Recent research indicates that greenhouse gas (GHG) emissionsfrom dry aquatic sediments are a relevant process in the freshwater carbon cycle. However, fluxes are difficult to measure because of the oftenrocky substrate and the dynamic nature of the habitat. Here we tested theperformance of different materials to seal a closed chamber to stony groundboth in laboratory and field experiments. Using on-site materialconsistently resulted in elevated fluxes. The artefact was caused both byoutgassing of the material and production of gas. The magnitude of theartefact was site dependent – the measured CO flux increasedbetween 10 and 208 %. Errors due to incomplete sealing proved to be moresevere 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 ispossible to get reliable gas fluxes from hard-substrate sites without usinga permanent collar. Our test experiments confirmed that CO fluxes fromdry aquatic sediments are similar to CO fluxes from terrestrial soils.
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