Investigation of water exposure time as a foundation for improving programs for coastal pollutant emission reduction

Abstract

For sustainable ocean development, coastal pollutant emission reduction (CPER) has been widely implemented to alleviate coastal environmental problems. CPER programs have primarily focused on determining the total amount of emission reduction; however, methods to determine the optimal time to conduct CPER to further improve the environmental benefits remains unclear. Therefore, this study proposed a method to determine the timing of CPER based on the water exposure time (WET) at the pollutant outlet, which involved conduct CPER when the WET was relatively high. Using numerical modeling of pollutant dispersion in the Subei Coastal Water and scenario simulations with different CPER programs, the reliability and superiority of this WET method was verified. Under the same annual mean 10% emission reduction, the CPER program based on WET obtained an average 14% reduction in coastal pollutant concentrations, which was over 40% more than the reduction by two other CPER programs. This finding suggests that WET is an effective indicator to determine the optimal time of CPER. Because of the high complexity and variability of coastal hydrodynamics, environmental management agencies should obtain the spatiotemporal variation characteristics of WET in coastal oceans before formulating corresponding environmental programs.