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| Titel |
A model for the benthic-pelagic coupling of silica in estuarine ecosystems: sensitivity analysis and system scale simulation |
| VerfasserIn |
S. Arndt, P. Regnier |
| 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 ; 4, no. 3 ; Nr. 4, no. 3 (2007-06-19), S.331-352 |
| Datensatznummer |
250001730
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| Publikation (Nr.) |
 copernicus.org/bg-4-331-2007.pdf |
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| Zusammenfassung |
| A transient, vertically resolved, analytical model for the early
diagenesis of silica has been developed to quantify the importance
of benthic-pelagic coupling in estuarine biogeochemical silica
cycling. A sensitivity analysis based on Monte-Carlo simulations is
carried out to assess the intensity and timing of benthic diffusive
fluxes in response to a pelagic diatom bloom. The diffusive flux
dynamics are analyzed over a realistic range of dissolution rate
constants (max kSi ε [6×10−3–3.6×10−1 d−1]), diffusion coefficients of dissolved silica
(DSi ε [35×10−6–35×10−5 m2 d−1]) and duration of dissolved silica depletion in the water
column (wPDSI ε [1–3 month]). Results show that the
diffusive silica flux responds with a time delay of 20 to 120 days
to the biogenic silica deposition pulse. For high max kSi,
simulated time lags are shortest and completely determined by the
dissolution kinetics. However, decreasing max kSi leads to a
slower benthic flux response. In addition, the variability increases
due to the increasing importance of transport processes. The
sensitivity study also allows us to constrain the uncertainties of a
system-scale simulation, where a large number of benthic
compartments (>50 000) are coupled to a high-resolution (100×100 m)
pelagic model of a macrotidal river and estuary (Western Scheldt,
B/NL). The model is applied to a diatom bloom event recorded in
2003, characterized by pelagic silica depletion in August. Benthic
processes are mainly modulated by the combined influence of local
hydrodynamic conditions and pelagic primary production dynamics, and
show therefore a high degree of spatial heterogeneity over short
distances. Spatially integrated deposition fluxes and dissolution
rates of biogenic silica are high throughout the growth period, with
maxima of 1.3×105 mol d−1 (=8.0 mmol m2 d−1)
and 7.8×104 mol d−1 (=4.8 mmol m2 d−1) in mid-August. The spatially integrated diffusive
flux reaches a maximum of 1.5×104 mol d−1 at the
end of a pelagic silica depletion period in September. However, the
total amount of dissolved silica released from the estuarine
sediments between June and December 2003 is small (2×106 mol) compared to the much higher riverine influx of dissolved
silica (5.9×107 mol) and plays a minor role in the
pelagic primary production dynamics. |
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