Assessment of Techirghiol Lake Surface Water Quality Using Statistical Analysis

The lakes' water quality can be considered a key contributor to the human health and for the conservation of therapeutically mud properties. This study involves the statistical evaluation of water quality data for one hypersaline lake from Constanta District, Romania. Techirghiol Lake (located in South of Dobrogea Region, Romania) constitutes an ecosystem with a special morphological structure and an interesting geological past. The physico-chemical average parameters of Techirghiol Lake, registered in the period 1990 -2011) are described, analyzed and modelled. Techirghiol Lake had the highest salinity 66.14 gIL in 2009, pH values were in the interval 7.97-8.71 with low seasonal variations, indicating well buffered waters. The concentrations of some anions and cations varied as follows: Cl- - 738.87 meq/L (in 1997) - 1019 meq/L (in 2009), HCO2+ - 2.20 meq/L (ml 992) - 1019 meq/L (in 2009), Ca2+ - 8.53 meq/L (in 1993) - 20.43 meq/L (in 1992), Mg2+ - 171.05 meq/L (in 1993) -230.26 meq/L (in 1995), and the dried residue - 51.50 g/L (in 2006) - 65.32 g/L (in 2004). We also report the evolution of pollution indicators: dissolved oxygen (DO), chemical oxygen demand by potassium permanganate method (COD-Mn) and biochemical oxygen demand (BOD5). The yearly averages of the quality parameters for all sampling sites ranged as follows: DO (mg/L) - 4.04 (in 2002) - 10.17 (in 2009); COD-Mn (mgO(2)/L) - 15.52 (in 1991) - 45.17 (in 1995); BOD5 (mgO(2)/L) - 2.78 (in 1993) - 20.25 (in 1995). Statistical analysis, including Kolmogorov-Smirnov [1], Levene [21, change points tests, Mann - Kendall test with Sen's slope [3, 4] calculation has been performed to evaluate the variation of statistical parameters. Hybrid linear -moving average models have been built for the series for which the hypothesis that the slope is significant has been accepted.