Temporary rivers also affect global CO2 emissions
Freshwaters play an important role in the global cycle of carbon due the decomposition of terrestrial plants which stimulates atmospheric emissions of carbon dioxide (CO₂). Despite having this impact, the role of temporary rivers -in which water stops flowing at some time during the year and can completely dry up- is unknown. An international collaboration project led by Thubault Datry, from IRSTEA (France), with the participation of researchers Núria Cid and Núria Bonada, from the Faculty of Biology and the Biodiversity Research Institute of the UB (IRBio), conducted the first global study on the contribution of temporary rivers to the carbon cycle that controls climate in the planet.
Freshwaters play an important role in the global cycle of carbon due the decomposition of terrestrial plants which stimulates atmospheric emissions of carbon dioxide (CO₂). Despite having this impact, the role of temporary rivers -in which water stops flowing at some time during the year and can completely dry up- is unknown. An international collaboration project led by Thubault Datry, from IRSTEA (France), with the participation of researchers Núria Cid and Núria Bonada, from the Faculty of Biology and the Biodiversity Research Institute of the UB (IRBio), conducted the first global study on the contribution of temporary rivers to the carbon cycle that controls climate in the planet.
The study, published in the science journal Nature Geoscience , shows these rivers have high levels of oxygen consumption and carbon dioxide emissions. According to the researchers, these results show the importance of the study of temporary rivers to know about the contribution of global water networks to CO₂ release into the atmosphere, especially when having in mind that there will be more rivers like these due the effects of climate change and the increasing water demand.
Sampling rivers in Girona, Castelló, Malaga and Cadiz
When a river stops flowing, such the case of temporary rivers, organic matter coming from terrestrial plants, mainly leaves and wood from the nearest river area, fall and pile up in dry river areas. In order to know what happens with these materials when water flows again, and therefore study the contribution of temporary rivers to the global cycle of carbon, The 1000 Intermittent Rivers did research on the quantity and quality of the organic terrestrial matter that piles up over the dry periods in 212 intermittent rivers in 22 different countries.
The UB is one of the 92 research institutions that took part in the consortium, bringing samples of organic matter that piled up in dry riverbeds in four temporary rivers in the Iberian Peninsula: the headwaters of Daró River (Girona), the headwaters of Cervol River (Castelló), Guadalmedina River (Malaga), and Hozgarganta River (Cadiz).
“The type and quantity of organic matter changes depending on the climate, riparian vegetation, channel width, length of dry periods and the riverʼs hydrological regime. Therefore, we got different hydrological information for each river in order to know the amount of days the river was dry, as well as data on the uses of the basin floors to assess potential human impacts, and the riparian coverage and substrate composition of the riverbeds of the sampled river”, says Núria Cid, member of the Department of Evolutionary Biology, Ecology and Environmental Sciences and member of FEHM (Freshwater Ecology, Hydrology and Management), affiliated to the Institute of Water Research (IdRA) of the University of Barcelona.
Simulation of temporary rivers behaviour
The materials of each river were classified, weighted and processed in order to send them to the coordinators of the project in IRSTEA. These laboratories simulated the behaviour of temporary rivers and analysed the effects on microbial communities, responsibles for the degradation of waste when water goes back to the basin. They measured respiration rates of these microorganisms (which reflect the reactivation of microbial communities) and checked this activity throws substantial CO2 quantities into the atmosphere.
“An estimated extrapolation shows that estimations of daily CO2 emissions of continental water courses could increase by a 7 and 152 % if we add data from temporary rivers to those existing data from perennial rivers, and that an only event of reactivation could contribute up to a 10 % of this increase”, says Núria Bonada, researcher of the mentioned Department and FEHM.
These results show the importance of temporary rivers in global flows with the atmosphere. When water flows again in temporary rivers, these emit CO2. Therefore, these rivers should be included in future studies in order to estimate the contribution of continental water masses to the carbon cycle at a global scale -the study concludes.