Organic matter (OM) is ubiquitous to all aquatic environments and plays an essential role in global biogeochemical cycles and transportation of organic carbon throughout the hydrological continuum. Excitation-emission matrix (EEM) fluorescence spectroscopy has been used to characterise naturally occurring aquatic fluorescent OM (AFOM), classifying this AFOM as either humic-like, derived from terrestrial sources, or protein-like, of microbial origin. The research here explores in situ bacterial-OM interactions and AFOM evolution over time by employing fluorescence techniques.
Protein-like AFOM, with a particular focus on Peak T, has been linked to bacterial activity. Previous research has related this AFOM to other water quality parameters, in addition to attempting to use it as a bacterial enumeration proxy. The work in this study provides extensive evidence for the bacterial production of Peak T, confirming the suggestions within the literature. However, the universal presence of Peak T within the bacterial cultures studied here, permits the conclusion that Peak T fluorescence cannot be used for bacterial enumeration but can provide information regarding microbial community presence and activity. In addition to this, the application of in situ Peak T fluorescence sensing for monitoring microbial activity in freshwater systems is explored. The development of a new generation multichannel fluorimeter is detailed, informed by the research undertaken within this thesis.
This research has challenged the current understanding of the role of bacteria in AFOM production and processing, highlighting the ability of bacteria to engineer both protein- and humic-like AFOM in situ. Using microbiological methods alongside fluorescence measurements, over a variety of temporal scales, has exposed the fast-acting dynamics of this AFOM production by metabolically active bacteria. The variation in AFOM production by different bacterial species has also been demonstrated here, determining fluorescence as a potential measurement for monitoring the presence of specific species using fluorescence peaks as biomarkers. This thesis has highlighted the potential application of in situ fluorimeters to provide essential biological information regarding water quality, although further work is required to validate this novel water quality parameter within the field.