Molecular characterisation of dissolved organic matter (DOM) in ground waters from the Aspo underground research laboratory, Sweden : a novel "finger printing" tool for palaeohydrological assessment

The molecular signature of dissolved organic matter (DOM) in groundwaters can be used
as a tool when investigating the palaeohydrological response of groundwater systems in relation
to changes in recharge environment, and also for examining groundwater compartmentalisation,
mixing and transport at underground repositories for radioactive waste. The DOM in
groundwaters from two compartmentalised bodies of groundwater of distinctly different origin
within the Äspö Underground Research Laboratory (URL), Sweden and in Baltic seawater has
been isolated using tangential flow ultrafiltration (TUF) and diafiltration. Recoveries of DOM
ranged from 34.7 to 0.1 mg/L with substantial differences in the concentrations of the
groundwaters collected only 120 m apart. Analysis by infrared spectroscopy (IR) and pyrolysisgas
chromatography-mass spectrometry (Py-GC-MS) of the isolated DOM revealed that the
groundwaters contained abundant alkylphenols which may represent heavily decomposed
proteins or lignins originating from biopolymers contained within soils. The difference in the
distribution and relative abundance of major pyrolysis products groups such as alkyphenols
confirmed that the groundwater and Baltic seawater DOM samples were chemically distinct
indicating minimal infiltration of marine groundwater derived by recharge from the Baltic or
earlier Littorina Sea within the two compartmentalised groundwater bodies.