Temporal and spatial evaluation of the effect of river environment changes caused by climate change on water quality

Rivers are affected by environmental changes caused by the anthropogenic influence on the climate and water quality. Therefore, it is important to evaluate water quality patterns based on changes in the aquatic environment. Eight multifunctional weirs (MWs) previously constructed in the Nakdong River, South Korea, have disrupted the river flow and increased the residence time by artificial floodgate control, thereby converting the river into a series of lakes. This study evaluates water quality in the Nakdong River using principal component analysis (PCA), the water quality index (WQI) and trophic state index (TSI), and self-organizing map analysis. The PCA identified that, following the construction of the MWs, nitrogen and phosphorus-based nutrients were the major water quality variables. Analysis via WQI and TSI confirmed that the amount of pollutants increased toward the downstream area. During the dry season, a continuous degradation in water quality occurs due to reduced water quantity and stagnated flow. Meanwhile, nutrients flow into the river in the form of nonpoint sources during rainfall accelerated eutrophication of the river after the monsoon period. The results of this study confirmed the influence of the formation of stagnant waters caused by MW construction on overall water quality.