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| Titel |
Spatial and temporal variations of dissolved organic matter dynamics in a disturbed Sphagnum peatland after hydrological restoration |
| VerfasserIn |
Franck Le Moing, Audrey Guirimand-Dufour, Nevila Jozja, Christian Defarge, Benoît D'Angelo, Stephane Binet, Sébastien Gogo, Fatima Laggoun |
| Konferenz |
EGU General Assembly 2015
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 17 (2015) |
| Datensatznummer |
250101750
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| Publikation (Nr.) |
 EGU/EGU2015-949.pdf |
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| Zusammenfassung |
| Peatlands contain a third of the world soil C in spite of their relatively low global area (3% of
land area). They can become sources of C because of human disturbances such as drainage.
The aim of this work is to assess the effect of an hydrological restoration on a disturbed
Sphagnum peatland. It concerns spatial and temporal variations of dissolved organic matter
(DOM) dynamics.
The investigated site was La Guette peatland (France, N 47°19’44”, E 2°17’04”, alt. 154m),
whose hydrological conditions are influenced by a road passing through its former area. The
road drain accelerates drying mechanisms, favouring thus vascular plants settlement to the
detriment of specific flora of peatlands (i.e.ÂSphagnum). Hydrological restoration was
undertaken in February 2014. It consisted in building thresholds to slow down drain runoff
and to promote the soil rewetting. Two transects of piezometers were settled in independent
two hydrological sub-systems: Trans-up and Trans-down. Trans-down is supposed to be
influenced by the hydrological restoration, while Trans-up is not. These transects cross the
peatland and follow water flow direction until the outlet. Six sampling campaigns
were performed before, during and after the vegetation period. Water conductivity
and pH were measured on site. Water samples were collected in the piezometers.
Samples were filtered in the field at 0.45 μm. Concentrations of dissolved organic
carbon (DOC), cations (Na+, K+, Ca2+, Mg2+, NH4+) and anions (Cl-, SO42-,
PO43-, NO2-, NO3-) were measured. Absorbance was measured by UV-VIS
spectrophotometer to assess SUVA254 and aromaticity of DOM. Three-dimensional
excitation–emission matrices (EEM) were undertaken to characterise fluorescent
DOM (FDOM). Humification (HIX) and biological (BIX) fluorescence indices were
calculated. PARAFAC algorithm was used to treat EEMs. Precipitations and water
levels were measured automatically by a weather station and automatic probes,
respectively. Rain water was also analysed to assess precipitation contribution in each
analysis.
Mean DOC concentrations are higher in Trans-up than in Trans-down (45 mg.L-1 vs 30
mg.L-1). Water table fluctuations are more important in Trans-up than in Trans-down (6 cm
vs 15 cm). In both sub-systems, DOC concentrations decrease from the upstream forest
border to the middle of the peatland and then increase until the outlet. DOM aromaticity
shows seasonal variability with a peak in summer. Maximum aromaticity is always reached in
the middle of transects. Measured emission/excitation couples are similar to those found in
peat standards and references (International Humic Substances Society). Fluorescence indices
show that DOM humification degree increases while crossing peatland following
water flow direction. Seasonal variations of fluorescent intensity ratios are wider in
Trans-up than in Trans-down due to higher water drawdown during summer in
Trans-up. DOM in the middle of the transects is mainly autochthonous, whereas
DOM near the limit of the peatland shows strong allochthonous influence from
neighbour systems. Ionic concentrations are correlated to DOC, showing charging and
discharging gradients in peat water. Results from characterisation of DOM and peat
water geochemistry show spatial and temporal variations in nature and origins of
DOM. This study emphasizes contrasts between control and hydrologically reworked
sub-systems. |
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