Contrasting platinum trajectories in three major French rivers using dated sediment cores (1910-2021): From geochemical baseline to emerging source signals.

Platinum (Pt) is a Technology Critical Element (TCE) which, since the 1990s, has been mainly used in the industry in catalytic converters for automobile emission control. Previous studies have shown Pt contamination of road-side sediments and surface sediments in urban rivers and lakes but few of them have addressed temporal variations. The present work presents historical Pt concentration trends in 137Cs-dated sediment cores from floodplains or secondary channels at the outlets of three major French watersheds (Loire, Rhone, and Seine Rivers) covering the past ∼110 years, i.e., from the 1910s to 2021. Platinum baseline levels in the sediment were estimated for the Loire River (0.76 ± 0.22 µg kg-1 for the period ∼1910-∼1955) and the Rhone River (1.64 ± 0.41 µg kg-1), and historical Pt variations seem to reflect variations in hydrodynamics and grain size composition. Since the early 2000s, Pt concentrations in the Loire and the Rhone River sediments tend to increase (>2.5 µg kg-1) and were attributed to the use of car catalytic converters, an emerging technology since the 1990s using >50 % of European Pt demand. High and variable historical Pt concentrations (up to 14.6 µg kg-1) in the Seine River sediments may reflect legacy Pt sources due to former anthropogenic activities in this watershed, such as the use of Pt-based catalysts for petroleum refinery since the end of the 1940s, coal handling and precious metals refining, probably concealing the likely presence of an emerging traffic-related Pt signal. This first comparison of historical Pt concentration trends in sediments from contrasting watersheds allows to distinguish signals originating from different natural and anthropogenic sources (background level, historical sources, road traffic).

Our Neighbor the Beaver: Anthropomorphism to Facilitate Environmental Mediation in Rural France.

The European Beaver came close to extinction in France at the beginning of the twentieth century. It has since been reintroduced across the country but its gradual expansion has caused conflicts linked to its behavior, exacerbated by strict enforcement of laws against poaching or the destruction of beaver dams. We conducted field research in 2021 in three municipalities, two in the Loire basin and one in the Seine basin. Using a reconciliation ecology perspective and participatory science methodology, we investigated the dynamics of beaver rejection and approaches to defuse them by emphasizing the anthropomorphic characters of the beaver. During successive meetings with study participants, we attempted to mitigate attitudes of human/nature opposition by presenting humans as part of ecosystems, engaged in social relations with other living beings using the concept of "neighborhood," which specifically places these relationships and has proven to be more readily adopted than the more abstract concepts of ecosystem, habitat, or biotope. We used a three-stage process of reconciliation/reconnection/protection to raise environmental awareness and concerns. Our results can provide guidelines for environmental agents and officers to engage local populations in conservation efforts. Supplementary Information: The online version contains supplementary material available at 10.1007/s10745-023-00406-z.

Deciphering sources of U contamination using isotope ratio signatures in the Loire River sediments: Exploring the relevance of 233U/236U and stable Pb isotope ratios.

A broad range of contaminants has been recorded in sediments of the Loire River over the last century. Among a variety of anthropogenic activities of this nuclearized watershed, extraction of uranium and associated activities during more than 50 years as well as operation of several nuclear power plants led to industrial discharges, which could persist for decades in sedimentary archives of the Loire River. Highlighting and identifying the origin of radionuclides that transited during the last decades and were recorded in the sediments is challenging due to i) the low concentrations which are often close or below the detection limits of routine environmental surveys and ii) the mixing of different sources. The determination of the sources of anthropogenic radioactivity was performed using multi-isotopic fingerprints (236U/238U, 206Pb/207Pb and 208Pb/207Pb) and the newly developed 233U/236U tracer. For the first time 233U/236U data in a well-dated river sediment core in the French river Loire are reported here. Results highlight potential sources of contamination among which a clear signature of anthropogenic inputs related to two accidents of a former NUGG NPP that occurred in 1969 and 1980. The 233U and 236U isotopes were measured by recent high performance analytical methods due to their ultra-trace levels in the samples and show a negligible radiological impact on health and on the environment. The determination of mining activities by the use of stable Pb isotopes is still challenging probably owing to the limited dissemination of the Pb-bearing material marked by the U-ore signature downstream to the former U mines.

Thermal signatures identify the influence of dams and ponds on stream temperature at the regional scale.

Anthropogenic impoundments (e.g. large dams, small reservoirs, and ponds) are expanding in number globally, influencing downstream temperature regimes in a diversity of ways that depend on their structure and position along the river continuum. Because of the manifold downstream thermal responses, there has been a paucity of studies characterizing cumulative effect sizes at the catchment scale. Here, we introduce five thermal indicators based on the stream-air temperature relationship that together can identify the altered thermal signatures of dams and ponds. We used this thermal signature approach to evaluate a regional dataset of 330 daily stream temperature time series from stations throughout the Loire River basin, France, from 2008 to 2018. This basin (105 km2) is one of the largest European catchments with contrasting natural and anthropogenic characteristics. The derived thermal signatures were cross-validated with several known catchment characteristics, which strongly supported separation into dam-like, pond-like and natural-like signatures. We characterize the thermal regime of each thermal signature and contextualize it using a set of ecologically relevant thermal metrics. Results indicate that large dams decreased summer stream temperature by 2 °C and delayed the annual stream temperature peak by 23 days relative to the natural regimes. In contrast, the cumulative effects of upstream ponds increased summer stream temperature by 2.3 °C and increased synchrony with air temperature regimes. These thermal signatures thus allow for identifying and quantifying downstream thermal and ecological influences of different types of anthropogenic infrastructures without prior information on the source of modification and upstream water temperature conditions.

Suspended particulate matter determines physical speciation of Fe, Mn, and trace metals in surface waters of Loire watershed.

This study investigates the spatiotemporal variability of major and trace elements, dissolved organic carbon (DOC), total dissolved solids (TDS), and suspended particulate matter (SPM) in surface waters of several hydrosystems of the Loire River watershed in France. In particular, this study aims to delineate the impact of the abovementioned water physicochemical parameters on natural iron and manganese physical speciation (homoaggregation/heteroaggregation) among fine colloidal and dissolved (< 10 nm), colloidal (10-450 nm) and particulate (> 450 nm) phases in Loire River watershed. Results show that the chemistry of the Loire River watershed is controlled by two end members: magmatic and metamorphic petrographic context on the upper part of the watershed; and sedimentary rocks for the middle and low part of the Loire. The percentage of particulate Fe and Mn increased downstream concurrent with the increase in SPM and major cations concentration, whereas the percentage of colloidal Fe and Mn decreased downstream. Transmission electron microscopy analyses of the colloidal and particulate fractions (from the non-filtered water sample) revealed that heteroaggregation of Fe and Mn rich natural nanoparticles and natural organic matter to the particulate phase is the dominant mechanism. The heteroaggregation controls the partitioning of Fe and Mn in the different fractions, potentially due to the increase in the ionic strength, and divalent cations concentration downstream, and SPM concentration. These findings imply that SPM concentration plays an important role in controlling the fate and behavior of Fe and Mn in various sized fractions. Graphical abstract Physical speciation by heteroaggregation of (Fe-Mn) compounds: high [SPM] → [Fe-Mn] particulate faction; low {SPM] → [Fe-Mn] colloid-dissolved fraction.

Nutrient inputs and hydrology together determine biogeochemical status of the Loire River (France): Current situation and possible future scenarios.

The Grafs-Seneque/Riverstrahler model was implemented for the first time on the Loire River for the 2002-2014 period, to explore eutrophication after improvement of wastewater treatments. The model reproduced the interannual levels and seasonal trends of the major water quality variables. Although eutrophication has been impressively reduced in the drainage network, a eutrophication risk still exists at the coast, as shown by the N-ICEP indicator, pointing out an excess of nitrogen over silica and phosphorus. From maximum biomass exceeding 120 µgChla l-1 in the 1980's, we observed decreasing maximum values from 80 to 30 µgChla l-1 during the period studied. Several scenarios were explored. Regarding nutrient point sources, a low wastewater treatment scenario, similar to the situation in the 1980's, was elaborated, representing much greater pollution than the reference period (2002-2014). For diffuse sources, two agricultural scenarios were elaborated for reducing nitrogen, one with a strict application of the agricultural directives and another investigating the impact of radical structural changes in agriculture and the population's diet. Although reduced, a risk of eutrophication would remain, even with the most drastic scenario. In addition, a pristine scenario, with no human activity within the basin, was devised to assess water quality in a natural state. The impact of a change in hydrology on the Loire biogeochemical functioning was also explored according to the effect of climate change by the end of the 21st century. The EROS hydrological model was used to force Riverstrahler, considering the most pessimistic SRES A2 scenario run with the ARPEGE model. Nutrient fluxes all decreased due to a >50% reduction in the average annual discharge, overall reducing the risk of coastal eutrophication, but worsening the water quality status of the river network. The Riverstrahler model could be useful to help water managers contend with future threats in the Loire River, at the scale of its basin and at smaller nested scales.

Storage and source of polycyclic aromatic hydrocarbons in sediments downstream of a major coal district in France.

During the 20th century, the local economy of the Upper Loire Basin (ULB) was essentially based on industrial coal mining extraction. One of the major French coal districts with associated urban/industrial activities and numerous coking/gas plants were developed in the Ondaine-Furan subbasins, two tributaries of the upper Loire main stream. To determine the compositional assemblage, the level and the potential sources of contamination, the historical sedimentary chronicle of the 16 US EPA priority polycyclic aromatic hydrocarbons (PAHs) has been investigated. PAH concentrations were determined using gas chromatography/mass spectrometry (GC/MS) in a dated core, sampled in the Villerest flood-control reservoir located downstream of the Ondaine-Furan corridor (OFC). The most contaminated sediments were deposited prior to 1983 (Σ16PAHs ca. 4429-13,348 ng/g) and during flood events (Σ16PAHs ca. 6380 ng/g - 1996 flood; 5360 ng/g - 2003 flood; 6075 ng/g - 2008 flood), especially in medium and high molecular weight PAHs. Among them, typical pyrogenic PAHs such as FLT, PYR, BbF and BaP were prevalent in most of the core samples. In addition, some PAHs last decade data is available from the Loire Bretagne Water Agency and were analyzed using high-performance liquid chromatography with postcolumn fluorescence derivatization (HPLC/FLD). These results confirm that the most highly contaminated sediments were found downstream of OFC (Σ16PAHs ca. 2264-7460 ng/g). According to the observed molecular distribution, PAHs are originated largely from high-temperature pyrolytic processes. Major sources of pyrogenic PAHs have been emphasized by calculation of specific ratios and by comparison to reported data. Atmospheric deposition of urban and industrial areas, wood combustion and degraded coal tar derived from former factories of coking/gas plants seem to be the major pyrogenic sources. Specifically, particular solid transport conditions that can occur during major flood events lead us to emphasize weathering of former contamination sources, such as more preserved coal tar.