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| Titel |
Modeling the impact of soil aggregate size on selenium immobilization |
| VerfasserIn |
M. F. Kausch, C. E. Pallud |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1726-4170
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| Digitales Dokument |
URL |
| Erschienen |
In: Biogeosciences ; 10, no. 3 ; Nr. 10, no. 3 (2013-03-01), S.1323-1336 |
| Datensatznummer |
250018126
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| Publikation (Nr.) |
 copernicus.org/bg-10-1323-2013.pdf |
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| Zusammenfassung |
Soil aggregates are mm- to cm-sized microporous structures separated by
macropores. Whereas fast advective transport prevails in macropores,
advection is inhibited by the low permeability of intra-aggregate
micropores. This can lead to mass transfer limitations and the formation of
aggregate scale concentration gradients affecting the distribution and
transport of redox sensitive elements. Selenium (Se) mobilized through
irrigation of seleniferous soils has emerged as a major aquatic contaminant.
In the absence of oxygen, the bioavailable oxyanions selenate, Se(VI), and
selenite, Se(IV), can be microbially reduced to solid, elemental Se, Se(0),
and anoxic microzones within soil aggregates are thought to promote this
process in otherwise well-aerated soils.
To evaluate the impact of soil aggregate size on selenium retention, we
developed a dynamic 2-D reactive transport model of selenium cycling in a
single idealized aggregate surrounded by a macropore. The model was
developed based on flow-through-reactor experiments involving artificial
soil aggregates (diameter: 2.5 cm) made of sand and containing Enterobacter cloacae SLD1a-1 that
reduces Se(VI) via Se(IV) to Se(0). Aggregates were surrounded by a constant
flow providing Se(VI) and pyruvate under oxic or anoxic conditions. In the
model, reactions were implemented with double-Monod rate equations coupled
to the transport of pyruvate, O2, and Se species. The spatial and
temporal dynamics of the model were validated with data from experiments, and
predictive simulations were performed covering aggregate sizes 1–2.5 cm in diameter.
Simulations predict that selenium retention scales with aggregate size.
Depending on O2, Se(VI), and pyruvate concentrations, selenium
retention was 4–23 times higher in 2.5 cm aggregates compared to
1 cm aggregates. Under oxic conditions, aggregate size and
pyruvate concentrations were found to have a positive synergistic effect on
selenium retention. Promoting soil aggregation on seleniferous agricultural
soils, through organic matter amendments and conservation tillage, may thus
help decrease the impacts of selenium contaminated drainage water on
downstream aquatic ecosystems. |
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