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

ABSTRACT 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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    • "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.
    Environmental Science and Pollution Research 12/2013; 21(20). DOI:10.1007/s11356-013-2343-0 · 2.76 Impact Factor
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    • "The model was originally conceived to predict the photochemical persistence of pollutants in the aqueous environment, a field in which it has been validated (Maddigapu et al., 2011; Vione et al., 2011). However, the model can be easily extended to the general study of photochemical reactions, including the long-term effects of human disturbance and climate change on surface-water photochemistry (Minella et al., 2011). "
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    • "The pH value of the surface water layer is substantially increased during the summer stratification period or during algal blooms, particularly if the water is rich in DOM and POM (Ishida et al., 2006; Blackford and Gilbert, 2007; Xiao et al., 2011; Minella et al., 2011). "
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    ABSTRACT: Algal toxins or red-tide toxins produced during algal blooms are naturally-derived toxic emerging contaminants (ECs) that may kill organisms, including humans, through contaminated fish or seafood. Other ECs produced either naturally or anthropogenically ultimately flow into marine waters. Pharmaceuticals are also an important pollution source, mostly due to overproduction and incorrect disposal. Ship breaking and recycle industries (SBRIs) can also release various pollutants and substantially deteriorate habitats and marine biodiversity. Overfishing is significantly increasing due to the global food crisis, caused by an increasing world population. Organic matter (OM) pollution and global warming (GW) are key factors that exacerbate these challenges (e.g. algal blooms), to which acidification in marine waters should be added as well. Sources, factors, mechanisms and possible remedial measures of these challenges to marine ecosystems are discussed, including their eventual impact on all forms of life including humans.
    Environmental Pollution 08/2013; 182. DOI:10.1016/j.envpol.2013.08.005 · 3.90 Impact Factor
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