Spatio-temporal variations of fluorescence properties of dissolved organic matter along the River Tet (Pyrenees-Orieetales, France)

摘要

Fluorescence excitation-emission matrices showed the spectral signature of dissolved organic matter (DOM) downstream in the River let at all seasons corresponding to humic substances with maximum fluorescence emission λem = 420-160 nm for excitations of λex = 340-360 nm and the occasional presence of tryptophan, tracer of anthropogenic pressure, spectroscopically identified by λex/λem = 310/350 nm. A factorial discriminant analysis, performed using the parameters selected (λex/λem pairs of wavelength), succeeded in a better discrimination of seasons than stations, and clearly showed the presence of two fluorophores. Fluorophore 1, with two absorption bands: λex = 260-320 nm and 330-390 nm for λem = 440-500 nm, and Fluorophore 2, with one absorption band: λex = 300-360 nm for λem = 410 nm, which are attributed to humic acid (HA) and fulvic acid (FA), respectively. Variations of DOM relative contents downstream in the River let, according to seasons and stations, showed high amounts of DOM (pedogenic character) along the river in the humid period, with the highest value obtained in the mountain section. In contrast, in summer, the DOM contents were low (aquagenic character). Moreover, DOM presents a relatively constant composition with a percentage of FA ranging from 40% at the mountain station to 48% at the mouth river, whatever the season.