Early summer phytoplankton responses to experimental manipulations of grazing and nutrients in unlimed and limed Lake Njupfatet, central Sweden
Archiv für Hydrobiologie Volume 140 Number 3 (1997), p. 321 - 346
published: Nov 10, 1997
ArtNo. ESP141014003005, Price: 29.00 €
Phytoplankton biomass and succession during the spring-early summer period were studied in oligotrophic, moderately acidic, Lake Njupfatet during two consecutive years, one before and one after whole-lake calcite treatment. Liming had little effect on the early summer phytoplankton community and three groups, Chrysophyceae, Dinophyceae and Chlorococcales, completely dominated before as well as after liming. Enclosure experiments were carried out to assess the role of nutrients and zooplankton in regulating the early summer community of phytoplankton in the unlimed and limed lake, respectively. Despite differences in starting point regarding phytoplankton development, the communities and most of their components responded in the same way in both experiments. Community biomass showed a positive response to nutrient additions in combination with a negative response to grazing. Edible organisms such as small and medium-sized chrysophytes and dinoflagellates, responded weakly to the nutrient additions but showed a negative response to grazing. Grazing-resistant forms, small coccoid green algae and large species in general, showed a positive response to nutrients but were indifferent to, or favoured by, grazing. The results are discussed against the background of general theories about phytoplankton succession. It is concluded that neither the acidic nor the limed system were disturbed with respect to regulation of the early summer phytoplankton community.