Recent land-use and soil-erosion history within a small catchment in Connemara, western Ireland: evidence from lake sediments and documentary sources

摘要

Environmental magnetism, elemental chemistry, pollen, macrofossil, and radioisotopes were studied on top-metre cores from Ballydoo Lough, Connemara, western Ireland, to reconstruct the impact of changing farming practices on soil erosion in a lake catchment. Documentary evidence, including detailed agricultural statistics, gave an independent land-use history over the period represented in the sediment record, i.e. most of the last two centuries. Maximum soil erosion, which involved unweathered coarse material as well as topsoil, was associated with a rapidly rising rural population and increased arable activity during the early 19th century. The Great Famine (1845-1847) halved the population, but arable and especially pastoral farming quickly recovered and were maintained at a high level from teh late 1850s until the late 1890s. During this time, the rate of soil erosion slowed down considerably and the contribution of coarse mineral material relative to topsoil declined. Erosion of peaty soilswas less important as potato cultivation declined and the middle slopes of the catchment were no longer cultivated. From the end of the 18th century to the 1970s, sediment accumulation and erosion rates were less and progressive podzolisation occurred aspastoral and particularly arable farming declined. The uppermost sedments record a sharp increase in soil erosion, involving mainly organic-rich soils from the upper slopes. This increase is attributed to a sharp rise in livestock numbers, especially sheep. A feature of the pollen record is the high arboreal pollen representation (43%-66% of total terrestrial pollen), which consists mainly of secondary pollen. It indicates a substantial input of pollen-bearing organic detritus derived from peaty soilsand peat cuttings in the catchment.