Abstract
Abstract. A large portion of terrestrially derived carbon outgasses as carbon dioxide (CO2) from streams and rivers to the atmosphere. Particularly, the amount of CO2 outgassing from small headwater streams is highly uncertain. Conservative estimates suggest that they contribute 36 % (i.e. 0.93 petagrams (Pg) C yr−1) of total CO2 outgassing from all fluvial ecosystems on the globe. In this study, stream pCO2, dissolved inorganic carbon (DIC), and δ13CDIC data were used to determine CO2 outgassing from an acidic headwater stream in the Uhlířská catchment (Czech Republic). This stream drains a catchment with silicate bedrock. The applied stable isotope model is based on the principle that the 13C ∕ 12C ratio of its sources and the intensity of CO2 outgassing control the isotope ratio of DIC in stream water. It avoids the use of the gas transfer velocity parameter (k), which is highly variable and mostly difficult to constrain. Model results indicate that CO2 outgassing contributed more than 80 % to the annual stream inorganic carbon loss in the Uhlířská catchment. This translated to a CO2 outgassing rate from the stream of 34.9 kg C m−2 yr−1 when normalised to the stream surface area. Large temporal variations with maximum values shortly before spring snowmelt and in summer emphasise the need for investigations at higher temporal resolution. We improved the model uncertainty by incorporating groundwater data to better constrain the isotope compositions of initial DIC. Due to the large global abundance of acidic, humic-rich headwaters, we underline the importance of this integral approach for global applications.
Highlights
Rivers and streams are the main carbon pathways from the continents to the oceans and constitute an important link in the global carbon cycle
The amount of CO2 outgassing from small headwater streams is highly uncertain
Stream pressure of CO2 (pCO2), dissolved inorganic carbon (DIC), and δ13CDIC data were used to determine CO2 outgassing from an acidic headwater stream in the Uhlírská catchment (Czech Republic)
Summary
Rivers and streams are the main carbon pathways from the continents to the oceans and constitute an important link in the global carbon cycle. In the process of transport, large amounts of carbon – mostly in the form of CO2 – outgas from the water surface to the atmosphere (Cole et al, 2007; Aufdenkampe et al, 2011; Regnier et al, 2013; Wehrli, 2013). This form of CO2 contributions to the atmosphere was estimated between 0.6 and 2.6 petagrams (Pg) of carbon per year (Raymond et al, 2013; Lauerwald et al, 2015; Sawakuchi et al, 2017; Marx et al, 2017a). Note that the upper value of the range still lacks a representative contribution from headwater streams (Marx et al, 2017a)
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