Sedimentary diatom and pigment-inferred recent anthropogenic accelerated eutrophication of a Mediterranean lake(Lake Dojran,Republic of North Macedonia/Greece)

Lake eutrophication is recognised as a serious global challenge,and many regional legislative programmes are being made to attempt to relieve nutrient pollution and restore deteriorated lake ecological state.However,it is of primary importance to understand the degradation processes and reference conditions.The palaeolimnological approach allows us to use ecological evidences preserved in lake sediments to track the changes of lake trophic status under human impact.Diatoms,a proxy for ecological and limnological change,and pigments,a proxy for algal production and composition,were analysed on a short sediment sequence from Lake Dojran(Republic of North Macedonia and Greece),and their preservation qualities were evaluated before environmental interpretation.Good diatom preservation is inferred mainly from the consistent co-occurrence of robust,highly-silicified taxa and small taxa throughout the sequence.Pigment evaluation of the comparison between wet sediment samples in dark and cold storage and their corresponding dry sediment samples lyophilized immediately after the recovery reveals that sediment restoration conditions are critical for the accuracy of analysis.We show that the increased chlorophyll and xanthophyll pigment concentrations,particularly the siliceous-algae pigment fucoxanthin and diatoxanthin,together with the distinct increase in diatom concentration,indicate accelerated lake eutrophication and a major ecological shift linked to intensified water abstraction practice and agricultural expansion in the late 18th to early 19th century.Evidence of diatom assemblage composition is muted probably by the dominance of widely-tolerant small fragilaroid species in diatom composition and the better competitive ability of cyanobacteria and chlorophytes than diatoms for low light under eutrophic and turbid conditions.This study improves our understanding of recent human-induced environmental change and current ecological restoration target in this lake.

Limited acid deposition inferred from diatoms during the 20th century--A case study from lakes in the Tatra Mountains

Mountain lakes are usually sensitive to the effects of global and regional environmental changes. Since the second half of the 20 th century, surface-water acidification has become a significant ecological problem, and many lakes in Europe and North America have anthropogenically acidified. Additionally, following reduction in emissions of sulfur（S） and nitrogen（N） compounds, recovery from acidification has been observed in many lakes. In this study, we used changes in diatom communities to reconstruct the p H histories based on changes recorded in nine Tatra lakes（Western Carpathians, Poland） since approximately1850 AD. Overall, results indicate that acidic precipitation had little influence on lake-water p H in the Tatra Mountain lakes. Changes in diatom-inferred p H（DI-p H） generally were small and showed little evidence of acidification during the time of the highest air pollution（since the 1960 s）, and have shown little change since the reduction of acidic deposition since the 1990 s. Lakes that showed some evidence of acidification included dystrophic lakes with low acid neutralizing capacity. However, as illustrated by the PCA trajectories of the diatom assemblages, the majority of the lakes currently contain diatom assemblages that are unlike the diatom floras that existed ca. 1850.