The analysis of spatiotemporal effects of environmental factors on harmful algal blooms in a bloom-prone river using partial least squares structural equation modeling.

Since rivers are adversely affected by harmful algal blooms (HABs), it is necessary to develop countermeasures through analyzing the relationship between environmental variables and HABs. This study focused on analyzing the connections between HABs and environmental variables in the middle reaches of the Nakdong River in South Korea. Partial least squares structural equation modeling (PLS-SEM) was used to identify those relationships. The study developed three different PLS-SEM models to investigate various aspects, including lagged effects of environmental factors, influences from upstream and tributaries, and interactions between genera of HABs. The results of the study revealed that the magnitude of HABs had the strongest relationships with nutrient concentrations, particularly 1 week prior to HABs measurement. Additionally, the magnitude of HABs showed stronger relationships with upstream nutrient concentrations compared with tributaries' nutrient concentrations. Furthermore, the dominant genus of HABs in the study area, Microcystis, showed significant relationships with temperature and nutrient concentrations. However, the study did not find significant relationships between Microcystis and other harmful cyanobacteria genera. The methodological framework provides valuable insight into the management of HABs. It allows for the analysis of multiple aspects of the relationships between environmental factors and HABs, which is crucial for effective water resource management.