Tracer study of CDOM for nitrogen and phosphorus pollution in the offshore Leizhou Peninsula, China

Abstract

Colorful dissolved organic matter (CDOM) is an optically important active substance in marine habitats that feature significant biochemical conservatism. Additionally, CDOM is an important tracer and indicator of pollution status in marine water masses. In this study, we use sampling data collected in September 2020 and May 2021 from the marine areas around the Leizhou Peninsula. This information is combined with the Delft 3D numerical simulation analysis to carry out a study on the relationship between the ag (355) in the marine areas and to determine the regional marine pollution levels. The results show that (1) the nearshore areas of the Leizhou Peninsula in spring and autumn are mainly lightly polluted. Compared with the same period in history, the pollution level has significantly decreased, and the ag (355), DIN, and DIP concentrations show a trend of high near the shore and low far from shore. The peak concentrations are mainly in the Zhanjiang Bay, Qiongzhou Strait, Wailuo Port, Liusha Port and Guangxi Tieshan Port. (2) ag (355) can be used as an indicator to characterize the degree of water pollution in the nearshore waters of the Leizhou Peninsula. In spring, the ag (355) interval of [0.115, 0.200] m−1, [0.201, 0.245] m−1 and [0.246, 0.484] m−1 can be considered clean, lightly polluted, and moderately polluted water, respectively. In autumn, the ag (355) interval of [0.180, 0.275] m−1, [0.276, 0.478] m−1, [0.479, 0.642] m−1, [0.643, 0.921] m−1 can be considered clean, lightly polluted, moderately polluted and heavily polluted water, respectively. (3) The response models between the ag (355) and pollutant dispersion trends were constructed in the Zhanjiang Bay and Tieshan Port. The RMSEs of the ag (355) validation points in the models were lower than 0.12 mg/L, and the MAPEs were lower than 30 %, the pollution traceability of CDOM is verified.