Characterising natural organic matter in runoff from upland peatlands

UoM administered thesis: Phd

  • Authors:
  • Felipe Rojas Parra

Abstract

Natural organic matter (NOM) is a critical component in aquatic environments as it has strong controls on water chemistry. Due to its heterogeneity it is complicated to understand its characteristics and evolution in the environment. Climatic warming has exacerbated the release of NOM to the environment posing challenges to water treatment, mobility of nutrients and the global carbon cycle. Peatlands are a major source of NOM, are important water collection spots and are undergoing rapid environmental change. This study, therefore aimed to investigate NOM in quantity and quality from peatland runoff and understand how it affects water quality. The work demonstrated that peatland degradation results in higher carbon fluxes, highlighting the importance of the dissolved fraction of NOM by using high resolution separation (tangential flow ultrafiltration –TFU). Furthermore, the importance of spatial and temporal factors is highlighted in this work. The interpolation and rating relationship methods resulted in relatively high variability. Therefore, this study draws special attention to high frequency sampling when calculating fluxes as it is essential to capture the most important lapses in the hydrological regime – short frequency high intensity discharge events. The characterisation of a complex material such as NOM is a challenge for research. This study analysed NOM size fractions from different sources present in peatlands (aquagenic vs pedogenic) with techniques ranging in complexity – Ultraviolet Visible (UV VIS), Fourier transfer infrared (FTIR), Fluorescence excitation emission (F-EEM) and Gas chromatography mass spectrometry (GCMS) – in order to discriminate composition and relate it to function in the environment. The results showed the resolution of most techniques was not high enough to do differentiate between samples except for the GCMS. This allowed selection of carbon for interaction experiments. The final sections refer to relevant NOM (dissolved fraction) for studies aiming to understand its role as a control of water quality. Iron (Fe) is an essential nutrient in biochemical processes in natural waters. Its behaviour is dependent on the presence of oxygen and NOM in the aquatic environment. The interaction of the Fe-NOM complex was simulated in this investigation to understand its behaviour in the hydrological path it undergoes – anoxic to oxic in the presence of NOM. The results of this study showed the influence of NOM and pH on the lability and speciation of Fe as it surfaces into the stream. Its association with NOM in the subsurface, although relatively low, affects its lability, specific surface area and therefore its evolution, having important implications in nutrient availability. NOM plays a major role in water disinfection as it produces disinfection by products (DBPs) when chemically treated. These compounds are an ongoing research topic for the complexity of NOM and techniques available for detection. This study used two techniques novel in DBP detection – thermal desorption GCMS and a photoionic detector (PID). The results show both techniques are able to measure DPBs in very low concentrations (ppb). The compound analysis by TD GCMS saw differences in DBP production as NOM size changed. The PID allowed for a bulk quantification of DBPs, creating a reliable, fast and cheap option for detection.

Details

Original languageEnglish
Awarding Institution
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Award date1 Aug 2020