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| Titel |
Do different components of terrestrial sources contribute to the riverine suspended load? |
| VerfasserIn |
B. M. Voss, B. Peucker-Ehrenbrink, T. I. Eglinton, V. Galy |
| Konferenz |
EGU General Assembly 2012
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250068683
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| Zusammenfassung |
| Establishing the relationship between source (bedrock, soil, floodplain sediments, vegetation)
and mobilized materials (bedload and suspended load) within a river drainage network is
critical to understanding the fate of particulate matter exported to the coastal ocean. First,
linking material carried in river channels to its terrestrial sources aides in predicting the
reactivity of organic matter associated with mineral particles and understanding which
portions of a watershed contribute substantially to organic carbon fluxes and transformations
in these systems. Second, identifying terrestrial reservoirs of future riverine suspended
material can enhance our ability to comprehensively characterize the chemical and physical
nature of fluvial sediments.
We present a study of sedimentological and bulk organic carbon properties of sediments
from across the Fraser River watershed in southwestern British Columbia, Canada. Bulk
samples and size fractions from surface soils and riverbank sediments, as well as vegetation,
are analyzed for metrics including carbon and nitrogen content, 13C and 14C composition,
and specific surface area. These are compared with measurements of riverine suspended
sediments and size fractions of sediments deposited in the Fraser estuary. The correspondence
of suspended sediment properties with different portions of soil, alluvial, and vegetation
pools from different sites suggests a complex link between source materials and exported
material. Such variability may stem from the heterogeneous nature of soil types,
hillslope morphology, and runoff regimes in different portions of the drainage basin;
settling/resuspension processes during river transit; and/or modification of particle structure
and organic matter between mobilization of terrestrial material and arrival at distant
downstream sites. The preferential loss/preservation of different size fractions within mineral
source materials highlights the unequal importance of different mineral phases and
continental regions to fluvial transport and fate of terrestrial carbon in the coastal
ocean.
A focus on the Fraser River basin is advantageous for its extraordinary diversity of rock
types and rainfall distribution (leading to stark contrasts in plant and soil types, as well as
organic and inorganic isotopic signatures), and the lack of intermittent storage reservoirs
(dams, lakes) on the main stem. The modest size (~240,000 km2) and excellent hydrological
monitoring of this watershed make it possible to characterize the basin in great detail. Such a
case study can readily be extended to basins less likely to exhibit distinct spatial variations
and systems with less available baseline data, in order to gain a broader perspective of global
processes. The exploitation of sediment size fractions to understand suspended
sediment properties further offers a potentially potent tool for better characterizing
materials which are typically difficult to collect in sufficiently large quantities for
detailed biogeochemical, sedimentological, and petrographical characterization. |
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