Is photodegradation the critical pathway in the transformation of DOM in aquatic systems during autumn and winter

  • Alun Owen

Student thesis: Master's ThesisMaster of Science by Research (MScR)


Dissolved Organic Matter (DOM) is ubiquitous to almost every aquatic system on earth, it affects nutrient loadings, metals concentrations and can impact upon human health. The last few decades have provided a vast insight into the transformation of DOM via microbial organisms but less so has been done on how the sun can affect DOM transformations (photodegradation).
The impact that photodegradation can have on aquatic DOM in the summer months has been extensively studied but DOM transformations in autumn and winter are currently poorly understood. With the increasing uncertainty from climate change there is a pressing need to better understand how photodegradation is impacting sites of different DOM character.
In order to bridge this research gap 6 sites were identified of varying land use and DOM character in Conwy and Hampshire Avon catchments. Samples taken at each site were divided between unfiltered samples and samples that had been filtered through a 0.1 µm cellulose nitrate filtered to remove any biota. This was to compare the effects of photodegradation alone vs the effect of photodegradation and the breakdown via biota on the transformation of DOM. The samples were incubated in autumn and winter at the same temperature and solar intensity of the month they were sampled in order to compare the transformations observed. Each day macronutrients, UV and fluorescence measurements were taken to monitor the change over 1 week.
The data analysis showed that DOM varied in concentration and composition between seasons and that photodegradation was still occurring even in winter. The data emphasised that neither photodegradation nor biodegradation were mutually exclusive and that more work needs to be done to identify the compound specific DOM transformations in autumn and winter.
Date of Award19 Mar 2019
Original languageEnglish
Awarding Institution
  • The University of Bristol
SupervisorPenny J Johnes (Supervisor)

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