22 Sett. 2015 - Ruben Sommaruga

When glaciers and ice‐sheets melt: consequences for planktonic
organisms

Presenta: Ruben Sommaruga
University of Innsbruck, Institute of Ecology, Lake & Glacier Ecology Research Group,
Innsbruck, Austria

The current melting of glaciers and ice sheets is a consequence of climatic change and their turbid meltwaters are filling and enlarging many new proglacial and ice‐contact lakes around the world, as well as affecting coastal areas. Paradoxically, very little is known on the ecology of turbid glacier‐fed aquatic ecosystems even though they are at the origin of the most common type of lakes on Earth. In this talk, the consequences of those meltwaters for planktonic organisms will be discussed. A remarkable characteristic of aquatic ecosystems receiving the discharge of meltwaters is their high content of mineral suspensoids, so‐called ‘glacial flour’ that poses a real challenge for filter‐feeding planktonic taxa such as Daphnia and phagotrophic groups such as heterotrophic nanoflagellates. In consequence, the planktonic food‐web structure in highly turbid meltwater lakes seems to be truncated and microbially‐dominated. Low underwater light levels leads to unfavorable conditions for primary producers, but at the same time, cause less stress by UV radiation. Further, meltwaters are a source of inorganic and organic nutrients that can stimulate secondary prokaryotic production and in some cases (e.g., in distal proglacial lakes) also phytoplankton primary production. The accumulating information on the consequences of glacier retreat for glacier‐fed lakes is crucial to predict ecosystem trajectories regarding changes in biodiversity, biogeochemical cycles, and function.

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