A methodology was developed to analyse chemical and biochemical
characteristics of DOM (Dissolved Organic Matter) on filtered natural water
samples. The analysis was based upon simple assays that were matched to
the reaction mechanisms occurring during humification. The chemical
characteristics of DOM and the surrounding water matrix, pH, conductivity,
temperature, TOC (Total Organic Carbon), complexing strength towards
phenol, fluorescence, colour, UV absorbency at 200 and 240 nm, total, polyand
monophenolics, were condensed into a graphical 'fingerprint'. Assays to
investigate the biochemical activity of DOM towards porcine pancreatic
lipase activity and towards the precipitation of BSA (Bovine Serum Albumin)
were developed.
The seasonal variation of DOM in six freshwater sites-, three rivers and three
wetlands, was investigated. Application of the 'fingerprinting' methodology
showed a small effect of season and a large effect of site, substantiating the
allochthonous origin of DOM. The application of multivariate statistics to the
results, using principle component analysis, separated the assays into two
groups relating to either chemical characteristics of DOM (polyphenolics,
total phenolics, TOC, complexing strength towards phenol, colour and UV
absorbance at 240 nm) or to the surrounding water matrix. The biochemical
activity of DOM originated either from a physicochemical phenomenon,
complexation, or the interaction of phenolics with protein. Humic and fulvic
acid samples submitted to the same analysis showed similar fingerprints and
responses in the protein precipitation assay, but inhibited lipase activity by
90 % compared to a maximum value of 30 % inhibition for the natural water
samples at a similar TOC level.
A controlled decomposition study of cellulose, chitin and lignin in nutrient
solution supplied with a broad-spectrum inoculant was performed. Two
different treatments 'light' and 'dark' were given for each unit. The 'light'
treatment induced algal growth and generated an additional microbially labile
carbon source during the decomposition. The chemical characteristics of the
DOM analysed after 15 months of degradation showed the 'fingerprint' to be
dependent upon the chemical characteristics of the substrate supplied. The
contribution of lignin to humification was substantiated by a high phenolic
content of the lignin-containing units. Chitin, containing intramolecular
nitrogen, was found to degrade rapidly, showing high values for
fluorescence, and UV absorption at 200 nm after 15 months. The
biochemical activity of the resulting DOM towards lipase activity was
inhibitory for lignin 'dark', lignin & chitin 'light' and 'dark' and stimulating for
chitin 'light'. The provision of cellulose & lignin as substrate had a neutral
effect upon lipase activity.
The conclusions from the work presented in this thesis substantiate the
importance of the chemical characteristics of the starting material for
humification. lntramolecular nitrogen allowed for rapid degradation.
Complexation and polymerisation with plant defence agents induce a
random structure slowing enzymatic breakdown and thus leading to
recalcitrance.