Sedimentation in a large lake: the importance of fluctuations in water level

1. A sediment trap study was conducted in the central basin of Lower Lough Erne, Northern Ireland. 2. The material caught was low in organic matter, ash weight was 77% of dry weight on average. 3. Mass deposition of material was shown to be correlated with lake water level. When lake water level fell or rose above the middle range, the amount of material caught by the trap increased markedly. The effect was exaggerated by an unusually dry summer in 1995 which caused abnormally low water levels in the lake. 4. Comparison of Erne data with Windermere shows similar deposition rate of many substances, but the deposition rate of iron is thirteen times higher in Erne than in Windermere, and iron made up 39% of the ash weight in the Erne trap data. 5. Only 17% of the silica removed from the water column during diatom growth was recovered in the trap over the same time period. 6. Trap data are compared with historical data for sediment deposition and the implications of sediment focusing are discussed.