Carbon dioxide dynamics in an agricultural headwater stream driven by hydrology and primary production

Marcus B Wallin,Mike Peacock,Joachim Audet,Mattias Winterdahl,Erik Sahlée

doi:10.5194/bg-17-2487-2020

Abstract

Abstract. Headwater streams are known to be hotspots for carbon dioxide (CO2) emissions to the atmosphere and are hence important components in landscape carbon balances. However, surprisingly little is known about stream CO2 dynamics and emissions in agricultural settings, a land use type that globally covers ca. 40 % of the continental area. Here we present hourly measured in situ stream CO2 concentration data from a 11.3 km2 temperate agricultural headwater catchment covering more than 1 year (in total 339 d excluding periods of ice and snow cover). The stream CO2 concentrations during the entire study period were generally high (median 3.44 mg C L−1, corresponding to partial pressures (pCO2) of 4778 µatm) but were also highly variable (IQR = 3.26 mg C L−1). The CO2 concentration dynamics covered a variety of different timescales from seasonal to hourly, with an interplay of hydrological and biological controls. The hydrological control was strong (although with both positive and negative influences dependent on season), and CO2 concentrations changed rapidly in response to rainfall and snowmelt events. However, during growing-season base flow and receding flow conditions, aquatic primary production seemed to control the stream CO2 dynamics, resulting in elevated diel patterns. During the dry summer period, rapid rewetting following precipitation events generated high CO2 pulses exceeding the overall median level of stream CO2 (up to 3 times higher) observed during the whole study period. This finding highlights the importance of stream intermittency and its effect on stream CO2 dynamics. Given the observed high levels of CO2 and its temporally variable nature, agricultural streams clearly need more attention in order to understand and incorporate these considerable dynamics in large-scale extrapolations.

Highlights

Fluvial systems are estimated to dominate the inland water CO2 source globally, surpassing CO2 emissions from lakes and reservoirs by a factor of 6 (Raymond et al, 2013)
Bodmer et al (2016) measured partial pressure of CO2 in German and Polish streams and examined differences between forested and agricultural catchments. They found that pCO2 was generally 2–3 times higher in agricultural streams compared to streams draining forested areas
In line with findings from similar studies from other environments (e.g. Rocher-Ros et al, 2019; Riml et al, 2019; Crawford et al, 2017; Peter et al, 2014; Dinsmore et al, 2013), we found a mixture of controls on stream CO2 operating at different timescales, generating a highly dynamic stream CO2 concentration pattern

Summary

Introduction

Fluvial systems (streams and rivers) are estimated to dominate the inland water CO2 source globally, surpassing CO2 emissions from lakes and reservoirs by a factor of 6 (Raymond et al, 2013). Bodmer et al (2016) measured partial pressure of CO2 (pCO2) in German and Polish streams and examined differences between forested and agricultural catchments. They found that pCO2 was generally 2–3 times higher in agricultural streams compared to streams draining forested areas.

Methods

Results

Discussion

Conclusion