Emmanuelle Petelet-Giraud

Improving the management of nitrate pollution in water by the use of isotope monitoring: the δ15N, δ18O and δ11B triptych

In spite of increasing efforts to reduce nitrogen inputs into ground water from intensive agriculture, nitrate (NO3) remains one of the major pollutants of drinking-water resources worldwide, with NO3 levels approaching the defined limit of 50 mg l−1 in an increasing number of water bodies. Determining the source(s) of contamination in water is an important first step for improving its quality by emission control. The Life ISONITRATE project aimed at showing the benefit of a multi-isotope approach (δ15N and δ18O of NO3, and δ11B), in addition to conventional hydrogeological analysis, to track the origin of NO3 contamination in water. Based on land use and local knowledge, four distinct cases were studied: (1) natural soil NO3, (2) natural denitrification, (3) single source of NO3 pollution and (4) multiple sources of NO3 pollution. Our results show the added value of combining isotope information, compared to knowledge based on local authorities’ experience, land use and the ‘classical’ chemical approach, by efficiently identifying the number and type of NO3 source(s) for each watershed studied.

Variability of 87Sr/86Sr in water draining granite revealed after a double correction for atmospheric and anthropogenic inputs

Abstract In a geochemical characterization of surface waters draining granites of the Vienne district, France, isotopic signatures strictly linked to water—rock interactions were determined by applying a double correction for atmospheric and anthropogenic inputs; the former based on the conservative behaviour of Cl and the latter based on the Sr concentrations and isotopic signatures, which are the only variables with clearly identifiable characteristics. The double-correction concept was validated by comparing the results with the theoretical Sr isotopic signature of water in equilibrium with the parent rock. The weathering model is based on the preferential dissolution of the three main Sr-bearing mineral phases: plagioclase, potassium feldspar and biotite. The Sr isotopic signatures of the waters are in good agreement with the calculated ones. The relative scattering observed for waters draining the same plutonic intrusion can be explained by water—rock interactions within different layers of the weathering profile.

Soil–Sediment–River Connections: Catchment Processes Delivering Pressures to River Catchments

This chapter presents and discusses the soil–sediment–river connections and summarises the pressures at the basin scale from their causes (natural and anthropogenic drivers) to their consequences (impacts on biophysical status). Nine important pressures on river basins are evidenced with respect to their temporal and spatial scale of occurrence and their impact on the river basin at the basin scale and concerns: erosion, sealing, compaction, hydromorphological changes, salinisation, contamination, changes in water quantity, acidification and reduction of soil organic matter. Each pressure can affect the biophysical status, and the simultaneous presence of pressures can have cumulative or compensatory impacts on biophysical status through propagation. Eight biophysical statuses were identified (concentration of chemicals, trophic status, biota status, buffering capacity, salinity, suspended matter and sediment, water level, morphology and pedology), and the pressures are described in this chapter in the sense of impacts on these biophysical status.

Boron isotope signatures in the coastal groundwaters of French Guiana

[1] Drinking water used by the population of French Guiana comes mostly from rivers and can induce major health impacts. Consequently, groundwaters are being studied in terms of an alternative drinking water supply. In this context, boron isotopes were applied to the coastal aquifers to better constrain the water-rock interactions. We found that the δ 1 1 B signatures vary between -2.98 and 49.35%o in the groundwaters and between 36.35 and 42.41%o in the river waters and that the local seawater gave a value of 40.76%o. We also noted an inverse correlation between groundwater pH and δ 1 1 B: this relationship, previously demonstrated experimentally, is particularly well defined in the French Guiana coastal aquifer because of the wide pH range (4.18 to 7.64) naturally present in the groundwaters. It would appear that the variations in δ 1 1 B values are linked to water-rock interaction processes (e.g., dissolution/precipitation of silicates).

Coastal groundwater salinization: Focus on the vertical variability in a multi-layered aquifer through a multi-isotope fingerprinting (Roussillon Basin, France)

The Roussillon sedimentary Basin (South France) is a complex multi-layered aquifer, close to the Mediterranean Sea facing seasonally increases of water abstraction and salinization issues. We report geochemical and isotopic vertical variability in this aquifer using groundwater sampled with a Westbay System® at two coastal monitoring sites: Barcarès and Canet. The Westbay sampling allows pointing out and explaining the variation of water quality along vertical profiles, both in productive layers and in the less permeable ones where most of the chemical processes are susceptible to take place. The aquifer layers are not equally impacted by salinization, with electrical conductivity ranging from 460 to 43,000μS·cm(-1). The δ(2)H-δ(18)O signatures show mixing between seawater and freshwater components with long water residence time as evidenced by the lack of contribution from modern water using (3)H, (14)C and CFCs/SF6. S(SO4) isotopes also evidence seawater contribution but some signatures can be related to oxidation of pyrite and/or organically bounded S. In the upper layers (87)Sr/(86)Sr ratios are close to that of seawater and then increase with depth, reflecting water-rock interaction with argillaceous formations while punctual low values reflect interaction with carbonate. Boron isotopes highlight secondary processes such as adsorption/desorption onto clays in addition to mixings. At the Barcarès site (120m deep), the high salinity in some layers appear to be related neither to present day seawater intrusion, nor to Salses-Leucate lagoonwater intrusion. Groundwater chemical composition thus highlights binary mixing between fresh groundwater and inherited salty water together with cation exchange processes, water-rock interactions and, locally, sedimentary organic matter mineralisation probably enhanced by pyrite oxidation. Finally, combining the results of this study and those of Caballero and Ladouche (2015), we discuss the possible future evolution of this aquifer system under global change, as well as the potential management strategies needed to preserve quantitatively and qualitatively this water resource.

Use of Compound-Specific Nitrogen (d 15 N), Oxygen (d 18 O), and Bulk Boron (d 11 B) Isotope Ratios to Identify Sources of Nitrate-Contaminated Waters: A Guideline to Identify Polluters

The use of various isotopes (d15N, d18O & d11B) to identify the sources of nitrate (NO3 −) present in natural waters is described. Then a new guideline of how to apply the multi-isotope approach is presented. This guideline is written for policy makers and scientists who are involved in the different steps and processes related to nitrate contaminated waters including monitoring and data interpretation. NO3 − is a common pollutant in water (both surface and groundwater). In several water bodies over Europe, point measurements identify that the level of this pollutant is higher than the reference value of 50 mgL−1, defined by the European Union (EU) Water Framework Directive 2000/60/EC (European Parliament, 2000). This directive also states that all waters have to reach a “good status” (i.e., good quality) by 2015. This statement implies that EU member states have to take actions to achieve this goal. One of the major obstacles with NO3 − contamination in water is the identification of the corresponding source(s) of pollution, a prerequisite for properly designing appropriate actions and remediation. Recent studies have proven the added value of analyzing compound specific isotopic signature (CSIA) of nitrate (both nitrogen (d15N), oxygen (d18O) and bulk boron (d11B) isotopic composition) to define the origin/source of NO3 − in waters. This definition is possible because different sources of nitrate have distinct isotopic signatures. The recent EU-LIFE ISONITRATE project demonstrated the benefit of the multi-isotope approach, while the presented guideline to implement this method is one of the outcomes of this project. More details on the scientific results of ISONITRATE are available at http://isonitrate.brgm.fr/.

Dissolved Fluxes of the Ebro River Basin (Spain): Impact of Main Lithologies and Role of Tributaries

The aim of this study was to evaluate, over more than 20 years, the export fluxes for dissolved loads on the catchment scale of the Ebro River basin in Spain. Data are compiled from the databank of the Confederacion Hidrografica del Ebro (CHE). The spatial and temporal distribution of daily discharges, physico-chemical parameters and chemical data covering the last two decades (1981–2003) were investigated in the Ebro Basin on five monitoring stations along the Ebro River (Mendavia, Castejon, Zaragoza, Sastago and Tortosa), as well as six stations at the outlet of the main tributaries (Arga, Aragon, Gallego, Jalon, Cinca and Segre). The dissolved load of the rivers at the Ebro Basin scale was characterised through the EC, total dissolved solids (TDS) and the major elements chemical data. The surface water can be classified into three main categories, a clear dominance of Ca–SO4 water type, a Ca–HCO3 type mainly encountered in the upper part of the basin and some data presenting a Na–Cl water type. The TDS values are highly variable, both in time and in space, in the range 390–1,360 mg L−1. The dissolved exportations to the Mediterranean Sea and the relative contribution of the different tributaries were calculated. The Ebro basin in its upper part (upstream Mendavia) contributes around 22.4% of the total exported flux near the outlet (Tortosa) over the studied period. The tributaries that mainly contribute to the total exported load are the Cinca and Segre (19% and 17% respectively). The Aragon, Gallego and Jalon contributions are very low, often less than 5% of the total exported flux. The specific TDS flux at the outlet of the Ebro is 70 ± 23 t km−2 year−1 and 108 ± 24 t km−2 year−1 upstream in Mendavia while the highest chemical erosion rate was calculated for the Arga with 251 ± 55 t km−2 year−1. The dissolved export fluxes represent the major export from the Ebro basin, and the respective contribution of carbonate and evaporite (gypsum) with respect to the TDS was then calculated using the major element concentrations and discharge data. In the upper part of the Ebro Basin, carbonate weathering is dominant compared to gypsum weathering while downstream the dissolved exportations are dominated by carbonate weathering. For the tributaries, most of them are dominated by evaporite weathering. The exportation rates at the outlet of the watershed shows dissolved exportation derived from gypsum weathering, that are about 1.5 times that derived from carbonate weathering.

Multi-layered water resources, management, and uses under the impacts of global changes in a southern coastal metropolis: When will it be already too late? Crossed analysis in Recife, NE Brazil

Coastal water resources are a worldwide key socio-environmental issue considering the increasing concentration of population in these areas. Here, we propose an integrative transdisciplinary approach of water resource, water management and water access in Recife (NE Brazil). The present-day water situation is conceptualized as an imbricated multi-layered system: a multi-layered water resource, managed by a multi-layered governance system and used by a multi-layered social population. This allows identifying processes of quantitative, qualitative, and sanitary conflicts between governance and population strategies regarding water supply, as well as the institutional and individual denials of these conflicts. Based on this model, we anticipate future water-related problematic fates. Concerning the water resource system, the rapid groundwater level decrease due to unsustainable water predatory strategies, and the very low recharge rate have drastically modified the aquifer system functioning, inducing hydraulic connection between shallow groundwater (contaminated and locally salty) and deep ones (mostly fresh, with local inherited salinity), threatening the deep strategic water resource. Concerning the water governance system, the investments to increase the capacity storage of surface water, the water regulation agencies and the public/private partnership should shortly improve the water supply and wastewater issue. Nevertheless, the water situation will remain highly fragile due to the expected water demand increase, the precipitation decrease and the sea-level increase. Concerning the water access system, the population variably perceives these current and further effects and the possible mitigation policies, and develops alternative individual strategies. Authorities, policymakers and water managers will have to implement a well-balanced water governance, taking into account the specificities of the PPP, public and private groundwater users, and with a strong political willingness for a sustainable water management to ensure water supply for all the population. In other words, an anticipatory and integrated vision is necessary to reduce the discrepancies in this complex system.

Autotrophic denitrification supported by biotite dissolution in crystalline aquifers (1): New insights from short-term batch experiments

We investigate denitrification mechanisms through batch experiments using crushed rock and groundwater from a granitic aquifer subject to long term pumping (Ploemeur, France). Except for sterilized experiments, extensive denitrification reaction induces NO3 decreases ranging from 0.3 to 0.6mmol/L. Carbon concentrations, either organic or inorganic, remain relatively stable and do not document potential heterotrophic denitrification. Batch experiments show a clear effect of mineral dissolution which is documented through cation (K, Na, Ca) and Fluoride production. These productions are tightly related to denitrification progress during the experiment. Conversely, limited amounts of SO4, systematically lower than autotrophic denitrification coupled to sulfur oxidation stoichiometry, are produced during the experiments which indicates that sulfur oxidation is not likely even when pyrite is added to the experiments. Analysis of cation ratios, both in isolated minerals of the granite and within water of the batch, allow the mineral dissolution during the experiments to be quantified. Using cation ratios, we show that batch experiments are characterized mainly by biotite dissolution. As biotite contains 21 to 30% of Fe and 0.3 to 1.7% of F, it constitutes a potential source for these two elements. Denitrification could be attributed to the oxidation of Fe(II) contained in biotite. We computed the amount of K and F produced through biotite dissolution when entirely attributing denitrification to biotite dissolution. Computed amounts show that this process may account for the observed K and F produced. We interpret these results as the development of microbial activity which induces mineral dissolution in order to uptake Fe(II) which is used for denitrification. Although pyrite is probably available, SO4 and cation measurements favor a large biotite dissolution reaction which could account for all the observed Fe production. Chemical composition of groundwater produced from the Ploemeur site indicates similar denitrification processes although original composition shows mainly plagioclase dissolution.