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| Titel |
Transport and retention of dissolved silica in rivers of the conterminous USA |
| VerfasserIn |
Ronny Lauerwald, Jens Hartmann, Nils Jansen, Hans H. Dürr |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250040687
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| Zusammenfassung |
| Dissolved silica (DSi) is an important nutrient in freshwater and coastal ecosystems. The
availability of DSi in aquatic ecosystems is governed by mobilization from the terrestrial
system and fluvial transport. Part of the mobilized DSi is retained in the rivers, associated
lakes and wetlands due to biotic uptake and sedimentation.
On large scale, fluvial DSi fluxes to coastal zones have been assessed mainly based on
data from sampling locations at or near the mouth of major world rivers, while for the limnic
retention of silica only first-order estimates exist (e.g. Beusen et al., 2009). DSi fluxes from
small basins are often neglected in analyses.
For the conterminous USA, the mobilization of DSi has recently been analyzed by Jansen
et al. (2010), who described an empirical DSi mobilization function trained on
headwater catchments in which limnic DSi retention is less likely to occur. It is here
hypothesized that for larger catchments retention of silica can be calculated as difference
between predicted DSi mobilization and DSi fluxes derived from hydrochemical
monitoring data. Based on this assumption, fluvial fluxes of DSi in the conterminous
USA were analyzed distinguishing mobilization, retention, and export to the coastal
zone.
River chemistry data from the USGS programs WQN and NAWQA were used to
calculate annual DSi fluxes for 638 sampling locations. For each water sampling location the
river catchment and its properties (e.g. lithology, land cover, lake area) were derived. DSi
mobilization was estimated spatially explicitly by applying a fitted mobilization function after
Jansen et al. (2010). Silica retention was calculated by subtracting DSi fluxes based
on USGS data from the predicted amount of mobilized DSi. Export of DSi was
estimated for distinct coastal segments. For the analyses, average annual runoffs
from two different data sets, gridded UNH/GRDC data (Fekete et al., 2002) and
PCR-GLOBWB (Van Beek, 2007), were used. The respective results are compared and
discussed.
Using runoff after Fekete et al. (2002) (and after Van Beek, 2007) an average DSi
mobilization of 1.6 t SiO2 km-2 a-1 (1.3 t SiO2 km-2 a-1) was calculated for the
conterminous USA. This results in a total mobilization of 12.9 Mt SiO2 a-1 (10.2 Mt
SiO2 a-1). 20% of the area account for up to 64% (62%) of the DSi mobilized,
whereas 39% (19%) of the area account for less than 0.1% of the mobilization.
Referring to 164 non-overlapping catchments covering the whole area for which DSi
fluxes have been calculated (78.4% of the conterminous USA), total retention within
freshwater ecosystems is estimated to be 13% (26%) of the mobilized DSi. These
values are about the order of magnitude of the 21 to 22% estimated by Beusen et
al. (2009) for the North American continent. Results underline that calculation of
mobilization, fluvial fluxes, and retention of DSi is sensitive to the applied hydrological
model.
References
Beusen, A.H.W., Bouwman, A.F., Dürr, H.H., Dekkers, A.L.M. and Hartmann, J., 2009.
Global patterns of dissolved silica export to the coastal zone: Results from a spatially explicit
global model. Global Biogeochemical Cycles, 23.
Fekete, B.M., Vörösmarty, C.J. and Grabs, W., 2002. High-resolution fields of global
runoff combining observed river discharge and simulated water balances. Global
Biogeochemical Cycles, 16(3).
Jansen, N., Hartmann, J., Lauerwald, R., Dürr, H.H., Kempe, S., Loos, S. and
Middelkoop, H., (2010). Dissolved silica mobilization in the conterminous USA. Chemical
Geology, DOI:10.1016/j.chemgeo.2009.11.008
Van Beek, L.P.H., 2007. PCR-GLOBWB model description, Integration of GFS Data
with PCR-GLOBWB using FEWS. WL Delft Hydraulics, Delft. |
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