Changes over time in organic matter dynamics and copper solubility in a vineyard soil after incorporation of cover crop residues: Insights from a batch experiment.

Cover crops (CCs) are increasingly used in viticulture because they benefit the soil and the environment in many ways. This study investigated the extent to which the incorporation of CC residues altered organic matter (OM) and Cu dynamics in a Cu-contaminated vineyard topsoil. A 92-day incubation period was used to monitor changes over time in carbon mineralization, carbon hydrolytic enzyme activity, concentration and optical properties of dissolved organic matter (DOM), and Cu solubility after the addition (or not) of two CC residues, oat or faba bean. The results revealed that adding CCs transitorily increased the concentration of DOM in soil solution, as well as the activity of C hydrolytic enzymes and C mineralization rates. DOM content was approximately two orders of magnitude higher in CC-amended soils than in the control soil on day 0, after which it gradually decreased to reach concentrations similar to those measured in the control soil on day 92. Analyses of DOM optical properties showed that its molecular weight and degree of humification increased over time with a decrease in its concentration. The close relationship between DOM and Cu concentrations in the soil solution suggests that degradation of CCs releases soluble forms of C capable of complexing and solubilizing Cu, and hence that incorporating CC residues can transitorily increase the solubility of Cu in vineyard topsoils. Despite their different C:N ratios, oat and faba bean had almost the same effect on Cu dynamics, implying that C inputs played a prominent role in explaining the interactions between OM and Cu within the timeframe of our experiment. In conclusion, this study enabled recommendations on how to mitigate the risk of Cu ecotoxicity associated with incorporating CCs in Cu-contaminated vineyard soils.

Sampling terrigenous diffuse sources in watercourse: Influence of land use and hydrological conditions on dissolved organic matter characteristics.

Diffuse and point sources of dissolved organic matter (DOM) in streams influence its composition, interactions and fate in the aquatic ecosystem. These inputs can be very numerous at the scale of a watershed, and their identification remains a challenge, especially for diffuse sources related to land use. The complexity of the transfer mechanisms and the reactivity of DOM throughout the soil-water column continuum raise questions about the sampling of diffuse sources in watercourses. To answer this issue, we compared the characteristics of soil-extracted DOM influenced by a particular land use (homogenous sub-catchment of forest and vineyard) and DOM collected from the watercourse adjacent to the soil samples. A 28-day incubation experiment of soil extracts was designed to remove the labile fraction of DOM. During the first 3 days, between 40 and 70 % of the DOC mass was lost for both types of soils. A set of optical indicators (UV-Visible, EEM fluorescence and HPSEC/UV-fluorescence) showed that the labile fraction was mostly composed by low (<1 kDa) and high (>10 kDa) protein-like molecules. At the end of the incubation, soil-extracted DOM was mainly composed of medium molecules (1-10 kDa) associated to terrigenous humic-like compounds. Its optical and size molecular signature tended towards that in the adjacent watercourses and was specific to land use. However, the characteristics of DOM in watercourses was also influenced by the hydrological conditions, probably due to a transfer of top soil DOM during high water periods and both deep soil and autochthonous DOM during low water periods. These results were obtained by a set of indicators, including novel ones derived from HPSEC/UV-fluorescence. Finally, this study demonstrated that it is possible to sample the DOM representative of a land use directly in the river downstream of the homogeneous sub-basin by multiplying the samples during contrasting hydrological conditions.

New insights into detecting alizarin from autofluorescence in marked glass eels.

Alizarin detection in fish fins is extensively employed because it is easy to use. However, in eels, the eelGFP fluorescent protein may impede the detection of the fluorescent markers in the eel tissues. The study tests the effectiveness of three of the most up-to-date alizarin-detecting technologies on the living body and fins of European glass eels (Anguilla anguilla L.). The findings demonstrated that the control group had a high autofluorescence at alizarin and eelGFP maxima bands. With fluorescence reflectance imaging (FRI), the eel living body autofluorescence impeded the detection of the marked eels. In contrast with experimental excitation-emission-matrix (EEM) fluorescence analyses, 99% of the marked eels were correctly assigned to their group from fluorescence analyses of their fin cellular contents. With epifluorometry (EPI), 100% of the marked eels were detected with the caudal fin tips when excited at 450-490 nm wavelengths due to a weaker autofluorescence signal. EEM and FRI assays unveiled an average fluorescence quenching 60% and 44% of the marked group respectively, in the alizarin and eelGFP maxima bands. The fluorescence quenching observed is discussed. Results will benefit experimental design by examining autofluorescence effects on mark detection and the development of non-invasive detection methods in this critically endangered species.

Do DOM optical parameters improve the prediction of copper availability in vineyard soils?

Accumulation of copper (Cu) in soils due to the application of fungicides may be toxic for organisms and hence affect winegrowing sustainability. Soil parameters such as pH and dissolved organic matter (DOM) are known to affect the availability of Cu. In this study, we investigated the contribution of chromophoric and fluorescent DOM properties to the prediction of Cu availability in 18 organic vineyard soils in the Bordeaux winegrowing area (France). The DOM parameters, assessed through absorbance and fluorescence analyses, and proxies for Cu availability (total soluble Cu and free ionic Cu2+) were measured in 0.01 M KCl extracts. Total soluble Cu (CuKCl) varied 23-fold while free ionic Cu2+ varied by a factor of 4600 among the soils. DOC concentrations were similar among the soils, but the samples differed in the quality of DOM as assessed by optical spectroscopy. Multilinear regression models with and without DOM quality parameters were investigated to predict Cu availability. The best model for CuKCl successfully explained 83% of variance and included pH, CuT, and two DOM fluorescence quality indices, the FI fluorescence index, which distinguishes between microbial and higher plant origins, and the HIX humification index. For the prediction of Cu2+, pH alone explained 88% of variance and adding DOM parameters did not improve modelling. The two Cu availability proxies were related to pH. This study confirms the prominent role of pH in Cu availability and underlines the importance of DOM quality to better predict Cu solubility.

Study of the dissolved organic matter (DOM) of the Auzon cut-off meander (Allier River, France) by spectral and photoreactivity approaches.

Wetlands are recognized for the importance of their hydrological function and biodiversity, and there is now a consensus to protect and restore them as well as to complete the knowledge on their functioning. Here, we studied the dissolved organic matter (DOM) of a wetland composed of the Auzon cut-off meander, the Allier River, the alluvial fluvial flow, and watershed aquifer. Water was sampled at different locations, in spring, summer, and autumn. For each sample, DOM was characterized for its chemical and optical properties and its photooxidant capacity through its ability to generate DOM triplet excited states (3DOM*) and singlet oxygen upon simulated solar light exposure. UV-visible and fluorescence indices revealed that DOM was mainly microbial-derived whatever the sampling sites with spatial and temporal variations in terms of aromaticity (5.5-22%), specific UV absorbance at 254 nm (0.28-2.82 L m-1mgC-1), ratio of the absorbance at 254 and 365 nm (4.6-10.8), fluorescence index (1.35-166), and biological index (0.812-2.25). All the samples generated 3DOM* and singlet oxygen, rates of formation of which showed parallel variations. Using principal component analysis (PCA), we found positive correlations between the sensitizing properties of DOM samples and parameters associated to the abundance of low molecular weight and low absorbing chromophores. Moreover, the parameter variation across the wetland reinforced the hydrological movements observed in a previous study, suggesting that these parameters could be used as water connection tracers.

The influence of natural dissolved organic matter on herbicide toxicity to marine microalgae is species-dependent.

Microalgae, which are the foundation of aquatic food webs, may be the indirect target of herbicides used for agricultural and urban applications. Microalgae also interact with other compounds from their environment, such as natural dissolved organic matter (DOM), which can itself interact with herbicides. This study aimed to evaluate the influence of natural DOM on the toxicity of three herbicides (diuron, irgarol and S-metolachlor), singly and in ternary mixtures, to two marine microalgae, Chaetoceros calcitrans and Tetraselmis suecica, in monospecific, non-axenic cultures. Effects on growth, photosynthetic efficiency (Ф'M) and relative lipid content were evaluated. The chemical environment (herbicide and nutrient concentrations, dissolved organic carbon and DOM optical properties) was also monitored to assess any changes during the experiments. The results show that, without DOM, the highest irgarol concentration (I0.5: 0.5 mg.L-1) and the strongest mixture (M2: irgarol 0.5 µg.L-1 + diuron 0.5 µg.L-1 + S-metolachlor 5.0 µg.L-1) significantly decreased all parameters for both species. Similar impacts were induced by I0.5 and M2 in C. calcitrans (around -56% for growth, -50% for relative lipid content and -28% for Ф'M), but a significantly higher toxicity of M2 was observed in T. suecica (-56% and -62% with I0.5 and M2 for growth, respectively), suggesting a possible interaction between molecules. With DOM added to the culture media, a significant inhibition of these three parameters was also observed with I0.5 and M2 for both species. Furthermore, DOM modulated herbicide toxicity, which was decreased for C. calcitrans (-51% growth at I0.5 and M2) and increased for T. suecica (-64% and -75% growth at I0.5 and M2, respectively). In addition to the direct and/or indirect (via their associated bacteria) use of molecules present in natural DOM, the characterization of the chemical environment showed that the toxic effects observed on microalgae were accompanied by modifications of DOM composition and the quantity of dissolved organic carbon excreted and/or secreted by microorganisms. This toxicity modulation in presence of DOM could be explained by (i) the modification of herbicide bioavailability, (ii) a difference in cell wall composition between the two species, and/or (iii) a higher detoxification capacity of C. calcitrans by the use of molecules contained in DOM. This study therefore demonstrated, for the first time, the major modulating role of natural DOM on the toxicity of herbicides to marine microalgae.

Asymmetrical flow field-flow fractionation of white wine chromophoric colloidal matter.

Two analytical separation methods-size-exclusion chromatography and asymmetrical flow field-flow fractionation-were implemented to evaluate the integrity of the colloidal composition of Chardonnay white wine and the impact of pressing and fermentations on the final macromolecular composition. Wine chromophoric colloidal matter, representing UV-visible-absorbing wine macromolecules, was evaluated by optical and structural measurements combined with the description of elution profiles obtained by both separative techniques. The objective of this study was to apply these two types of fractionation on a typical Chardonnay white wine produced in Burgundy and to evaluate how each of them impacted the determination of the macromolecular chromophoric content of wine. UV-visible and fluorescence measurements of collected fractions were successfully applied. An additional proteomic study revealed that grape and microorganism proteins largely impacted the composition of chromophoric colloidal matter of Chardonnay wines. Asymmetrical flow field-flow fractionation appeared to be more reliable and less invasive with respect to the native chemical environment of chromophoric wine macromolecules, and hence is recommended as a tool to fractionate chromophoric colloidal matter in white wines. Graphical Abstract An innovative macromolecular separation method based on Asymmetrical Flow Field-Flow Fractionation was developed to better control colloidal dynamics across Chardonnay white winemaking.

Development of solid-phase microextraction to study dissolved organic matter--polycyclic aromatic hydrocarbon interactions in aquatic environment.

Solid-phase microextraction coupled with gas chromatography and mass spectrometry (SPME-GC-MS) was developed for the study of interactions between polycyclic aromatic hydrocarbons (PAHs) and dissolved organic matter (DOM). After the determination of the best conditions of extraction, the tool was applied to spiked water to calculate the dissolved organic carbon water distribution coefficient (K(DOC)) in presence of different mixtures of PAHs and Aldrich humic acid. The use of deuterated naphthalene as internal standard for freely dissolved PAH quantification was shown to provide more accuracy than regular external calibration. For the first time, K(DOC) values of 18 PAHs were calculated using data from SPME-GC-MS and fluorescence quenching; they were in agreement with the results of previous studies. Competition between PAHs, deuterated PAHs and DOM was demonstrated, pointing out the non-linearity of PAH-DOM interactions and the stronger interactions of light molecular weight PAHs (higher K(DOC) values) in absence of high molecular weight PAHs.

Copper addition by organic matter degradation in the freshwater reaches of a turbid estuary.

This study reports on the relationship between copper (Cu) behavior and organic matter (OM) transformation along the turbidity gradient in the freshwater reaches of the Gironde Estuary. During a one-year survey, surface water and suspended particulate matter (SPM) were sampled at least monthly at three sites along the Garonne Branch, representing the main fluvial branch of the Gironde Estuary. Additionally, a longitudinal high resolution profile was sampled along the Garonne Branch, covering the turbidity gradient from the river water endmember to the maximum turbidity zone (MTZ). Seasonal variability and spatial distribution of Cu in both the dissolved phases (<0.2 µm, Cu(0.2) and <0.02 µm, Cu(0.02)) and particulate Cu (Cu(P)) clearly suggested Cu(0.2) addition during summer, that increased the Cu(0.2) concentrations by a factor ~2, mainly manifested by an increase in the Cu(0.02) fraction. At the annual timescale (2004), this internal Cu reactivity increased Cu(0.02) fluxes in the Garonne Branch by ~20% (3.6 t year(-1)), with the equivalent of ~2.9 t year(-1) derived from the Cu(P) fraction and ~0.7 t year(-1) from the colloidal (0.02-0.2 µm) fraction, without involving and/or affecting the Cu(C18) (hydrophobic metal-organic complexes) fraction. Combining data on Cu speciation with the results obtained by several independent techniques (DOC and POC measurements, 3D-fluorescence, and TEM) suggested close relationships between Cu behavior and OM transformation/restructuration along the turbidity gradient in the Garonne Branch. The observed Cu(0.02) addition was related to increasing humification (humification index HIX increased from 9 to 12, network formation) and labile OM degradation (Iγ/Iα ratio decreased from 0.70 to 0.44), going along with decreasing DOC and POC concentrations. Mass-balances suggest that in the studied system, degradation of OM may account for the release of ~25 µmol potentially bioaccessible Cu(0.02) per mole of particulate organic carbon mineralized.