Andmebaasi logo

3. Doktoritööd

Selle kollektsiooni püsiv URIhttp://hdl.handle.net/10492/2490

Sirvi

Sirvi 3. Doktoritööd Märksõna "ainevahetus" järgi

Nüüd näidatakse 1 - 1 1
  • Pisipilt
    Kirje
    Productivity and nutrient retention of lakes on seasonal, interannual and morphometric scales
    (Eesti Maaülikool, 2012) Laas, Alo; Nõges, Tiina
    Despite the considerable percentage of inland waters in the temperate zone land cover, their role in the global carbon balance is not clear and the existing data suggest large type specific differences. Respiratory CO2 release from inland waters is a major process in the global carbon cycle, retaining more than half of the carbon flux from terrestrial sources that otherwise would reach the sea. The strongly lake-type-specific balance between primary production and respiration determines whether a lake acts regionally as a net sink or source of CO2. In the global change context even small changes in photosynthesis and respiration rates and/or in the loadings of organic matter or nutrients (e.g. phosphorus) may change the metabolic type of the lake and turn it from autotrophic to heterotrophic system or vice versa. Todays in situ sondes fitted with sensitive and accurate optical oxygen probes have become a useful tool for estimating lake ecosystem metabolism through high frequency continuous measurements. The sonde method provides an alternative to more traditional methods of measuring metabolism that only use discrete samples. Continuous sampling by sondes overcomes many of the limitations of discrete samples and makes it possible to measure metabolism in a wide variety of systems. Long-term observations across many years define the range of natural variability of ecological systems and provide a baseline from which to assess whether a system has changed significantly. Regular hydrological data on large and shallow (area 270 km2; mean depth 2.8 m) Lake Võrtsjärv have been collected for more than 80 years. Regular measurements of nutrients and ecosystem components started in 1960s. Lake Võrtsjärv was intensively studied for more than 50 years before the first monitoring buoy was deployed for high frequency measurements of physical and chemical parameters. Phytoplankton primary production in situ measurements with monthly frequency started in Võrtsjärv already in 1982 but the dataset has many gaps. Present thesis summarizes for Lake Võrtsjärv: the first data on seasonal changes of the ecosystem metabolism based on high frequency measurements; the reconstruction of long term series of phytoplankton primary production by bio-optical modelling; the incoming and outgoing fluxes of carbon, nitrogen, phosphorus, and silicon; and gives an overview of phosphorus retention in Lake Võrtsjärv compared with 54 lakes and reservoirs in different climate regions around the world.