Etat trophique du lac de Morat indiqué par le zoobenthos: tendance 1980-1998

Abstract

Trophic state of Lake Morat indicated by the zoobenthos: the 1980-1998 trend. -Total phosphorus concentrations have strongly decreased between 1982 and 1998 in the water of Lake Morat (Switzerland). In response to this improvement, the numbers of tubificids (Tubifex tubifex and Potamothrix hammoniensis mostly) decreased in the deepest area (40-45 m), but the other species (Limnodrilus profundicola and L. hoffmeisteri) present therein, remained scarce. In contrast at a depth of 20 m, chironomid larvae (Chironomus and Procladius) and the tubificid Potamothrix moldaviensis became more abundant in 1998. These changes indicated a slow improvement of benthic conditions but, in 1998, the zoobenthos was always characteristic for a eutrophic lake.

Reconstruction of trophic state shifts over the past 90 years in a eutrophicated lake in western Switzerland, inferred from the sedimentary record of photosynthetic pigments

“…These give a good match with the varve formation in the sediments associated with high algal biomass and low oxygen conditions in the lake. These findings agree with zoobenthos composition for the period from 1980-1998 in Lake Morat (Lang 2000). Lang's results indicated a slow improvement of benthic conditions for the examined period however, the main species found in 1998 were characteristic of a eutrophic lake.…”

Réponse anormale du zoobenthos (oligochètes et chironomides) à la baisse du phosphore dans le lac de Neuchâtel

“…Dans la zone profonde d'un lac eutrophe comme le lac de Morat (Lang, 2000a) Neuchâtel en 1980, y a été observée pour la première fois en 1984 (Lang, 1999). Son extension pourrait avoir été favorisée par l'augmentation de la température de l'eau (Lang, 1998) qui a été constatée au cours de cette période (Pokorni, 2000).…”