Rivers play a substantial role in the global carbon cycle through their high rates of carbon respiration and sequestration. Dissolved organic carbon (DOC) in such ecosystems is an integral part in biogeochemical cycling. Microorganisms are the key organism group responsible for DOC turnover providing a crucial ecosystem function. However, rivers are impacted in multiple ways by anthropogenic pollution and climate change whereas salinization and temperature rise is a global trend. Hence, the goal of this research is to investigate the effects of salinity and temperature on microbial communities and their ecosystem function to degrade DOC in river water and sediments. The influence of these stressors is studied on an urban river in laboratory microcosms and in outdoor mesocosms. The degradation rates of DOC to CO2 were quantified via a novel Reverse Stable Isotope Labelling method measuring isotope ratios in CO₂ with an isotope analyzer. Our results showed that raising the salinity by 250 mgCl/L and temperature by 3 °C significantly increased degradation rates in river sediments from 0.34 to 1.34 mgC/L/d after stress release, while having no significant effect during stress application. In the water column an increase of salinity by 1.5 gCl/L and temperature by 5 °C tripled the degradation rates in the recovery phase where the stress was released. Carbon degradation rates in water were 30 times lower than in sediments presumably due to lower organic matter quantity and the 10-fold lower organism density as revealed by flow cytometric analysis.

Primary Presenter: Daria Baikova, University of Duisburg-Essen (baikovadaria@gmail.com)

Authors:

Daria Baikova, University of Duisburg-Essen  (baikovadaria@gmail.com)

Rainer Meckenstock, University Duisburg-Essen  (rainer.meckenstock@uni-due.de)

Verena Brauer, University Duisburg-Essen  (verena.brauer@uni-due.de)

Iris Madge Pimentel, University Duisburg-Essen  (iris.madge-pimentel@uni-due.de)

Guido Sieber, University Duisburg-Essen  (guido.sieber@uni-due.de)