Long-term and Seasonal Water Quality Changes in the Yeongsan River

This study analyzed long-term water quality variations in the Yeongsan River, focusing on organic matter, algae, and nutrients at eight locations. The Yeongsan River shows distinct spatial and temporal patterns in BOD and COD. BOD were high at Gwangju 2 but decreased significantly towards Muan 2, with a trend of decreasing from 2001-2015 and increasing from 2011-2015. BOD was higher in spring and lower in autumn. COD continuously increased from Gwangju 1 to Muan 1 and consistently rose from 2001-2005, peaking in summer and lowest in autumn. Chl-a decreased to 2006-2010 but increased thereafter, especially in Naju and Yeongsanpo, due to weir construction. Chl-a was highest in winter and generally lower in autumn. Harmful cyanobacteria are relatively more prevalent in Juksan Weir. In Seungchon Weir, harmful cyanobacteria were most prevalent in autumn, while in Juksan Weir, they were most prevalent in summer. In both Seungchon and Juksan Weirs, the most dominant harmful cyanobacterium was identified as Microcystis. Total nitrogen (T-N) decreased to 2006-2010 and stabilized thereafter, with high concentrations at Gwangju 2 and a sharp reduction towards Naju, linked to advanced sewage treatment. T-N was highest in winter and lowest in summer. Total Phosphorus (T-P) showed minimal changes in the upper regions but significantly declined at Gwangju 2 due to improved nutrient removal processes, being higher in summer and lower in winter. The seasonal N/P ratio varied, with higher values observed in winter and lower values in summer. This study shows improvements in water quality over time in the Yeongsan River. Specifically, phosphorus levels have been improved due to advanced sewage treatment. However, the increase in harmful cyanobacteria, particularly Microcystis, in weirs raises concerns for the ecosystem and human health. Continuous monitoring and adaptive management are needed to maintain the river's health.