Effects of storms and COVID-19 on the state of rivers in the Barcelona area

Section of Tordera river in Hostalric in May 2020, year of Storm Gloria.

Section of Tordera river in Hostalric in May 2020, year of Storm Gloria.

All the analysed rivers in the 2020 CARIMED report on the ecological quality of rivers in the provincial area of Barcelona flowed with water -both in spring and in summerand there were no dry spots like in previous years. This is a unique hydrological condition within the 26-year period of scientific monitoring of the river network in Barcelona, carried out by the Freshwater, Hydrology and Management (FEHM) research group of the University of Barcelona.

The new report collects the results of the analysis of the ecological state of a network of 111 study areas distributed around the five hydrological basins and the rivers and streams that flow away in the provincial area of Barcelona: the rivers Besòs, Foix, Llobregat, Ter and Tordera, and the coastal streams in Maresme. Other participants in the study are the members of the Biodiversity Research Institute ( IRBio ) and the Water Research Institute ( IdRA ) of the UB, and the Catalan Water Agency ( ACA ) and the Center for the Study of Mediterranean Rivers ( CERM , University of Vic-Central University of Catalonia) and the Tordera Observatory (Besòs-Tordera Consortium), among other institutions.

The study of the ecological state of rivers in Barcelona started in 1979 under the supervision of Professor Narcís Prat, from the Department of Evolutionary Biology, Ecology and Environmental Sciences of the UB, and founder of FEHM, which is now led by Núria Bonada, lecturer at the Faculty of Biology. This river network is the base of a monitoring program of the UB funded annually by the Barcelona Provincial Council, which provided one of the most comprehensive scientific data series on river studies worldwide. The new report highlights the scientific interest in providing long-term temporary series to assess the effects of extreme episodes (floods, droughts, fires) on the environmental state of rivers and streams.

2020, the year of Storm Gloria

Since Storm Gloria took place -it affected the Iberian Peninsula in January 2020- several episodes of heavy rain which caused a significant increase of river flows. Some river basins -in particular, Tordera and Terunderwent several affectations in the stream areas and floodplains, usually occupied by agricultural, industrial or urban infrastructures. River areas with natural stream spots and less anthropic alterations are resilient to floods and generate fewer losses, as stated by the experts of the FEHM group in a chapter in the volume Sobre el temporal Gloria (Miquel Canals and Jaume Miranda, ICE 2020).

How did recurring floods affected the state of rivers and streams?

The swelling of river flows -higher than usual, mainly in springprovided a higher dilution of all pollutants that end up in rivers, coming from towns, cities, agricultural, industrial and mining areas, etc. Therefore, there has been an exceptional improvement in the physical and chemical quality and biological indicators of river flows over time, specially in bigger basins such as in Llobregat and Ter.

According to Núria Bonada, co-director of the project, “a clear example of the observed improvement in these rivers is seen in the historical evolution of the values in the IBMWP index, an indicator of the quality of water based on the macroinvertebrate community, in the samples of the river Llobregat in Puda (Olesa de Montserrat)’.

Regarding smaller rivers and streams -such as Foix or Anoiaor areas where human activity is higher -Besòs basin-, the ecological quality values of water are high in some headwater river spots. In mid and low areas, the results are moderate, even poor, like in previous years. “We think that when it stops raining, after a few days or weeks, the only water running through the Congost-Besòs is the one from water treatment plants’, notes Narcís Prat, co-director of the project.

Surprisingly, river and stream heads —some are included in the protected areas by the Network of Parks of the Barcelona Provincial Council -high biodiversity has been found both in spring and in summer —in some cases, even higher in summer—, and this had not been seen before. “In spring, the macroinvertebrate community was recovering from swelling water flows in which many water organisms had been dragged downstream’, notes Pau Fortuño, technical coordinator of the project.

“In summer —he continues—, macroinvertebrate communities could recover and colonized rivers and streams so that the organism richness was, in general, higher than in spring. These results show the great recovery abilities of these organisms regarding perturbations’.

COVID-19, confinement and ecological quality of rivers

The COVID-19 pandemic brought a severe change in our lifestyle, as well as the way we work and move, but also in the way we interact with the environment. Apart from the constancy of the impact of SARS-CoV-2 in treatment plant waters, everything indicates there are no other relevant effects of the virus in the ecological quality of the river network in Barcelona.

The report indicates the ecological state of rivers and streams was previously altered due to heavy rains. Also, despite the population confinement, the house water consumption was not much altered, and a slight increase in both flow and pollution would be expected. At the same time, the industrial sector, agriculture and livestock did not stop using water resources.

According to the conclusions, the effects in the ecological quality are quite contrasted according to the situation of the river. In remote areas —with a good ecological State in previous years— the combined effect of the rise of water and a lower attendance due to COVID-19 has translated into good indicators of ecological quality during 2020 without previous years’ drought effects.

In those places that were frequented but which had a good ecological quality, such as Fonts del Llobregat, the situation remains the same and has even slightly improved. In contrast, the rise of flows has improved the ecological quality of water in summer in the mid stretches of rivers and some streams with moderate or high flows (with important inflows of low-quality waters from treatment plants or from industrial or agricultural areas).

In the small rivers, flow alterations due to human activity (for instance, taking springs for residential areas) or the bomb effect of forests (they take most of the water to grow) made the changes to be less or even non-existent.

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