Intermittent rivers are those that dry during part of their annual cycle, whose information is not taken into account when determining the global contribution of rivers in the release of CO2 into the atmosphere despite the fact that they represent over half the current global river network
The University of Granada has participated in an international study carried out by 94 researchers from all continents, framed within the 1000 Intermitent River Project and published in Nature Geoscience
An international team of researchers, which has counted with the participation of the University of Granada (UGR), has quantified for the first time the CO2 emissions associated with the ‘intermittent rivers’ of the planet, which currently account for half the global river network and that will be increasingly frequent due to climate change.
This study, with the participation of researchers from all around the globe and led by the French Research Institute of Science and Technology for Environment and Agriculture (IRSTEA, from its name in French), has been published in Nature Geoscience. This is the first contribution from the 1000 Intermitent River Project, an international program dedicated to the study of largely ignored members of the fluvial networks: intermittent rivers and ephemeral streams (IRES), that is, those that dry completely during part of their annual cycle.
In perennial rivers, where water flows uninterrupted throughout the year, leaves, branches and other litter are rapidly decomposed by normally active detritivores and decomposers, thus releasing CO2 into the atmosphere in a more or less continuous way.
In intermittent rivers, on the other hand, litter –dead matter that comes from the decomposition of organic sources– accumulates during dry periods and is not totally decomposed until water flows again. This fact produces significant CO2 emissions in the form of pulses, which until now had been practically ignored by the scientific community.
In order to carry out this work, researchers sampled a total of 212 intermittent rivers in 22 countries, from polar regions to the heart of tropical forests and dry deserts, during the drought months of 2015 and 2016.
Analysis of intermittent rivers
The material collected for the study was subjected to various laboratory tests and rigorous statistical analyzes. Researchers have found that climate, aridity, cover of riparian vegetation, channel width and dry‑phase duration explained most variability in the quantity and decomposability of plant litter in IRES, thus affecting CO2 emissions.
Besides, there are many other factors that influence CO2 emissions. As explained by Marcos Moleón Paiz, researcher at the UGR Department of Zoology and one of the authors of this work, «in arid environments such as the deserts of Namibia, where vegetation is scarce and large populations of elephants and rhinos are still present, a great part of the litter accumulated on dry riverbeds comes from the feces of these animals, which are able to move vasts amounts of plant matter from remote places to rivers, and vice versa. Studying the role of this megafauna is a major challenge, and also urgent, since there are a lot of threats looming over those species.»
The results of this study indicate that excluding intermittent rivers leads to a significant undervaluation of the global contribution of rivers in the release of CO2 into the atmosphere.
According to global calculations, estimates of CO2 emissions associated with watercourses would be increased by 7% to 152% if information regarding intermittent rivers were added.
«In conclusion, one can not fully and accurately understand global carbon‑cycling assessments without taking into account the processes taking place in intermittent rivers,» the UGR researcher says.
Bibliographic reference:
Datry et al. A global analysis of terrestrial plant litter dynamics in non-perennial waterways. Nature Geoscience. May 2018.
DOI: 10.1038/s41561-018-0134-4
Images:
Marcos Moleón Paiz, researcher from the Department of Zoology, participated in this international study
Moleón performed a sampling of several intermittent rivers in Namibia, such as the Ugab
Contact info:
Marcos Moleón Paiz
Department of Zoology, University of Granada
Phone number: (+34) 958 241 000 ext. 20096
E‑mail: mmoleon@ugr.es
