03701naa a2200313 a 450000100080000000500110000800800410001902200140006002400270007410000130010124501670011426000090028150009400029052018190123065300100304965300260305965300160308565300130310165300180311465300160313270000150314870000170316370000190318070000230319970000270322270000150324970000160326477301070328010639772023-04-27       2023    bl uuuu     u00u1 u    #d  a1354-10137 a10.1111/gcb.165872DOI1 aKRUK, C.  aRise of toxic cyanobacterial blooms is promoted by agricultural intensification in the basin of a large subtropical river of South America.h[electronic resource]  c2023  aArticle history: Received 6 July 2022, Accepted 27 November 2022, First published online 06 January 2023. --  Corresponde author: Kruk, C.; Instituto de Ecología y Ciencias Ambientales, Facultad de Ciencias, Udelar, Uruguay; email:ckruk@yahoo.com -- FUNDING: This work is part of the project ?Modelización de los efectos del cambio y la variabilidad climática en la intensificación de las floraciones de cianobacterias tóxicas en el río Uruguay y Río de la Plata? financed by Research for Climate (2021)-National Innovation and Research Agency of Uruguay (ANII) (ICC_X_2021_1_171370) and the project ?Algoritmos automatizados para la predicción espacio-temporal de calidad de agua mediada por floraciones tóxicas en sistemas de relevancia para el agua potable y la recreación? financed by Inteligencia artificial para el manejo de crisis y la construcción de resiliencia (Uruguay, Argentina: ANII, IDRC, CONICET and FAPESP).  aToxic cyanobacterial blooms are globally increasing with negative effects on aquatic ecosystems, water use and human health. Blooms? main driving forces are eutrophication, dam construction, urban waste, replacement of natural vegetation with croplands and climate change and variability. The relative effects of each driver have not still been properly addressed, particularly in large river basins. Here, we performed a historical analysis of cyanobacterial abundance in a large and important ecosystem of South America (Uruguay river, ca 1900 km long, 365,000 km2 basin). We evaluated the interannual relationships between cyanobacterial abundance and land use change, river flow, urban sewage, temperature and precipitation from 1963 to the present. Our results indicated an exponential increase in cyanobacterial abundance during the last two decades, congruent with an increase in phosphorus concentration. A sharp shift in the cyanobacterial abundance rate of increase after the year 2000 was identified, resulting in abundance levels above public health alert since 2010. Path analyses showed a strong positive correlation between cyanobacteria and cropland area at the entire catchment level, while precipitation, temperature and water flow effects were negligible. Present results help to identify high nutrient input agricultural practices and nutrient enrichment as the main factors driving toxic bloom formation. These practices are already exerting severe effects on both aquatic ecosystems and human health and projections suggest these trends will be intensified in the future. To avoid further water degradation and health risk for future generations, a large-scale (transboundary) change in agricultural management towards agroecological practices will be required. © 2023 John Wiley & Sons Ltd.  aCrops  aCyanobacterial blooms  aHealth risk  aLand use  aPrecipitation  aTemperature1 aSEGURA, A.1 aPIÑEIRO, G.1 aBALDASSINI, P.1 aPÉREZ-BECOÑA, L.1 aGARCÍA-RODRÍGUEZ, F.1 aPERERA, G.1 aPICCINI, C.  tGlobal Change Biology, 2023, volume 29, issue 7, pp. 1774-1790. doi: https://doi.org/10.1111/gcb.16587