River metabolism is regulated by light and flow

A researcher from the UPV/EHU-University of the Basque Country has taken part in a study analysing the metabolism of more than 200 rivers across the United States

  • Research

First publication date: 20/05/2022

Maite Arroita. | Photo: Fernando Gómez. UPV/EHU.

According to a study published in the PNAS journal, the factors that regulate the metabolism of rivers are light and flow. This conclusion drawn from millions of data from 222 US gauging stations is important for scaling and modelling the dynamics of river ecosystems, and may change the way they are studied. A researcher from the UPV/EHU's Department of Plant Biology and Ecology participated in the study.

Temperature and precipitation determine much of the variation in productivity in terrestrial ecosystems, and are used to specify biomes. "On land, changes taking place in ecosystem metabolism at both seasonal and system level are very well known. We know that the main factors controlling such changes are temperature and precipitation, and based on that, we know what kind of vegetation and fauna we will encounter, what physiognomy they will have, we can predict how an ecosystem will function, etc. However, this is not the case with rivers. We had a major handicap, especially because we lacked data," explained Maite Arroita, PhD holder in the UPV/EHU’s Stream Ecology research group.

In this respect, the researcher in the department of Plant Biology and Ecology at the UPV/EHU Maite Arroita has been collaborating with various universities in the USA in a study in which they concluded that river metabolism is regulated by light and river flow. The prestigious PNAS journal has reported on this study, which used millions of data from water quality gauging stations in 222 US rivers. "Temperature, oxygen concentration, flow rate, pH, conductivity, etc. are parameters that are measured frequently, depending on the season: every 10 to 15 minutes, every half hour, etc., over several years. We used all this data to calculate river metabolism; we analysed the seasonality of the rivers and looked for patterns to see which factors mark these spatial and temporal differences," she explained.  

A breakthrough in river science

"Photosynthesis is one of the main metabolic processes. Without light there is no photosynthesis. The availability of light varies greatly from one season to another, but also from one system to another, depending on topography, climate, riparian forest cover, turbidity, etc. This variability of light accounts for most of the changes that occur in the metabolism," the researcher explained.

Another of the most important characteristics of rivers is the flow or hydrologic regime. The researcher explained it thus: "Flow rate may affect the metabolism in several ways. For instance, after a storm, there is an increase in sediment inputs into rivers; turbidity increases and the availability of light decreases. Apart from this, when torrential rains occur, the effect of the flow may be even greater, as it is capable of moving even sediments and the living creatures inhabiting them. Biomass then decreases as it gets washed downstream. When the flow is highly variable, these disturbances are very frequent, and the accumulated biomass becomes considerably limited".

This work fills a gap that has existed until now. With a classification scheme based on these two factors, "a lot of progress can be made in river science, as we now have a better understanding of what really controls river metabolism. It can also serve as a basis for river management, as it improves the ability to scale and model the dynamics of river ecosystems, and can substantially change the way rivers are investigated", said Arroita. Climate change will exert a major impact on the functioning of river ecosystems "and the results obtained will make it possible to better predict the changes or consequences that will occur, and how to prevent them".

Basing herself on the methodologies and tools used in this work, Dr Arroita wants to analyse the database of the rivers of Gipuzkoa: “The Chartered Provincial Council of Gipuzkoa has a very extensive database. We have data taken over a 20-year period at 13 gauging stations located in different rivers across Gipuzkoa. Nowhere else is there such a large database in terms of time. I want to analyse temporal changes, to determine, for example, the history of rivers and the changes that have taken place, and to make forecasts, etc."

Bibliographic reference

  • Emily S. Bernhardt, Phil Savoy, Michael J. Vlah, Alison P. Appling, Lauren E. Koenig, Robert O. Hall Jr., Maite Arroita, Joanna R. Blaszczak, Alice M. Carter, Matt Cohen, Judson W. Harvey, James B. Heffernan, Ashley M. Helton, Jacob D. Hosen, Lily Kirk, William H. McDowell, Emily H. Stanley, Charles B. Yackulic, and Nancy B. Grimm Light and flow regimes regulate the metabolism of rivers PNAS DOI: 10.1073/pnas.2121976119