Current indices for assessing the biological status and quality of rivers are designed to study perennial rivers, so they are not suitable for temporary rivers. This is because the lack of a constant flow of water in the riverbed affects the connectivity and dispersal of organisms, thereby reducing species diversity for natural rather than anthropogenic reasons.
Now, a study led by researchers Zeynep Ersoy and Núria Bonada, from the Freshwater Ecology, Hydrology and Management (FEHM-Lab) research group of the Faculty of Biology and the Biodiversity Research Institute (IRBio-UB) of the University of Barcelona, opens up new possibilities for transforming the way ecological quality of intermittent rivers is assessed, ecosystems that are increasingly common across the European continent. The first co-authors of the article are Zeynep Ersoy, from the Global Change Research Institut of the Rey Juan Carlos University (IICG-URJC), and David Cunillera, from the Budapest Ecological Research Centre (Hungary).
The study, published in the Journal of Applied Ecology, analyses how the loss of connectivity caused by the drying of ephemeral rivers alters the functionality of the biological indices used in the management of riverine ecosystems. As the study warns, this can drastically reduce the ability of these indicators to detect impacts related to human activities.
A metacommunities model to understand what happens when the river runs dry
As part of the study, the team has simulated thousands of metacommunities — a set of interconnected communities — subjected to varying drought conditions and human impact. This approach allows the integration of local processes, such as habitat loss, and regional processes, such as connectivity and the dispersal of macroinvertebrates, two key factors in rivers that alternate between dry and wet phases.
“The results show that low spatiotemporal connectivity leads to a decrease in the richness and values of biological indices. As temporal variability increases, the index’s effectiveness decreases exponentially. For example, if half of the river network dries up, the viability of the indices falls by 60%,” says Professor Núria Bonada, head of the FEHM-Lab Research Group and member of the Department of Evolutionary Biology, Ecology and Environmental Sciences at the UB.
Implications for the management of ecological monitoring and its future
The results show that current biological indices fail in intermittent rivers, “since species loss is not always due to human impacts, but to hydrological fragmentation,” explains expert Zeynep Ersoy.
“The study represents a first step towards developing digital tools that incorporate the temporal dynamics of river networks; they could help managers, in a context of global change, to carry out effective biomonitoring of these ecosystems,” the researchers conclude.
The study was been carried out as part of the DRY-Guadalmed project, funded by the Ministry of Science, Innovation and Universities, through the State Research Agency, and led by researchers Núria Cid (IRTA-La Ràpita) and Núria Bonada (UB-IRBio), with the aim of developing advanced tools to assess the ecological status of Mediterranean ephemeral rivers during dry periods.