Natural groundwater outflows in the Biebrza Valley: Temporal stability, geochemical composition and role in ecohydrological processes of valley wetlands

Natural groundwater outflows are very sensitive to changes in the environment. In the era of changing climate and progressive anthropogenic activity, they often disappear, retreat, and water quality deteriorates. Inefficient sources in lowland areas are the most vulnerable to these processes. In 2021, we conducted an inventory of natural groundwater outflows in the Biebrza Valley. Most of the existing outflows are non-concentrated outflows (exudations, linear leakages, fens). The outflow of several outflows exceeded 5 dm³·s⁻¹. Their distribution within the Biebrza Basin is uneven. We identified the largest concentration of linear seepages on the right bank of the lower Biebrza basin near the village of Ruś. The most common types in the BNP are di- and tri-ionic waters, characteristic of lowland areas of Poland. The increase in nitrogen and phosphorus compounds in the spring water indicates the impact of the developing agricultural activity (cattle breeding). The increase in DOC concentration may reflect changing hydro-meteorological conditions (droughts and torrential rains). The values of most parameters in spring water were lower than in shallow groundwater. This gives a better picture of the quality of shallow groundwater. The physical and chemical characteristics of natural groundwater outflows in the BNP fall within the hydro-chemical background of the waters of the first aquifer in this area.