Carbon dynamics during flood events in a lowland river: the importance of anabranches

Abstract

Summary 1. Our objective was to measure the influence of hydrological connection with anabranch channels on the availability of major carbon sources in a lowland, anabranching floodplain river landscape. 2. Results show that anabranch channels are sinks for large quantities of sediment-associated carbon, facilitated by high rates of sediment deposition, and are sources for dissolved organic carbon (DOC), partly via inundation-stimulated release from surface sediments and leaf litter. This dual role influences ecological pattern and process at multiple spatial and temporal scales, including within-flow pulse phase differences in carbon availability and anticlockwise hysteresis in the DOC–discharge relationship. 3. Hydrological connection with anabranch channels in riverine landscapes appears to increase the retention, concentration and diversity of carbon sources over both space and time, changing the timing of carbon transport downstream and shortening the carbon spiral at a landscape scale. 4. In contrast to floodplains, anabranches exchange carbon sources with the river ecosystem during flow pulses below bankfull. They are relatively easy to target for management because they have definable commence-to-flow levels and require relatively small amounts of water for connection. However, the type and amount of carbon exchanged between the anabranches and the river channel will vary depending on the frequency, magnitude and duration of flow pulses. 5. Managed, periodic connection of anabranch channels via environmental flows should be considered as an option between large flood events.