Recruitment of Pollen to the Seston and Sediment of Some Lake District Lakes

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Abstract
Cores of surface sediment (of known accumulation rate) from 5 Lake District lakes [Scotland; United Kingdom] were analyzed quantitatively for pollen. Recent rates of total pollen deposition in mid-lake (cm2/yr) were estimated to be about 5 times higher in Blelham Tarn and Esthwaite Water than in Ennerdale Water, Wastwater and Windermere and appear to be related to the area and/or diameter of the lakes sampled. The vegetation within 1 km of the 5 lakes (especially the area or proportion of woodland cover), is not consistently reflected by either pollen deposition rates or pollen percentages in surface sediment. This anomaly was further investigated by measuring pollen deposition per unit area per unit time in floating traps and in submerged seston traps at Blelham Tarn and Ennerdale Water, lakes which contrast in size and in vegetational setting. Catches in the seston traps varied seasonally according to the relative recruitment of fresh airborne pollen, and settled pollen resuspended from the mud surface. Input of stream-born pollen was nonseasonal, however. Pollen trapped in relation to volume and dry weight of seston varied seasonally with plankton production, and nonseasonally with input of stream-borne material. The annual ratio pollen:seston was lower in shallow, productive Blelham Tarn than in deep, oligotrophic Ennerdale Water, but in each lake pollen trapped was approximately equivalent cm2/yr to pollen deposited recently at the mud surface. Proportional recruitment of regional pollen rich in arboreal pollen is greater in large lakes than small ones. This may explain in part the percentage over-representation of tree pollen in the sediments of those large lakes investigated which have a low proportion of woodland cover within 1 km.