Physicochemical Characteristics of Dam Lakes in Southwestern Bulgaria

TRAYKOV, I., A. TOSHEVA and E. UZUNOVA, 2010. Physicochemical characteristics of dam lakes in Southwestern Bulgaria. Bulg. J. Agric. Sci., 16: 350-357 The validity of the defined water body types in Bulgaria and the relationships between the nutrient concentration and the response variables to eutrophication was tested in eight reservoirs in the Struma River Basin. The applicability of different classification schemes based on reservoirs’ morphological and physicochemical characteristics are presented and discussed. The similar response of the lakes to changes in TP has proved the relationships underlining the classification of lakes relative to eutrophication, and suggests possible restriction, or at least a redistribution of the reservoirs among the lake types. All tested variables responded markedly to eutrophication, and only the aquatic plants showed limitation both at low as well as at high nutrient levels. The theoretical residence time and the fluctuation of the water table influence the nutrient levels and thus the response variables to the eutrophication in the reservoirs. This emphasizes the problem of how a rather limited sampling program, based on one or a few annual samplings, can provide an adequate and correct definition of the ecological state in the future. Further studies, concerning the validity of the typology system in Bulgaria are needed before the establishment of type specific reference conditions and a consequent calculation of the EQR values for the individual biological quality elements.