PLANKTON AND CHEMICAL PHYSICAL DEVELOPMENT IN 6 SWEDISH WEST-COAST LAKES UNDER ACIDIC AND LIMED CONDITIONS

Increases in pH from 4.5-5.3 to 7-7.6 after liming (1978-85) in six ac idified lakes in the west coast area of Sweden caused increased concen tration of humic compounds and decreased transparency compared with le vels before liming. Concentrations of total P increased markedly where as those of NO3-N decreased. The phytoplankton composition changed com pletely in all lakes shortly after liming, but a species richness simi lar to that in unacidified lakes was not reached until after 2-5 yr, a nd in the previously most acidified lakes, several species remained ab sent. The composition of the phytoplankton indicated increased primary production. The volumetric dominance within the zooplankton shifted g enerally from Eudiaptomus-Holopedium to Cyclops-Daphnia. The occurrenc e of Rotatoria and Cladocera species increased and the composition bec ame similar to that in unacidified lakes 2-5 yr after liming. The biot ic development is largely explained by chemical-physical changes such as increased pH, reduced Al concentration, increased P concentration, and increased organic content, particularly humus.