Local and regional drivers of headwater streams metabolism: Insights from the first AIL collaborative project

Pastor, Ada
Lupon, Anna
Gómez Gener, Lluís
Rodriguez Castillo, Tamara
Abril, Meritxell
Arce, María Isabel
Aristi, Ibon
Arroita, Maite
Bravo, Andrea G.
Castro Català, Núria de
Campo, Rubén del
Casas Ruiz, Joan Pere
Estévez, Edurne
Fernández, Diego
Fillol Homs, Mireia
Flores, Lorea
Giménez Grau, Pau
Hernández del Amo, Elena
Martin, Eduardo J.
Martínez, Aingeru
Monroy, Silvia
Mora Gómez, Juanita
Palacin Lizarbe, Carlos
Pereda, Olatz
Poblador, Silvia
Rasines Ladero, Ruben
Reyes, Marta
Rodríguez Lozano, Pablo
Ruiz, Celia
Sanpera Calbet, Isis
Solagaistua, Libe
Catalán, Núria
Local and regional drivers of headwater streams metabolism: Insights from the first AIL collaborative project 68 Pastor et al. Streams play a key role in the global biogeochemical cycles, processing material from adjacent terrestrial systems and transporting it downstream. However, the drivers of stream metabolism, especially those acting at broad spatial scales, are still not well understood. Moreover, stream metabolism can be affected by hydrological changes associated with seasonality, and thus, assessing the temporality of metabolic rates is a key question to understand stream function. This study aims to analyse the geographical and temporal patterns in stream metabolism and to identify the main drivers regulating the wholeecosystem metabolic rates at local and regional scales. Using a coordinated distributed experiment, we studied ten headwaters streams located across five European ecoregions during summer and fall 2014.We characterized the magnitude and variability of gross primary production (GPP) and ecosystem respiration (ER) with the open-channel method. Moreover, we examined several climatic, geographical, hydrological, morphological, and physicochemical variables that can potentially control stream metabolic rates. Daily rates of stream metabolism varied considerately across streams, with GPP and ER ranging from 0.06 to 4.33 g O 2 m -2 d -1 and from 0.72 to 14.20 gO 2 m -2 d -1 , respectively. All streams were highly heterotrophic (P/R < 1), except the southernmost one. We found that the drier climates tended to have the highest GPP, while humid regions presented the highest ER. Between the sampling periods no statistical differences were found. Partial-least squares models (PLS) explained i"80% of the variance in GPP and ER rates across headwater streams and included both local and regional variables. Rates of GPP varied primarily in response to the local variables, such as streambed substrate and stream water temperature. In contrast, regional variables, such as the mean annual temperature or the land use of the catchment, had more relevance to explain ER. Overall, our results highlight that stream metabolism depends on both local and regional drivers and show the positive experience of a young network of researchers to assess scientific challenges across large-scale geographic areas ​
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