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Alternating Drying and Flowing Phases Control Stream Metabolism Through Short‐ and Long‐Term Effects: Insights From a River Network.

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Title: Alternating Drying and Flowing Phases Control Stream Metabolism Through Short‐ and Long‐Term Effects: Insights From a River Network.
Authors: López‐Rojo, Naiara1 (AUTHOR) naiara.lopez.rojo@gmail.com, Sarremejane, Romain1,2 (AUTHOR), Foulquier, Arnaud3 (AUTHOR), Singer, Gabriel4 (AUTHOR), Diamond, Jacob1,5 (AUTHOR), Rioux, Delphine3 (AUTHOR), Miquel, Christian3 (AUTHOR), Mulero, Stephen3 (AUTHOR), Lionnet, Clément3 (AUTHOR), Peñas, Francisco J.6 (AUTHOR), Rodeles, Amaia A.6 (AUTHOR), Datry, Thibault1 (AUTHOR)
Source: Journal of Geophysical Research. Biogeosciences. Mar2025, Vol. 130 Issue 3, p1-15. 15p.
Subject Terms: *Carbon emissions, *Oxygen in water, Algal communities, Metabolic regulation, Lead time (Supply chain management), Respiration, Oxygen consumption
Abstract: Stream metabolism is a key biogeochemical process in river networks, synthesizing the balance between gross primary production (GPP) and ecosystem respiration (ER). Globally, more rivers and streams are drying due to climate change and water abstraction for human uses and this can alter the organic carbon residence time leading to decoupled ER and terrestrial organic matter supply. Although the consequences of drying on CO2 emissions have been recently quantified, its effects on stream metabolism are still poorly studied. We addressed the long‐term effects of drying and rewetting events on stream metabolism by monitoring oxygen dynamics at 20 reaches across a drying river network, including perennial (PR) and nonperennial reaches (NPR) for one year. We also calculated several climatic and land use variables and characterized local abiotic conditions and biofilm and sediment communities at five sampling dates. ER was significantly higher in NPR than in PR reaches demonstrating in situ the effects of drying on stream metabolism. When analyzing the long‐term drivers of ER and GPP, we found a direct positive effect of drying on ER and a negative effect on GPP. Drying also altered microbial community composition with algal communities from NPRs being different from those in PRs. In the short‐term, the total oxygen consumption (respiration) during rewetting events was positively related to the duration of precedent nonflow period. Our results show that drying had an important effect on stream metabolism both in the short‐ and long term, supporting the need for including NPRs in global estimates of stream metabolism. Plain Language Summary: Stream metabolism is the balance between primary production (fixation of carbon through photosynthesis: GPP) and respiration (excretion of CO2: ER). Globally, more rivers and streams are drying due to climate change and water abstraction potentially altering their metabolism. Although we know that drying affects river CO2 emissions, understanding of its effects on stream metabolism is still limited. We assessed the effects of drying on stream metabolism by measuring water oxygen concentration for one year at 20 sites, including permanently flowing and drying reaches (i.e., alternating dry‐flowing periods) and also various environmental variables and microbial communities at five sampling dates. ER was higher in drying than in permanently flowing reaches, demonstrating the effects of drying on respiration. When analyzing the variables affecting ER and GPP, we found a positive effect of drying on ER and a negative effect on GPP. Drying also altered microbial communities with algal communities from drying reaches differing from those in permanently flowing ones. The amount of oxygen consumed when flow resumed at dry sites was positively related to the duration of the precedent dry period. Our results show that drying has an important effect on stream metabolism, supporting the need of including drying rivers in global estimates of CO2 emissions. Key Points: Drying patterns were key determinants of metabolism in a nonperennial river network metabolism through both direct and indirect effectsDrying had a direct positive effect on ecosystem respiration and a negative effect on gross primary productionAlgal community composition of nonperennial reaches was different from those of perennial ones [ABSTRACT FROM AUTHOR]
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Abstract:Stream metabolism is a key biogeochemical process in river networks, synthesizing the balance between gross primary production (GPP) and ecosystem respiration (ER). Globally, more rivers and streams are drying due to climate change and water abstraction for human uses and this can alter the organic carbon residence time leading to decoupled ER and terrestrial organic matter supply. Although the consequences of drying on CO2 emissions have been recently quantified, its effects on stream metabolism are still poorly studied. We addressed the long‐term effects of drying and rewetting events on stream metabolism by monitoring oxygen dynamics at 20 reaches across a drying river network, including perennial (PR) and nonperennial reaches (NPR) for one year. We also calculated several climatic and land use variables and characterized local abiotic conditions and biofilm and sediment communities at five sampling dates. ER was significantly higher in NPR than in PR reaches demonstrating in situ the effects of drying on stream metabolism. When analyzing the long‐term drivers of ER and GPP, we found a direct positive effect of drying on ER and a negative effect on GPP. Drying also altered microbial community composition with algal communities from NPRs being different from those in PRs. In the short‐term, the total oxygen consumption (respiration) during rewetting events was positively related to the duration of precedent nonflow period. Our results show that drying had an important effect on stream metabolism both in the short‐ and long term, supporting the need for including NPRs in global estimates of stream metabolism. Plain Language Summary: Stream metabolism is the balance between primary production (fixation of carbon through photosynthesis: GPP) and respiration (excretion of CO2: ER). Globally, more rivers and streams are drying due to climate change and water abstraction potentially altering their metabolism. Although we know that drying affects river CO2 emissions, understanding of its effects on stream metabolism is still limited. We assessed the effects of drying on stream metabolism by measuring water oxygen concentration for one year at 20 sites, including permanently flowing and drying reaches (i.e., alternating dry‐flowing periods) and also various environmental variables and microbial communities at five sampling dates. ER was higher in drying than in permanently flowing reaches, demonstrating the effects of drying on respiration. When analyzing the variables affecting ER and GPP, we found a positive effect of drying on ER and a negative effect on GPP. Drying also altered microbial communities with algal communities from drying reaches differing from those in permanently flowing ones. The amount of oxygen consumed when flow resumed at dry sites was positively related to the duration of the precedent dry period. Our results show that drying has an important effect on stream metabolism, supporting the need of including drying rivers in global estimates of CO2 emissions. Key Points: Drying patterns were key determinants of metabolism in a nonperennial river network metabolism through both direct and indirect effectsDrying had a direct positive effect on ecosystem respiration and a negative effect on gross primary productionAlgal community composition of nonperennial reaches was different from those of perennial ones [ABSTRACT FROM AUTHOR]
ISSN:21698953
DOI:10.1029/2024JG008369