Assessing eutrophication and reference conditions for Scottish freshwater lochs using subfossil diatoms

摘要: 1. The European Council Water Framework Directive requires reference conditions to be determined for all water body types including lakes. We examined the role of palaeolimnology, specifically diatom record, as a tool assessing eutrophication and defining lake ecological status.2. Sediment cores (representing c. AD 1850 present day) were taken from 26 Scottish freshwater loch basins. Radiometric dating techniques (Pb-210 Cs-137) established chronology each core. Two levels analysis employed: relatively high resolution (15-20 samples) at 21 lochs considered interest, lower (four five remaining sites.3. Detrended correspondence dissimilarity measures applied core top (present bottom (reference state, 1850) samples assess floristic change site. Significant change, indicative nutrient enrichment, occurred in 18 along broad trophic gradient.4. Two-way indicator species (TWINSPAN) was (c. classify 'reference' assemblages thereby characterize floras different types. TWINSPAN identified four site end-groups, with characteristic assemblage, although there some overlap taxa groups. depth productivity key factors that explained groupings.5. Diatom transfer functions reconstructed total phosphorus (TP) concentrations used evaluate eutrophication. Nineteen had increases diatom-inferred (DI) TP > 5 mug l(-1) (five these 20 l(-1)), six no or negligible DI-TP (<2 evidence decline one over period represented by sediment cores. inferred significant 12 lochs.6. Synthesis applications. Our data indicate it may difficult find minimally impacted waters act sites, particularly shallow, lowland types, current population. derivation site-specific record is valuable approach such cases. Ordination, clustering palaeodata, combined functions, offer powerful characterizing chemical conditions, deviation state.