Characterization of groundwater humic substances: Influence of sedimentary organic carbon.

A total of 35 groundwaters from 4 different aquifer systems in Germany are investigated for their physico-chemical properties, dissolved organic C (DOC) and humic and fulvic acids. Humic substances are isolated and characterized for their elemental composition, UV/Vis and fluorescence spectroscopic properties, size distribution by gel permeation chromatography (GPC) and 14C content. For isolation of sufficient quantities of humic substances a mobile sampling system is developed based on a combination of reverse osmosis (RO) and XAD–8 adsorption chromatography. One of the aquifer systems (Gorleben) covers a wide range of hydrogeochemical conditions, whereas the other 3 aquifer systems (Munich, Franconian Albvorland and Fuhrberg) have less diverse properties. One specific feature of the Gorleben aquifer system is the presence of a very high DOC, which, in contrast to other aquifer systems, contains considerable amounts of aquatic humic acid. This is attributed to the release of aquatic humic substances originating from sedimentary organic C (SOC) that is abundant in Gorleben sediments. The results show that aquatic humic substances from different aquifer systems have dissimilar properties which differ from one another. Systematic differences are found among humic substances from different regions of the Gorleben aquifer system. Such differences are considered to be caused by the mixing of humic substances from the SOC. However, exact quantification of such mixing appears difficult because overlapping effects of different geochemical processes feigning a dissolution of SOC cannot be excluded