Spatial distribution and comparative evaluation of phosphorus release rate in benthic sediments of an estuary dam

A series of experiments and simulations were performed to ascertain the rate at which phosphorus is released using a water quality model in Saemangeum Lake, an artificially constructed lake located in an estuary. The general inflow of seawater once a day contributed to the formation of a halocline in the lake water, which caused variation in the vertical concentration of dissolved oxygen. The halocline was mainly observed in the deep downstream regions of Saemangeum Lake that are close to the open sea. In contrast, the shallower regions upstream, which are under the influence of pollutant-loading from upstream rivers, exhibited high concentrations of chemical oxygen demand, total phosphorus, and Chl-a, resulting in lower water quality than the downstream regions. Laboratory experiments investigating the release of phosphorus at five representative locations showed that the upstream release flux, where the halocline was weaker, was higher than that downstream, where the initial level of phosphorus sedimentation was high. In particular, a need for an accurate evaluation method for the release of phosphorus at each site was suggested as slight differences were obtained depending on the estimation method used at each representative location. The results of the phosphorus release experiments led to the use of time-weighted integration (TWI), terminated time evaluation, and statistical mean value; the Environmental Fluid Dynamics Code–National Institute of Environment Research model, a widely used water quality model for studying retention watersheds, was applied to the simulation of hydraulic and water quality characteristics for the Saemangeum Lake and its surrounding waters. The result of the water quality simulation indicated the highest reproducibility for release-time TWI so that TWI values were more useful in predicting phosphorus concentrations and the subsequent management of water quality.