Characterization of organic pollution in the Dianchi Caohai Lake at the transition between the dry and rainy seasons

Abstract

Dianchi Caohai Lake is heavily polluted, and a significant increase in chemical oxygen demand (COD) occurs during the transition from the dry season to the rainy season. In order to analyze the cause of COD increase, the compositional characteristics of organic matter were investigated using three-dimensional fluorescence spectroscopy technology. The results showed that the most polluted area was located in the geographic center of the outer Caohai Lake, where COD reached 29 mg/L and was elevated by 52%, and protein-like and humus-like features were evident in the organic matter fractions. By measuring the characteristics of water in Caohai Lake, it was found that the fluorescence indexes were greater than 2.47, the biological index was distributed between 0.67 and 1.06, and the humification index was distributed between 1.81 and 3.12. It indicated that the lake had low humification and showed strong autochthonous source characteristics. The bloom outbreak was one of the main reasons for the elevated COD concentration. This study will provide theoretical support for the control of organic pollution in Dianchi Lake.