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| Titel |
A continental scale model for dissolved silica mobilization in North America |
| VerfasserIn |
N. Jansen, R. Lauerwald, J. Hartmann, H. H. Dürr, S. Loos, S. Kempe, H. Middelkoop |
| 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 |
250029210
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| Zusammenfassung |
| Silicon is one of the few elements that link to both the organic and inorganic carbon cycles.
Dissolved silicon (DSi) is an important nutrient in terrestrial and aquatic ecosystems. Cations
accompanying the release of DSi by chemical silicate rock weathering are generally balanced
by soil/atmospheric CO2. Chemical weathering is the major source of “new” bioavailable DSi
for continental aquatic systems to compensate for the loss of DSi by outflow or organic
precipitation and burial.
We use river water chemistry data from 164 monitoring stations from the conterminous
United States (WQN and NAWQA networks). Selected stations are characterized by low
population density and low influence of water bodies to minimize human and DSi retention
impact. Observed DSi yield in these catchments is assumed to represent natural DSi
mobilization by chemical weathering. The catchments have an average size of 4400 km2
(Median: 991 km2) with a discharge weighted average DSi yield of 4.34 t SiO2
km-2a-1.
To predict mobilization of DSi from chemical weathering a lumped non-linear
empirical model is developed, considering control factors such as climate, morphology,
hydrology, land cover, soil and lithology. A multi-lithological model approach is
chosen because only very few mono-lithological catchments were identified in
the dataset. The model is then extrapolated to the conterminous United States to
regionally quantify the amount of DSi that is released into the river systems by chemical
weathering.
Small outcrops of certain lithological classes characterized by a high DSi yield are not
represented on previously available small scale lithological maps. Because such localities
may have a major influence on DSi fluxes from small catchments (Hartmann et al., 2009) a
new high resolution lithological vector-map for North America is developed and applied in
the introduced model.
In accordance with previous studies, runoff and lithology are identified as the major
predictors for specific DSi flux (Bluth and Kump, 1994; Hartmann et al., 2009). Only in
relation to some lithological classes, temperature and terrain slope constitute significant
predictors. An influence of land cover, soil properties or other predictors is not observed. This
is partly attributed to geodata resolution and classification. Lithological classes “Basic
Volcanics and Pyroclastics” and “Basic and Intermediate Plutonics” show the highest DSi
yields, with respect to a given discharge. The lithological class “Siliciclastic Sedimentary
Rocks” is characterized by the lowest DSi yield. The model explains 89% of the DSi yield
variance; the average yield of catchments employed in model calibration is 4.32 t SiO2
km-2a-1, somewhat above the global average yield of 3.3 t SiO2 km-2a-1 (Dürr et al.,
2009).
The model quantifies DSi fluxes from the terrestrial into the continental aquatic systems.
This helps to estimate DSi retention within fluvial systems (Lauerwald et al., submitted) and
improves understanding of this part of the silicon cycle.
References:
Bluth, G.J.S., and Kump, L.R., 1994, Lithologic and Climatologic Controls of River
Chemistry: Geochimica Cosmochimica Acta, 58, 2341-2359.
Dürr, H.H., Meybeck, M., Hartmann, J., Laruelle, G.G., and Roubeix, V., 2009, Global
Spatial distribution of natural riverine silica inputs to the coastal zone: Biogeosciences, (in
review), bgd-2008-0173.
Hartmann, J., Jansen, N., Dürr, H.H., Harashima, A., Okubo, K., and Kempe, S., 2009,
Predicting riverine dissolved silica fluxes into coastal zones from a hyperactive region and
analysis of their first order controls: International Journal of Earth Sciences, (DOI
10.1007/s00531-008-0381-5).
Lauerwald, R., Jansen N., Hartmann, J., Dürr, H.H., Loos, S., Kempe, S., Middelkoop, H.,
submitted, Modeling dissolved silica retention in the limnic system of North America.
(Submitted to this session). |
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