RELATIONSHIPS BETWEEN ZOOPLANKTON COMMUNITY STRUCTURE AND PHYTOPLANKTON IN 2 LIME-TREATED EUTROPHIC HARDWATER LAKES

I. North Halfmoon Lake and Lofty Lake (Alberta, Canada) were chosen fo r whole-lake liming experiments as a new restoration technology to enh ance calcite precipitation and reduce eutrophication. During a 3-year study (1991-93) the relationships between zooplankton and phytoplankto n were assessed, together with the effects of lime additions. 2. Zoopl ankton communities were numerically dominated by rotifers, while the m ajor contribution to biomass was due to large filter-feeding Daphnia d uring the first half of the summer season. In Lofty Lake, cladocerans made up to 93% of biomass, whereas in North Halfmoon Lake both cladoce rans and calanoids were strongly represented. 3. Total zooplankton and cladoceran biomasses were inversely correlated with chlorophyll a (ch l a). The same relationship was found between large Daphnia (greater t han or equal to 1 mm) and chi a. These relationships suggest that the decline in Daphnia may have been caused by an increase in cyanobacteri a biomass during bloom events. 4. There were minor changes in rotifer populations after liming; however, these changes have been caused by n atural year-to-year Variation rather than liming. In general, cladocer ans showed an increase in body size and population biomass when pre an d post-treatment data were compared by means of ANCOVA. Statistical an alysis showed that there were more cladocerans per unit of chi a after liming; however, further research is needed to relate these patterns unambiguously to the application of lime as a restoration technology.