Enhanced weathering (EW) is proposed as a key strategy for climate change mitigation and carbon dioxide removal technology. Dissolution of silicate minerals enhances the alkalinity of the pore water, resulting at a shift of the carbonate system towards carbonate and bicarbonate, leading to higher dissolved inorganic carbon when the water is equilibrated with the atmosphere. Here, we evaluated the effects of EW on a crop ecosystem under future climate change conditions within a macro-scale ecotron – an enclosed facility enabling complete quantification of carbon fluxes among the atmosphere, vegetation, soil, and leachates. We monitored all greenhouse gases in deep mesocosms representative of marginal soil conditions and, after liming and fertilization, applied 10 t ha−1 of basalt at the start of the experiment. EW treatment resulted in an almost three-fold enhancement of measured carbon flux into the soil, achieving rates up to 1.5 t ha−1 during the growing season. Moreover, the observed carbon sequestration surpassed the levels expected from weathering processes alone. This is notable because the near-neutral soil pH environment was not favourable to EW kinetics. Therefore, we conclude that EW facilitated significant carbon accrual in our simulated ecosystems via not only carbonate precipitation but also enhanced biogeochemical activities promoting additional carbon storage. Based on these findings, we speculate on the underlying pathways responsible for such outcomes.

According to the United Nations Educational, Scientific and Cultural Organization (2024), the quality and quantity of water available for all our uses will become the major challenge of the 21st century. Increased temperatures, problems of oxygenation, (micro)pollutants concentrations are some of the problems to be dealt with, whose consequences are many, not only for livestock farming, fishing and aquatic biodiversity, but also for drinking water production. In Europe the Water Framework Directive (WFD) aims to assess the ecological and chemical status of surface waters at the level of the river basin district (i.e., “an area of land and sea, comprising one or more river basins and associated groundwater and coastal waters, identified as the main unit for the purposes of river basin management”). Small streams, typical of watershed headwaters, are not monitored in the WFD. However, they are estimated to account for up to 80% of the total hydrographic length in a river watershed, making a major contribution to the water supply of downstream ecosystems (MacDonald and Coe 2007). Since 2010, the LTSER Zone Atelier du Bassin de la Moselle has been involved on the long-term monthly monitoring, with the help of forest rangers, of an initial set of 16 pristine headwater streams in the Vosges Mountains (https://acev.otelo.univ-lorraine.fr/ , https://deims.org/22915474-7c50-47c1-8239-6c59fa924a1b). These streams are running on granite or sandstone soils in forests dotted with wetlands of various size. The monitoring stations are upstream of any anthropogenic activity, except forestry and extensive tourism. This initial set has been progressively expanded with other nearby streams. However, all of them belong to the same mountainous typology. With this in mind, a participatory research project, O'CitEaux (https://ociteaux.fr/), has been set up to monitor the quality of small rivers in a wider context, using new low-cost sensors. We believe in the importance of such monitoring in the face of climate change (Whyte et al. 2024, von Gönner et al. 2024). Together with an increase of temperature, longer periods of drought interspersed with episodes of heavy rainfall are expected in the coming decades. The flow of small rivers and the quality of their water are therefore likely to be significantly altered. The O'CitEaux participants are: fishing association members (A), primary and secondary school teachers and their students (B), or just people interested in quality of the aquatic environment (C). fishing association members (A), primary and secondary school teachers and their students (B), or just people interested in quality of the aquatic environment (C). Participants A and B are equipped with a low-cost water case which enables them to measure pH, conductivity and temperature in-situ and in the future dissolved organic matter (Ritson et al. 2014). Participants A measure the water level and the width of the watercourse, which can be used for estimation of the discharge rate after proper calibration. All participants collect water samples (one-shot or on a monthly basis, depending upon their level of implication), filtrate them and send them immediately to the research laboratory. Additional information about the location of the station and its immediate surroundings, as well as on biodiversity (odonata, fish, etc.), is collected. Samples collected either by researchers or by O'CitEaux participants follow the same analysis process: filtration at 0.45 µm, analysis of dissolved organic and inorganic carbon, dissolved total nitrogen and major anions and cations, DOM spectral characteristics by UV-visible spectroscopy (aromaticity and molecular weight scoring) and fluorescence spectroscopy (DOM humification, etc.). To date, 150 streams (mainly in France, UK and Scandinavia) have been sampled (i.e., 400 samples) in addition to the 40 streams monitored directly by the researchers on a monthly basis (Fig. 1). The variety of their typology is shown in Fig. 2: high dissolved inorganic carbon concentrations reflect rivers running on calcareous soils, when high dissolved organic carbon concentrations characterized rivers influenced by forests and peatlands. The presentation will discuss the water quality results in function of geology, land use and season and compare them to WFD data collected at a larger scale. An example of data analysis is shown in Fig. 3 for dissolved nitrogen, with a gradient between the forested Vosges Mountains and the western zone where agriculture is more intensive. Citizen involvement (motivation, effectiveness, fear of doing the wrong thing, etc.) will be discussed as well as the best ways for feedback (database, website, counseling).

In rural areas, nitrate concentrations in surface waters most often originate from the leaching of excess N fertilizer in agricultural lands, whereas forested catchments often have good water quality. However, Douglas-fir plantations may induce nitrogen cycle unbalances which may lead to an excess of nitrate production in the soil. We hypothesize that the excess of production of nitrate in the soil and nitrate leaching to streamwater is greater in catchments planted with Douglas fir. We used paired catchments in both France and Luxembourg with different land covers (Douglas-fir, Spruce, Deciduous, Grassland and clearcut) which were monitored over a 3-5 year period in order to assess the effect of Douglas-fir plantations on the chemical composition of surface water. Nitrate concentration in the soil and groundwater were also monitored. The results show that nitrate concentrations in streams draining Douglas-fir catchments were two to ten times higher than in streams draining other land covers, but were similar to the clearcut catchment. Nitrate concentrations under Douglas-fir in groundwater (up to 50 mg L-1) and in the soil were also higher than under all other land covers. Soil nitrate concentration was related to stream nitrate concentration. This suggests that soil processes, through excessive nitrate production under Douglas-fir, are driving the nitrate concentration in the stream water and our hypothesis of a transfer of a fairly large proportion of this excessive production from the soil to the stream is supported. This study also shows that nitrate concentrations in surface and ground waters in rural areas could also originate from Douglas fir forested catchments. The impact of Douglas-fir is nevertheless reduced downstream through a dilution effect: mixing tree species at the catchment scale could thus be a solution to mitigate the effect of Douglas-fir on nitrate concentration in surface waters.

The knowledge of the sources of base cations in stream water is a prerequisite to assess potential effects of changing environmental conditions such as changing rainfall, weathering or groundwater flows on cation export with stream water. This study use stable Mg isotopes to identify potential sources in the well-studied catchment of Krycklan located on gneissic bedrock covered by quaternary sediments in Sweden. Samples were collected from open filed rain, throughfall, stream, soil, rock and litterfall. The δ26Mg values of these samples was determined and the contributions of different sources to Mg fluxes in the stream were determined from the variation of the Mg isotope and Sr / Mg ratios.

Many forest soils are acidic and have very low plant-available pools of magnesium. Past and present sylvicultural, nutritional and/or climatic pressures endured by forest ecosystems can result in net losses of nutrients and ecosystem function losses. Liming with a carbonate product is an alternative to counteract these degradations but the effects of liming on the biogeochemical cycling of nutrients over time and the dynamics of Mg released from liming products are still unclear. We studied the Mg isotopes composition in four paired-treatment experimental beech forest ecosystems in northern France. At the sites where dolomitic lime was applied, the variation in exchangeable and foliar δ26Mg demonstrated the direct contribution of dolomite-derived Mg to the replenishment of topsoil exchangeable pools and to tree nutrition improvement: dolomite-derived Mg was incorporated into the biological cycling which allows its retention on the mid to long term in the soil–plant system. At the sites limed with calcium carbonate, the changes in exchangeable and foliar Mg contents and δ26Mg observed on the long term suggest that the applied product contained a small amount of Mg and/or that Mg cycling changed after liming, to cope in particular with the low Mg availability. Lastly, our results highlight the high δ26Mg of the organic layer (humus): fractionation processes occurring within this layer (mineralization/ageing of organic matter, preferential retention of 26 Mg) could explain these singular signatures that could greatly influence the topsoil Mg exchangeable pools.

Some 30 years ago, surveys of the surface water quality in the Vosges Moutains revealed a strong headstream water acidification, with high concentrations in dissolved aluminium, and the observed consequences on the aquatic biodiversity (Probst et al., 1990). In the early 2000s some of these headstreams (Grand Clos, Ventron, Rouge Rupt, Cellet) were included in a set of 16 headstreams which constitute the Vosges Acidification Observatory of the Zone Atelier du Bassin de la Moselle. Their surface water has been sampled monthly and analyzed in terms of major anions and cations, as well as dissolved aluminium and, since 2012, in terms of dissolved organic matter. In spring 2021, a new survey of the headstreams investigated in the 1990s was organized. Nineteen streams could be sampled. All the streams running on granite bedrock had a higher pH than in 1990. Most of them showed lower aluminium concentrations. The improvement for headstreams running on sandstone seems more limited and new data need to be collected. The presentation will include data collected in summer 2021 as well as long term data for the headstreams included in the Vosges Acidification Observatory to check seasonal and yearly effects.

Liming with Ca and Mg carbonates is commonly used to reduce soil and stream acidity and to improve vegetation growth and nutrition in forests. Ten years ago, dolomite lime was experimentally applied to a forest catchment on granite in the Vosges Mountains (northeast France), which is characterized by acid soils and drained by an acid stream. The average Mg isotope composition of the dolomite lime (-1.75‰) was low compared with that of tree foliage (-0.70‰), granite and deep soil layers (-0.40‰), and stream water (-0.80‰) in the control catchment. After liming, the exchangeable Mg concentrations in surface soil layers, which were initially very low, increased, and the Mg isotope composition decreased (up to -0.60‰). The decrease was smaller in deeper layers but not in proportion to the increase in exchangeable Mg content, suggesting contributions from mineralization of organic matter and/or displacement of exchangeable Mg from surface layers. Before application, Mg concentration in beech and fir leaves was low, and that of 1-yr-old fir needles was lower than that in current needles. Internal Mg translocation within fir needles also resulted in a lower δMg of older needles. Three years after dolomite application, the Mg isotope composition of plant leaves was lower than that in the control catchment; this decrease (up to -1.00‰) was attributed to direct uptake of Mg from dissolving dolomite. Liming doubled the concentration of Mg in the stream, whereas the Mg isotope composition decreased correspondingly from -0.80 to -1.20‰, indicating a fast transfer of dolomite Mg to the stream. Our findings indicate that monitoring of δMg may be a promising tool to study the fate of dolomitic inputs in terrestrial and aquatic ecosystems.

The monitoring of nitrates using the second derivative of UV–vis spectra has been tested for a large set of samples (≈900) covering a large range of freshwater environments in the Moselle River drainage basin (headwater streams in the Vosges Mountains; tributaries, including the Madon River and Vologne River; and waters of various origins exposed to anthropogenic activities in villages). Satisfactory linear correlations (coefficient of determination>0.74) were obtained between nitrate concentrations (measured by ion chromatography with a conductivity detector) and the maxima of the second derivative in the UV range for sets of mesotrophic and eutrophic samples. The meaningfulness of the linear regressions was verified by applying a Fisher-Snedecor test using a level of confidence of 0.05. The quality of the correlation decreased when the samples came from oligotrophic environments due to the limited sensitivity of the ion chromatography technique. UV–vis spectroscopy combined with the second derivative method appears to be a good alternative for monitoring nitrate-related eutrophication in the laboratory as well as in situ using submersible spectrophotometers.

Using nutrient budgets, it has been proven that atmospheric deposition of Mg and Ca sustains the fertility of forest ecosystems on base-poor soils. However the fate of this nutrient input within the ecosystem was presently unknown. Our hypothesis is that the biological cycling of these nutrients is very rapid and conservative to prevent further Mg and Ca losses most especially in ecosystems on base-poor soils. Stable isotopes of magnesium and calcium (26Mg and 44Ca) were used to trace the dynamics of throughfall Mg and Ca in the forest soil of a 35-year-old beech stand. The aim of the present study was to (1) understand the processes and the velocity of the incorporation of tracers in the biogeochemical cycles and (2) compute Mg and Ca budgets for the ecosystem by isotope dilution. Rainfall Mg and Ca were strongly and rapidly retained mainly by ion exchange in the thin OL litter-layer. However, Ca was much more strongly retained in the litter-layer than Mg. As a result, 2 years after the application of tracers (2012), 92 % of 26Mg and 67 % of 44Ca was released and transferred to the soil or taken up by trees. The vertical transfer of Mg was very slow only 15 % of 26Mg was found below 15 cm depth in 2012. Ca was slower than 26Mg only 9 % of 44Ca was found below 5 cm depth. Although matrix flow was the main vertical transfer process of Ca and Mg, preferential transfer in macropores occurred. Overall, Mg was more rapidly leached through the soil profile than Ca because the soil CEC was mainly composed of organic charges which affinity for Ca is much higher than for Mg. 27 % of 26Mg and 20 % of 44Ca was found in tree biomass and total tracer recovery was close to 100 %. These results suggest that no tracers were lost to drainage over the 2 years. Finally, applying the isotopic dilution theory to the whole-ecosystem enabled us to estimate Mg and Ca budgets −0.9 kg ha−1 year−1 for Mg, which was close to computed input–output budgets −0.8 and 0 kg ha−1 year−1 for Ca, which was very different from input–output budgets (−3.1 kg ha−1 year−1). Our results suggest that a Ca source is underestimated or not taken into account. Over all, organic matter of the litter-layer and in the soil profile played an essential role in the retention of throughfall Mg and Ca and their cycling within the forest ecosystem.

Environmental pressures in France and in most European countries during the last decade have led to the development of more environmentally acceptable preservation methods. In this context, wood heat treatment is one of the most investigated alternative methods. Important chemical modifications resulting from thermo-degradation reactions confer new properties to wood, like increased decay resistance or higher dimensional stability, while mechanical properties like tensile strength decrease after treatment. However, the improved durability of heat treated wood is not sufficient to allow its utilization in ground contact, where it is subjected to insect and fungi attacks. Impregnation with borax before thermal treatment could be an interesting method to improve the properties of thermally modified wood. Boron is a relatively harmless biocide that improves resistance to fungi and insects like termites. Additionally, borax can also improve wood fire resistance due to its fire retardant effect. To reduce boron leachability, two additives previously developed in the laboratory corresponding to water soluble polymerizable polyglycerol derivatives were added to the borax solution, taking advantage of thermal treatment to fix the latter through polymerization within the wood structure limiting boron leachability.

Many forest stands grow on acid and nutrient poor soils. To better understand how they cope with very low mineral resources, we investigated (1) Mg and Ca uptake in relation to depth, and (2) the allocation of these elements from the roots to the canopy, using a multi-isotopic (26Mg, 44Ca) tracing experiment in a beech stand on a very poor soil. The distribution of the tracers in the soil was taken from van der Heijden et al. (Plant Soil 369:33–45, 2013a, Geoderma 195–196:12–22, 2013b, For Ecol Manag 293:65–78, 2013c). A model simulating Mg, Ca, 26Mg and 44Ca uptake was developed and applied to estimate the vertical distribution of Mg and Ca uptake in the soil profile. The vertical distribution of tracers in aboveground biomass was measured from four felled trees 2 years after the application of the tracers. The modeled distribution of root uptake in relation to depth shows differences between Mg and Ca: the main source of Mg uptake is the litter layer (circa. 43 % of total uptake) and the top mineral soil (0–5 cm) for Ca (circa. 42 %). The deeper soil layers (15–60 cm) also contribute to uptake. The study does not show clear evidence that uptake occurs in the very deep soil layers (>70 cm). The distribution of tracers in the aboveground biomass shows a vertical gradient from the stump to the canopy with no or very small amounts of tracers being observed in the foliage during the 2 years after the application of tracers. This suggests that Mg and Ca transport from roots to leaves along the xylem sap flow is quite slow. As Ca and Mg supply to the trees from deep soil horizons is not evidenced, and tracer transport from roots to the leaves is slow, we suggest that the tree internal pool of Ca and Mg may be more active than previously thought. This pool may act as a buffer when nutrient availability is in shortage.

Accurate nutrient budgets in forest ecosystems are needed in order to plan sustainable forest management on poor soils. Such budgets require precise measurements of water and nutrient leaching through the soil. This study aims to characterize the hydrological processes and compute hydrological budgets occurring in a very poor and acidic soil under a 30-year-old beech stand in the Morvan Mountains (France). A forest plot was set up with rain collectors, lysimeters and TDR probes, and we used a deuterated water tracing experiment and two hydrological models (BILJOU and HYDRUS-1D) to estimate the proportion of preferential and slow convective water flow, and to compute the influence of preferential flow paths on nutrient leaching.Preferential flow paths were evidenced by the deuterium tracing experiment. Tracer dynamic through the soil and soil water content variations were successively modeled. This approach enabled us to define the main condition leading to preferential flow generation (rainfall above 3.5 mm/h) and quantify the proportion of preferential flow (54%). Finally, the computed nutrient leaching fluxes of major elements Ca, Mg, NO3 and Al were strongly increased when considering preferential flow paths. The experimental and modeling approach proved to be complementary and we recommend the use of tracing experiments for better model calibration, especially when their outputs are used to compute nutrient leaching fluxes. (c) 2012 Elsevier B.V. All rights reserved.

The sustainability of forest ecosystems may be at stake especially in forests on base-poor soils due to reduced nutrient deposition and intensified silvicultural practices. Understanding nutrient availability and cycling is therefore essential to manage forest soil fertility. This study aims to assess in a beech plot Mg and Ca vertical transfer in soil and root uptake using an isotopic tracing experiment.

Compared to conifers, broadleaf forests are less prone to soil and water acidification, because (1) they often have soils with larger exchangeable base cation pools, (2) the pollution scavenging capacity of deciduous trees is lower, and (3) they grow more slowly and are often less intensively managed. Since the 1980s, atmospheric deposition acidity has strongly decreased in forest ecosystems, so that the present acidification status of broadleaf forests should be improving. We used a 35 year-old beech plot in the Morvan Mountains (Burgundy, France) to question past and present acidification processes in broadleaf ecosystems.Soil exchangeable Mg, Ca and K pools measured from samples collected in 1974 and 2001 were compared and input-output budgets were computed over the 2003-2008 period. The objectives were (i) to assess Mg and Ca pool size changes over 1974-2008, (ii) to discuss the potential causes of these changes and, (iii) discuss the limits of conventional methods to study nutrient pool size changes (soil data comparison and nutrient budgets).Soil exchangeable Mg pools decreased during the 1974-2001 period while Ca and K pools remained constant, and very small. Soil solution monitoring and input-output budgets over the 2003-2008 period suggested an ongoing loss of exchangeable Ca and Mg, partly due to the desorption of sulphate from the soil which induced Mg, Ca and K depletion. Given the very low concentration in exchangeable base cations, and assuming no change in soil spatial variability, we computed that resampling soils at 10 years intervals may not unequivocally demonstrate a gain/loss of exchangeable base cations. Foliar Mg concentrations were continuously below the deficiency level, K and N concentrations decreased but Ca did not.From this, we discuss the validity/limits of the different approaches used, how the ecosystem can cope with such low levels of nutrients, and the fluxes and processes within the ecosystem that should be investigated in this perspective. (C) 2013 Elsevier B.V. All rights reserved.