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Geophysical and stratigraphical evidence for sediment dynamics and catchment landscape evolution in UK lake basins


Project Description

Understanding the evolution of landscapes is important. They record the complex interplay of natural processes, extreme events (magnitude and frequency), and with the intensification of land use, anthropogenic influences. The study of lacustrine sediments has proven a highly-valuable method for characterising the biological, physical, and anthropogenic processes effecting landscape character. Lake sediments can contribute by characterising the ‘natural’ baseline conditions and processes before various stages of human influence, for example pre-early agriculture, pre-mechanised agriculture or before mining influence. Since Mackereth (1966) demonstrated that lake sediments lain down since deglaciation can be identified as ‘a series of soils eroded from the drainage basin and deposited chronologically in the lake bed’, there has been a broader utilisation of lacustrine sediments as a recorder of catchment-wide erosion.

Lake sediment profiles have been used to explore sediment dynamics through deglaciation, Holocene changes in vegetation cover including deforestation and the establishment of an anthropogenic landscape. This erosion signal is manifested as changes in sediment accumulation rate and sediment composition identified using changes in accumulation rate, environmental magnetic characteristics of the sediments, the balance between organic and inorganic content, and in sediment geochemistry (Chiverrell, 2006; Chiverrell et al. 2008, Foster et al., 2008). This studentship would apply a novel combination of shallow-water geophysics (multi-beam and sub-bottom profiling), sediment coring, characterisation and optically-stimulated luminescence (OSL) dating to better constrain the post-glacial sediment infill of British lake basins. These integrated lacustrine sediment data will enable hypotheses-testing about the controls of changing sediment dynamics relating to:deglacial processes, paraglacial adjustment, as well as disentangling the influence of anthropogenic forcing, and elucidating evidence for climate change and extreme events.

Project Summary:
This studentship will build on existing sedimentary investigations at lakes in the English Midlands, Lake District and Scotland to test how shallow geophysical techniques can improve our understanding of post-glacial sediment dynamics. Anthropogenic threats to UK lakes include excess fine sediment flux, water brownification from excess Dissolved Organic Carbon (DOC) and changing water quality (eutrophication/ acidification). Lake sediments can record the pre-disturbance baseline, the impacts and the recovery of ecosystems. Acoustic surveys would collect shallow-water multibeam bathymetric data to map the lake bed geomorphology and high-resolution sub-bottom profiling (e.g. small CHIRP systems) would image the sedimentary record. These data in combination with new and existing sediment cores would better constrain the basin sediments and test the heterogeneity to basin infill and sediment flux. The geochemical and physical stratigraphy of lake sediments can provide unambiguous evidence of variations in sediment supply.
The deglacial sediments are denser and minerogenic, with little or no organic matter, and often laminated sequences with a strong acoustic signal. Landscape stabilization and the development of mixed deciduous woodland led to more organic rich sediments and later deforestation encouraged erosion of catchment soils and more minerogenic sediments.
These types of environmental change are reflected very well in the sediment geochemistry and magnetism and have potential to leave an acoustic stratigraphy. Dating the sediments would employ a duel strategy of 14C ages from the NERC Radiocarbon Facility and OSL dating the sediments at Liverpool. Recent testing of OSL dating through the last 1000 years at Loch of the Lowes in the Southern Uplands is extremely promising. The integration of acoustic stratigraphy with compositional analysis of the sediment sequences will quantify magnitude of for example the anthropogenic drivers in catchment land use changes and sediment regime. Core profiles typical only often offer a snap-shot window, and patterns of sediment deposition can vary significantly across lake basins; whereas, the spatial patterns discerned from the acoustic stratigraphy offer the potential for the first time to quantify sediment budgets and catchment-to-lake sediment flux.

The PhD will include training in geophysical data collection and processing, gain full access and equipment training in geomagnetism including 2G RAPID magnetometer which is in the process of being upgraded with an IRM pulse magnetiser ideal for characterising the magnetic properties of lake sediments. Training in OSL dating with be conducted through the University of Liverpool Luminescence Laboratory. Training in soft sediment characterization by XRF, FTIR, FT-NIRS and Laser Granulometry will be through the Environmental Change Laboratories at Liverpool.

Supervisors:
Professor Richard Chiverrell (University of Liverpool)
Professor Andy Biggin (University of Liverpool)
Dr Rachel Smedley (University of Liverpool)
Dayton Dove (Marine Geoscience, British Geological Survey)

Funding Notes

Full funding (fees, stipend, research support budget) is provided by the University of Liverpool. Formal training is offered through partnership between the Universities of Liverpool and Manchester in both subject specific and transferable skills to the entire PhD cohort and at each University through local Faculty training programmes.

References

Chiverrell RC. 2006. Past and future perspectives upon landscape instability in Cumbria, northwest England. Regional Environmental Change 6: 101-114.
Chiverrell RC, F Oldfield, PG Appleby, D Barlow, E Fisher, R Thompson. 2008. Evidence for changes in Holocene sediment flux in Semer Water and Raydale, North Yorkshire, UK. Geomorphology 100 (1-2), 70-82
Foster GC, RC Chiverrell, AM Harvey, JA Dearing, H Dunsford 2008. Catchment hydro-geomorphological responses to environmental change in the Southern Uplands of Scotland. The Holocene 18 (6), 935-950
Mackereth FJH (1966) Some chemical observations on post-glacial lake sediments. Philoso Trans R Soc Lond B 250:165–213
Schillereff DN, Chiverrell RC, Macdonald N, Hooke JM. 2016a. Hydrological thresholds and basin control over paleoflood records in lakes. Geology 44: 43-46
Schillereff DN, RC Chiverrell, N Macdonald, JM Hooke, KE Welsh, 2016b. Quantifying system disturbance and recovery from historical mining-derived metal contamination at Brotherswater, northwest England
Journal of Paleolimnology 56 (2-3), 205-221

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