Geographic variation in the potential transport of cyanobacterial blooms to the main water utility of Uruguay

Cyanobacterial blooms pose potential health and economic risks, particularly when transported to drinking water intakes. River basins with intensive agricultural production have numerous small- and medium-sized (0.25–30 ha) productive freshwater reservoirs that create favorable conditions for excessive growth of phytoplankton. The phytoplankton can then be transported downstream after heavy rainfall events, which are projected to worsen under future climate scenarios. These environments have been identified as potential sources of cyanobacterial biomass in Uruguay’s main drinking water intake, located in the Santa Lucía River Basin. To pinpoint areas with the highest potential for export of cyanobacterial biomass, this study integrated chlorophyll <i>a</i> concentration monitoring in 325 reservoirs using Sentinel-2 satellite images with meteorological and structural information from the reservoirs. Spatial distribution patterns explored through geostatistical and multivariate analyses showed that the southern and western zones, characterized by intensive agricultural land uses such as dairy farming and horticulture, suggest a high potential for biomass export. By contrast, the northeastern zone exhibited the lowest potential, aligning with extensive cattle ranching practices associated with low nutrient export to aquatic systems. This study marks the first effort to assess the potential for transporting cyanobacterial biomass from numerous, widely geographically distributed reservoirs to Uruguay’s primary drinking water intake. We propose that such a spatially explicit analysis can be used to develop a biomass export indicator as a fundamental input for an early warning system of cyanobacteria bloom events in drinking water plants located downstream.