PALEOENVIRONMENTAL RECORD FROM LAKE SAN LORENZO, MONETBELLO, CHIAPAS, MEXICO

Lake San Lorenzo is one of the lakes at the NW karstic plain of the "Parque Nacional Lagunas de Montebello", Chiapas, Mexico, that currently have eutrophic, turbid waters. To understand the recent history of this lake, multi-elemental contents determined by X-ray fluorescence analysis, organic matter and carbonate contents -determined by loss on ignition-, C-org/N ratios and diatom analyses from a 41 cm-long sedimentary sequence, were performed. The chronology of the sequence was established by one C-14 date from the basal sediments, which allowed establishing that the studied record began in 1956. These new data are consistent with previously published analysis of a profile from the nearby Lake Balamtetik, that could not be dated by C-14, therefore this work provides a better chronological resolution of events. The diatom community along the Lake San Lorenzo sequence was dominated by high nutrient tolerant species, which allows inferring that the lake was already turbid and eutrophic since 1956. Erosion indicators (titanium and magnetic susceptibility) allowed identifying two episodes of basin-wide erosion associated with long distance sediment transport to the lake (very likely through the "Rio Grande de Comitan") the first episode from 1970 to 1985 and the second one from 1990 to 2000.