Abstract
Abstract. Recent research indicates that greenhouse gas (GHG) emissions from dry aquatic sediments are a relevant process in the freshwater carbon cycle. However, fluxes are difficult to measure because of the often rocky substrate and the dynamic nature of the habitat. Here we tested the performance of different materials to seal a closed chamber to stony ground both in laboratory and field experiments. Using on-site material consistently resulted in elevated fluxes. The artefact was caused both by outgassing of the material and production of gas. The magnitude of the artefact was site dependent – the measured CO2 flux increased between 10 and 208 %. Errors due to incomplete sealing proved to be more severe than errors due to non-inert sealing material.Pottery clay as sealing material provided a tight seal between the chamber and the ground and no production of gases was detected. With this approach it is possible to get reliable gas fluxes from hard-substrate sites without using a permanent collar. Our test experiments confirmed that CO2 fluxes from dry aquatic sediments are similar to CO2 fluxes from terrestrial soils.
Highlights
CO2 emissions from dry freshwater systems represent a largely overlooked process in the global carbon cycle
The ability of different sealing materials to provide a tight seal was tested with the closed chamber on a paving slab in the laboratory
When measuring with closed chambers on rocky ground the most important concern is to get a proper seal between chamber and atmosphere
Summary
CO2 emissions from dry freshwater systems represent a largely overlooked process in the global carbon cycle. Recent research indicates that drying and rewetting of freshwater sediments creates hotspots of carbon mineralization and CO2 emissions, which are probably relevant on a global scale (Gomez-Gener et al, 2015; Reverey et al, 2016; Von Schiller et al, 2014). The closed-chamber approach is the most widespread method to measure gas fluxes from terrestrial habitats on a small scale (Livingston and Hutchinson, 1995). Pushing the chamber into the soil minimizes lateral diffusion through the soil under the chamber (Hutchinson et al, 2000) This approach has been successfully used to quantify greenhouse gas (GHG) fluxes from muddy dry aquatic sediments (Jin et al, 2016; Koschorreck, 2000). Turbulence created by a permanent installation might erode the sediment
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