Marcela Bastidas Navarro

Effect of light on particulate and dissolved organic matter production of native and exotic macrophyte species in Patagonia

Biological invasions are one of the main drivers of changes in ecological features in aquatic environments. Invasive alien species may have far-reaching effects on the host environment that need to be explored. In this study, we compared particulate and dissolved organic matter (POM and DOM) production from two common Patagonian wetland plants, one native (Eleocharis pachycarpa) and one exotic (Potentilla anserina), under different light conditions (exposed or not to ultraviolet radiation (UVR+, UVR−) and darkness). Our results indicated that when exposed to UVR both macrophytes differed in their POM production and DOM release: while in E. pachycarpa we observed an increase in the POM production P. anserina released significantly higher amount of DOM. The DOM produced by the exotic species showed lower photoreactivity, and had more colour than that produced by the native E. pachycarpa. The invasion by macrophytes may produce changes in the stoichiometric balance and ecological relationships that could modify the characteristics of wetland food web.

Seasonal patterns of organic matter stoichiometry along a mountain catchment

Organic matter (OM) nutrient content is expected to change as OM is transported from upstream forested reaches downstream to open land, and these changes could depend on seasonal patterns. The aim of this study was to analyze OM carbon nitrogen and phosphorus content, from headwater reaches to open reaches downstream. We sampled four sites along a mountain catchment over the course of one year and quantified fine particulate organic carbon (FPOC) in transport and dissolved organic carbon (DOC) concentration and elemental content. Both FPOC and DOC concentration decreased downstream, and changes in OM stoichiometry depended on the season. Stoichiometry of FPOM and DOM along the catchment was similar in autumn, with higher C:P and C:N ratios upstream, which could be associated with the relative importance of allochthonous versus autochthonous OM origin. Conversely in spring, C:N was very low in the forest sites. Our results highlight that headwaters running through pristine forests are a source of POM and DOM for downstream ecosystems, and that the quality of such resources depends on season.

Effect of glacial lake outburst floods on the light climate in an Andean Patagonian lake: implications for planktonic phototrophs

Climate change is altering temperature and precipitation patterns all over the world. In North Patagonia, glaciers of the Tronador mountain (41°S) show a continuous and maintained recession, and these meltwaters are transported to Lake Mascardi via the Upper Manso River that carries a large amount of glacial clay. These suspended sediment particles cause a very sharp light longitudinal gradient along the western branch of Lake Mascardi (Tronador arm). Here we analysed changes in the water transparency along the gradient, in particular before and after a glacial lake outburst flood (GLOF) event that occurred in the headwaters that feed Lake Mascardi. The GLOF caused a significant decrease in turbidity over the years following the event. The depth of the deep chlorophyll maxima (DCM) was directly related to the light penetration, and the decrease in suspended solids load deepened the DCM in the years after the GLOF event. Among photosynthetic organisms, picocyanobacteria and total nanoflagellates abundances increased after the GLOF event when transparency increased due to the decrease in the clay and sediment inputs into the lake. Our data demonstrated that the DCM and phytoplankton are useful variables to predict changes in the lake light climate.

Differences in bacterial community-level physiological profiles between deep and shallow North-Patagonian Andean lakes

The utilization of carbon substrates by bacteria results in a process of great ecological significance for aquatic ecosystems. Bacteria are capable of consuming a wide range of organic molecules, but despite the highly diverse functional abilities, environmental availabilities can influence the composition of the community. Thus, differences in dissolved organic matter (DOM) and nutrient bulk between shallow and deep lakes would affect bacterial metabolic capacities. Here, we used the metabolic profiles obtained with Biolog EcoPlates® as a proxy of bacterial processing of DOM, and compared the bacterial community-level physiological profile (CLPP) from 20 North-Andean Patagonian lakes, including shallow (piedmont and high altitude, Zmax < 15 m) and deep piedmont lakes. In addition, we carried out an incubation experiment of bacterial communities from one shallow lake to assess the response of the CLPP enriched with algal exudates or leaf leachates. Our results show that the lakes have contrasting limnological features relatable to the obtained CLPP. Shallow lakes have higher nutrient and dissolved organic carbon concentrations than deep lakes and high-altitude shallow lakes. Accordingly, bacterial CLPP differed between piedmont shallow lakes and deep lakes, with a higher ability of using carboxylic acids in deep lakes. The incubation experiment shows that bacteria can develop different metabolic capacities depending on the DOM (leachates versus algal exudates) offered during incubation, increasing the consumption of the carbohydrate Dcellobiose in the algal exudate treatment. Our results show that resource availability (concentration and origin) is an important metabolic-capacity driver of bacterial communities.