The contribution from inflow streams to pollen in lake sediments was examined by comparison of percentage and absolute pollen data from sediment cores taken from two small lakes (5 and 10 h) within the same lowland region of south Cumbria; one in an enclosed basin (a large interdrumlin hollow) and the other receiving streams. The vegetation histories of the last 7000 years, interpreted from percentage pollen analysis, were similar. Calculated rates of annual influx of pollen to the sediments were at all times lower in the enclosed basin; in it they agreed with present deposition into pollen traps from respectively forest, incompletely vegetated land, and grassland. These rates are accepted as estimates of the amount of pollen per unit area which annually reaches a small lake by deposition from the air. Differences between these rates and those to the open lake, for each successive vegetation type, give estimates of the contribution from streams to sediments of the open lake. This contribution constituted < 50 % of the total during the forest period and increased to > 80 % at the horizon of extensive forest clearance. In the open lake, parallel changes in pollen and geochemistry at this clearance horizon show that the source of increased pollen influx lay in organic soils (mor); distribution of the tracer pollen Ilex shows that these soils must have formed on this catchment after initial disturbance of primary forest, and thereafter constituted a source of pollen of ages older than the time of deposition in the lake. Disruption of the vegetation cover on this catchment by deforestation and ploughing appears to have increased permanently the rate at which streams transported sediment, including pollen, to the lake. Only in the enclosed lake do rates of pollen influx remain in equilibrium with vegetation changes recorded in the percentage data. In this lake, with a similar history of changing land use, there is no perturbation of rates of annual pollen influx. The absolute pollen data for Tilia cordata in the enclosed lake confirm for this site the distribution history suggested for this species by Pigott and Huntley (1978). Copyright © 1979, Wiley Blackwell. All rights reserved
