S t r e s z c z e n i e Dolina dolnej Biebrzy stanowi bardzo cenny, w duzym stopniu naturalny, torfowo-bagienny kompleks fizycznogeograficzny. Zachowaly sie tutaj siedliska bagienne pierwotne lub zblizone do naturalnych, o duzych walorach przyrodniczych. Obserwuje sie jednak niekorzystne przeksztalcenia pokrycia roślinnego, ktore wynikają najprawdopodobniej ze zmian uwilgotnienia siedlisk hydrogenicznych, jak rowniez jakości wod zasilających. W tej cześci doliny nastąpily najmniejsze zmiany stosunkow wodnych, jednak dalsze przeksztalcenia mogą zagrazac wyginieciem naturalnych zbiorowisk roślinności bagiennej i cennych torfowisk. Niezbedne są dzialania, mające na celu wprowadzenie nowych zasad gospodarowania wodą, ktore zapewnilyby utrzymanie odpowiedniego uwilgotnienia gleb bagiennych, tak by nie dopuścic do przesuszenia torfow i ich degradacji. Wykorzystując badania modelowe, wydzielono strefy zasilania doliny wodami roznego pochodzenia. Umozliwilo to opracowanie zalecen gospodarowania wodą pod kątem ochrony walorow przyrodniczych siedlisk hydrogenicznych. Wykorzystując badania terenowe i modelowe w basenie dolnej Biebrzy, przedstawiono wyniki pomiarow stanow wod powierzchniowych i podziemnych. Do opisu przeplywu wod podziemnych wykorzystano dwa modele matematyczne – SIMGRO i FLOTRANS, ktore posluzyly do oceny źrodel zasilania doliny dolnej Biebrzy.

The valley of the Biebrza River has the status of a National Park, which means it has the highest protection status in Poland. The preservation of this wetland, unique for Europe, mainly depends on the preservation of high water levels in the peat soil and also on the existence of large open areas used as meadows. It is important to have a good understanding of the hydrological systems to conduct a proper water management in the valley. The study concentrates on understanding the regional groundwater flow and its relation with the surface water, taking into consideration water quantity and quality. The paper focuses on the functioning of the hydrological system in terms of the sources of water fluxes including spring floods to the different ecosystem types in the Biebrza Lower Basin. The physically based groundwater and surface water model SIMGRO was used to gain insight in the regional groundwater flow patterns. The SIMGRO model simulates the regional water movement in the unsaturated zone, the saturated zone and the surface water in an integrated manner. The FLOTRANS is two-dimensional model for saturated zone. Using the results of the groundwater models, flow lines were calculated, giving information on the sources of water flows to the different ecosystem types in the river basin. The numerical calculations with the field measurements of groundwater table together with analysis of soils and plants allowed to distinguish the discharge and recharge areas and the different sources of water filling of river valley. All this information is important for preserving suitable hydrological conditions for the various wetland types. It can be used to pinpoint problem areas and for determining measures for restoration in balance with land use and landscape.

The Biebrza National Park, situated in north-east Poland, is a unique environment of wetland with very well developed zones of peat ecosystems. At present the wetlands are threatened by numerous factors associated with human activity (drainage, ceasing of mowing) as well as natural succession. Understanding the hydrology gives a proper basis for nature management in the area. The physically-based groundwater and surface water model SIMGRO was used to gain insight in the regional ground-water flow. Using these results, flow lines were calculated, giving information on the sources of water flows to the different ecosystem types in the river basin. Major sources of water are from the glacial plateau, the river water system as water flowing to the Biebrza river and a local system in the flood plains of the Biebrza valley. All this information is important for preserving suitable hydrological conditions for the various wetland types.

The Biebrza National Park (BNP), situated in northeast Poland, represents a unique environment of wetland with meso- and eutrophic peat ecosystems. One of the dangers for the park wetland is the over-drying of the soil caused by the drainage works carried out in the past. To counterbalance the negative effects, the Biebrza National Park aims to restore the hydrology. However, farmers owning land along the rivers may experience negative effects on their farmland resulting from these measures. The physical ly-based groundwater and surface water model SIMGRO was used to predict the effect of raising the water levels. It was found that reduction of the discharge in the drainage canals to about 5% of the present flow, with the remaining water flowing via the rivers, leads to a considerable rewetting of the wetland area but unavoidably also leads to higher water levels in part of the agricultural area.

The results of field investigation and simulation of groundwater levels in the Jegrznia River Valley (Biebrza National Park, Poland) are presented. Calculations were carried out for climatic conditions prevailing in 1992 to analyse various scenarios for surface water distribution. The combined groundwater and surface water model SIMGRO has been used to predict the effect of human intervention. The research demonstrated that surface water has a minor influence on groundwater levels. In the central part of the valley, further away from the surface water, the changes in groundwater level mainly depend on weather conditions, i.e. precipitation and evapotranspiration. Spring flooding is needed to raise groundwater levels and to restore the nature potential.