SUBFOSSIL CLADOCERA SUCCESION IN TROPICAL LAKE TACÁMBARO (WESTERN MEXICO)

We present the results of subfossil Cladocera analysis from a tropical lake located in western Mexico. The main aim of the research was climatic reconstruction in the region, identification of natural climatic fluctuation and also pre-Hispanic and modern impact. Sediments were collected from lake Tacámbaro, located in the Trans Mexican Volcanic Belt (19°12’40”N 101°27’30°W, 1,460 m asl). This lake is 0.3 km² and has a maximum water depth of 30 m, and a small closed catchment. The 8.1 m long sediment core was taken from the central part of the lake by means of modified Livingston piston corer.

Reconstruction of past environment was done on the basis of multi-proxy analysis such as: lithology, geochemical composition of sediments, radiocarbon data, pollen, Cladocera and diatoms. We present the results of subfossil Cladocera analysis. The Cladocera fauna is represented in sediment by the remains of planktonic and littoral species belonging to 3 different families: Bosminidae, Daphniidae and Chydoridae. Changes of the particular species existence and the frequency of specimens allowed distinguishing four main units:

Unit 1 (806 - 454cm, ca. 9.2-6.2 kyr cal BP) planktonic and littoral Cladocera are abundant and Bosmina longirostris is dominant, suggesting eutrophic water of the lake at the time.

Unit 2 (454-372cm, ca. 6.2 – 5.3 kyr cal BP) period of transition characterized only by presence of littoral species of Cladocera.

Unit 3 (372-116cm, ca. 5.3 – 0.68 kyr cal BP) species composition and the abundance of Cladocera (vary between 0 and 10%) indicates that nutrients were limited in the lake at the time.

Unit 4 (116- 1 cm, 680 cal BP to present) Cladocera remains are again abundant. In uppermost part of profile is registered the influence of human activity on lake’s ecosystem and surroundings.