Revealing organic carbon-nitrate linear relationship from UV spectra of freshwaters in agricultural environment.

A strong non linear relationship between nitrate and organic matter (assessed by dissolved organic carbon, DOC) has been recently demonstrated by Taylor and Townsend (2010), namely for freshwaters. In this context, our study explores this relation from the behavior of sets of normalized UV spectra (same area under each spectrum) of different water samples showing a hidden isosbestic point (HIP) around 225 nm. This HIP is linked to the existence of a simple relation between nitrate and DOC, the proportions of which vary according to the sampling location and environmental factors. In a second step, a simple linear model is proposed for nitrate-DOC relationship (α⋅NO3+ß⋅DOC=1) and a validation is proposed for more than 150 samples of different Brittany rivers and lakes. For samples of the largest watershed, a complementary exploitation from data acquired during the different campaigns confirmed the seasonal evolution between spring (high nitrate/low DOC) and autumn (high DOC/low nitrate). Further investigation on other freshwater samples is needed in order to improve the limits of this linear model.

Issues of drinking water quality of small scale water services towards climate change.

As climate change could impact water quantity and quality, important concerns are related to water quality degradation in small scale water services (SSWS). SSWS using surface waters resources (rivers and lakes) for drinking water production are particularly vulnerable to short term transient events due to their low adaptation capacity and their lack of support and technical knowledge compared to major centralized systems. Based on weather and water quality databases, a case study was conducted on a SSWS in Brittany (France) pumping from surface water. Results show an important vulnerability in treatment efficiency related to the lowest and highest river flows and provide first assumptions about the impacts of an increase in extreme weather events with climate change on drinking water quality.

Interaction of pyrene fluoroprobe with natural and synthetic humic substances: Examining the local molecular organization from photophysical and interfacial processes.

The direct and indirect interaction mechanisms of pyrene with: (i) various molecular weight fractions of a synthetic humic-like substance (SyHA) and (ii) extracts of natural humic acids (NHA) from Moselle River suspended matter were investigated using quenching fluorescence and surface tension measurements. Humic materials were characterized in a previous study. The Stern-Volmer associative constants were determined from the quenching technique. Surface tension measurements revealed an increase in surface activity as a function of concentration for each humic fraction independently of the pyrene presence in solution, even during the formation of humic micelles. The results obtained suggest the possibility of specific intermolecular interactions occurring during pyrene entrapment within humic acids. In addition, we show that molecular weight, aliphatic chains (especially those containing nitrogen groups) and number of acidic groups are determinant characteristics for pollutant entrapment capacity at concentrations below the critical micellar concentration (CMC) of humic substances.

Impacts of climate change on surface water quality in relation to drinking water production.

Besides climate change impacts on water availability and hydrological risks, the consequences on water quality is just beginning to be studied. This review aims at proposing a synthesis of the most recent existing interdisciplinary literature on the topic. After a short presentation about the role of the main factors (warming and consequences of extreme events) explaining climate change effects on water quality, the focus will be on two main points. First, the impacts on water quality of resources (rivers and lakes) modifying parameters values (physico-chemical parameters, micropollutants and biological parameters) are considered. Then, the expected impacts on drinking water production and quality of supplied water are discussed. The main conclusion which can be drawn is that a degradation trend of drinking water quality in the context of climate change leads to an increase of at risk situations related to potential health impact.

Coagulation of humic substances and dissolved organic matter with a ferric salt: an electron energy loss spectroscopy investigation.

Transmission electron microscopy (TEM) coupled with electron energy loss spectroscopy (EELS) and energy dispersive X-ray spectroscopy (EDXS) was used to investigate the coagulation of natural organic matter with a ferric salt. Jar-test experiments were first conducted with a reconstituted water containing either synthetic or natural extracts of humic substances, and then with a raw water from Moselle River (France). The characterization of the freeze-dried coagulated sediment by EELS in the 250-450 eV range, showed that Fe-coagulant species predominantly associate with the carboxylic groups of organic matter, and that this interaction is accompanied by a release of previously complexed calcium ions. The variation of Fe/C elemental ratio with iron concentration provides insightful information into the coagulation mechanism of humic substances. At acid pH, Fe/C remains close to 3 over the whole range of iron concentrations investigated, while a much lower atomic ratio is expected from the value of optimal coagulant dosage. This suggests that a charge neutralization/complexation mechanism is responsible for the removal of humic colloids, the aggregates being formed with both iron-coagulated and proton-neutralized organic compounds. At pH 8, the decrease in Fe/C around optimal coagulant concentration is interpreted as a bridging of stretched humic macromolecules by Fe-hydrolyzed species. Aggregation would then result from a competition between reconformation of humic chains around coagulant species and collision of destabilized humic material. EELS also enabled a fingerpriting of natural organic substances contained in the iron-coagulated surface water, N/C elemental analyses revealing that humic colloids are removed prior to proteinic compounds.