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abstracts
Sediment sourcing and environmental reconstruction using particle size-specific magnetic fingerprinting: Bassenthwaite Lake, UK
Robert Hatfield, Barbara Maher
Here we use particle size-specific magnetic fingerprinting to better understand sediment sourcing in the Bassenthwaite Lake catchment, UK, which currently suffers issues associated with fine sediment delivery. Ferrimagnetic grain size and magnetic ‘hardness’ vary significantly between the suspended sediments from the three inflows. The 8-31μm and 31-63μm fractions appear most useful for sediment sourcing as they displaying greatest magnetic contrasts between sources, whilst post-depositional formation of bacterial magnetosomes is evident in the <8μm fraction of the lake sediments. Mineral magnetic techniques identify significant variations in sediment source and flux over the last 6000 years. Using a quantitative fuzzy-clustering technique, we show that between 2500BP and 1700AD sediment fluxes to the lake were low and dominated by material sourced through the Derwent sub-catchment (presently providing 80% of the hydraulic load). Post-1700AD, lake sediments became dominantly sourced from Newlands Beck (providing ~10% of the lake’s hydraulic load). Three successive, increases in sediment flux appear linked to specific activities; mining in the late 19th century, agricultural intensification in the mid-20th century and, within the last decade, the additional impact of climate change. Despite significant land-use change from 3,500BP the catchment was able to ‘buffer’ such pressures up until the last few hundred years. Thus, novel application of magnetic parameters has shown greatest rates of change in the most recent period resulted from exceedance of the catchments natural buffering capacity. These results are important for upland areas as modifications in climate are progressively superimposed upon the effects of previous and/or ongoing anthropogenic catchment disturbance.
Robert Hatfield, Department of Earth and Environmental Sciences, University of Windsor,401 Sunset Avenue, Windsor, Ontario, N9B 2B9, Canada, hatfield@uwindsor.ca
Barbara Maher, Lancaster University, Lancaster Environment Center, Lancaster, LA1 4YQ, United Kingdom
Session: F4: Human-Climate-Ecosystem Interactions
Download Poster:
> PAGES_OSM09_Hatfield.pdf
Download Talk:
> YSM09_OralG_Hatfield.pdf
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