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| Titel |
Process-oriented investigation of the nitrate-removal-capacity of the aquifers in the Hessian Ried |
| VerfasserIn |
Christoph Kludt, Frank-Andreas Weber, Axel Bergmann, Elena Knipp, Indriani Preiß, Christoph Schuth |
| Konferenz |
EGU General Assembly 2013
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 15 (2013) |
| Datensatznummer |
250074477
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| Zusammenfassung |
| The quarternary sediments of the Hessian Ried, a part of the Rhine valley, hold an important
groundwater resource for the densely populated Rhine-Main region in germany. Studies
related to the implementation of the EU Water Framework Directive (WFD) have shown high
nitrate concentrations in the groundwater, especially in the upper parts of the aquifers.
Recently, there are signs which indicate that the nitrate-removal-capacity may be exhausted
and the denitrification is slowing down.
In aquifers, microbial autolitho- and heterotrophic denitrification is coupled to the
consumption of the reactive phases pyrite (FeS2) and organic carbon (TOC), respectively.
These reducing phases occur often only in trace amounts which makes it difficult to
determine their distribution, reactivity and content in the field. However, a process-based
knowledge of the occurring reactions and the quantification of the nitrate-removal-capacity
and -kinetic is required to predict future nitrate fate.
For this aim we combined different methods on a laboratory and field scale to identify the
relevant nitrate degradation processes in the Hessian Ried. For determining the reactive
phases (TOC and pyrite) in sediment samples, we modified and validated a combination of
methods, ranging from sequential combustion for TOC and XRF for elemental and chromium
reducible sulphur (CRS) for sulphide/disulphide determination. The analyses of core samples
from different field sites in the Hessian Ried (forest and agricultural area) showed that
especially the sediments under agricultural areas have much lower pyrite contents.
Laboratory batch experiments with these sediment samples showed a much faster
denitrification for sediments having higher sulphide content. δ34S isotope analyses of
solid-phase sulphide and water-phase sulphate proved to be a good tool for determining the
progress of the autolithotrophic denitrification. With in-situ multi-parameter measurements
(Eh, pH, nitrate, temperature and conductivity) in several monitoring wells in combination
with water analyses, especially sulphur-isotopic-ratios, we were able to identify
high risk areas with a low nitrate-removal-capacity which is mainly caused by the
consumption of the pyrite during the denitrification process. Furthermore, we are
focusing on process-based investigations of denitrification using δ15N-isotopes and
N2/Ar-measurements.
The identified high risk areas allow intensifying the implementation of programs planed
under the WFD in agricultural areas with low nitrate removal capacity. |
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