Dissolved organic matter (DOM) characterization in subantarctic shallow lakes and beaver ponds

One important fraction of carbon (C) in aquatic environments is the dissolved organic matter (DOM). The present study analyzes the optical characteristics of DOM in two common freshwater environments from the southernmost area of Patagonia, Tierra del Fuego (Argentina), shallow lakes and beaver ponds. In contrast to natural shallow lakes, beaver ponds are lentic water bodies created by beavers, which were introduced in the area in the past century. Based on absorbance and fluorescence techniques, we compared shallow lakes and beaver ponds in terms of DOM quantity and quality. Our results reveal that dissolved organic carbon (DOC) concentrations ranged from similar to 3 to 9 mg L-1, and that DOM origin in all the studied environments was allochthonous and highly influenced by terrestrial inputs. The comparison between shallow lakes and beaver ponds showed significantly higher DOC concentration in shallow lakes, while DOM quality in beaver ponds was significantly different. The quality of DOM in beaver ponds was characterized by high aromaticity (SUVA index), high humic content (humification index) and low recently produced DOM (biological index). A possible explanation for this pattern is that they might be more influenced by terrestrial inputs, more likely due to the smaller size and the higher forest cover (similar to 47% in comparison to similar to 28% in shallow lakes). Parallel factor modeling (PARAFAC) validated only two humic-like components. This study is the first report that compares DOM quantity and quality in Subantarctic shallow lakes and beaver ponds. Our results confirm the idea of the humic shallow lakes and enlighten new features of the DOM quality in beaver ponds.