To interpret the remains of Cladocera in lake sediments in relation to pH history, fish abundance, vegetation change, trophic level change and other historic events, it is necessary to understand the balance of abiotic and biotic forces responsible for their present distribution, population dynamics and morphological types. Once these factors are understood, we can reverse the arguments to infer past lake conditions. Many cladoceran species are influenced by fish and invertebrate predation. Some species, especially in the plankton, also show a clear physiological relation to pH and aluminium levels in lakes. Moreover, several littoral-benthic species have a habitat distribution restricted to rock, sand, mud, vegetation, or a combination of some of these. Remains of littoral and planktonic cladocerans were analysed in surface sediments of 18 Norwegian lakes with pH ranging from 4.5-7.5. In addition, sediment cores from four sites in Norway, four in Scotland and one in Sweden were analysed. The majority of sites showed evidence of recent acidification. In lakes with non- planktivorous fish, analyses of cladoceran remains gave no information on past fish populations, but indicated the pH history of the lakes. In lakes with present or past populations of planktivorous fish, the cladoceran record could be used to assess past fish status as well as past pH. In some lakes changes in the cladoceran communities could be related to changes in macrophyte distribution.
Spatial distribution of perfluoroalkyl acids in surface sediments of the German Bight, North Sea