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Palaeolimnology without a core: 153 years of diatoms and cultural environmental change in a shallow lowland lake (Belgium).

2009; Česká algologická společnost; Volume: 9; Issue: 2 Linguagem: Inglês

10.5507/fot.2009.031

1805-4927

Luc Denys,

Geology and Paleoclimatology Research

Time series of diatom assemblage composition can be obtained from samples of various collection materials.This allows assessment of 'more natural' conditions and their temporal variability in shallow lakes and ponds, similar to traditional core-based palaeolimnology.Such information is useful to underpin restoration targets that are ecologically relevant and that conform to legal requirements posed by the European Water Framework Directive.Using sediment samples from herbarium macrophytes and other sources, historical conditions are documented for a shallow man-made soft-water lake in lower Belgium (Kraenepoel, Aalter).Both assemblage composition and diatom-inferred water chemistry varied considerably from 1853 to the first half of the 20 th c.The lake was used for pisciculture during this time.From this situation, two alternatives are envisaged to determine the lake's ecological potential, depending on whether it is kept hydrologically isolated or reconnected to the brook that supplied its water originally.Later in the 20 th c., inflow of polluted water and altered management caused considerable eutrophication up to the time when restoration measures were undertaken (1999)(2000)(2001)(2002).Since then both diatom-inferred and measured physical-chemical conditions have improved considerably, even to the point of approaching those in the early 20 th c.Post-restoration sediment assemblages reflect some functional and structural rehabilitation of the lake ecosystem, but return to a former species composition was limited.The most recent observations ( 2006) suggest a possible reversal of the recovery process warranting further vigilance.The potential of using sediment assemblages for monitoring lentic water bodies is highlighted.