Suspended POM plays an important role in nutrient cycling in freshwater. However, information regarding its composition and dynamic interactions with the dissolved phase are still poorly defined. Here, we explore the chemical and microbial composition of suspended POM at contrasting sites in a lowland river (River Chew, UK). Composite samples were characterised using a selection of hyphenated mass spectrometry techniques to target different individual and compound classes, including building-block compounds (hydrolysable amino acids and neutral carbohydrates), semi- and non-polar compounds of natural and anthropogenic origin (e.g., n-alkanes, fatty acids, sterols, dicarboxylic acids and flame retardants), and macro-molecular material derived compounds (e.g., polysaccharides and lignin). Particle-attached microbial communities were characterised through next-generation amplicon sequencing. We also investigate the molecular-level mechanisms in which these particle-attached microorganisms assimilate low molecular weight DOM. Incubation experiments were carried out using isotopically labelled glutamate (C and N) over a 6-day period. Microbial assimilation was traced via compound-specific stable isotope analysis of proteinaceous amino acids using GC-C-IRMS. Our results demonstrate both spatial changes in the complex composition of suspended POM, and changes in the rates of assimilation of C and N from the organic substrate, suggesting a distinctive metabolism which is potentially related to the changes in composition as well as in the environmental conditions.

Primary Presenter: Leonardo Mena-Rivera, Universidad Nacional (lmena@una.ac.cr)

Authors:

Leonardo Mena-Rivera, School of Chemistry, Universidad Nacional, Campus Omar Dengo, Heredia 83-3000, Costa Rica  (lmena@una.ac.cr)

Charlotte Lloyd, School of Geographical Sciences, University of Bristol, University Road, Bristol BS8 1SS, UK  (charlotte.lloyd@bristol.ac.uk)

Tim Goodall, UK Centre for Ecology & Hydrology, Wallingford, Oxfordshire OX10 8BB, UK  (timgoo@ceh.ac.uk)

Daniel Read, UK Centre for Ecology & Hydrology, Wallingford, Oxfordshire OX10 8BB, UK  (daniel.read@ceh.ac.uk)

Penny Johnes, School of Geographical Sciences, University of Bristol, University Road, Bristol BS8 1SS, UK  (penny.johnes@bristol.ac.uk)

Richard Evershed, Organic Geochemistry Unit, School of Chemistry, University of Bristol, Cantock’s Close, Bristol BS8 1TS, UK  (R.P.Evershed@bristol.ac.uk)