Dams in South Europe: socio-environmental approach and eDNA-metabarcoding to study dam acceptance and ecosystem health

Under current climate warming, dams and reservoirs are main options to ensure water supply in dry regions. However, the presence of these infrastructures encompasses impacts on ecosystem due to the alteration of connectivity and river habitat. We expect that as a result of the relation between water supply as a resource and the population will depend on their use or demand, so the benefits of dams compensate their negative impacts in regions with droughts while not having the same perception in zones where water supply is not a problem, so the public acceptance of dams is expected to change depending on the area. Here, we have employed a multidisciplinary approach to study dam acceptance and also measure ecosystem health in two dammed areas, Guadalhorce and Nalon rivers, Mediterranean dry south and Atlantic humid north of Spain, respectively. The methodology employed has included the use of Environmental DNA for phytoplankton inventory and surveys to stakeholders and ordinary citizens to measure dam's acceptance. Worse bioindicators of water quality associated to dams were found in Guadalhorce than in Nalon River. However, stakeholders valued more the ecosystem services provided by Guadalhorce dams, especially of cultural nature, than those provided by Nalon dams. Most citizens consulted (N = 319 and 300 in Guadalhorce and Nalon regions) were favourable to the presence of dams and reservoirs. They would also increase their annual taxes to restore river connectivity, especially in Guadalhorce River, while dam demolition was the least supported. The generally positive views would help to identify actions for improvement of dammed rivers highlighting the importance of restoring river connectivity without dam demolition for local river users.

Automated summary

Dams and reservoirs are important options for water supply in dry regions, but their presence has impacts on the ecosystem. A study in two dammed areas found that most citizens were favorable to the presence of dams.