Freshwater DOM quantity and quality from a two-component model of UV absorbance |
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Authors: | Carter Heather T Tipping Edward Koprivnjak Jean-Francois Miller Matthew P Cookson Brenda Hamilton-Taylor John |
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Affiliation: | a Centre for Ecology and Hydrology, Lancaster Environment Centre, Bailrigg, Lancaster LA1 4AP, United Kingdom b Environmental and Resource Studies Program, Water Quality Centre, Trent University, Peterborough, Ontario K9J 7B8, Canada c U.S. Geological Survey Water Science Center, 121 West 200 South Moab, UT 84532, USA d Lancaster Environment Centre, Lancaster University, Lancaster LA1 4YQ, United Kingdom |
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Abstract: | 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 DOC L−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). |
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Keywords: | Dissolved organic carbon Dissolved organic matter Model UV absorbance |
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