Spatial and Temporal Distribution Characteristics of Total and Dissolved Microcystins in Recreational Areas of the Lower Geum River

This study investigated the spatial and temporal distribution of total and dissolved microcystins in recreational areas of the lower Geum River and evaluated differences according to sampling position. Water samples were collected monthly from May to October 2025 at nine shoreline sites, and cross-sectional composite samples were additionally collected at two representative sites during the cyanobacterial bloom period (August–September). Total microcystins ranged from ND to 9.878 μg/L and generally increased toward downstream sites. MC-RR was the dominant congener in total microcystins, whereas dissolved microcystins showed a relatively lower contribution of MC-RR and a higher contribution of MC-YR. Dissolved microcystins were detected at low concentrations (ND–0.091 μg/L) and exhibited limited temporal and spatial variability. Total microcystins were significantly associated with cyanobacteria, chlorophyll-a, water temperature, and pH. Comparison of shoreline and cross-sectional samples showed similar temporal trends and dominant congeners but differences in concentration levels and environmental relationships. These results indicate that shoreline observations reflect localized exposure conditions, whereas cross-sectional samples represent average river-section characteristics. The findings provide useful information for microcystin monitoring and spatial representativeness assessment in recreational river environments.