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| Titel |
Experimental studies of aluminum mobility in organic rich riparian soil and stream water in Sweden |
| VerfasserIn |
H. Wonisch, N. Cory, I. Buffam, H. Laudon, K. Bishop, M. Dietzel, S. J. Köhler |
| 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 |
250027239
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| Zusammenfassung |
| The role of organic acids in mobilizing and controlling aluminum (Al) from a riparian soil
profile into a small humic-rich stream draining a forested catchment area was studied in
Northern Sweden. Three in-situ soil and stream water manipulation experiments were
performed by changing total concentrations of Al and silica while keeping pH constant
between 4.8 and 5.6 to decipher the processes regulating stream Al solubility and
export. Removal of added silica could not be observed along the 80 m stream reach
during the stream manipulation despite a saturation index for Proto-Imogolite higher
than 2.5. Removal of dissolved Al and DOC in the stream and the superficial soil
solutions of the unsaturated zone occurred at molar Al/DOC ratios above 0.13±0.01.
For the lower soil horizons that are in permanent contact with groundwater (45-65
cm) and supply the stream with water during the largest part of the year a ratio
above 0.073±0.01 was sufficient to induce Al removal. In all experiments (lab
and field) an apparent ion activity product (IAP) for Al(OH)3 of 10.5±0.5 was
necessary to induce Al removal. This IAP is rarely reached in the soil solutions or the
adjacent stream despite large temporal fluctuations of both TOC and pH during the last
10 years. Al/TOC ratios in both environments are independent of pH and have a
constant Al/TOC ratio with minimal variation; 0.013±0.002 (n=61) for the stream
and 0.037±0.010 (n=135) for the riparian soil waters within the catchment. The
similarities in the riparian soil depth profiles for BaCl2 exchangeable Al and TOC
concentrations indicate that the soil organic exchanger complex may explain the
small variability of the Al/TOC ratio in the soil. The loss of Al from the soil water
during the transport through the riparian zone into the stream might be controlled
by organic matter and not an inorganic Al bearing phase. However, to decipher
the exact mechanism for the fixation of more than 70% of the soil solution Al in
the riparian zone further studies on the exchange of Al with the soil complex are
necessary.
Analyses of long time series of streams and rivers of different size (2-40000 km2) all
within the boreal zone show average ratios of Al/TOC between 0.002-0.016 (n=20). Many of
these ratios are quite constant over many years. This range is within that reported by other
authors and may indicate that such specific ratios contribute to control aluminum release in
boreal landscapes. |
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