Study on spatial and temporal distribution, influencing factors and control measures of water transparency of Nanhu Lake water system

The seasonal variation and spatial distribution of water transparency (SD) in Nanhu Lake were analyzed according to the data of field survey from 2018 to 2019, and the influencing factors and the target value required by submerged plants of SD were explored. The results indicated that SD of Nanhu Lake was between 10.0 cm to 46.0 cm, with an average value of 24.8 cm, which was significantly lower than some lakes in China. The low SD existed near the estuary into Nanhu Lake and channel, and Nanhu Lake had lower SD in May, September and October. SD of the surrounding river network ranged from 8.0 to 71.0 cm, with an average value of 27.6 cm, and the low values mainly existed in the western part of the outer river network and the northern estuary. Correlation analysis showed that SD was significantly correlated with inorganic suspended solids (ISS) and absorption coefficient of chromophoric dissolved organic matter at 254 nm, with the correlation coefficient (R²) of 0.68 and 0.34, respectively, and ISS had the higher influence on SD. Combining with the underwater terrain and the light compensation depth, SD restoration value in the initial stage of Nanhu Lake was determined by 80 to 100 cm. Reducing the concentrations of SS and DOM should be conducted to improve SD of Nanhu Lake.