Melting of clean and debris-rich ice differentially affect nutrients, dissolved organic matter and bacteria respiration in the early ontogeny of the newly formed proglacial Ventisquero Negro Lake (Patagonia Argentina)

MODENUTTI, BEATRIZ; BASTIDAS NAVARRO, MARCELA; MARTYNIUK, NICOLÁS; BALSEIRO, ESTEBAN

FRESHWATER BIOLOGY (PRINT)

WILEY-BLACKWELL PUBLISHING, INC

Año: 2018 vol. 63 p. 1341 - 1351

0046-5070

Summary1.      Climate change affects glaciers all over theworld causing glacial recession with the formation of new lakes. Glaciers ofMount Tronador (41° S, Patagonia, Argentina) underwent an increase of more than200 m in the equilibrium-line altitude (ELA), from 1994 to 2016. The proglaciallake Ventisquero Negro showed a continuous increase in lake surface since 2009,when a glacial outburst flood (GLOF) occurred. The Ventisquero Negro glacier is a debris-covered glacier located belowthe timberline, thus the lake receives melt from both clean and debris-rich ice.2.      The present study analyzes the proglacial lakeafter the GLOF event, particularly the nutrient content, dissolved organicmatter and bacterial respiration. Our main hypothesis was that the melting of debris-richand clean ice would differentially affect nutrient inputs and bacterialrespiration in the early ontogeny of the lake. 3.      Sampling was conducted in austral spring-summerseasons (2012 to 2016) following the GLOF event. We carried out bacterialrespiration experiments with lake water and two treatments enriched with cleanor debris-rich ice from the glacier. Additionally, we carried out an anotherenrichment experiment with Phosphate-P and Glucose-C alone or in combination. 4.      The lake exhibited high turbidity levels due toa high concentration of suspended solids. Vertical light profiles showed thatalmost the entire water column was aphotic.  Phosphorus (P) concentration was high and waspositively related to total suspended solids. Accordingly, P concentration washigher in debris-rich than in clean ice. However, the dissolved organic carbon concentrations in the lake were foundto remain relatively constant through time (less than 50 µmol L-1). 5.      Analyzing fluorescent excitation?emissionmatrices, we determined that the dissolved organic matter is very simple withonly two peaks, one corresponding to protein-like compounds (C1) and the otherto humic-like compounds (C2), coming from clean ice and debris-rich ice, respectively.  C1 was present in all samples while C2 wascomparatively more important during summer, coinciding with higher temperaturesand melting. 6.      Bacterial respiration increased with theaddition of debris rich ice and in the P enrichment, Therefore, bacterialrespiration appeared to be P limited.