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)

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

FRESHWATER BIOLOGY (PRINT)

WILEY-BLACKWELL PUBLISHING, INC

Año: 2018 p. 1341 - 1351

0046-5070

Climate change affects glaciers all over the world causing glacial recession withthe formation of new lakes. Glaciers of Mount Tronador (41° S, Patagonia,Argentina) underwent an increase of more than 200 m in the equilibrium-linealtitude (ELA), from 1994 to 2016. The proglacial Lake Ventisquero Negroshowed a continuous increase in lake surface area since 2009, when a glacialoutburst flood (GLOF) occurred. The Ventisquero Negro glacier is a debris-coveredglacier located below the timberline; thus, the lake receives meltwater fromboth clean and debris-rich ice.2. This study analyses the proglacial lake after the GLOF event, particularly thenutrient content, dissolved organic matter and bacterial respiration. Our mainhypothesis was that the melting of debris-rich and clean ice would differentiallyaffect nutrient inputs and bacterial respiration in the early ontogeny of the lake.3. Sampling was conducted in austral spring?summer seasons (2012 to 2016) followingthe GLOF event. We carried out bacterial respiration experiments withlake water and two treatments enriched with clean or debris-rich ice from theglacier. Additionally, we carried out an another enrichment experiment withphosphate-P and glucose-C alone or in combination.4. The lake exhibited high turbidity levels due to a high concentration of suspendedsolids. Vertical light profiles showed that almost the entire water column wasaphotic. Phosphorus (P) concentration was high and was positively related tototal suspended solids. Accordingly, P concentration was higher in debris-richthan in clean ice. However, the dissolved organic carbon concentrations inthe lake were found to remain relatively constant through time (less than50 μmol/L).5. Analysing fluorescent excitation?emission matrices, we determined that the dissolvedorganic matter is very simple with only two peaks, one corresponding toprotein-like compounds (C1) and the other to humic-like compounds (C2), comingfrom clean ice and debris-rich ice, respectively. C1 was present in all samples,while C2 was comparatively more important during summer, coinciding withhigher temperatures and melting.This study supports the hypothesis that melting of clean and debris-rich icewould affect DOM and P input at early stages of a proglacial lake formed by therecession of a debris-covered glacier. Bacterial respiration was observed to bepositively affected by debris-rich ice melting and to be P limited. Thus, P is amajor controlling factor for carbon dynamics in a newly formed proglacial lake.