EN
The Biebrza River valley is the most valuable wetland’s complex in Poland. The biodiversity of endangered plants and animals observed in this region is outstanding. The lower river valley is considered as one of the most natural wetland area in Europe since, only small reach of this valley was drained. The conservation of this valuable object depends also on maintaining of high soil moisture, therefore the knowledge about the water balance dynamic of this ecosystem seems to be crucial. The evaporation process is a common element of both water and heat cycles thus wetland surface heat balance studies will be helpful for modeling of local hydrological conditions. The paper presents the methodology of grassland ecosystem heat balance structure research which have just started at the Biebrza River valley. The automatic measurement system was developed at the Division of Meteorology and Climatology, and it is consisted of net radiometer – net radiation measurement, heat fl ux plates – soil heat fl ux density measurement, 3D sonic anemometer used for direct measurement of sensible heat fl ux (eddy covariance approach). Two thermohygrometers were installed additionally, which allow to estimate the latent heat flux density using the Bowen ratio method.