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Cyanobacterial toxic blooms on Uruguayan coasts: Addressing the challenges from a socio-ecological perspective

  • 1 February, 2021
  • Wageningen University, Aquatic Ecology and Water Quality Management
  • dr ir MFLLW Lürlingdr M Holmgren
  • Dr. Zurbriggen

Harmful algal blooms (HABs) pose substantial health risks to drinking water supplies, beach users, seafood consumers, and biodiversity. These HAB events have become more frequent and severe with climate warming and the anthropogenic eutrophication of freshwaters and coastal systems. Coastal systems have a high socioeconomic value related to a wide variety of ecosystem services including recreation, tourism, land protection, carbon sequestration and habitat for many species. The Uruguayan Eastern beaches are privileged vacation sites, attracting national and regional tourism (representing almost 7% of the country GDP). In the summer of 2019 exceptional HABs consisting of the cyanobacterium Microcystis aeruginosa were reported on the beaches of Río de la Plata and Atlantic Ocean. The accumulated cyanobacteria generated alarm in beach users, tour operators and the local authorities, which was reflected in the media and in the abundant queries made to experts in the field. The concerns pointed not only to the possible impacts that these events may have on human health and well-being, but also to the possible causes of such HABs. It has been hypothesized that these HABs had a common origin, mainly associated with zones with high nutrient concentrations and high water residence time in the lower Río de la Plata basin (the second largest basin in South America). At the basin level, increasing land clearing and runoff of sediments and nutrients associated with intensive agriculture may have contributed to the eutrophication of coastal systems during the last decades. This process may be accentuated with climate change as warmer waters may accelerate the growth of algae and higher rainfall pulses may intensify runoff from land to freshwater and coastal systems. It is therefore likely that increased eutrophication and water-born algae toxicity may become more frequent in South America in the coming years. Despite the expected trends, the HAB events were not anticipated at the institutional level. This is reflected, for example, in the diagnosis and actions developed for the National Coastal Adaptation Plan which did not include HABs as a main issue.
In this PhD proposal, I aim to develop a large integrated assessment of HABs to identify the best adaptation strategies for Uruguay. In particular, I will assess:
1.- Patterns, trends and drivers of HABs on the beaches of Montevideo, Canelones, Maldonado and Rocha, especially the influence of changes in land use and climate conditions.
2.- Impacts of HABs on recreation and sun and beach tourism.
3.- The associated multilevel governance system (Río de la Plata basin, national, departmental and municipal level) to identify the mechanisms needed to anticipate and adapt to the occurrence of HABs.
4.- Identify measures to reduce the risk of cyanotoxin exposure on the Uruguayan coast.
The nature of the problem requires a transdisciplinary approach that considers different scales and dimensions as well as the interrelation between ecological and social aspects. The framework of socio-ecological systems (understood as adaptive complex systems) seems very appropriate to generate explanations and alternatives for transformation.
Methods like remote sensing, land cover analysis, agent-based modelling, participatory modelling and planning, comparative case study analysis and futures analysis will be fundamental for this research.

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Ana Lía Ciganda Garrido

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