Diffuse pollutant load predictions in areas that implement the total maximum daily load due to climate change

Abstract

Total maximum daily load (TMDL), which is implemented for water quality management in a watershed, necessitates the use of a watershed model to predict the load. However, such a model consumes a lot of time and effort until the results are simulated. Therefore, the present study aimed to compare and evaluate load changes following the revision of the land-based diffuse pollutant unit load values, which are used to calculate the diffuse pollutant discharge loads in the total maximum daily load (TMDL) guidelines established for TMDL control by watersheds in South Korea, using the Natural Resources Conservation Service (NRCS) method. When the revised unit load was used, the loads were reduced by an average of 56.8% compared with the prior unit load. The descending order of load change rate was biochemical oxygen demand (BOD) > total phosphorus (TP) > total nitrogen (TN). Although the difference in load discharge trends between the Representative Concentration Pathway (RCP) 2.6 and RCP8.5 scenarios was insignificant, the load discharge under the worst scenario (RCP8.5) may increase. When the future period was split into 30-year increments, the load of precipitation and diffuse pollutants increased in the intermediate future (2041–2070). This study examined how the management ratio of diffuse pollutants in a watershed changes when the legal standard value of institutionally managed diffuse pollutants changes. The findings of this study provide useful information for the efficient management of present and future diffuse pollutants.