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Environmental changes during the last millennium recorded in subfossil Cladocera, diatoms and sediment geochemistry from Lake El Sol (Central Mexico)

Zawisza E., Cuna E., Caballero M, Ruiz-Fernandez A. C., Szeroczyńska K., Woszczyk W., Zawiska I.

Geological Quarterly

2017

Vol. 61, No. 1

81--90

High-altitude lakes, which are very sensitive ecosystems and respond rapidly to climatic changes, are one of the best targets for palaeolimnological studies. Here, we present the record of environmental changes over the last millennium that are recorded in the sediments of El Sol, a tropical, high-altitude, volcanic crater lake on the Nevado de Toluca, Central Mexico. Palaeolimnological reconstructions are based on subfossil Cladocera, diatoms, magnetic susceptibility and chemical analysis of the sediments. In general, Cladocera occurring in tropical regions, and especially at high altitude, have been studied very little. Our data indicate that in the sequence studied, the species diversity of subfossil Cladocera is very low. Only four species were recorded, and the assemblage is dominated by littoral species. Two Cladocera taxa, Alona manueli and Ilyocryptus, found at Lake El Sol are endemic. Cladocera, diatoms and the sediment chemistry show changes in Lake El Sol which are mostly related to climate. The most pronounced climatic signal was obtained for the early Little Ice Age (1350–1625 AD). This cold episode was expressed by a reduction in the frequency of zooplankton (individuals/cm2/yr) and diatoms (valves/g of dry sediment) and by changes in the organic carbon content in the sediment. Our results show that human activity was very limited throughout the study period. According to historical data the presence of humans at the lake shore was mostly occasional, usually for ceremonial and ritual purposes, and humans did not have an important influence on the lake ecosystem. Only one period was identified when human activity was important. This period corresponds to the introduction of fish into the lake at the beginning of the 20th century.

500 years of ecological changes recorded in subfossil Cladocera in a high-altitude, tropical Lake Lago de la Luna, central Mexico

Zawisza E., Caballero M, Ruiz-Fernandez C

Studia Quaternaria

2012

Vol. 29

23--29

We present the last 500 years of history of a high-altitude tropical lake Lago de la Luna located at Nevado de Toluca crater, Central Mexico, based on subfossil Cladocera analysis. Through the studied sedimentary sequence only five Cladocera species were present. Cladocera community was dominated by littoral species (4) and among them one (Ilyocryptus nevadensis) is endemic. The detailed analysis of the sediments (every 1 cm) allowed us to track contemporary climatic and anthropogenic changes. Our results showed that Lago de la Luna is a very sensitive ecosystem and has strong response to climatic changes. The most remarkable change in the Cladocera community was observed between 1683-1780 yr, which was well correlated with the Little Ice Age. PCA results implied that modern state of the lake Lago de la Luna is very similar to one 400-500 yr ago. Only one period was identified when human impact was of importance. This period seemed to correlate with changes in the lake ecosystem due to fish introduction in the 1950s.