Improved simulation-optimization approach for identifying critical and developable pollution source regions and critical migration processes for pollutant load allocation.

Simulation-optimization approaches are widely used in land-based pollutant load allocation and management. However, existing simulation-optimization approaches do not optimize the entire pathway of pollution (i.e., generation, transportation, and emission). Thus, the selected allocated load scheme and its reduction management are incomplete and non-optimal in supporting effective reduction measures to set in further. This study aims to establish a simulation-optimization load allocation approach covering the entire pathway of pollution and construct separate allocated loads for each migration process. By comparing the allocated loads to the actual pollutant loads, the critical and developable pollution source regions (CPSRs and DPSRs) and the critical pollution migration processes (CPMPs) are identified, and specific pollution management indicators are established for each pollution source region. This approach is applied to the Bohai Rim, which is currently a major economic development center with a most seriously deteriorating sea area in China. The CPSRs, DPSRs, and CPMPs for total nitrogen are identified, and comparisons of the management indicators with existing approaches are made. Water quality under the allocated load emissions is simulated via a simulation water quality model and compared with that of the actual pollutant loads. Quantitative results indicate that the new approach combines the specific mitigation indicators for each CPSR and CPMP when allowing the extra generation of allocated loads for DPRSs while keeping the water quality of the Bohai Sea under control.