THE SEDIMENT DIATOM ASSOCIATION AND CHEMISTRY OF SURFACE SEDIMENTS OF LAKE BELAUER SEE, NORTHERN GERMANY

Abstract

Within-lake variability in diatom associations deposited on the surface sediments (0–1 cm) of a hypereutrophic lake, Lake Belauer See, northern Germany, was compared with spatial variations in sediment composition, which were used to identify environmental gradients. Numerical analysis was used to explore the data for major patterns in order to interpret die complex diatom associations. Non-uniform hydrodynamics and sedimentary conditions related to the bipartite basin geometry and morphometry were found to have a major influence on surface sediment composition and explain the main trends in diatom assemblage structure. The planktonic diatoms Stephanodiscus spp (S. parvus, S. minutulus, S. neoastrae/rotula, S. hantzschii) and Cyclostephanos dubius were dominant in the majority of the surface samples. Non-planktonic forms, including very high frequencies of fragilarioid species (amongst these, especially Staurosira construens and Pseudo-staurosira brevistriata), were dominant only in shallow and/or marginal parts of the lake. Superimposed on this pattern of life-form categories is the influence of local pollution sources in die lake. While odierwise rare or absent, diatoms such as Amphora pediculus, Navicula scutelloides, N. cari, N. radiosa, N. gothlandica increase in abundance in those parts of the lake which receive the highest input of nutrients. Apart from düs large-scale pattern, marginal sites often have site-specific assemblages, which are believed to reflect direct or indirect influences of die erosional transport along shores and inwash from die catchment. To overcome die problems of spatial heterogeneity when dealing with communities of non-planktonic diatoms a multiple core strategy and higher diatom counts are advisable.