Dynamics of Nitrogen and Phosphorus Forms Content in Dojlidy Retention Reservoir

The Dojlidy Ponds, which include Dojlidy water dam, are located within Bialystok city limits in Podlasie area, Poland. The reservoir with a water surface of 34 ha and average depth of 1.75 m was constructed in 1962 as a result of Biala River damming. The researches were conducted in July, October and December 2014 as well as in March 2015. Each time five test samples were collected from spots located along the reservoir. Water samples were tested for the presence of ammonia nitrogen, nitrite nitrogen, organic nitrogen, phosphates and organic phosphorus. The values of nutrient indicators exhibited high variability during the study period. The highest concentration of nitrite and nitrate nitrogen were observed in July, while the lowest in October – nitrite nitrogen, and in December – nitrate nitrogen. Different situation was observed after the analysis of phosphorus forms – the highest concentrations of organic phosphorus and phosphates were observed in December and the lowest in July. Relatively high concentrations of nitrogen and phosphorus forms identified in water samples were most likely caused by tributaries, due to the pollution from the reservoir catchment. Technical parameters of the object and location of the reservoir have undoubtedly an impact on the tested parameters contents.