MODENUTTI Beatriz Estela
congresos y reuniones científicas
Microbial communities under the pumice: Testing the effect of the Puyehue-Cordón Caulle mega-eruption on microbial communities of Patagonian lakes
Congreso; SAME 13; 2013
On 4 June 2011, a mega-eruption in the Puyehue volcanic complex (Chile) discharged massive amounts of ash and pumice to the surrounding landscape.  As a consequence, large and small lakes in the area were partially or completely covered by a floating pumice layer.  In nature, the event brought about increases in phosphorus (P) concentrations, and decreases in solar irradiation in the surface layers in the heavily affected lakes.  To test the mechanisms of these responses on the microbial community, we performed an outdoor experiment in 20 L mesocosms in three treatments: 1- full solar radiation (equivalent to the mean irradiance received in lake mixolimnion), 2- covered with pumice, and 3- dark.  We used natural lake water of two lakes that differed in dissolved organic carbon concentration: Lake Gutiérrez and Lake Escondido. We measured nutrient concentration, alkaline phosphatase (APA) and ß-glucosidase (BG) activities and determined the different component of the microbial food web. In addition, we performed laboratory experiments measuring bacteria respiration and organic matter lability. Results showed similar trends between lakes, though intensity of processes may differ, with significant differences between treatments.  While the treatment full solar radiation did not exhibited significant changes, under the pumice we observed an increase of 85% of P concentration with a concurrent decrease in APA activity.  During the first week of experimentation we observed a decrease in chlorophyll a concentration with an increase in dissolved organic carbon, and consequently bacteria respiration and BG activity increased.  After 15 days of experimentation, we observed in the treatment covered by pumice a recover of phototroph nanoflagellates with a concurrent decrease in P, while in the dark this recover was not observed. These results indicated that the effect of volcanic eruptions may affect all the microbial food webs, although processes occurred with a higher significant strength in the lake with high dissolved organic matter concentration.