Investigating the in-situ production and processing of aquatic fluorescent organic matter by freshwater bacteria

Perrin, Eva

Abstract

Dissolved organic matter (DOM) is one of the largest reservoirs of carbon on the planet, and is ubiquitous throughout aquatic systems. It plays an essential role in global biogeochemical cycles and the transport and storage of carbon through the hydrological continuum. Intensifying anthropogenic pressures such as sewage discharge and agricultural runoff and impacting on microbial activity in freshwaters. As such, the interface between microbial activity and the processing of essential nutrients such as DOM is becoming increasingly complex, with potentially profound implications on the fate and transport of aquatic DOM. There is a need to advance our understanding of the mechanisms that underpin aquatic DOM processing my microorganisms, and the ways in which they are being impacted by anthropogenic pressures, alongside developing and implementing technological solutions to monitor this effectively through time and space.

Aquatic DOM is often ‘fingerprinted’ using the optical properties of its fluorescing component, aquatic fluorescent dissolved organic matter (AFOM), which is conventionally divided into ‘autochthonous’ (in-situ produced, labile, protein-like) and ‘allochthonous’ (terrestrially-derived, recalcitrant, humic-like) fractions. Peak T has conventionally been used as a biological marker for bacterial enumeration or contamination in freshwaters. To further explore the origin of bacterial-derived AFOM in freshwaters, this research utilizes findings from experimental studies enabling controlled observations of underpinning DOM processing dynamics. Through the development of a novel laboratory-based simulated freshwater model, this study provides evidence of the in-situ production of humic-like, complex AFOM from a simple bioavailable carbon substrate. The model laboratory system provides evidence that the effect of nutrients on freshwater bacterial processing can influence type of AFOM produced by bacteria. Furthermore, this study evidences a direct link between AFOM production and biological activity, underscoring the use of fluorescence as a biological marker for an upregulated metabolic state in freshwater bacteria. This research challenges current assumptions regarding the contribution of bacteria to the freshwater OM pool, and suggests that disruption of aquatic systems may be altering the balance of labile vs recalcitrant OM in aquatic systems.

In addition, the implementation of a novel fluorescence-based sensor is investigated on the River Thames and Taplow, Maidenhead, UK. A long-term (16 month) monitoring programme was undertaken, with fluorescence monitored at hourly intervals alongside conventional water quality parameters. This has highlighted the use of fluorescence as an efficient marker for in-stream biological activity, showing that this multi-channel fluorescence-based sensor can differentiate between algal and bacterial activity in the Tryptophan fluorescence region.

• Thesis Type: Thesis
• Deposit Date: Dec 31, 2022
• Publicly Available Date: Apr 12, 2024
• Public URL: https://uwe-repository.worktribe.com/output/10277981
• Award Date: Apr 12, 2024