In early January, I had the opportunity to participate in a research project that explores the effects of volcanic pumice on deep oligotrophic (low nutrient) lakes in Argentina. Back in June 2011, some of us might remember hearing of a volcano eruption in Chile that had affected airports in several cities in South America AND Australia. This volcano was part of the Puyehue-Cordon Caulle volcanic complex. The last time it erupted was about fifty years ago, back in 1960s. During the eruption, a large amount of pumice and ashes spurt out from the volcano landed in the small tourist town of Bariloche and various lakes in Argentina, in the Patagonian region. In addition to causing thousands of people to run for their lives during the eruption, the volcano's ash deposition on nearby parks and lakes became a major perturbation to the ecosystem. Until today, there are still ashes coming out from the volcano and occasionally, when the wind blows the 'wrong' way, Bariloche looks like it is going to drown in ashes.
The video above was taken by Dr. Esteban Balseiro at Bariloche, looking out Lago Nahuel Huapi.
Dried volcanic pumice
Volcanic pumice looks like rocks but are extremely porous, causing it to float on water instead of sinking to the sediment. It is not very nutritious (<1% C and undetectable N) but we have found that pumice releases a large amount of phosphorus. The availability of the released phosphorus is still under investigation. A more concerning issue is that the pumice have significantly reduced the amount of light that goes through the water column for light-dependent bacteria in the water. This is especially an issue for small lakes, such as Lago Pire, where the pumice have covered almost the entire lake. The picture below was taken on February 8, 2012, nine months after the eruption. The pumice does not seem to be going anywhere...
Lago Pire, February 8, 2012
Floating pumice
In Patagonia, the larger lakes such as Lake Nahuel Huapi are very deep (> 400m) and the microbes such as ciliates and photosynthetic bacteria are found to be mostly 30-40m deep. Mind you, a lot of these are light-dependent microbes. The water is so clear that light penetrates deep with high amount of UV radiation at the surface. In fact, from the amount of light measured by our collaborators in Universidad Nacional del Comahue at Bariloche, there are more light at 30m deep in the lake than there is on his desk!! But now...the pumice have turned the lights off for the bacteria.
Lago Nahuel Huapi
My goal for this research project is to determine if bacteria takes up residence on this P releasing pumice. If it is too dark under the pumice, maybe it will be better to stay on the pumice? Or will the pumice cause the light-dependent bacteria to starve and eventually the entire microbial community to crash? (the heterotrophic bacteria, which are dependent on the phototrophs may also run out of food source). So I joined Dr. Esteban Balseiro and Dr. Beatrice Modenutti's lab in several sampling trips to collect pumice from several lakes around Bariloche, along with the water to determine if the pumice colonizers are dependent on the 'inoculum' (the community the pumice is exposed to) or only a few types of bacteria will grow on the pumice, no matter where the pumice is collected from. Dr. B and Dr. M had also collected pumice from the 2 most disturbed lakes (by the pumice) over time since the deposition in June 2010. We want to see if there is a succession of bacterial community colonizing the pumice. As for now, we know that some of the pumice are high in microbial biomass (based on amount of DNA/g pumice) while some barely have any microbes on it. In addition to that, our Argentinian colleagues (and a Chilean group) have found that diatoms community increases in abundance and are found colonizing the pumice. Why? …stay tune until I process all the samples.
