Nutrients, organic matter and bacteria community composition at early stages of the proglacial lake of Ventisquero Negro (Mountain Tronador, Patagonia, Argentina).

B. MODENUTTI,; E. BALSEIRO,; MARTYNIUK, N; BASTIDAS NAVARRO, M.,

Turin

Congreso; SIL Torino; 2016

SIL

Climate change affectsglaciers all over the world causing glacial recession with the formation of newlakes. These proglacial lakes are characterized by heavy glacial clay inputs thatcause a turbidity-induced attenuation of photosynthetically active radiation(PAR), therefore they can be expected as environments with light limitation forprimary producers. The aim of this study was to assess temporal shifts in nutrients,organic matter and bacteria abundance, diversity and respiration, in the proglaciallake of Ventisquero Negro located in Mountain Tronador (Patagonia, Argentina).  Samplings were conducted during four successiveaustral summers (2012/15).  We measurednutrient concentrations, bacteria abundances assessing different components ofbacterial community structure using next-generation sequencing of the 16S rRNAgene. In addition we conducted experiments measuring oxygen consumption bybacteria communities and spectrofluorometric analysis of the dissolved organicmatter.  Results showed that chlorophyll a concentrations were low (0.571±0.33 µg L-1) because of the light limitation imposed by the high turbidity due tototal suspended solids. Bacteria community analysisusing the 16S rRNA gene identified a total of 2135 OTUs consisting mainly of Proteobacteria,Firmicutes, Actinobacteria and Bacteroidetes. Dissolved organiccarbon (DOC) concentrations in the lake were low (0.43± 0.16 mg L-1) and analyses indicated the presence of twocomponents one corresponds to protein-like and the other to humic-likesubstances.  Ice presented higher DOCconcentration (1.6 ± 0.18 mgL-1) than the lake and analyses showedthe dominance of protein-like component. High bacteria respiration rates were attained incoincidence with the presence of one protein-like component in the dissolved organic matter, while no relationship wasobserved between bacteria respiration and chlorophyll a concentration.