Reservoirs act as a barrier to sediment flow along the water-ocean continuum and host processes of organic matter (OM) sedimentation and mineralization through which nutrients are retained from downstream water bodies, leading to decreased river functioning. Moreover, OM mineralization in sediment is enhanced during reservoir operation by sediment exposure to oxygen or by littoral vegetation influencing reservoirs GHG footprint. Hence, dam removals are becoming more common once they are no longer functional, but the fate of the accumulated sediment is still not well understood. Here we investigate the effect of changes in sediment water content on GHG emission, nutrient leaking, and macrophytes-sediment interaction by means of sediment mesocosms collected from a reservoir in southern Sweden.  Mesocosms were divided into treatments simulating pre and after dam removal conditions with and without vegetation. We hypothesize that the presence of macrophytes increases the degradation of sediment organic carbon to carbon dioxide (CO2) under drying condition, while under water-logged condition they facilitate methane release. We further hypothesize that macrophytes will reduce nutrients leakage to the water. Preliminary results show that vegetated sediments act as CO2 sinks while methane emission shows dependence on plant species but both independently of hydrological conditions. Macrophytes also hamper nutrient release in sediment pore water. Results from this experiment is expected to inform strategies for minimizing environmental impacts from sediments at dam removal.

Primary Presenter: Anna Bottone, Uppsala University (anna.bottone@ebc.uu.se)

Authors:

Anna Bottone, Uppsala University  (anna.bottone@ebc.uu.se)

Charlotte Grasset, Uppsala University  (charlotte.grasset@ebc.uu.se)

Gustaf Granath, Uppsala University  (gustaf.granath@ebc.uu.se)

Sebastian Sobek, Uppsala University  (sebastian.sobek@ebc.uu.se)