North Patagonian Andean Deep Lakes: Impact of Glacial Recession and Volcanic Eruption

North Patagonian Andean deep lakes (>100 m depth) are ultraoligotrophic, and thus are high light-low nutrient environments. In this chapter, we present examples and discuss the effect of particle input due to climate change (changes in glacial clay due to glacial recession) and volcanic eruption (volcanic ashes) in the water column of these lakes. The best descriptor of water column functioning was the vertical position of the deep chlorophyll maximum that was very sensitive to changes in underwater light and may be used as a simple variable to track changes in the dynamics of lakes. Mixotrophy is particularly important in the plankton of these lakes, and here we show how glacier recession affects, through the glacier clay, the bacterivory of these protists. Finally, we present results on how volcanic ashes triggered the disappearance of cladoceran populations, and changes in glacier clay affect zooplankton filter feeders, modifying the food quality (C:P ratio) that drives the coexistence between cladocerans and copepods.