Response of high altitude lakes to global changes

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Most of the running water in the world comes from mountains. The evapotranspiration rates in high mountains are lower than in lowlands because temperatures are lower and rainfall higher and because the incoming air is forced to rise, cooling and causing precipitation. As a consequence, almost all the major rivers and groundwater aquifers flow from the mountains. High mountain lakes are small with a shorter and simpler trophic webs than in lowland lakes, because some of them lack top-predators such as fish. They are thus natural laboratories, excellent for understanding and measuring ecological processes. Because of their location in remote areas, high mountain lakes are also studied to investigate the structure and metabolism of lakes in isolation from human influence, and subject to natural forcing (such as climate variability) or long-range human impact such as the transport of atmospheric pollutants.

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Research

Our research activity includes both the study of long-term trends in water quality and studies of the abundance and composition of biological assemblages in relation with biotic and abiotic factors and human influence. Most of the studied lakes are located in the Alps and the Himalayas, but other studies are carried out in different remote areas, such as the Andes and Tibet. Limnological studies performed on mountain lakes include: hydrology, thermal stratification, water chemistry, phytoplankton, benthic algae, zooplankton, benthic fauna and fish. We also focus on the role of bacteria and mixotrophic eukaryotes.

The main topics of recent studies include:

1. role and fate of nitrogen compounds in remote lakes;
2. bacterial loop in high mountain lakes;
3. effects of high radiation and enhanced UV in controlling high mountain lake biota, and the production of UV-screening pigments;
4. genetic characterization of high mountain organisms;
5. endemic species and the spread of invaders.

Regional limnology makes it possible to identify differences in the ecology of lakes located in different areas of the world. For example, some remote areas of the globe were compared from the point of view of nitrogen content in lake water and showed wide differences in total nitrogen concentration, related to the different inputs of nitrogen from atmospheric deposition (Fig. 1).

Alpine lakes are characterized by a short summer season. Bacteria first utilize DOC after the ice melt. Mixotrophs graze on bacteria but are then grazed by Daphnia, which appear in late August and mobilize reactive phosphorus from the bottom, triggering primary production in September.