Contribution of Peatland Permafrost to Dissolved Organic Matter along a Thaw Gradient in North Siberia.

Permafrost peatlands are important carbon stocks currently experiencing rapid evolution after permafrost thaw. Following thaw, dissolved organic matter (DOM) is a potentially important pathway for the release of permafrost carbon. This study investigates the origin and composition of DOM across sites at different stages of thaw in a discontinuous permafrost area of North Siberia. We determine the optical properties, molecular composition, and stable isotopic (δ13C) and radiocarbon (14C) contents of DOM. Early stages of thaw are characterized by high DOC concentrations, high aromaticity, contribution of vegetation-derived DOM, and a high contribution of permafrost carbon. In contrast, in later stages, the microbial contribution to DOM increases, and only modern carbon is detected. This work links DOM composition with its radiocarbon content in permafrost peatlands. It shows that DOM originating from previously frozen permafrost peatlands is highly aromatic and previously processed. It highlights the variability of post-thaw carbon dynamics in boreal and arctic ecosystems.

Nanoplastic in the North Atlantic Subtropical Gyre.

Plastics can be found in all ecosystems across the globe. This type of environmental pollution is important, even if its impact is not fully understood. The presence of small plastic particles at the micro- and nanoscales is of growing concern, but nanoplastic has not yet been observed in natural samples. In this study, we examined four size fractions (meso-, large micro-, small micro-, and nanoplastics) of debris collected in the North Atlantic subtropical gyre. To obtain the nanoplastic portion, we isolated the colloidal fraction of seawater. After ultrafiltration, the occurrence of nanoscale particles was demonstrated using dynamic light scattering experiments. The chemical fingerprint of the colloids was obtained by pyrolysis coupled with gas chromatography-mass spectrometry. We demonstrated that the signal was anthropogenic and attributed to a combination of plastics. The polymer composition varied among the size classes. At the micro- and nanoscales, polyvinyl chloride, polyethylene terephthalate, polystyrene and polyethylene were observed. We also observed changes in the pyrolytic signals of polyethylene with decreasing debris size, which could be related to the structural modification of this plastic as a consequence of weathering.

Chemical Characterization and Botanical Origin of French Ambers.

The molecular composition of 10 Cretaceous and one Eocene ambers from France was analyzed by infrared spectroscopy, solid-state (13)C nuclear magnetic resonance spectroscopy, and thermochemolysis gas chromatography-mass spectrometry. The terpenoids identified in the samples were used as biomarkers for the botanical origin of the resins. The Cretaceous samples, comprising the so-called Alpine, Anjou, Charentese, Provence, Pyrenean, and Vendean ambers, ranged from the Albian-Cenomanian transition to the early Santonian (100 to 85 Ma) and correspond to class Ib resins typical of conifers. The extinct conifer family Cheirolepidiaceae was proposed as the plant source of Pyrenean and brown Charentese ambers. Araucariaceae or Cheirolepidiaceae were the plant sources of the Cenomanian Alpine, Anjou, and yellow Charentese ambers. The Santonian ambers of Provence and Vendée were found to derive from the Cupressaceae. The Eocene Oise amber (ca. 53 Ma) is a class Ic resin typical of angiosperms and was produced by a Fabaceae. The evolution of resin sources from the early Cretaceous to the Eocene periods is discussed. Finally, a possible fingerprint hitherto unveiled is proposed for cheirolepidiaceous resins, defined by the simultaneous presence of phenolic diterpenoids, labdanoic acids, callitrisate structures, and their respective derivatives.

Evidence of colloids as important phosphorus carriers in natural soil and stream waters in an agricultural catchment.

Colloids (1-1,000 nm) are important phosphorus (P) carriers in agricultural soils. However, most studies are based on colloids from soil waters extracted in the laboratory, thus limiting the understanding of the natural transfer of colloidal P along the soil-to-stream continuum. Here, we conducted a field study on the colloidal P in both natural soil waters and their adjacent stream waters in an agricultural catchment (Kervidy-Naizin, western France). Soil waters (10-15 cm, Albeluvisol) of two riparian wetlands and the adjacent stream waters were sampled monthly during wet seasons of the 2015-2016 hydrological year (seven dates in total). Ultrafiltration at three pore sizes (5 kDa, 30 kDa, and 0.45 µm) was combined with inductively coupled plasma mass spectrometry (ICP-MS) to investigate variability in colloidal P concentration and its concomitant elemental composition. Results showed that colloidal P represented, on average, 45 and 30% of the total P (<0.45 µm) in the soil waters and stream waters, respectively. We found that colloidal P was preferentially associated with (a) organic carbon in the fine nanoparticle fraction (5-30 kDa) and (b) iron-oxyhydroxides and organic carbon in the coarse colloidal fraction (30 kDa-0.45 µm). The results confirmed that colloidal P is an important component of total P in both soil waters and stream waters under field conditions, suggesting that riparian wetlands are hotspot zones for the production of colloidal P at the catchment scale, which has the potential to be transported to adjacent streams.

Faecal biomarkers can distinguish specific mammalian species in modern and past environments.

Identifying the presence of animals based on faecal deposits in modern and ancient environments is of primary importance to archaeologists, ecologists, forensic scientists, and watershed managers, but it has proven difficult to distinguish faecal material to the species level. Until now, four 5ß-stanols have been deployed as faecal biomarkers to distinguish between omnivores and herbivores, but they cannot distinguish between species. Here we present a database of faecal signatures from ten omnivore and herbivore species based on eleven 5ß-stanol compounds, which enables us to distinguish for the first time the faecal signatures of a wide range of animals. We validated this fingerprinting method by testing it on modern and ancient soil samples containing known faecal inputs and successfully distinguished the signatures of different omnivores and herbivores.

Quantitative multimolecular marker approach to investigate the spatial variability of the transfer of pollution from the Fensch River to the Moselle River (France).

The lipidic fraction from 8 sediments sampled at the confluence between the Fensch River (FR) and the Moselle River (MR) have been analyzed by gas chromatography-mass spectrometry (GC-MS) in order to investigate the transfer of organic micropollutants from the FR to the MR. Molecular markers have been quantified and classified into five categories: natural, petrogenic, pyrogenic and sewage water markers and non-specific molecules. This classification coupled with the quantification of the molecules allows the comparison between anthropogenic and natural inputs and the source apportionment of anthropogenic molecules that are not covalently bound to sedimentary organic macromolecules. The transfer and the fate of organic micropollutants in river sediments seem to be controlled by the water flow. Low water flow conditions induce the settling of fine particles, which could limit the biodegradation. This leads to the preservation of the original anthropogenic fingerprint that is rich in low molecular weight molecules. In high water flow conditions, sediments are mainly composed of coarse particles, limiting the preservation of organic matter, which leads to a persistent anthropogenic fingerprint, mainly composed of high molecular weight compounds.

Evolution of the source apportionment of the lipidic fraction from sediments along the Fensch River, France: a multimolecular approach.

The Fensch River (FR) is one of the most contaminated rivers in France due to the population density and the concentration of industrial activities in this small watershed area. From upstream to downstream, the organic matter extracted from sediments has been analyzed by gas chromatography-mass spectrometry and molecules have been quantified and classified into natural, petrogenic, pyrogenic and sewage water (SW) markers. Upstream the river, anthropogenic molecules are already predominant and represent 87.1% of the molecules quantified. This proportion increases from upstream to downstream and rises to 96.8% at the confluence of the FR with the Moselle River. In the upper part of the FR the contamination is mainly due to human waste (coprostanol: 36.44 microg/g; 42.1% of anthropogenic markers). In the lower part, the contribution of SW markers decreases from 42.1 to 2.4% and the proportion of pyrogenic molecules increases from 29.6 to 59.6%. The major sources of pyrogenic organic matter have been determined by calculation of specific ratios on polycyclic aromatic hydrocarbons and by comparison with reported data. Coal tar, road runoff and atmospheric depositions of urban particles seem to be the major pyrogenic sources. Along the river, the proportion of petrogenic molecules remains constant and those molecules seem to be mainly inherited from road runoff, in the upper part of the FR. Industrial lubricants that occur in steel plant sludge are an additional source in the lower part of the river.

Application of a microbial source tracking based on bacterial and chemical markers in headwater and coastal catchments.

This study identified sources of fecal contamination in three different French headwater and coastal catchments (the Justiçou, Pen an Traon, and La Fresnaye) using a combination of microbial source tracking tools. The tools included bacterial markers (three host-associated Bacteroidales) and chemical markers (six fecal stanols), which were monitored monthly over one or two years in addition to fecal indicator bacteria. 168 of the 240 freshwater and marine water samples had Escherichia coli (E. coli) or enterococci concentrations higher than "excellent" European water quality threshold. In the three catchments, the results suggested that the fecal contamination appeared to be primarily from an animal origin and particularly from a bovine origin in 52% (Rum2Bac) and 46% (Bstanol) of the samples and to a lesser extent from a porcine origin in 19% (Pig2Bac) and 21% (Pstanol) of the samples. Our results suggested a human fecal contamination in 56% (HF183) and 32% (Hstanol) of the samples. Rainfall also impacted the source identification of microbial contamination. In general, these findings could inform effective implementation of microbial source tracking strategies, specifically that the location of sampling points must include variability at the landscape scale.

Release of dissolved phosphorus from riparian wetlands: Evidence for complex interactions among hydroclimate variability, topography and soil properties.

In agricultural landscapes, establishment of vegetated buffer zones in riparian wetlands (RWs) is promoted to decrease phosphorus (P) emissions because RWs can trap particulate P from upslope fields. However, long-term accumulation of P risks the release of dissolved P, since the unstable hydrological conditions in these zones may mobilize accumulated particulate P by transforming it into a mobile dissolved P species. This study evaluates how hydroclimate variability, topography and soil properties interact and influence this mobilization, using a three-year dataset of molybdate-reactive dissolved P (MRDP) and total dissolved P (TDP) concentrations in soil water from two RWs located in an agricultural catchment in western France (Kervidy-Naizin), along with stream P concentrations. Two main drivers of seasonal dissolved P release were identified: i) soil rewetting during water-table rise after dry periods and ii) reductive dissolution of soil Fe (hydr)oxides during prolonged water saturation periods. These mechanisms were shown to vary greatly in space (according to topography) and time (according to intra- and interannual hydroclimate variability). The concentration and speciation of the released dissolved P also varied spatially depending on soil chemistry and local topography. Comparison of sites revealed a similar correlation between soil P speciation (percentage of organic P ranging from 35-70%) and the concentration and speciation of the released P (MRDP from <0.10 to 0.40mgl-1; percentage of MRDP in TDP from 25-70%). These differences propagated to stream water, suggesting that the two RWs investigated were the main sources of dissolved P to streams. RWs can be critical areas due to their ability to biogeochemically transform the accumulated P in these zones into highly mobile and highly bioavailable dissolved P forms. Hydroclimate variability, local topography and soil chemistry must be considered to decrease the risk of remobilizing legacy soil P when establishing riparian buffer zones in agricultural landscapes.

Impact of a highly contaminated river on a more important hydrologic system: changes in organic markers.

The Fensch River is a tributary of the Moselle River. It is a highly contaminated river that drains an industrial area. The objective of this preliminary study is to determine its impact on the Moselle River by analysing the extractable organic matter (EOM) coming from the sediments at the molecular scale. EOM is described in term of aromatic hydrocarbons, aliphatic hydrocarbons and polar compounds. EOM coming from Fensch River sediments is mainly composed of anthropogenic molecules. Aromatic hydrocarbons are dominated by parent Polycyclic Aromatic Hydrocarbons (PAHs) underlining the pyrogenic origin of this fraction. Aliphatic hydrocarbons consist of diagenetic hopanes and a broad UCM that are characteristics of thermal mature organic matter. Upstream the confluence the EOM of the Moselle River is mainly from vegetal origin. It is composed of high molecular weight n-alkanes with an odd over even predominance, degredation products of phytol and stigmasterol. The occurrence of PAHs and diagenetic hopanes underlines that the Moselle River is already contaminated before the confluence. The Fensch River input drastically changes the EOM of the Moselle River. Amount of PAHs is doubled and the fingerprints of both aliphatic hydrocarbons and polar compounds highlight the combination of both natural and anthropogenic sources.

Are fecal stanols suitable to record and identify a pulse of human fecal contamination in short-term exposed shellfish? A microcosm study.

In this study, the capacity of oysters to bioaccumulate fecal stanols and to record a source-specific fingerprint was investigated by the short-term contamination of seawater microcosms containing oysters with a human effluent. Contaminated oysters bioaccumulated the typical fecal stanols coprostanol and 24-ethylcoprostanol and their bioaccumulation kinetics were similar to that of the Fecal Indicator Bacteria Escherichia coli used in European legislation. Although stanol fingerprints of contaminated water allowed the identification of the human specific fingerprint, this was not the case for oysters. This discrepancy is attributed to (i) high concentrations of endogenous cholestanol and sitostanol, responsible for "unbalanced" stanol fingerprints, (ii) different accumulation/depuration kinetics of fecal coprostanol and 24-ethylcoprostanol and (iii) the limits of the analytical pathway used. These results show that fecal stanols bioaccumulated by oysters are useful to record fecal contamination but the usefulness of stanol fingerprints to identify specific sources of contamination in shellfish currently seems limited.

Development of the analysis of fecal stanols in the oyster Crassostrea gigas and identification of fecal contamination in shellfish harvesting areas.

The objective of this work was to study the effects of washing and purification steps on qualitative and quantitative analysis of fecal stanols in the oyster Crassostrea gigas using either single or a combination of lipid purification steps on silica gel or aminopropyl bonded silica gel (NH2) or a washing step. Among the three analytical pathways compared, the two including water extraction or NH2 purification did not lead to higher recoveries and decreased repeatabilities of extractions compared to the single purification on silica gel. This latter led to similar recoveries (ca. 80%) and repeatabilities (ca. 10%) for both spiked standards (coprostanol and sitostanol). This analytical pathway has been applied to oysters collected in a harvesting area in Brittany (France) where fecal contaminations are important and allowed to quantify eight stanols in oysters. The relative proportions of fecal stanols of these oysters were combined with principal component analysis in order to investigate the usefulness of their stanol fingerprints to record a fecal contamination and to distinguish its source between human, porcine and bovine contaminations. Oysters non-fecally contaminated by Escherichia coli did not present specific stanol fingerprints while oysters fecally contaminated had a bovine fingerprint, suggesting a contamination of these samples by bovine sources. As a consequence, the method developed here allows the use of stanol fingerprints of oysters as a microbial source tracking tool that can be applied to shellfish harvesting areas subjected to fecal contaminations in order to identify the different sources of contamination and improve watershed management.

Microscale investigations of the fate of heavy metals associated to iron-bearing particles in a highly polluted stream.

As it flows through a dense steelmaking area, the Fensch River does transport iron-rich particles and colloids, displaying high contents in metallic contaminants (Zn, Cr, Pb, Cu, Ni, and As). Chemical analysis using inductively coupled plasma mass spectrometry (ICP-MS) was carried out on three compartments-waters, suspended materials, and sediments-along the river linear. The variations of metallic trace element concentrations along the river were shown to be partially related to external inputs (industrial and domestic wastewaters and urban surfaces leaching). However, some discrepancies of element partitioning were evidenced. Pb, Cu, and Mn tend to concentrate in suspended particulate and in dissolved fraction, while Cr and As follow the trend of Fe and concentrate within sediments of the most downstream station, just before the junction with Moselle waters. Zn appears strongly associated to iron-rich particles, resulting in a decrease of its concentration in waters for the last station. Along the Fensch linear, the variation of metal partitioning between water and particulate phases is accompanied with strong modifications of the nature and mineralogy of iron-rich particles, as evidenced by microanalyses using electron and X-ray beams. The combination of bulk analyses using ICP-MS and microanalyses applied to the three compartments allowed us to propose a three-step process "settling-weathering-resuspension" to explain Zn partitioning.

Quantification of fossil organic matter in contaminated sediments from an industrial watershed: validation of the quantitative multimolecular approach by radiocarbon analysis.

The quantitative multimolecular approach (QMA) based on an exhaustive identification and quantification of molecules from the extractable organic matter (EOM) has been recently developed in order to investigate organic contamination in sediments by a more complete method than the restrictive quantification of target contaminants. Such an approach allows (i) the comparison between natural and anthropogenic inputs, (ii) between modern and fossil organic matter and (iii) the differentiation between several anthropogenic sources. However QMA is based on the quantification of molecules recovered by organic solvent and then analyzed by gas chromatography-mass spectrometry, which represent a small fraction of sedimentary organic matter (SOM). In order to extend the conclusions of QMA to SOM, radiocarbon analyses have been performed on organic extracts and decarbonated sediments. This analysis allows (i) the differentiation between modern biomass (contemporary (14)C) and fossil organic matter ((14)C-free) and (ii) the calculation of the modern carbon percentage (PMC). At the confluence between Fensch and Moselle Rivers, a catchment highly contaminated by both industrial activities and urbanization, PMC values in decarbonated sediments are well correlated with the percentage of natural molecular markers determined by QMA. It highlights that, for this type of contamination by fossil organic matter inputs, the conclusions of QMA can be scaled up to SOM. QMA is an efficient environmental diagnostic tool that leads to a more realistic quantification of fossil organic matter in sediments.