Author(s): I. W. Seo; J. S. Kim
Linked Author(s): Il Won Seo
Keywords: 2D numerical model; Algal bloom; Advection-dispersion equation; Finite element method; Nakdong River
Abstract: Algal bloom is the natural biomass of diverse algae which degrades ecological values in aquatic systems. This phenomenon causes enormous polluted river and threats the public health. Therefore, it is indispensable to implement a forecasting model on analysis of algal bloom. Development of 2D model on non-conservative pollutant mixing is essential in a real river system because the 1D model does not consider the direct hydraulic effect of changes like tributary inflow and nutrient entry. This study is aimed at developing a 2D numerical model to analyze spatial and temporal transport on algal boom forecasting using the finite element method to resolve complex geometry of a natural river. Based on environmental factors such as nutrient, light, temperature and predation to primarily affect algae growth, it allows building a new 2D advection-dispersion model adding a sink-source term which represents a biochemical mechanism occurring between algae and the four factors. The application site is defined between Gangjung weir and Dalsung weir in about 15 km section at Nakdong River. During summer, the river has suffered aberrant growth of blue-green algae called cyanobacteria due to precipitation deficiency, high temperature and runoff from industrial facilities. Furthermore, the weirs built across the river have impeded natural streamflow to stimulate colonization of the cyanobacteria with brisk assimilation with plenty of the nutrients. Through simulations, using the newly developed model in this study, it demonstrates that algae rapidly propagates away from center of an area where flow velocity become slower in the condition of continuous intrusion of nitrate and phosphate from wastewater treatment plants. During summer, temperature and light are relatively constant, so these two factors do not have large impact on the algal growth. Consequently, control of nutrient runoff and flow are critical to restrain the cyanobacteria propagation in the Nakdong River.