Water supply and sulfate pollution of groundwater under agricultural and forested areas. Sub-project 2: Hydrochemical studies on S sources and on the kinetics of the reaction processes in aquifers as a basis for forecasting sulfate pollution levels Final report / Wasserversorgung und Sulfatbelastung des Grundwassers unter land- und forstwirtschaftlich genutzten Flaechen. Teilprojekt 2: Hydrochemische Untersuchungen zu den S-Quellen und zur Kinetik der Umsetzungsprozesse in Grundwasserleitern als Grundlage einer Prognose der Sulfatbelastung Abschlussbericht

A significant increase in sulphate concentration in groundwater and raw water has been observed in many waterworks in alluvial aquifers in Germany. Quantifying sulphate inputs into groundwater and release from soils is necessary for a sulphur balance and a prognosis of future sulphate concentrations in groundwater. Aims of the project included the identification and quantification of sulphur sources and processes which control sulphate concentrations in aquifers in regions used for agriculture. Hydrogeochemical investigations were focussed on a catchment area with high sulphate concentrations in groundwater (Waterworks Mockritz, River Elbe valley). Three different zones with sulphate concentrations between 200 and 1000 mg/L in the upper aquifer have been distinguished. Applied methods for the interpretation of groundwater quality data allowed to characterise ongoing hydrogeochemcial processes in the aquifer. High sulphate concentrations in groundwater near the surface were found to be a result of pyrite oxidation by oxygen and nitrate. A large amount of sulphur has been accumulated in the unsaturated zone during former periods of excessive sulphur inputs (atmospheric deposition, fertilisation). A methodology including 8 different analytical methods has been developed to characterise sulphur pools in soils. Therewith, the total sulphur content and 7 sulphur species concentrations can be measured and 5 more sulphur species concentrations can be calculated. Based on a detailed investigation of sulphur species in soils exchange processes between these species were described. After identification of sulphur input sources at the field site, laboratory experiments have been carried out to study FeS_2-oxidation and sulphate reduction. Pyrite oxidation by oxygen (air) in the unsaturated zone was about 20 times faster than oxidation by dissolved oxygen. Pyrite oxidation follows a first-order reaction and depends on the surface area of FeS_2. Autotrophic denitrification could be described as zero-order reaction related to nitrate. Hydrogeochemical modelling with PHREEQC has been used to corroborate hypotheses about main transport processes along two cross-sections. Furthermore, a common concept for the investigation of sources and transport behaviour of sulphate has been developed and measures for groundwater management have been compiled. (orig.) / SIGLE / Available from TIB Hannover: F03B1193+a / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische Informationsbibliothek / Bundesministerium fuer Bildung und Forschung, Berlin (Germany) / DE / Germany