Responses of Water Quality Parameters to El Niño in the Curuá‐Una Reservoir, Amazon Basin

ABSTRACT The El Niño phenomenon in the Amazon is associated with extreme drought and lower atmospheric humidity, leading to environmental disturbances, such as wildfires and decreased river levels. An exceptionally intense El Niño occurred between 2015 and 2016, reaching historic magnitudes. This study evaluated its influence on water quality parameters in the Curuá‐Una Hydroelectric Power Plant reservoir, located near Santarém, Pará, in the Brazilian Amazon. Data from 2012, used as a baseline, were compared with those obtained in 2015, during the event. The 2012 dataset was provided by the company responsible for reservoir monitoring, whereas water samples in 2012 were collected at eight stations during both rainy and dry seasons. Results highlighted significant differences in most water quality parameters, particularly lower pH, phosphate, and ammonium concentrations, together with higher total dissolved solids (TDSs) and chlorophyll a during the 2015 dry season. Principal component analysis revealed distinct seasonal patterns, with higher phosphate contributions in the rainy season and greater influence of TDSs, chloride, chlorophyll a, phosphate, and ammonium in the dry season. These findings suggest that the 2015 El Niño drought was associated with marked changes in water quality, particularly during the dry season, highlighting the sensitivity of Amazonian reservoirs to extreme climatic events.