Dynamics and potential drivers of CO2 concentration and evasion across temporal scales in high-alpine streams

Åsa Horgby,Nicolas Escoffier,Tom J Battin,Lluís Gómez-Gener

doi:10.1088/1748-9326/ab5cb8

Abstract

Carbon dioxide (CO2) evasion from streams greatly contributes to global carbon fluxes. Despite this, the temporal dynamics of CO2 and its drivers remain poorly understood to date. This is particularly true for high-altitude streams. Using high-resolution time series of CO2 concentration and specific discharge from sensors in twelve streams in the Swiss Alps, we studied over three years the responsiveness of both CO2 concentration and evasion fluxes to specific discharge at annual scales and at the scale of the spring freshet. On an annual basis, our results show dilution responses of the streamwater CO2 likely attributable to limited supply from sources within the catchment. Combining our sensor data with stable isotope analyses, we identify the spring freshet as a window where source limitation of the CO2 evasion fluxes becomes relieved. CO2 from soil respiration enters the streams during the freshet thereby facilitating CO2 evasion fluxes that are potentially relevant for the carbon fluxes at catchment scale. Our study highlights the need for long-term measurements of CO2 concentrations and fluxes to better understand and predict the role of streams for global carbon cycling.

Highlights

Inland waters are recognized as important components of the global carbon cycle (Cole et al 2007, Battin et al 2009, Drake et al 2018) with total carbon (C) evasion fluxes to the atmosphere possibly as high as 3.88 Pg C yr−1 (Drake et al 2018)
Based on the previous considerations, we present a framework based on the relationship between the responsiveness of CO2 concentration to q and the responsiveness of FCO2 to q, with the aim to gain mechanistic understanding of the dynamics of CO2 evasion from streams and its linkage to processes operating at catchment scale
Streamwater CO2 concentration dynamics Overall, we found low streamwater CO2 concentrations, which is consistent with other reports on similar streams (e.g. Schelker et al 2016, Kuhn et al 2017, Qu et al 2017, Horgby et al 2019)

Summary

Introduction

Inland waters are recognized as important components of the global carbon cycle (Cole et al 2007, Battin et al 2009, Drake et al 2018) with total carbon (C) evasion fluxes to the atmosphere possibly as high as 3.88 Pg C yr−1 (Drake et al 2018). Headwater streams—the smallest but most abundant streams in fluvial networks—are estimated to contribute approximately one third to the global carbon dioxide (CO2) evasion flux (Marx et al 2017). The response of streamwater solute concentrations (C) to discharge (Q), or specific discharge (q) (here we use q for the sake of crosscatchment comparability), provides information on the sources of solutes within the catchment, their size and arrangement, and mobilization and transportation to the streams (e.g. Godsey et al 2009, Meybeck and Moatar 2012). Invariant responses of C to q are indicative of chemostasis and may reflect a uniform distribution of solutes within the catchment (e.g. in soils), where changes in hydrological connectivity and flow-paths position do not alter C in the streamwater. Chemodynamic responses indicates a change of C transportation limits CO2 concentration and FCO2. Depending on the limitation the system state can move to an alternative domain (as indicated by the blue arrow) where limitation relief results in a higher responsiveness of FCO2 to q

Methods

Results

Conclusion