Pollen and microalgae in sediments at southern margin of Colhue Huapi Lake, Chubut; Argentina. An insight to among shore comparison

Abstract

A soil profile from the southern margin of Colhue Huapi Lake, at La Campanita site (45º38' S, 68º37' W), was analysed for pollen and algae content to know the past vegetation communities and to infer changes in lake water level occurred during the Late Holocene. Samples were dated by AMS 14 C methods. Radiocarbon ages were of 1711 ± 35 14 C yr BP at the base, 95cm depth, and another of 979 ± 42 14 C yr BP at 40cm depth. The record was dominated by no arboreal taxa, Chenopodiaceae being the principal shrub taxon and Cyperaceae the herbaceous one. Changes in the pollen record occurred mainly at a local scale and few differences were observed in the input of regional and extra regional pollen. From 1711 ± 35 14 C yr BP until ca. 1212 yr BP, a high lake water level was indicated by the low representation of Cyperaceae associated with few shallow areas available to be colonized and high percentages of Pediastrum and Botryococcus algae. Between ca. 1212 and 414 yr BP a period of changes with several fluctuations in water depth developed. This trend would modify at 979 ± 42 14 C yr BP with a decrease in the waters reflected by the expansion of Cyperaceae and algal reduction. From ca. 414 yr BP until 195 yr BP lake water level continued falling with a less fluctuating and net trend as indicated by the highest percentage of Cyperaceae in the sequence and a low algal representation. The subsequent reduction in Cyperaceae percentage and the moderate increase in the algae would indicate a recovery of the lake water level for the last ca. 195 yr BP. Additionally La Campanita sequence was statistically compared with a sequence obtained from the northwestern margin of the lake. Both sites registered a similar trend before 979 ± 42 14 C yr BP.

Geomorphology context and characterization of dunefields developed by the southern westerlies at drying Colhué Huapi shallow lake, Patagonia Argentina

“…9F). Consequently, the aeolian sand layers recognized in the southwest LCH bottom could likely correlate with the expansion of Cyperaceae and algal reduction identified by Fabiani et al (2014)around 979 ± 42 14 C yr BP, both related with a decrease in the water level. Also, the incorporation of dune sediments into the lake basin bottom from the development and shift of the SWD contribute to its silting, because this process causes a progressive loss of depth, favoring its desiccation.…”

“…The LCH dynamics from mid-Holocene was registered at least since 1750 yrs BP to the present by Fabiani et al (2014)through pollen and algae content in core obtained southeast of the lake. The fluctuations of its surface promote the intermittently exposure of lakebed sediments to erosion, transport and deposition by wind.…”

“…Radiocarbon dates obtained at archaeological sites suggest that the Sarmiento palaeolake level would have had a height of 30 m above the current level of LM during the end of mid Holocene (4000-5000 yrs BP; Moreno et al, 2016). Significant fluctuations in the lake level during the last 1750 yrs BP 14 C were recognized from the study of pollen and microalgae, showing that desiccation was not continuous (Fabiani et al, 2014).…”