Summary:

Based upon investigations the concentrations of nitrogen and phosphorus compounds in tributaries of the Dobczyce reservoir were determined. The investigations were carried out in the period between July and December 2003 and during the hydrological years 2005. The Dobczyce reservoir which is the source of water for Cracow has maximum volume of 125 mln m³. The Raba river is the main tributary of the reservoir. The reservoir is also supplied by own basin of area 78,2 km² with several small streams having total area 64,4 km². Apart from the Raba river streams of direct basin are suppliers of biogenic compounds to the reservoir. The work was based upon analysis of concentrations of NH₄, NO₃, NO₂ i PO₄ in samples of water taken from the following streams at their inflow to the reservoir bowl: Brzezówka, Ratanica, Trzemeśnianka, Dębnik and Wolnica. The samples were taken once a month. Obtained results point that the concentrations of biogenic compounds in water of direct tributaries did not determine serious threat for quality of water of the Dobczyce reservoir in the second half of 2003. The similar state was noticed in the hydrological year 2005. Waters of investigated streams in analyzed period were moderately abundant in nitrogen compounds and much more abundant in phosphorus compounds. Comparing mean concentrations of investigated indicators between analyzed periods one can state that in case of the Dębnik stream improvement of water quality except of NO₃ took place. In case of the Wolnica stream deterioration of water quality in the scope of three indicators and small improvement in PO₄ occurred. Based upon results in the hydrological year 2005 the evaluation of quality of water in the streams Dębnik and Wolnica was carried out according to the Ordinance of Environment Minister from 2004 concerning classification for presentation of surface water state (Rozporządzenie Ministra Środowiska z 2004 r. w sprawie klasyfikacji dla prezentowania stanu wód powierzchniowych). Waters of both Wiolnica and Dębnik taking into account concentrations of NH₄, NO₂ i PO₄ were classified to the I class wile regarding NO₃ to the II class.