Single sample magnetic susceptibility measurements are used to correlate synchronous levels in 16 cores of dated (210Pb, 137Cs) recent sediment taken from the deep and oligotrophic Llyn Peris, N. Wales, in order to provide a basis for calculating total sediment and chemical influx through time. Results show that sediment influx has steadily increased since c. 1750 A.D. to reach peak levels in the period 1966–1976 A.D., equivalent to a rise in erosion in the catchment from c. 5 t km−2 yr−1 to c. 42 t km−2 yr−1. Comparison of down-core susceptibility fluctuations with sediment pollen and organic pigment data indicates that maximum susceptibility values relate to periods of channel erosion and minimum susceptibility values relate to periods of slate debris inwash from spoil tips in the catchment. A study of historical records reveals that pre-twentieth-century peak levels of erosion were due to the effects of extractive industries, while twentieth-century erosion has been caused by overgrazing, increased trampling pressure, and heavy construction works in the catchment.

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