Assessing temporal changes in the quantity and quality of shallow groundwater in the Biebrza valley in the 21st century

Wetlands play a crucial role in the hydrological cycle, controlling flood generation, dry season flows, and water quality. This emphasizes the part of the Biebrzański National Park in protecting naturally valuable habitats. Our research aimed to assess (quantitatively and qualitatively) the state of groundwater affecting the condition of wetlands. The analyses carried out in 2021 were compared with the results of hydrological and hydro-chemical mapping of the first groundwater level from 1998.

Quaternary formations serve as the main groundwater reservoir in the Biebrza Valley. These formations consist of pore water located at shallow depths, usually ranging from 0.5 to 10.95 meters. Most often, the first aquifer occurred at 1–3 meters deep. No significant reduction was observed when comparing the current water table levels with data from 1998. More than half of the surveyed dug wells are used for economic purposes. The Biebrza River is an outflow for shallow groundwater, as the hydroizohypses system indicates.

The shallow groundwater resources in the Biebrzański National Park include mainly low and medium mineralization waters. A significant increase in the concentration of nitrogen compounds (NH₄⁺-N, NO₂⁻-N, and NO₃–N), phosphorus, and dissolved organic carbon was recorded. This trend is evident in areas with intensive cattle breeding and is associated with excessive use of manure and slurry. The research confirmed the mosaic nature of the chemical composition observed in 1998 and the wide range of variability of the chemical properties of shallow groundwater.