Environmental change since AD 1080 in the Grijalva watershed, Mexico, inferred from Lake Chicuacan sediments

Abstract

Little research has been done on recent environmental and climatic change in Mexico. This study presents an environmental reconstruction since the Postclassic Era (~ AD 1080) for the southeastern part of Mexico. A lacustrine core from laguna Chicuacan, located in the Grijalva watershed, Tabasco, Mexico has been analyzed on diatom and pollen content. The diatom and pollen data have been used to reconstruct variations in lake level as well as changes in trophic state of the lake. An age-depth model for the core was established by the use of radiocarbon dates. Laguna Chicuacan experienced fluctuations in water depth, suggested by varying Aulacoseira spp. abundances. Ever since the formation of laguna Chicuacan at the end of the 11th century, water levels have slightly decreased. Shallowest lake levels probably occurred around AD 1660. After AD 1800, the relative abundance of Aulacoseira spp. and Cyperaceae pollen increased, indicating a slight increase in water depth. These variations in lake level are presumably caused by precipitation changes. This study shows evidence for several phases of nutrient supply to laguna Chicuacan as well, suggested by the varying occurrences of Staurosira spp. and Staurosirella pinnata. This enhanced nutrient supply occurred in the time period between approximately ~AD 1080 and 1505. More recent anthropogenic eutrophication occurred from AD 1950 until recent. Current flora on the lakeshore supports the finding that laguna Chicuacan is a eutrophic lake at present.