title: Assessing the optical changes in dissolved organic matter in humic lakes by spectral slope distributions.
abstract: The impact of photodegradation and mixing processes on the optical properties of dissolved organic matter (DOM) was examined using a distribution of absorption spectral slopes and fluorescence measurements in two Argentine lakes. By examining the variability of the absorption spectral slopes throughout the ultraviolet and visible wavelengths, it was possible to determine which wavelength intervals were most sensitive to dominant loss processes. For DOM photodegradation, results show that increases in the absorption spectral slope between 265 and 305 nm were highly sensitive to increased exposure to solar ultraviolet radiation. A slightly larger wavelength range (265-340 nm) was found to be influenced when both mixing and photodegradation processes were considered, in terms DOM residence time, DOM absorption and UV diffuse attenuation coefficients. This same interval of spectral slopes (265-340 nm) was found to highly correlate with changes in fluorescence emission/excitation in wavelengths that are typically associated with terrestrial humic-like DOM. The identification of specific wavelength intervals, rather than the use of standard wavelength intervals or ratios, improved our ability to identify the dominant dissolved organic matter (humic-like) and major loss mechanisms (photodegradation) in these lakes.
authors.affiliation: Dipartimento Farmaco Chimico Tecnologico, CSGI, University of Siena, Siena, Italy.
authors.forename: Luisa
authors.initials: L
authors.lastname: Galgani
authors.forename: Antonio
authors.initials: A
authors.lastname: Tognazzi
authors.forename: Claudio
authors.initials: C
authors.lastname: Rossi
authors.forename: Maso
authors.initials: M
authors.lastname: Ricci
authors.forename: J Angel
authors.initials: JA
authors.lastname: Galvez
authors.forename: Arduino M
authors.initials: AM
authors.lastname: Dattilo
authors.forename: Andres
authors.initials: A
authors.lastname: Cozar
authors.forename: Luca
authors.initials: L
authors.lastname: Bracchini
authors.forename: Steven A
authors.initials: SA
authors.lastname: Loiselle
mesh_terms: D000042:Absorption; D004784:Environmental Monitoring; D005618:Fresh Water / Q000737:chemistry*; D006812:Humic Substances / Q000032:analysis*; D009930:Organic Chemicals / Q000737:chemistry*; D010782:Photolysis; D013050:Spectrometry, Fluorescence; D014466:Ultraviolet Rays
chemical_list: D006812:Humic Substances; D009930:Organic Chemicals