Abstract

Central Chile is well known as a biodiversity hotspot yet lacks studies on inland aquatic biota. Ciénagas del Name wetland (35°45.024′S-72° 13.029′W) is part of an altitudinal gradient from the coast to the Andes, 33º-35ºS. This coastal wetland is affected by perturbations in the coupled ocean-atmosphere tropical Pacific system, located along a subsidence zone between the Nazca and South American plates, and surrounded by agriculture and ranching areas: strong modifier agents of coastal ecosystems. We use diatoms as bioproxies to infer past environmental conditions. In 2008, three cores were obtained with a gravity corer: NAME1, 2 and 3 (2.6 and 1 m depth; lengths: 48, 47 and 27 cm), in 2012 we obtained another three with a gravity corer(CN1202SC 1, 2 and 3 at 1.7 m depth, lenghts: 60 cm) and two with a Livingstone corer: CN1202AT, BT and CT (1.7 m depth and lengths: 242 cm). Cores were opened, photographed and described sedimentologically. NAME2 and CN1202BT (AMS date of 200±50 14C yrs BP) were volumetrically subsampled every 5 cm, aliquots were taken for diatomic analysis, processed according to standard methods for diatoms, permanent slides mounted and observed under an optical microscope. Presence/absence analysis of NAME2 diatoms associations showed for N42cm (base), 28 spp: epiphytic dominant (47.8%), most abundant genus Navicula (5spp, 23%) would indicate high conductivity, moderate pollution and circumneutral to alkaline pH, pristine conditions; N27cm, 6 spp: benthic (60%), Sellaphora (2spp, 38.5%) would indicate moderate pollution and N2cm, 36 species, epiphytic (51.6%), Eunotia (8spp, 15.3%) would indicate acidic to circumneutral pH (current 7.5), stages of human intervention.