Comparison of mineral and organic phosphorus forms in regulated and restored section of a small lowland river (NE Poland)

A two-year study on water quality changes with particular concern about forms of phosphorus in two sections (regulated and restored) of a small lowland river in north-eastern Poland, was carried out. Analyses were performed 7 years after restoration treatment. A clear, significant differences in water quality between the two investigated sections were observed. In the case of different phosphorus (P) forms: soluble reactive phosphorus (SRP), dissolved hydrolysable phosphorus (DHP), total dissolved phosphorus (TDP) and total phosphorus (TP), concentrations were by about 40% lower within restored than in regulated river section. There has been a significant influence of hydro-meteorological conditions on P concentrations in the river. Contrary to the assumptions, concentrations of all P forms, with the exception of DHP, were lower in more humid period than in year characterized by smaller precipitation sum, and minor differences between two compared sections of the river were noted. These decreases of P forms concentrations were not only induced by dilution effect. Better catchment hydration (even degraded/regulated one) prevents rapid transport of P to the surface waters. Numerous relationships between P concentrations and other water quality parameters were found (e.g. with Cl−, NO2−, NO3−, NH4+, Na+ and K+). The comparative study on the regulated and restored river sections confirms that the preservation or construction of riparian land/water buffer zones can be recommended to reduce P forms concentrations in lowland rivers. Even small-scale restoration efforts in the estuary sections of rivers may be important factor improving the quality of water leaving degraded catchment.