A model approach to assess the long-term trends of indirect photochemistry in lake water. The case of Lake Maggiore (NW Italy). Sci Total Environ

Dipartimento di Chimica Analitica, Università di Torino, Via P. Giuria 5, 10125 Torino, Italy.
Science of The Total Environment (Impact Factor: 4.1). 06/2011; 409(18):3463-71. DOI: 10.1016/j.scitotenv.2011.05.028
Source: PubMed


A model-based approach is here developed and applied to predict the long-term trends of indirect photochemical processes in the surface layer (5m water depth) of Lake Maggiore, NW Italy. For this lake, time series of the main parameters of photochemical importance that cover almost two decades are available. As a way to assess the relevant photochemical reactions, the modelled steady-state concentrations of important photogenerated transients ((•)OH, ³CDOM* and CO₃(-•)) were taken into account. A multivariate analysis approach was adopted to have an overview of the system, to emphasise relationships among chemical, photochemical and seasonal variables, and to highlight annual and long-term trends. Over the considered time period, because of the decrease of the dissolved organic carbon (DOC) content of water and of the increase of alkalinity, a significant increase is predicted for the steady-state concentrations of the radicals (•)OH and CO₃(-•). Therefore, the photochemical degradation processes that involve the two radical species would be enhanced. Another issue of potential photochemical importance is related to the winter maxima of nitrate (a photochemical (•)OH source) and the summer maxima of DOC ((•)OH sink and ³CDOM* source) in the lake water under consideration. From the combination of sunlight irradiance and chemical composition data, one predicts that the processes involving (•)OH and CO₃(-•) would be most important in spring, while the reactions involving ³CDOM* would be most important in summer.

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Available from: Davide Vione, Sep 11, 2015
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    • "An even stronger negative relationship is often observed between DOC and CO 3 −@BULLET , because DOM both scavenges CO 3 −@BULLET and inhibits its formation by consuming • OH (Canonica et al., 2005; Vione et al., 2014). In contrast, • OH and CO 3 −@BULLET often positively correlate with nitrate and nitrite, and CO 3 −@BULLET with inorganic carbon species as well (Minella et al., 2011). The transients 3 CDOM* and 1 O 2 are produced by CDOM irradiation and they are poorly scavenged by DOM, thus they positively correlate with DOC. "
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    ABSTRACT: Based on long-term trends of water chemistry parameters of photochemical significance from four lakes located in the Alps (Iseo, Garda, Piburgersee, Geneva), we calculated the corresponding steady-state concentrations of photoinduced transient species with an ad-hoc photochemical model. Such transients were the hydroxyl ((•)OH) and carbonate (CO3(-•)) radicals, singlet oxygen ((1)O2), and the triplet states of chromophoric dissolved organic matter ((3)CDOM*). Among the investigated lakes, Lake Iseo, for example, showed a long-term near-stability in chemical parameters that resulted in a photochemical stability. By contrast, Piburgersee underwent important chemical modifications, but the interplay of compensation (parallel increase of both inorganic and organic carbon) and near-saturation effects (organic matter as main (•)OH source and sink) prevented the modelled photochemistry to undergo significant shifts over time. This result suggests the occurrence of a sort of "photochemical buffering" in some lake ecosystems, which would dampen modifications of the steady-state concentration of the photochemically-formed reactive transients, even in the case of significant changes in water chemistry. Finally, in lakes Garda and Geneva, long-term changes in water chemistry had an effect on photochemistry. While in Lake Garda the small increase in DOM was associated to a small increase in (1)O2 and (3)CDOM*, in Lake Geneva, the increases in pH and bicarbonate and the decrease in nitrite resulted in an (•)OH decrease. Overall, our results predict very different lake photochemistry patterns in relation to alterations in water chemistry parameters caused by climate change, such as changes in water alkalinity and dissolved organic carbon concentration.
    Full-text · Article · Sep 2015 · Science of The Total Environment
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    • "Due to the lack of sunlight absorption, phenol direct photolysis is fairly weak [10]. Therefore, indirect photolysis is mainly process for the transformation of phenol in the environment [11]. For indirect photolysis, NO 3 -and NO 2 -reported play crucial roles, which are ubiquitous in surface water and absorb sunlight radiation to reach an excited state, subsequently generating free radicals comprised of reactive oxygen species (e.g., hydroxyl radicals (@BULLETOH), peroxyl radicals (ROO@BULLET), and singlet oxygen ( • O 2 )) and other non-ROS transients [12-16]. "
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    ABSTRACT: Phenol, as an extensively used compound, could be detected in a great variety of environmental water. In this study, the environmental behavior of phenol photo-induced degradation in aqueous solution in the presence of nitrate (NO3-) and nitrite (NO2-) under simulated sunlight irradiation was investigated. The results showed that the degradation of phenol followed pseudo-first order kinetics model in both NO3- and NO2- conditions and the phenol disappearance rate decreased with decreasing nitrite concentration. The effect of environmental parameters including pH and humic acid on the phenol degradation by NO3- and NO2- were also performed. The photodegradation rates of phenol were strongly influenced by these parameters. In addition, the hydroxyl radical (center dot OH) formation was identified by the photoluminescence spectra (PL) using terephthalic acid as trapping molecule and the pathways of center dot OH generated in the phenol degradation by the NO3- and NO2- ions are proposed.
    Full-text · Article · Jan 2015 · Fresenius Environmental Bulletin
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    • "The chemical composition of water sampled near the surface was considered in the photochemical modelling Fig. 3 Modelled time trends of [·OH] (smoothed red solid line) and [CO 3 ·− ] (smoothed black solid line ) in the top 1-m layer of Lake Maggiore. For both series, the linear fit line (black solid thin) is reported with the related error band (95 % confidence level, black dashed line (Minella et al. 2011) is quite easy. The results are reported in Fig. 5 (Minella et al. 2013b). "
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    ABSTRACT: Information concerning the link between surface-water photochemistry and climate is presently very scarce as only a few studies have been dedicated to the subject. On the basis of the limited knowledge that is currently available, the present inferences can be made as follows: (1) Warming can cause enhanced leaching of ionic solutes from the catchments to surface waters, including cations and more biologically labile anions such as sulphate. Preferential sulphate biodegradation followed by removal as organic sulphides in sediment could increase alkalinity, favouring the generation of the carbonate radical, CO3 ·−. However, this phenomenon would be easily offset by fluctuations of the dissolved organic carbon (DOC), which is strongly anticorrelated with CO3 ·−. Therefore, obtaining insight into DOC evolution is a key issue in understanding the link between photochemistry and climate. (2) Climate change could exacerbate water scarcity in the dry season in some regions. Fluctuations in the water column could deeply alter photochemistry that is usually favoured in shallower waters. However, the way water is lost would strongly affect the prevailing photoinduced processes. Water outflow without important changes in solute concentration would mostly favour reactions induced by the hydroxyl and carbonate radicals (·OH and CO3 ·−). In contrast, evaporative concentration would enhance reactions mediated by singlet oxygen (1O2) and by the triplet states of chromophoric dissolved organic matter (3CDOM*). (3) In a warmer climate, the summer stratification period of lakes would last longer, thereby enhancing photochemical reactions in the epilimnion but at the same time keeping the hypolimnion water in the dark for longer periods.
    Full-text · Article · Dec 2013 · Environmental Science and Pollution Research
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