LATE HOLOCENE DIATOM RECORD FROM LAKE CHALCHOAPAN, EASTERN MEXICO

Chalchoapan (18°24’N, 95°08’W, 386 m SNM) is a crater lake (43 m deep, 550 m diameter) in the tropical lowlands of Eastern Mexico. Currently it is an eutrophic lake with phytoplankton dominated by cyanobacteria (Mycrocystis spp.) and very low diatom abundance. As in many tropical settings it is likely that Chalchoapan has undergone cultural eutrophication related to the agricultural activities in the nearby tobacco plantations, however there is a lack of previous limnological data to identify the original condition of this lake or evaluate its current status. With this purpose short cores (<50cm) were retrieved from this lake and chronology established by 210-Pb. According to the diatom data the highest disturbance in the lake is recorded by peak in Achnanthidium minutissimum between 1960 and 1990 which also correlates with high magnetic susceptibility values indicating high erosion rates.