title: Effects of filtration and pH perturbation on freshwater organic matter fluorescence.
abstract: Fluorescence of organic matter from six contrasting freshwaters was analysed after filtration (1.2 microm and 0.2 microm filter sizes) and pH perturbation (+/-2 pH units from ambient conditions). Two fluorophores were compared in detail: tryptophan-like fluorescence, whose filtration and pH characteristics are relatively poorly understood, and humic-like fluorescence, which is better characterised. Although there was some variability in both fluorophores, the tryptophan-like fluorescence showed the most significant decrease in fluorescence intensity between raw and 1.2 microm filter samples, and a much smaller decrease between 1.2 and 0.2 microm, demonstrating a significant source associated with particulate material as well as a significant <0.2 microm fraction. In contrast, humic-like fluorescence shows little change with filtration, suggesting that the majority of this fluorescence is associated with truly dissolved material. The pH perturbation experiments demonstrate that tryptophan-like fluorescence is less impacted by pH than with filter fraction. For humic-like fluorescence, pH effects are weak and are not as consistent as those reported in the literature for extracted humic substances. pH perturbation of the freshwaters shows a wide range of sample specific pH responses, significantly more variable than that observed in experiments using extracted humic substances and tryptophan standards, demonstrating the natural variability of freshwater dissolved organic matter.
authors.affiliation: School of Geography, Earth and Environmental Sciences, The University of Birmingham, Birmingham, B15 2TT, United Kingdom. a.baker.2@bham.ac.uk
authors.forename: Andy
authors.initials: A
authors.lastname: Baker
authors.forename: Sarah
authors.initials: S
authors.lastname: Elliott
authors.forename: Jamie R
authors.initials: JR
authors.lastname: Lead
mesh_terms: D005374:Filtration; D005453:Fluorescence; D005618:Fresh Water / Q000032:analysis*; D006812:Humic Substances / Q000032:analysis*; D006863:Hydrogen-Ion Concentration
chemical_list: D006812:Humic Substances