Trophic characterization, pelagic food web structure and comparison of twomesotrophic lakes in Brandenburg (Germany)

We conducted comprehensive field investigations to characterise the trophic status and food web structure of Grosser Vatersee (GV) and Kleiner Vaterse e (KV), two stratified lakes in the Baltic lake region of northeastern Germ any. The lakes will be used as manipulation (GV) and reference (KV) ecosyst ems in food web studies. Both lakes are mesotrophic to slightly eutrophic w ith mean epilimnetic total phosphorus (P) concentrations of 24 and 21 mu g L-1 in GV and KV, respectively. Mean phytoplankton biomass was 0.9 and 0.5 cm(3) m(-3) in GV and KV. During summer, the algal community of both lakes was dominated by cyanobacterial picoplankton and Ceratium spp. Filamentous cyanobacteria (mostly Planktothrix sp.) prevailed in a deep chlorophyll max imum found within the chemocline of both lakes. Bacterial biomass in the ep ilimnion of GV usually ranged between 1 and 3 cm(3) m(-3). Mean ciliate abu ndance was 13 ind. mL(-1) in GV and 14 ind. mL(-1) in KV. While Oligotricha dominated in GV, Scuticociliata were found most frequently in KV. Mean ann ual crustacean biomass was high in both lakes (GV 2.5 cm(3) m(-3), KV 1.2 c m(3) m(-3)); Eudiaptomus gracilis, E. graciloides and Daphnia spp. were the most prominent species. Total fish biomass of both lakes was dominated by roach (GV 52%; KV 57%) and perch (GV 24%; KV 34%) Vaucheria dichotoma and C hara spp. dominated the macrophyte community in GV; Chara spp. dominated in KV. The slightly more eutrophic character of GV was most likely a result o f greater P accumulation in the sediments due to external loading, which re sulted in greater hypolimnetic P concentrations throughout the summer in GV . However, on an annual basis these differences were only occasionally refl ected at higher trophic levels. The differences in fish biomass, however, m ight have been a consequence of higher structural diversity in GV provided by submersed macrophytes rather than its more eutrophic character. We concl ude that the trophic characteristics and food web structure of Grosser Vate rsee and Kleiner Vatersee are similar enough to be suitable as manipulation and reference lakes in food web experiments.