Hydrochemical Characteristics of River/Groundwater Exchange in the Hyporheic Zone of the Struga Dobieszkowska Suburban Stream (LóDź Agglomeration, Poland)

The hyporheic zone (HZ) performs important filtering functions contributing to the reduction of pollutants from surface waters. It can be important in areas where the watercourse is subjected to strong human pressure. The study aimed to identify the hydrochemical conditions of the potential HZ of a spring watercourse in an area subjected to strong settlement pressure in the suburban area of Łódź. The study was conducted in two measurement periods: spring (April–May 2021) and autumn–winter (November–January 2021/2022). On the 860-metre section of the northern arm of the Struga Dobieszkowska watercourse (NSD) following parameters were measured: vertical hydraulic gradients (VHG) in the riverbed, physicochemical properties, and concentrations of mineral forms of nutrients in river, spring and hyporheic waters. The ratio of points with positive VHG to those with negative VHG was at a similar level in both research cycles, i.e., 78:21 and 74:18. The flow rate ranged from 20.7 to 22.3 dm³ · s⁻¹. Research indicates that in downwelling zones, there are favourable conditions for the occurrence of water self-purification processes.