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| Titel |
Forced gradient infiltration experiments: effect on the release processes of mobile particles and organic contaminants |
| VerfasserIn |
B. Pagels, K. Reichel, K. U. Totsche |
| Konferenz |
EGU General Assembly 2009
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 11 (2009) |
| Datensatznummer |
250029310
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| Zusammenfassung |
| Mobile colloidal and suspended matter is likely to affect themobility of polycyclic aromatic
hydrocarbons (PAHs) in the unsaturatedsoil zone at contaminated sites.
We studied the release of mobile (organic) particles (MOPs), which include among others
dissolved and colloidal organic matter in response to forced sprinkling infiltration and
multiple flow interrupts using undisturbed zero-tensionlysimeters. The aim was to assess the
effect of these MOPs on the exportof PAHs and other contaminants in floodplain soils.
Seepage water samples were analyzed for dissolvedand colloidal organic carbon (DOC),
PAH, suspended particles, pH, electrical conductivity, turbidity,zeta potential and surface
tension in the fraction smaller 0.7μm. In additional selected PAH were analysed in the size
fraction > 0.7 μm. Bromide was used as a conservative tracer to determine the flow
regime.
First arrival of bromide was detected 3.8 hours after start of irrigation. The
concentration gradually increased and reached a level of C/C0=0.1 just before the flow
interrupt (FI). After flow was resumed, effluent bromide concentration was equal to the
concentration before the FI. Ongoing irrigation caused a breakthrough wave, which
continuously increased until the bromide concentration reached ~100% of the input
concentration.
A high-intensity rain event of 4 L m -2 h-1 upon summer-dried lysimeters results in a
release of particles in a the size of 250-400 nm. In addition it seems that with the initial
exported seepage water surface-active agents are released which is indicated by the decrease
of the surface to 60 mN m-1 (Pure water: 72mN m-1). The turbidity values range from
8-14 FAU. The concentration of DOC is about 30-40 mg L-1 in the initial effluent
fractions and equilibrates to 15 mg L-1 with ongoing percolation. The PAHs in the
fraction < 0.7 μm amount to 0.02 μg L-1, and 0.05 μg L-1 in the fraction > 0.7
μm.
After establishing steady state flow conditions, first arrival of bromide was detected after
6 hours of irrigation. If uniform flow at water-saturated conditions were assumed, first arrival
of bromide would be expected not earlier than 16 hours (approx. 0.3 pv) after start of
irrigation. The much earlier arrival points to the fact, that transport along preferential flow
paths controls part of the bromide transport. Round 30% of the total infiltrated solution
remains in the lysimeter and might comprise ~ 70% of the water holding capacity of the
micro- and mesopores (equivalent pore diameter < 0.2 μm and 200- 0.3 μm, resp.). Flow and
transport in response to the simulated heavy rain event seem to be controlled by the
macropores. This in turn affects the release of PAHs, in particular those associated with
particles.
Singular events, like the studied heavy rain events, drying/rewetting or freezing/thawing
cycles seem to be the most prominent trigger of PAH mobilization and transport in surface
soil horizon not only at floodplain sites. |
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