| Popis: |
Since 1980, Lake Geneva and Lake Neuchâtel (Switzerland) have been recovering from man-made eutrophication. Assessments of trophic state based on oligochaetes and on chironomid larvae were compared in 29 surveys made in the profundal of both lakes between 1982 and 1995. Mean relative abundance of oligotrophic species in oligochaete communities was computed in two ways to indicate the trophic state of each survey: either all samples were included (OST) or only those in which oligotrophic species were present (OSP). The indicative value of chironomid communities was expressed as proposed by SAETHER (1979). According to chironomids and selected samples of oligochaetes (OSP), 59 % of the surveys were classified as oligotrophic whereas, according to oligochaetes (OST), only 14 % were oligotrophic. Chironomids and selected samples of oligochaetes (OSP) seemed to indicate the potential extent of recovery, whereas oligochaetes (OST) indicated rather the actual recovery of sediments. |
