PALEOLIMNOLOGICAL ANALYSIS OF WHOLE-LAKE EXPERIMENTS - AN OVERVIEW OFRESULTS FROM EXPERIMENTAL LAKES AREA, LAKE-227

High resolution analysis of laminated sediments from experimentally fe rtilized Lake 227 was used to compare sediment geochemistry and fossil abundance (siliceous algae, pigments, cladoceran remains) with 20 yr (1969-1989) of continuous historical records. Members of all fossil gr oups were correlated to the biomass of their respective producer popul ations (r = 0.52-0.66, P < 0.05, n = 20). Correlations were greatest w hen fossil abundance was expressed per unit organic matter and least w hen calculated as the accumulation rate. Comparison of groups showed t hat fossils of soft-bodied zooplankton (copepods, rotifers) and pigmen ts from dinoflagellates were completely unreliable. The most informati ve fossils were chitinous remains of zooplankton (e.g., Bosmina), rema ins of siliceous algae, and pigments from chlorophytes and cyanobacter ia. Ecosystem-level paleolimnology showed that fertilization was the m ost significant eutrophication event in the last 400 yr and that it im pacted both pelagic and littoral communities. However, fossil zooplank ton and pigment analyses indicated that food-web interactions (zooplan ktivory, herbivory) also regulated plankton abundance and composition. Additionally, fossil analyses showed that some natural eutrophication occurred prior to 1969 and that plankton communities have continued t o vary since 1975, despite constant rates of fertilization with nitrog en and phosphorus.