In 2010 the department of Lake Research (project management) started a long time study (ten years) with emphasis on impact of climate change on selected Austrian lakes in cooperation with different partners (Austrian Federal Forestry Office, the Federal States of Upper Austria and Salzburg, and “Konsortium Zeller-Irrsee”.
One of the principal aims of the study is to gather a detailed, high-resolution long time data set from Austrian lakes for the first time. Documentation of limnological and fish ecological changes due to climate changes and as a consequence the ability to forecast possible effects of further warming of Austrian lakes are the major objectives.
In all five lakes, a measuring buoy with temperature dataloggers was installed at the deepest point for high-resolution temperature recording. These dataloggers record the prevailing temperature hourly at different depth increments (1 m increments to 15 m; then 10 m increments) from the surface to the bottom and are read out at regular intervals. Furthermore, in addition to the regularly examined parameters (physico-chemical and phytoplankton (algae) according to the Water Condition Monitoring Ordinance), the zooplankton and the fish population are surveyed.
The zooplankton samples are taken with a closing net at different depth levels in the area of the buoy. The zooplankton samples are evaluated in terms of abundance and biomass at the species level.
The fish biomass was surveyed using a SIMRAD EK 60 echo sounder with a 7°x7° composite split beam transducer at a working frequency of 120 kHz. The sounder is mounted horizontally on the side of the boat at a water depth of 0.2 m using a special mounting system. The recordings will take place on three dates (October, November and December), with the lakes being sonicated in a zigzag course along transverse transects. Recordings will be made at night, with boat speeds of about 5 km/h, and data will be continuously stored on the hard drive of a laptop computer. A special computer program is later used to analyze the recordings for fish abundance and biomass. When viewed together, the results of the study can also be used as an important basis for fisheries management measures and for estimating the sustainable yield that can be achieved.