Postglacial shifts in lake trophic status based on a multiproxy study of a humic lake

Abstract

The long-term development of a humic lake ecosystem in Poland was investigated via palaeoecological analyses of age-dated sediment cores. Peat and lacustrine deposit records spanning approximately 12,000 years of lake history were analysed with regard to palynomorphs, plant macrofossils, degree of peat decomposition, Cladocera and geochemistry. Our study demonstrated the difficulty of classifying sediments deposited in humic lakes. We considered it inadequate to classify dy sediment exclusively using macroscopic criteria in the absence of geochemical parameters. Our study of the palaeoecology of the humic lake suggested three primary shifts in its trophic status: from oligotrophy to mesotrophy (Allerød-Boreal), to eutrophy (Atlantic), and to humotrophy (from the Sub-Boreal to the present). The results indicated that shifts in the trophic status occurred in response to climatic changes and factors linked to the catchment. The transformation from a clearwater lake of high trophic status to a humic lake was possible, such that the latter may originate not only from an oligotrophic lake. As a result of our pioneering study, we determined that a humic water body may even develop because of transformation of a eutrophic lake.