When a lake stops deep water turnover with climate warming: Drastic consequences for primary producers

Il 16/01/2018 ore 11.00 - 12.30

Istituto per lo studio degli ecosistemi, Ise-Cnr
Largo Tonolli 50, 28922 Verbania Pallanza

Seminario di Thomas Posch (Limnological Station, Department of Plant and Microbial Biology, University of Zurich, Kilchberg, Switzerland)

After strong fertilization in the 20th century, many deep lakes in Central Europe are again nutrient poor due to long-lasting restoration (re-oligotrophication). In line with reduced phosphorus and nitrogen loadings, total organismic productivity decreased and lakes have now historically low nutrient and biomass concentrations. This caused speculations that restoration was overdone and intended fertilizations are needed to ensure ecological functionality. Here Thomas Posch will show that recent re-oligotrophication processes indeed accelerated, however caused by lake warming. Rising air temperatures strengthen thermal stabilization of water columns which prevents thorough turnover (holomixis). Reduced mixis impedes down-welling of oxygen rich epilimnetic (surface) and up-welling of phosphorus and nitrogen rich hypolimnetic (deep) water. However, nutrient inputs are essential for algal spring blooms acting as boost for annual food web successions. It is shown that repeated lack (since 1977) and complete stop (since 2013) of holomixis caused drastic epilimnetic phosphorus depletions and an absence of phytoplankton spring blooms in Lake Zurich (Switzerland). By simulating holomixis in experiments, Dr Posch and his group could induce significant vernal algal blooms, confirming that there would be sufficient hypolimnetic phosphorus which presently accumulates due to reduced export. Thus, intended fertilizations are highly questionable, as hypolimnetic nutrients will become available during future natural or artificial turnovers.

Organizzato da:
Cnr Ise - Istituto per lo Studio degli Ecosistemi

Referente organizzativo:
Cristiana Callieri
0323 518300

Modalità di accesso: ingresso libero

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