Non-pollen palynomorphs show human- and livestock-induced eutrophication of Lake Nussbaumersee (Thurgau,Switzerland) since Neolithic times (3840 bc )

Abstract

Lake Nussbaumersee, located SW of Lake Constance (Switzerland/Germany), was studied at high temporal resolution for non-pollen palynomorphs (NPPs) within a calcareous gyttja sediment core from the deepest part of the lake. At the Nussbaumersee lakeshore, three pile-dwelling settlements have been excavated and dendrochronologically dated (to the Neolithic, 3840–3695 bc; late Early Bronze Age, 1580–1538 bc; and Late Bronze Age, 850–780 bc). The NPP study revealed three peaks of cyanobacteria, likely related to three settlement phases causing phosphate eutrophication of the lake water. The fast decline in cyanobacteria and reduction in green algae blooms after the abandonment of the Neolithic village and the quick recovery of the lake water back to oligotrophic conditions indicate a high prehistoric resilience of the lake ecosystem. After the second eutrophication phase starting around 2500 bc, the density of NPP eutrophication indicators remained at much higher levels, probably showing a loss of resilience of the lake ecosystem due to repeated human disturbance.