Application of Diatom Analysis to Water Quality Assessment. Case Study: The Nakdong River in the Republic of Korea

It is important to maintain a good level of water quality and river health in ecosystems because water is of the essence for humans and any living organism. Thanks to the advantages of diatoms, diatom-based indices are used to assess river health but a short-term assessment using one year of monitoring duration and one to two samples per year in the frequency is dominant. As a result, a holistic understanding of river health on a long-term scale lacks and the changes in diatom assemblages have been poorly understood despite the amass of the government diatom datasets in South Korea. The Nakdong river, one of the largest rivers in South Korea, has eight barrages, constructed during 2010--2012, which control the river flow using sluices. This project aims to understand the relations between water quality and diatom assemblages regarding the construction of the barrages in the Nakdong river and its tributaries over the period 2009--2018. This research demonstrates a holistic understanding of river health by looking at changes in water quality and diatom assemblages over ten years using species composition and multivariate analyses. Findings show that the barrages have caused significant changes to the flow regime and thermal system in the main river through impoundment and increased water levels with worsening trends of water quality. The construction has also triggered the significant changes in diatom assemblages in the main river, while the tributaries remain similar. In these findings, diatoms are central to the link between hydrological change, water quality, and the construction of the barrages. This study is a prime example of river health assessment on a multiple-years scale by providing a whole picture of river health in time and space.