Presented by: 
Nina Welti from the National Centre for Groundwater Research and Training at the University of Queensland
Thu 22 Mar, 3:00 pm - 4:00 pm
Room 442, Priestly Building Number 67

Nitrogen cycling in restored and disturbed riverine floodplain
N.Welti, E. Bondar-Kunze, G. Singer, M. Tritthart, G. Pinay, T. Hein

Increasing pressure on rivers results in the decoupling of the naturally occurring floodplains, resulting in a loss of the ecosystem services provided by these transition zones. Efforts to restore floodplains by reconnecting them to their source rivers have primarily focused on re-establishing the unique habitats found in floodplains. However, the resulting biogeochemical changes are not well documented. The purpose of this study was to understand the effects of this large-scale change to the biogeochemical cycling of two floodplain systems in the Danube River Basin in Austria. In this talk, I will present a recent study which focuses on floodplain reconnection and disconnection to understand the effects on potential biogeochemical cycling.

We measured potential microbial respiration (SIR) and denitrification (DEA) and compared a degraded floodplain section of the Danube River with a reconnected and restored floodplain in the same river section. Re-establishing surface water connection altered the controls on sediment microbial respiration and denitrification ultimately impacting potential microbial activities. Meta-variables were created to characterize the effects of hydrology, morphology, and the available carbon and nutrient pools on potential microbial processing. Mantel statistics and path analysis were performed and demonstrate a hierarchy where the effects of hydrology on the available substrates and microbial processing are mediated by the morphology of the floodplain. In addition, these processes are highest in the least connected sites. Surface water connection, mediated by morphology regulates the potential denitrification rate and the ratio of N2O: N2emissions, demonstrating the effects of restoration in floodplain systems. A hydromorphological model assessed areas of potential high rates and nitrous oxide release in the study floodplains under different river discharge conditions. Using the produced modelling tool, patterns of high activity in areas which were frequently inundated by the Danube River were identified.