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| Titel |
Preliminary response of a pristine aquifer when facing toluene contamination |
| VerfasserIn |
S. Qiu, A. Herzyk, P. Maloszewski, M. Larentis, C. Griebler, M. Elsner |
| Konferenz |
EGU General Assembly 2012
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250065110
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| Zusammenfassung |
| Toluene is a common groundwater contaminant due to the wide spread of gasoline and
industrial solvents. The understanding of how and when ecosystems initially respond to the
presence of toluene is yet limited, because field investigations rarely start before a
contamination has occurred. In order to investigate for the first time such a scenario, a
pristine indoor aquifer model (0.8 Ã 0.7 Ã 5 m) was constructed, filled with natural
sediment, flushed with natural groundwater at a rate of 9 L/hr, and subsequently
exposed to a toluene contamination. Investigation was done to the chemical and
biological parameters of the model, including oxygen concentration (9.6 mg/L), nitrate
concentration (5.8 mg/L), small organic carbon content (0.8 mg/L), microbial abundance (4
x 104 cell/mL), and ATP (0.01 nM). This agreed with the condition of a typical
pristine and oligotrophic aquifer. A 30-hr aqueous toluene pulse (water saturated
with toluene) was injected into the system together with a conservative tracer (90%
D2O). Water samples were collected 4.2 m away from the injection source. The
comparison between the toluene and D2O breakthrough curves indicated that a portion of
toluene was removed by degradation at a pseudo 1st order rate of 0.017/hr. Stable
carbon isotope values of toluene were also measured along with the breakthrough
curves. δ13C values were more positive than the original input, confirming that
biodegradation had taken place. Subsequent to the pulse, a constant injection of aqueous
toluene together with bromide was applied to obtain a deeper insight of the biological
and geochemical processes in the aquifer. High resolution water sampling over
the entire aquifer model was conducted 80 hrs after the start of constant injection.
Microbial abundance and living biomass (ATP) were observed to be 10 Ã and 100 Ã,
respectively, higher than under pristine conditions. Biodegradation was detected by
comparing the concentration of toluene and bromide, and was confirmed by a significant
depletion of oxygen concentrations in the center of the plume. Subsequent sediment
sampling revealed a pronounced decrease in bacterial diversity and evenness in the
toluene plume, indicating fast establishment of the degraders and disappearance of
sensitive members. Changes of microbial community composition were accompanied
by a build up of biomass and high bacterial carbon production rates. Our study
shows that microbial degradation of toluene occurs immediately (within 50 hrs)
after exposure of the pristine aquifer to the contaminant. Changes in biological and
geochemical processes give additional evidences that the system responds very fast
towards toluene contamination and has a high potential for natural attenuation. |
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