[en] Magnetic susceptibility, ²¹⁰Pb, ¹³⁷Cs, ¹⁴C, and paleomagnetic secular variation are used to establish the chronology of sedimentation in a set of cores from Loch Frisa in western Scotland. The ¹⁴C dates obtained are not compatible with the chronology derived from all the other techniques and this is ascribed to inwash of old particulate carbon from the watershed. Central cores show little evidence of changes in sedimentation rate over the last 150 years whereas marginal cores contain evidence of major increases arising from ploughing and from drainage associated with catchment afforestation since 1935. The results illustrate the value of a multiple core approach to sedimentation and erosion studies even where complex lake morphometry precludes calculation of sediment budgets

[en] 1. A multi-disciplinary approach within the framework of the lake catchment ecosystem provides a basis for studying environmental processes through time. 2. Using magnetic susceptibility measurements, it is possible to correlate a large number of sediment cores economically and rapidly, and hence to calculate sediment volumes and masses, and chemical flux. A combination of radiometric (²¹⁰Pb and ¹³⁷Cs) and palaeomagnetic dating methods allows influx data to be placed on an absolute timescale. 3. Linking the sediment influx records to a landscape history derived from pollen, diatom and land use records suggests that sediment yield from the catchment has been most affected by anthropogenic activity. In particular, early deforestation accelerated sediment loss from ca. 0.25 t ha^-1 yr^-1 to 0.86-2.5 t ha^-1 yr^-1 within a period of 1000 yr. The period AD 1300-1550 witnessed a drop in sediment yield to 0.5-1.5 ha^-1 yr^-1, perhaps related to the agrarian depression, and recent expansion of the cultivated area has led to a 1.5 fold increase in sediment yield. 4. Reconstructions of P flux in present and AD 1682 catchments suggests that in contrast to the highly subsidised present system, the earlier system ran at a net loss with losses of P at a rate of 1.5 kg ha^-1 yr^-1. 5. Close calibration of sediment and environmental records may form the basis for reconstructing environmental processes and for quantifying environmental thresholds, time-lags, response and recovery rates. This represents an important extension to contemporary process studies based on monitoring over short timescales. (author)

[en] Industrial activity such as burning of fossil fuels produces magnetically enhanced particulates. These particulates consist of coarse-grained multidomain and stable single domain magnetic minerals. Two threshold values of low field magnetic susceptibility (χ_LF) and frequency dependent susceptibility percentage (χ_FD%) discriminate ferrimagnetic minerals of these sizes and can act as a tracer of magnetic pollution. Application of the thresholds to a magnetic topsoil data set (n = 5656 across England and Wales) revealed 637 samples potentially dominated by pollution particulates. The magnetic parameters of these samples display a negative correlation with distance to urban areas and positive correlations with metals associated with anthropogenic activity (Cu, Pb, and Zn). Results of experimentation with threshold values and modelling of magnetic anomalies suggest that regional factors such as geology and potential for pedogenic secondary magnetic enhancement should be considered when setting threshold values. - An application of magnetic susceptibility and frequency dependent susceptibility thresholds across England and Wales to determine topsoil dominated by pollution derived particles.