Concentration Changeability of Phosphorus, Calcium and Magnesium in Selected Partial Drainage Basins of the River Drwęca

The paper presents the results of the research conducted between November 2008 and October 2009. The research included seasonal dynamics of the flow and runoff of phosphorus compounds (TP and P-PO₄³⁻), as well as Ca²⁺ and Mg²⁺ from 13 partial drainage basins of the River Drwęca. Water levels were registered automatically every day by recorders, and measurements of the flow were conducted once a month. Major differences were found in the water abundance as indicated by specific discharges in individual, partial drainage basins: from 1.87 dm³ s⁻¹ km⁻² (Lubianka—a lower part of the River Drwęca drainage basin) to 8.22 dm³ s⁻¹ km⁻² (Gizela—an upper part of the River Drwęca drainage basin). The studied rivers were characterised by very diverse average content of total phosphorus compounds: from 0.047 mg dm⁻³ (Iłga) to 0.816 mg dm⁻³ (Sandela); calcium: from 47.18 mg dm⁻³ (Iłga) to 131.65 mg dm⁻³ (Trynka); and magnesium: from 9.71 mg dm⁻³ (Wel) to 36.76 mg dm⁻³ (Struga Rychnowska). Analysis of variance carried out on hydrochemical properties of the studied rivers divides the rivers into two separate groups: rivers with much higher content of phosphorus, calcium and magnesium compounds (Struga Rychnowska, Trynka, Ruziec, Lubianka, Kujawka, Sandela and Gizela), and a group of rivers with low content of these compounds (Brynica, Brodniczanka, Skarlanka, Wel, Iłga).