Seasonal and vertical dynamics of the water temperature and oxygen content in Kardzhali reservoir, Bulgaria

I. Iliev, L. Hadjinikolova
Abstract. The aim of the study was to determine the seasonal and vertical dynamics of water temperature and oxygen content in the aquatory of Kardzhali Reservoir, situated in the Eastern Rhodope Mountains at the altitude of 290 m. Water samples from six sampling stations, set in order to fully cover the water area near the cage farms; the aquatory free from net cages and the part near the dam wall were analyzed. In the surface layers for the period of the study, the water temperature ranges from 11.8°C to 25°C respectively in April and in July. With the increase of the air temperature in spring, the surface water layer is heated rapidly. The zone of the temperature shift (thermocline) of the stratifying lake is especially clearly observed during the months May – September between 5–15 meters. During the period of the study were established significant variations in the oxygen content in the water between 2.98 mg.l-1–13.66 mg.l-1 (0.5 m) and 0.16 mg.l-1 –10 mg.l-1 (30 m). The highest average values of this parameter in vertical in the range of 10.47 mg.l-1 were reported in April.