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| Titel |
Targeting sediment management strategies using sediment quantification and fingerprinting methods |
| VerfasserIn |
Sophie Sherriff, John Rowan, Owen Fenton, Phil Jordan, Daire Ó hUallacháin |
| Konferenz |
EGU General Assembly 2016
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250135535
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| Publikation (Nr.) |
 EGU/EGU2016-16413.pdf |
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| Zusammenfassung |
| Cost-effective sediment management is required to reduce excessive delivery of fine sediment
due to intensive land uses such as agriculture, resulting in the degradation of aquatic
ecosystems. Prioritising measures to mitigate dominant sediment sources is, however,
challenging, as sediment loss risk is spatially and temporally variable between and within
catchments. Fluctuations in sediment supply from potential sources result from variations in
land uses resulting in increased erodibility where ground cover is low (e.g., cultivated,
poached and compacted soils), and physical catchment characteristics controlling
hydrological connectivity and transport pathways (surface and/or sub-surface).
Sediment fingerprinting is an evidence-based management tool to identify sources of
in-stream sediments at the catchment scale. Potential sediment sources are related to a
river sediment sample, comprising a mixture of source sediments, using natural
physico-chemical characteristics (or ‘tracers’), and contributions are statistically
un-mixed.
Suspended sediment data were collected over two years at the outlet of three intensive
agricultural catchments (approximately 10 km2) in Ireland. Dominant catchment
characteristics were grassland on poorly-drained soils, arable on well-drained soils and arable
on moderately-drained soils. High-resolution (10-min) calibrated turbidity-based suspended
sediment and discharge data were combined to quantify yield. In-stream sediment samples
(for fingerprinting analysis) were collected at six to twelve week intervals, using
time-integrated sediment samplers. Potential sources, including stream channel banks,
ditches, arable and grassland field topsoils, damaged road verges and tracks were sampled,
oven-dried (<40oC) and sieved (125 microns). Soil and sediment samples were
analysed for mineral magnetics, geochemistry and radionuclide tracers, particle
size distribution and soil organic carbon. Tracer data were corrected to account for
particle size and organic matter selectivity processes. Contributions from potential
sources type groups (channel – ditches and stream banks, roads – road verges and
tracks, fields – grassland and arable topsoils) were statistically un-mixed using
FR2000, an uncertainty-inclusive algorithm, and combined with sediment yield
data.
Results showed sediment contributions from channel, field and road groups were 70%,
25% and 5% in the poorly-drained catchment, 59%, 22% and 19% in the well-drained
catchment, and 17%, 74% and 9% in the moderately-drained catchment. Higher channel
contributions in the poorly-drained catchment were attributed to bank erosion accelerated by
the rapid diversion of surface runoff into channels, facilitated by surface and sub-surface
artificial drainage networks, and bank seepage from lateral pressure gradients due to confined
groundwater. Despite the greatest proportion of arable soils in the well-drained
catchment, this source was frequently hydrologically disconnected as well-drained
soils largely infiltrated rainfall and prevented surface soil erosion. Periods of high
and intense rainfall were associated with greater proportions of field losses in the
well-drained catchment likely due to infiltration exceeding the saturated hydraulic
conductivity of soils and establishment of surface hydrological connectivity. Losses from
field topsoils dominated in the moderately-drained catchment as antecedent soil
wetness maintained surface flow pathways and coincided with low groundcover
on arable soils. For cost-effective management of sediment pressures to aquatic
ecosystems, catchment specific variations in sediment sources must be considered. |
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