Small springs in a big city: Status, stressors, and long-term changes of their water properties across Warsaw

The present study attempted to identify the current status and stressors affecting spring water properties in an urban area, using the example of the Warsaw agglomeration. For this purpose, they study monitored hydrological and hydrochemical properties of three springs, each draining a Quaternary porous aquifer and representing different anthropopressure across the city. The measurements of discharge and physico-chemical parameters were carried out regularly twice a month from June 2023 to May 2024, while the chemical composition, including main cations and anions, was determined once every two-month period using ion chromatography. The results documented a good agreement between the degree and timing of impact of human-induced alternations and the physico-chemical properties of spring waters. The highest total dissolved solids (TDS) and concentrations of Cl−, SO42−, and Na+ were measured in the most urbanised areas. Seasonal changes in the spring water chemistry, primarily in terms of main anions, confirmed their anthropogenic origin, related to different deposition and migration over time. A comparison with archival data proved significant long-term transformation of spring properties, including gradual decrease of their discharge, increase in water temperature, and changes to the hydrochemical type. Such an evolution of groundwater quality reflects the impact of climate warming and human activities, including increase in the degree of imperviousness as a result of urbanisation, application of road maintenance chemicals, and emission of pollution to the atmosphere. The results provide the most recent insight on shallow groundwater status and stressors in Warsaw and reflect intensive modification of the aquifer system across the urban environment.