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In mixed oak-beech forests in the undulating Keuper region of Luxembourg extensive areas of the forest floor are litter-free or covered with worm casts during many months of the year. This creates an opportunity for splash erosion or erosion by (saturation) overland flow. A systematic investigation of the occurrence and seasonality of the litter-free areas resulting from the action of the earthworm species Lumbricus terrestris, L. was undertaken in a forest with poorly to imperfectly drained, silty clay loam soils. This forest exhibits microtopographic depressions of a few hundred square metres which are damper than the immediate surroundings and which seem to favour the activity of L. terrestris. A vegetation survey showed that the depressions also have a slightly different vegetation from the immediate surroundings. The activity of L . terrestris, which pulls leaves from the surface into its hole, was followed by establishing 11 plots, 5 x 5 m in size, and surveying these with monthly intervals during a year. The percentage of bare soil ranged from zero during the winter for all plots to a maximum of 60 per cent in July and August for some plots. Rates of leaf removal were found to follow trends in soil moisture content. The relationship observed between the occurrence of bare soil and composition of the understorey vegetation allowed the vegetation map of the forest to be used to estimate the area of exposed soil.The effects of the cast producing species AUolobophoru nocturnu, Sav. and A. longa, Ude. were studied in a mixed oak-beech forest with sandy loam to sandy clay loam soils. These soils are moderately well drained. Cast production was measured within a fenced-off area of 50 x 45 m, in which 10 plots of 1 mZ each were located at random. A fine nylon netting 30 cm above the soil surface prevented splash erosion of the newly formed casts between the monthly visits. The cast material was collected, dried and weighed. Splash erosion of the casts was investigated with 50 cm high splash collectors. The percentage of bare soil in front of the splash boards was estimated from photographs. From the limited data available the yearly rate of cast production appears to be approximately 1.5 kg/m2 (15 ton/ha). No significant correlations were obtained so far in most cases between amount of soil caught in the splash traps and percentage of soil covered with worm casts.

AbStlXCt The structure of a knowledge-based decslon-support system for the samphng of aquatlc sedunents m lakes IS dlscussed The system IS m the unplementatlon stage and wdl adwse on a sampling strategy that reveals as much as possible of the pollution level of the underwater sod, based on geomorphic mformatlon and analytical results for previous samples (If avadable) Constraints such as the desired precision and maximum samphng costs are taken mto account A case study on Ketelmeer lake (Netherlands) Illustrates the techniques and heunstxs that wdl be used m the deaslon-support system Bywords Decalon-support system, Samphng, Sediments, Waters

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