Paleoenvironmental record from lake San Lorenzo, Monetbello, Chiapas, Mexico

Abstract

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-, Corg/N ratios and diatom analyses from a 41 cm-long sedimentary sequence, were performed. The chronology of the sequence was established by one 14C 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 14C, 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 ”Río Grande de Comitán”) the first episode from 1970 to 1985 and the second one from 1990 to 2000.

Ostracods response to environmental anthropogenic disruption in a neotropical karstic lake in southern Mexico

“…The San Lorenzo sedimentary record was collected in July 2013 from the north part of the basin with a UWITEC gravity corer at 12 m depth, and sediments were sampled every 1 cm. For constructing the age model (Caballero et al 2022; Fig. 2) 210 Pb results were acquired with relatively constant high activity values along the sequence (60-90 Bq/kg).…”

“…However, the high frequency 137 Cs variations prevents the identi cation of individual events and suggest that Lake San Lorenzo has been constantly receiving 137 Cs contaminated soils eroded from the catchment (Poreba 2006; Appleby et al 2019). For more information about the geochronology see Caballero et al (2022). Elemental concentrations of Mn were determined by X-Ray uorescence (FRX) using a portable Niton XL3t95 equipment.…”

“…However, during the past decades anthropogenic activity has damaged this area and enhanced input of sewage water, fertilizers and pesticides have turned some of these lakes turbid with unpleasant odours (Alcocer et al 2016). Recent research in the area based on geochemistry, magnetic susceptibility and diatoms suggest two main periods of basin-wide disturbance, from 1970 to 1985 and from 1990 to 2000 (Caballero et al 2022). During these periods, Lake San Lorenzo´s turbidity and nutrient concentration increased as a result of long-distance sediment transport through the "Río Grande de Comitán" (RGC) caused by deforestation, intense agriculture, and land use changes.…”

“…In this work, we present the ostracod analysis from the sedimentary record of Lake San Lorenzo and compare our results with the diatom record and geochemical data presented by Caballero et al (2022) with the aim to assess the anthropogenic impact on the ML area. Moreover, our results also include ephippium counts, which are resting eggs that Cladocera produces when environmental stress increases (Ramírez 1981).…”

“…In this work we present ostracod and ephippium records of Lake San Lorenzo sediments dating from 1956 to 2013. Diatom and geochemical data presented by Caballero et al (2022) are also considered for the discussion. The ostracod assemblage consists of Darwinula stevensoni, Cypridopsis okeechobei, Cytheridella ilosvayi and two unidenti ed species.…”