Streams and rivers are globally relevant emitters of greenhouse gases (GHG). Emission estimates are typically based on field data with limited temporal and spatial resolution. However, GHG emissions may differ substantially between different habitat types, especially in larger rivers. We measured GHG emissions in different habitat types at river Elbe in Germany, to assess the effect of intra-system variability as well as diurnal variability on GHG emission upscaling. CH₄ emissions near the shore and in groyne fields were higher than in the middle of the stream due to CH₄CH₄ production in the sediments. In contrast, CO₂ emissions were highest in the middle of the stream, where gas transfer coefficients were higher. Thus, both spatial variability of dissolved gas concentrations and gas transfer velocity contributed to spatial variability. Day-night variations in aquatic CO₂ emissions were larger than the differences measured between sites, while spatial differences compared to temporal variability predominated for CH₄ emissions. We observed considerable spatiotemporal variability of GHG emissions from dry sites and diurnal fluctuations of CO₂ emissions were larger at dry than aquatic sites. CH₄ flux measurements at dry fallen sediments revealed a heterogeneous pattern of sources and sinks depending on different controlling factors. Thus, both small-scale spatial and temporal patterns were different for the two considered gases. Our results imply that in large rivers, CH₄CH₄ and CO₂ call for different measuring strategies in order to obtain optimal whole-system emission estimates.

Primary Presenter: Matthias Koschorreck, Helmholtz Centre For Environmental Research - UFZ (matthias.koschorreck@ufz.de)

Authors:

Claudia Schütze, Helmholtz Centre for Environmental Research – UFZ  (claudia.schuetze@ufz.de)

Uta Ködel, Helmholtz Centre for Environmental Research – UFZ  (uta.koedel@ufz.de)

Norbert Kamjunke, Helmholtz Centre for Environmental Research – UFZ  (norbert.kamjunke@ufz.de)

Michael Rode, Helmholtz Centre for Environmental Research – UFZ  (michael.rode@ufz.de)

Ingeborg Bussmann, Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research  (Ingeborg.Bussmann@awi.de)