The influence of weather conditions on mid-field ponds situated in a reclaimed area in Sępopolska Plain.

The investigations were conducted in northeastern Poland near Lidzbark Warminski (54° 08" N, 20° 36" E). Five mid-field ponds situated on grasslands were chosen: four of them were dredged and deepened, and one of them remained as a natural reservoir. The aim of this paper was to assess the influence of weather conditions on the quantity and quality of water in mid-field ponds situated in agricultural areas. It was found that the quantity of water in mid-field ponds was related much more to the air temperature, which was responsible for either water evaporation or snow melting, rather than to the amount of precipitation. The reduction in the volume of water stored in the ponds during very dry years had a negative influence on its quality. During the observation period, the dredged ponds were characterized by permanent water tables, whereas the natural reservoir dried out in very dry years. Atmospheric conditions influenced the concentrations of ammonium nitrogen and calcium and chlorine ions in the studied water bodies. The volume of water retained in mid-field ponds influenced the concentrations of phosphorus and sulphates. Increased precipitation sums caused lower water pH; however in warmer periods, at increased pH and CODCr, a decrease in dissolved oxygen was noted. It was revealed that increases in precipitation sums during the year caused increases in the load of mineral nitrogen and calcium and magnesium ions in pond water. [ABSTRACT FROM AUTHOR]