EVALUATION OF THE CURRENT STATE OF WATER QUALITY IN THE GORGOVA-UZLINA DEPRESSION (DANUBE DELTA, ROMANIA), USING PHYSICO-CHEMICAL PARAMETERS STUDY CASE: UZLINA, POJARNIA, CHIRIL, ISACOVA AND DURNOLIATCA LAKES

The Gorgova-Uzlina Depression situated on the fluvial delta plain, bordered by the Sulina branch in the north and by Sf. Gheorghe branch in the south-east, is an important hydrographic unit, hosting numerous of native plant and animal species, as well as several recreational navigation, fishing, and water tourism spots. The water quality of this area may be heavily affected by natural or local human-related factors as agricultural activities, fishery exploitation, navigation along the water courses etc. The present study aimed to identify factors or processes that set out the water quality of investigated lakes. Thereby, surface water samples from fifty-four sampling points were collected in July 2017 and analyzed for different common physico-chemical parameters (pH, DO, N-NO2-, N-NO3-, P-PO43-, EC, TDS, SO42-, turbidity, TSS, chl"a", SiO2, ORP etc.). Furthermore, on the basis of a limited number of punctual sampling stations, was measured the distribution of heavy metals in the surface water samples. The obtained results were related to standard water quality criteria to assess the current state of the surface water quality of explored lakes. Generally, the common water quality parameters results showed comparable mean values, without significant exceedances of regulatory criteria. Particularly, in some incidental cases were exceeded the value orientations imposed by environmental quality standards. It was noticed that few samples were significantly less saturated with oxygen, sporadically the nitrite levels meet the class I criteria, and the orthophosphates, infrequently, meet the class I and V criteria of the national standard. Other samples contained higher amounts of total suspended solids and higher turbidity levels. The heavy metal concentration generally agreed with the criteria of national water quality standard. The exceptions were represented by Ba and Ni that meet the class I standard, including Mn that meet the class I and II criteria. Taking into consideration the widely-known spatial-temporal variability of surface water quality, this evaluation suggested that the water quality is in a relatively good condition. The disturbances in seasonal concentrations of some physico-chemical parameters did not show detectable levels of potential concern and are probably due to local natural circumstances (climate variability, flow rate and hydrologic characteristics, surficial geology and substrate etc.). The water quality in the investigated perimeter is consistent with the freshwater environment under deltaic natural circumstances, probably, due to intense self-purification capacity.