Photochemical production of organic matter triplet states in water samples from mountain lakes, located below or above the tree line

Abstract

davide.vione@unito.it (D.V.). AbstractThe production of triplet states (T*) of chromophoric dissolved organic matter (CDOM), reacting with the probe molecule 2,4,6-trimethylphenol (TMP) was measured upon irradiation of water samples, taken from lakes located in a mountain area (NW Italy) between 1450 and 2750 m above sea level. The lakes are located below or above the tree line and surrounded by different vegetation types (trees, alpine meadows or exposed rocks). The most photoactive samples belonged to lakes below the tree line and their fluorescence spectra and CDOM optical features suggested the presence of a relatively elevated amount of humic (allochthonous) material. The lowest (negligible) photoactivity was found for a lake surrounded by exposed rocks. Its CDOM showed an important autochthonous contribution (due to in-lake productivity) and considerably higher spectral slope compared to the other samples, suggesting low CDOM molecular weight and/or aromaticity.Among the samples, CDOM photoactivity (measured as the rate of TMP-reactive T* photoproduction) decreased with changing vegetation type in the order: trees, meadows, rocks. It 3 could be connected with decreasing contribution from catchment runoff and increasing contribution from autochthonous processes and possibly precipitation.

Photogeneration of reactive transient species upon irradiation of natural water samples: Formation quantum yields in different spectral intervals, and implications for the photochemistry of surface waters

“…The UVA-F3 CDOM * data reported here are quite in the range of those obtained by irradiation of samples from lakes located in temperate regions (De Laurentiis et al, 2012). Interestingly, they are much lower than those reported for lakes in Antarctica (De Laurentiis et al, 2013b), but in that case it is possible that the unusually elevated reactivity was closely linked with extreme environmental features (e.g.…”

“…While pH might affect lake-water photochemistry, much larger differences than those observed in the studied samples would be required for pH to be really an issue ). Actually, a much more important effect on CDOM and its properties could be provided by the fact that the mountain lakes are above the treeline and surrounded by alpine meadows and exposed rocks, while the other lakes are located in partially forested areas (De Laurentiis et al, 2012). As far as the spectroscopic parameters are concerned, one can see that water from the mountain lakes (Balma and SdS) had lower values of E 2 /E 3 and S compared to the lowland lakes.…”

Long-term trends of chemical and modelled photochemical parameters in four Alpine lakes

“…APEX is based on a photochemical model that predicts steady-state concentrations of transient species ( • OH, CO 3 −• , 1 O 2 , 3 CDOM*) as a function of the seasonally variable sunlight spectrum, water chemistry and depth (Vione, 2014;Bodrato and Vione, 2014). APEX allows for instance for the prediction of the phototransformation kinetics of xenobiotics, on which basis the photochemical model was validated upon comparison with available field data (Maddigapu et al, 2011;De Laurentiis et al, 2012;Marchetti et al, 2013). The absorption of radiation by photosensitisers (CDOM, nitrate and nitrite) and xenobiotics is computed by taking into account competition for sunlight irradiance in a Lambert-Beer approach (Braslavsky, 2007;Bodrato and Vione, 2014).…”

UV–vis spectral modifications of water samples under irradiation: Lake vs. subterranean water

“…Apart from these features that occur in every EEM plot, peaks are present that are peculiar to the fluorescent moieties of CDOM, also termed FDOM. From the peak position, identified by the (λ ex , λ em ) couple of values, it is possible to identify different fluorescent substances that may occur in surface waters [11,24,25]. Interestingly, all the samples except sample 3 show the presence of very significant amounts of humic-like substances, which are identified from their peak A (λ ex = 210/275 nm, λ em =375/500 nm) and peak C (λ ex = 270/325 nm, λ em = 400/430 nm) [11].…”