Abstract

Diatoms are the most common and diverse group of algae in wetlands, however the strong influence of acidity on distribution of diatom taxa has rarely been studied in Central Chile. Humedal de Batuco (33°12,152’S, 70°49,490’W) is a coastal wetland and has great relevance due to the landscape gradients that occur associated to disturbances of the coupled ocean-atmosphere system of the tropical Pacific. We use diatoms as bioproxies to infer past environmental conditions. In 2008 (under the multiproxy approach of LINCGLOBAL) a shortcore was obtained with a gravity corer: BAT1 (length 35 cm, 0.3 m depth). BAT1 (AMS date of 200±5014C yrs BP) was opened, photographed, described sedimentologically and volumetrically subsampled every 5 cm. Aliquots were taken for diatomic analysis, processed according to standard methods for diatoms, permanent slides mounted and the first 5 cm were observed under an optical microscope, understanding that the surface sediments represent an integrated sample of the diatoms of the wetland, both spatially and temporally. We identified 29 species belonging to Bacillariophyceae and calculated the generic relative abundance: Actinocyclus (1; 7,8%), Anomoeoneis (2; 3,9%), Aulacoseira (1; 2%), Cocconeis (1; 2%), Craticula (1; 3,9%), Cyclotella (2; 9,8%), Cymatopleura (1; 2%), Encyonema (1; 2%), Epithemia (1; 2%), Eunotia (4; 17,6%), Gomphonema (3; 5,9%), Navicula (4; 15,7%), Nitzschia (4; 11,8%), Pinnularia (1; 2%), Tabellaria (1; 2%) and Tryblionella (1; 7,8%). These results, based on presence-absence of species and generic relative abundance variations would indicate conditions of oscillating pH between alkaline and acidic in recent times.