Project A02

Effect of multiple stressors on the microbial ecosystem functions DOC degradation and biomass recycling in water and sediment

Hypothesis 1 Hypothesis 1 Hypothesis 1 ARC 2 AquaFlow ExStream Field studies Bacteria DOC degradation Nutrient cycling

Project leader

Prof. Dr. Rainer U. Meckenstock & Dr. Verena Brauer

Project Summary

Our research goals are to elucidate the effects of multiple stressors on microbial DOC degradation and biomass recycling, which play crucial roles for river ecosystem functioning. As a first step, we want to monitor the natural dynamics of these two processes in two lotic systems, the rivers Boye (Emscher catchment) and Bieber (Kinzig catchment), for a period of 2 years. We will survey the composition of the bacterial communities over time and determine the relative contribution of protists and of different bacteria to biomass recycling.

Alongside we will incubate samples with DOC, nitrogen and phosphorus to investigate factors that naturally limit DOC degradation in the two rivers. As a second step, we will study acute and long-term effects of multiple stressors on microbial DOC degradation and biomass recycling, whereby we focus on the effects of salt and temperature stress, both individually and in combination. Effects of salt and temperature stress will be studied at microcosm and mesocosm scales using the AquaFlow and ExStream installations. DOC degradation will be quantified with our recently developed Reverse Stable Isotope Labelling (RIL). This novel method allows for detecting minute amounts of DOC degradation as CO2 production down to 10 μg/l.

Biomass recycling will be investigated in microcosms by adding 13C-labelled living E. coli biomass or necromass to environmental samples and measuring degradation activity as 13CO2 evolution. Specific inhibitors will also allow us to distinguish the relative importance of bacteria and protists and to identify specific necromass-degrading bacteria via stable isotope probing (SIP). We will apply flow cytometry for absolute quantification of different microorganisms and 16S rRNA gene amplicon sequencing for determining the composition of bacterial communities. The project will provide novel insights into the effects of multiple stressors on the microbial turnover of DOC and nutrients in lotic ecosystems.