title: Spatial and seasonal changes in optical properties of autochthonous and allochthonous chromophoric dissolved organic matter in a stratified mountain lake.
abstract: In this study, we present results on seasonal and spatial changes in CDOM absorption and fluorescence (fCDOM) in a deep mountain lake (Salto Lake, Italy). A novel approach was used to describe the shape of CDOM absorption between 250-700 nm (distribution of the spectral slope, S(lambda)) and a new fluorescence ratio is used to distinguish between humic and amino acid-like components. Solar ultraviolet irradiance, dissolved organic carbon (DOC), DOM fluorescence and absorption measurements were analysed and compared to other physicochemical parameters. We show that in the UV-exposed mixed layer: (i) fluorescence by autochthonous amino acid-like CDOM, (ii) values of S(lambda) across UV-C and UV-B wavebands increased during the summer months, whereas (i) average molar absorption coefficient and (ii) fluorescence by allochthonous humic CDOM decreased. In the unexposed deep layer of the water column (and in the entire water column in winter), humic-like CDOM presented high values of molar absorption coefficients and low values of S(lambda). UV attenuation coefficients correlated with both chlorophyll a concentrations and CDOM absorption. In agreement with changes in CDOM, minimal values in UV attenuation were found in summer. The S(lambda) curve was used as a signature of the mixture between photobleached and algal-derived CDOM with respect to the unexposed chromophoric dissolved compounds in this thermal stratified lake. Furthermore, S(lambda) curves were useful to distinguish between low and high molecular weight CDOM.
authors.affiliation: Biosystems Chemistry Group, Dipartimento Farmaco Chimico Tecnologico, Centro Sistemi Complessi and Consorzio Interuniversitario per lo studio dei Sistemi a Grande Interfase, CSGI, University of Siena, via Aldo Moro 1, 53100, Siena, Italy. bracchini@unisi.it
authors.forename: Luca
authors.initials: L
authors.lastname: Bracchini
authors.forename: Arduino Massimo
authors.initials: AM
authors.lastname: Dattilo
authors.forename: Vincent
authors.initials: V
authors.lastname: Hull
authors.forename: Steven Arthur
authors.initials: SA
authors.lastname: Loiselle
authors.forename: Luciano
authors.initials: L
authors.lastname: Nannicini
authors.forename: Maria Pia
authors.initials: MP
authors.lastname: Picchi
authors.forename: Maso
authors.initials: M
authors.lastname: Ricci
authors.forename: Chiara
authors.initials: C
authors.lastname: Santinelli
authors.forename: Alfredo
authors.initials: A
authors.lastname: Seritti
authors.forename: Antonio
authors.initials: A
authors.lastname: Tognazzi
authors.forename: Claudio
authors.initials: C
authors.lastname: Rossi
mesh_terms: D000596:Amino Acids / Q000032:analysis*; D004784:Environmental Monitoring / Q000379:methods*; D005618:Fresh Water / Q000032:analysis*; D006812:Humic Substances / Q000032:analysis*; D012621:Seasons; D013050:Spectrometry, Fluorescence / Q000379:methods; D013053:Spectrophotometry / Q000379:methods
chemical_list: D000596:Amino Acids; D006812:Humic Substances