions. Principal experimental reactions comprise the decomposition of anorthite, K-feldspar, biotite and jarosite as mineral components of the original sandstone rock and the formation of clay minerals of the smectite group (Ca-montmorillonite, beidellite), and iron hydroxides as secondary minerals. Mobilisation of fluid inclusion in quartz grains contributes to Na and Cl concentrations in the leachates. The evolution of deep groundwater circulation proceeds by mineral alteration reactions calculated by the inverse modelling of both primary and secondary minerals to produce low-T mineral phases. The dissolution of K-feldspar converts Ca-montmorillonite to illite (illitisation). The formation of Na-beidellite correlates with decreasing concentration of Na in solution. Mineral reactions further proceed to the formation of kaolinite as stable mineral phase. As indicated by modelled adsorption curves, the decrease of SO4 concentrations during groundwater evolution relates to the adsorption of SO4 on iron hydroxides. The leaching of calcite indicated for individual groundwaters relates to the distribution of loess in the appropriate catchment areas.
Document Type: Research Article
Affiliations: 1: Wasser und Boden, Am Heidepark 6, 56154, Boppard-Buchholz, Germany, Email: email@example.com 2: Department of Environment, University of Freiburg, Schwedinstr. 12, 79102, Freiburg, Germany, Email: firstname.lastname@example.org 3: Institute of Mineralogy and Geochemistry, University of Freiburg, Albertstr. 23b, 79104, Freiburg, Germany, Email: email@example.com
Publication date: March 2011