Sediment respiration in a complex river–floodplain ecosystem: The role of habitat heterogeneity and inundation dynamics

M. Doering, U. Uehlinger, K. Tockner, and T. Ackermann.Department of Limnology, EAWAG/ETH, Switzerland

We studied spatial heterogeneity of respiration in aquatic and terrestrial habitats in a large braided floodplain river (Tagliamento River, NE Italy). In terrestrial habitats, CO₂ production was measured with an IRGA. In aquatic habitats, sediments were enclosed in chambers, and respiration was measured as O₂ consumption. In addition, we studied the influence of inundation on sediment respiration. To simulate inundation we submersed terrestrial sediments in artificial river water and monitored O₂ consumption over six days at three different temperatures (4, 12 and 20 °C). Average daily respiration rates (normalized at 15°C) ranged from 0.3 g C m^-2 d^-1 in exposed gravel sediments to 5.6 g C m^-2 d^-1 in riparian forest soils. In parafluvial ponds, respiration rates averaged 0.9 g C m^-2 d^-1 and in river channels 1.6 g C m^-2d ^-1. In all habitats respiration rates were highly temperature dependent, except in exposed gravel. Inundation led to a decline in respiration of 64 to 90% within 6 hours, except for gravel sediments where respiration increased by 40 to 60%. Our study demonstrates a high spatio–temporal heterogeneity of sediment respiration, mainly as a consequence of habitat heterogeneity and inundation dynamics.