We hypothesize that an increase of the surface water level induces an increased relevance of algal activity in surface biofilms in WWTP-receiving streams. In this sense, the low O2 levels observed in the hyporheic zone (i.e., stream bed sediments) under dominance of sub-surface flow paths will increase due to diffusion of O2 produced by algae. Subsequently, it is expected that the relative abundance of nitrifiers and denitrifiers will be changed in the hyporheic zone and probably denitrification will be reduced, which will be reflected by the change in DIN (dissolved inorganic nitrogen) concentrations in this zone.
To answer the question, the water level will be manipulated in channels with and without helophytes (flume n=6) so the channels are exposed to a) only sub-surface water flow, b) to surface and sub-surface water flow, and c) back to only sub-surface water flow. Water samples for chemical characterization as well as sediment samples will be taken along the channels before, during and after surface flow conditions.
Leading scientist: Tim Vaessen, PhD researcher at CEAB-CSIC.