Freshwater DOM quantity and quality from a two-component model of UV absorbance.
We present a model that considers UV-absorbing dissolved organic matter (DOM) to consist of two components (A and B), each with a distinct and constant spectrum. Component A absorbs UV light strongly, and is therefore presumed to possess aromatic chromophores and hydrophobic character, whereas B absorbs weakly and can be assumed hydrophilic. We parameterised the model with dissolved organic carbon concentrations [DOC] and corresponding UV spectra for c. 1700 filtered surface water samples from North America and the United Kingdom, by optimising extinction coefficients for A and B, together with a small constant concentration of non-absorbing DOM (0.80 mg DOCL⁻¹). Good unbiased predictions of [DOC] from absorbance data at 270 and 350 nm were obtained (r² = 0.98), the sum of squared residuals in [DOC] being reduced by 66% compared to a regression model fitted to absorbance at 270 nm alone. The parameterised model can use measured optical absorbance values at any pair of suitable wavelengths to calculate both [DOC] and the relative amounts of A and B in a water sample, i.e. measures of quantity and quality. Blind prediction of [DOC] was satisfactory for 9 of 11 independent data sets (181 of 213 individual samples).
Centre for Ecology and Hydrology, Lancaster Environment Centre, Bailrigg, Lancaster LA1 4AP, United Kingdom.
Heather T
HT
Carter
Edward
E
Tipping
Jean-Francois
JF
Koprivnjak
Matthew P
MP
Miller
Brenda
B
Cookson
John
J
Hamilton-Taylor
D000042:Absorption / Q000528:radiation effects; D002244:Carbon / Q000032:analysis; D005618:Fresh Water / Q000737:chemistry*; D008956:Models, Chemical; D009930:Organic Chemicals / Q000032:analysis* / Q000592:standards*; D012995:Solubility / Q000528:radiation effects; D013056:Spectrophotometry, Ultraviolet; D014466:Ultraviolet Rays
D009930:Organic Chemicals; D002244:Carbon