Streams and rivers are characterized by a high variability of microhabitats colonized by bacterial communities (i.e., biofilms) which perform a variety of biogeochemical processes associated to the nitrogen cycle. Denitrification is the biogeochemical pathway by which specialized bacteria oxidize nitrate to N2 (gas) to generate energy for grow. Denitrification is a key process to understanding the self-purification capacity of streams and rivers, one of the ecosystem services that these systems provide. High nitrate concentration and presence of anoxic zones in sediments of WWTP-receiving streams and rivers should favor denitrification and thus ameliorate water quality. However, previous studies indicate that denitrification is not the dominant biogeochemical pathway in these systems. Denitrifying microorganisms are heterotrophic, thus they require external organic C sources. Therefore, a low quality C coming from the WWTP effluent may limit denitrification in streams and rivers.
To address this question, we will use a waste product in the elaboration of beer, rich in labile carbon compounds (i.e., mono- and disaccharide) to study whether it can promote denitrification. Furthermore, it is well known that vascular plants (i.e., helophytes) can modify the physicochemical conditions of the ambient in which they develop, thus they can affect the activity of biofilms. Therefore, we will perform additions of the waste product in several channels with 3 different species of helophytes: Iris pseudachorus, Phragmites australis and Scirpus lacustris. In addtion, we will also consider 3 unvegetated channels, which serve as control.
Leading scientist: Miquel Ribot, postdoctoral researcher CEAB-CSIC.