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| Titel |
Measuring event- and century-scale changes in sediment sources to the upper Mississippi River |
| VerfasserIn |
Patrick Belmont, Jane Willenbring, Julia Marquard |
| Konferenz |
EGU General Assembly 2011
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250046174
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| Zusammenfassung |
| We document changes in sources contributing sediment to the upper Mississippi River over
individual storm event and century timescales using meteoric 10Be concentrations in
suspended sediment and in the sedimentary record of Lake Pepin, a naturally dammed
lake on the Mississippi River south of St. Paul, Minnesota, USA. Sedimentation
rates in Lake Pepin have increased ten-fold since Euro-American settlement and
widespread agriculture began in 1830. The Minnesota River Basin (MRB) comprises only
38% of the Lake Pepin watershed, but throughout the Holocene and modern record
has consistently contributed 75-90% of the sediment deposited in the lake. This
disproportionate sediment yield of the MRB is primarily attributed to the fact that the
mainstem Minnesota River incised as much as 70 meters as a result of catastrophic
drainage of Lake Agassiz 13,400 years ago. This incision was experienced as a nearly
instantaneous drop in base level for the Minnesota River tributaries, which have been
aggressively incising since that time. We use 10Be concentrations in suspended
sediment to document changes in sediment sources (field versus non-field) over the
course of individual storm hydrographs in the Le Sueur River, a tributary to the
Minnesota River. The 10Be concentrations indicate systematic differences in the
dominant sediment sources above and below the rapidly incising portion of the
channel network as well as transitions between field and non-field sources within the
storm hydrographs. In the Lake Pepin sedimentary record low 10Be concentrations
prior to 1830 indicate minimal upland sediment sources prior to Euro-American
settlement. Between 1830 and 1940, steadily increasing 10Be concentrations document
an increase in the proportion of upland sediment that coincides with increasing
intensity of agriculture and poor land management practices. Interestingly, 10Be
concentrations in modern deposits document a dramatic decrease in field sediment and
significant increase in non-field sources. The decrease in field sediment indicates that
conservation practices have been somewhat successful in reducing agricultural erosion.
However, the increase in non-field sediment indicates that changes in hydrology from a
combination of climate change, systematic changes in cropping patterns, and enhanced
tile and ditch drainage systems are amplifying erosion of near-channel sediment
sources. This finding calls for a paradigm shift in conservation efforts in the MRB to
focus on management of the hydrologic regime and specifically those natural and
human-induced factors that are amplifying erosion of near-channel sediment sources. |
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