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Algae and cyanobacteria are important contributors to the natural organic matter (NOM) of eutrophic water resources. The objective of this work is to increase knowledge on the modifications of algal organic matter (AOM) properties in the long term to anticipate blooms footprint in such aquatic environments. The production of AOM from an alga (Euglena gracilis) and a cyanobacteria (Microcystis aeruginosa) was followed up and characterized during the stationary phase and after one year and four months of cultivation, in batch experiments. Specific UV absorbance (SUVA) index, organic matter fractionation according to hydrophobicity and apparent molecular weight were combined to assess the evolution of AOM. A comparison between humic substances (HS) mainly derived from allochthonous origins and AOM characteristics was performed to hypothesize impacts of AOM transformation processes on the water quality of eutrophic water resources. Each AOM fraction underwent a specific evolution pattern, depending on its composition. Impacts of humification-like processes were predominant over release of biopolymers due to cells decay and led to an increase in the hydrophobic compounds part and molecular weights over time. However, the hydrophilic fraction remained the major fraction whatever the growth stage. Organic compounds generated by maturation of these precursors corresponded to large and aliphatic structures.

Infrared analyses of clay minerals samples are usually performed by transmission techniques. While transmission measurements are easy and inexpensive, the sample preparation plays a primordial role in the quality of the data. Alternatively, attenuated total reflection (ATR) provides a powerful and often simpler analysis method. However, the ATR spectra reveal strong differences when compared to transmission spectra leading sometimes to confusion in the interpretations. Indeed, optical effects play a prominent role in the ATR spectral profile and their identification is mandatory for obtaining quantitative information regarding molecular/particle orientation or film thickness. Here, exact spectral simulations of montmorillonite films are performed by making use of the optical theory, following the determination of the anisotropic optical constants from the experimental reflectance spectra by Kramers-Kronig transformation. This methodology can advantageously be used (i) to choose the appropriate optical conditions for advanced and reliable characterization of clay minerals, (ii) to extract quantitative information such as the estimation of the film thickness, and (iii) to discriminate optical phenomena (optical interferences) from chemical/structural features of the sample.