Spatio-Temporal Variation of Water Quality in Lake Luoma, Jiangsu Province, China

Water physicochemical parameters were monitored at 10 sites in Lake Luoma from January to December 2014, for assessment of quality and trophic status of the lake water and for analysis of spatio-temporal variation of the water quality with multi statistical analysis methods, including cluster analysis. One-way ANOVA shows that secchi depth, conductivity and concentrations of dissolved oxygen, nitrogen, phosphorus and Chl-a differed significantly from month to month, while spatial differentiation analysis reveals that only water depth varied remarkably between sites, indicating that water quality little varied spatially in the lake. The monthly mean value of TN, TP, COD_Mn and Chl-a varied in the range of 0.71-2.08 mg·L^-1, 23.82-71.78 μg·L^-1, 1.87-5.09 mg·L^-1 and 4.49-10.83 μg·L^-1, respectively, indicating that Lake Luoma fell into the categories of Ⅲ-Ⅴ in water quality in 2014 according to the standard for surface water quality (GB 3838-2002), with TN being the principal pollutant. The comprehensive trophic level index (TLI) indicates that the lake reached the mesotrophic to light eutrophic level. Cluster analysis divided the 12 months of a year into two clusters (winter-spring group and summer-autumn group). The former was apparently higher than the latter in secchi depth, DO, TN and NO₃^--N, but lower in Chl-a and TP. Cluster analysis also divided the ten sampling sites into two groups, the north and the south groups. The former was significantly higher than the latter in TN, NO₃^--N and conductivity, which were the main factors responsible for differentiation of water quality in the lake.