Impact of nitrogenous fertilizers on carbonate dissolution in small agricultural catchments: Implications for weathering CO2 uptake at regional and global scales

The goal of this study was to highlight the occurrence of an additional proton-promoted weathering pathway of carbonate rocks in agricultural areas where N-fertilizers are extensively spread, and to estimate its consequences on riverine alkalinity and uptake of CO2 by weathering. We surveyed 25 small streams in the calcareous molassic Gascogne area located in the Garonne river basin (south-western France) that drain cultivated or forested catchments for their major element compositions during different hydrologic periods. Among these catchments, the Hay and the Montousse´, two experimental catchments, were monitored on a weekly basis. Studies in the literature from other small carbonate catchments in Europe were dissected in the same way. In areas of intensive agriculture, the molar ratio (Ca + Mg)/HCO3 in surface waters is significantly higher (0.7 on average) than in areas of low anthropogenic pressure (0.5). This corresponds to a decrease in riverine alkalinity, which can reach 80% during storm events. This relative loss of alkalinity correlates well with the NO3 content in surface waters. In cultivated areas, the contribution of atmospheric/soil CO2 to the total riverine alkalinity (CO2 ATM-SOIL/HCO3) is less than 50% (expected value for carbonate basins), and it decreases when the nitrate concentration increases. This loss of alkalinity can be attributed to the substitution of carbonic acid (natural weathering pathway) by protons produced by nitrification of Nfertilizers (anthropogenic weathering pathway) occurring in soils during carbonate dissolution. As a consequence of these processes, the alkalinity over the last 30 years shows a decreasing trend in the Save river (one of the main Garonne river tributaries, draining an agricultural catchment), while the nitrate and calcium plus magnesium contents are increasing. We estimated that the contribution of atmospheric/soil CO2 to riverine alkalinity decreased by about 7–17% on average for all the studied catchments. Using these values, the deficit of CO2 uptake can be estimated as up to 0.22–0.53 and 12–29 Tg1 yr1 CO2 on a country scale (France) and a global scale, respectively. These losses represent up to 5.7–13.4% and only 1.6–3.8% of the total CO2 flux naturally consumed by carbonate dissolution, for France and on a global scale, respectively. Nevertheless, this loss of alkalinity relative to the Ca + Mg content relates to carbonate weathering by protons from N-fertilizers nitrification, which is a net source of CO2 for the atmosphere. This anthropogenic CO2 source is not negligible since it could reach 6–15% of CO2 uptake by natural silicate weathering and could consequently partly counterbalance this natural CO2 sink

Impact of nitrogenous fertiliser-induced proton release on cultivated soils with contrasting carbonate contents: A column experiment

An experimental study was carried out in order to evaluate the impact of nitrogen fertiliser-induced acidification in carbonated soils. Undisturbed soil columns containing different carbonate content were sampled in the field. Fertiliser spreading was simulated by NH4Cl addition on top of the soil column. Soil solution composition (mainly nitrate and base cations) was studied at the soil column’s base. Nitrification occurred to a different extent depending on soil type. Higher nitrification rates were observed in calcareous soils. In all the soil types, strong correlations between leached base cation and nitrate concentrations were observed. Regression coefficients between base cations, nitrate and chloride were used to determine the dominant processes occurring following NH4Cl spreading. In non-carbonated soils, nitrogen nitrification induced base cation leaching and soil acidification. In carbonated soils, no change of soil pH was observed. However, fertilisers induced a huge cation leaching. Carbonate mineral weathering led to the release of base cations, which replenished the soil exchangeable complex. Carbonated mineral weathering buffered acidification. Since direct weathering might have occurred without atmospheric CO2 consumption, the use of nitrogen fertiliser on carbonated soil induces a change in the cation and carbon budgets. When the results of these experiments are extrapolated on a global scale to the surface of fertilised areas lying on carbonate, carbonated reactions with N fertilisers would imply an additional flux of 5.7 x 1012 mol yr -1 of Ca + Mg. The modifications of weathering reactions in cultivated catchments and the ability of nitrogen fertilisers to significantly modify the CO2 budget should be included in carbon global cycle assessment

L'Inspection du Travail au féminin, 1878-1974. Itinéraires et statuts

rapport dactylographié à la DARES, 2 tomes; le 2e tome est un annuaire des Inspectrices du Travail, 1878-1974La loi de 1892 qui scelle la professionnalisation de l'Inspection du travail — avec un concours de recrutement national, la rémunération des inspecteurs et inspectrices par le Ministère — n'organise pas exactement le même métier pour les Inspecteurs que pour les Inspectrices. Si la rémunération est convenue identique (ce qui n'est pas le cas dans l'enseignement), par contre les lieux d'exercice diffèrent ; ainsi seuls les Inspecteurs peuvent visiter des ateliers comprenant une majorité d'hommes et/ou des machines et ce n'est qu'en 1932 qu'une épreuve technique est incluse dans leur concours. Lors des conflits et des arbitrages du Front populaire, l'activité des inspectrices montre qu'elles sont confinées dans des secteurs à main-d'œuvre très féminine et où dominent les petites entreprises. Par ailleurs, les femmes sont, par le texte de la loi de 1892, exclues de la promotion, puisque seuls les Inspecteurs peuvent accéder au grade d'Inspecteur divisionnaire, c'est-à-dire celui de la responsabilité et du commandement sur les autres. Jusqu'à la Seconde guerre mondiale, pour ces quelques dizaines d'inspectrices, les recrutements sont rares, les concours féminins s'ouvrent rarement (tous les six ou sept ans) et la concurrence y est rude. De fait, le recrutement est plus compétitif aux inspectrices qu'aux inspecteurs ; les centaines de candidates qui se présentent pour sont bien plus diplômées que leurs confrères et font même partie des « pionnières » pour l'acquisition des diplômes de l'enseignement supérieur. La hauteur de leurs diplômes correspond à celle des maris et des pères: une moitié de ces femmes sont filles et épouses d'industriels, de négociants, d'hommes des professions libérales où dominent les médecins. Si ces Inspectrices sont des femmes actives, elle ne travaillent donc pas par nécessité financière, ni par désœuvrement familial (elles sont mères de famille pour les deux tiers d'entre elles), mais bien par souci d'équité sociale et/ou de réalisation individuelle. À partir de 1946, avec la mise en place du Statut de la fonction publique et surtout de 1974, avec la mixité des concours de recrutements des fonctionnaires, des mutations égalitaires s'organisent. À partir de 1946, les circonscriptions deviennent mixtes, les Inspectrices peuvent organiser la mobilité géographique qui permet la promotion. Pourtant, même si les textes du Statut énoncent l'égalité, les Inspectrices n'accèdent toujours pas aux grades qui autorisent la prise décision et l'autorité sur les autres, en particulier comme directeur régional du travail : il faut attendre 1974 pour que leurs carrières commencent à être comparables à celles de leurs collègues masculins. 1974 est aussi la date de la fusion des corps de l'Inspection, avec l'intégration des Inspecteurs de l'Agriculture et des Transports, où les femmes étaient toujours interdites de concours de recrutement

Long and short-term trends of stream hydrochemistry and high frequency surveys as indicators of the influence of climate change, agricultural practices and internal processes (Aurade agricultural catchment, SW France)

The hydrochemical time series of stream water from a cultivated catchment were investigated at different time scales and survey frequencies. A 35-year time series of nitrate concentration and discharge, a 15-year time series of major elements and dissolved organic carbon (DOC) concentrations were analysed from a yearly to a daily/hourly basis during discharge recession after storm event periods, to determine the origin of elements, the time trends and the main controlling factors of the trends. A significant decrease over time of nitrate, base cations and other major anions was observed. These trends were controlled by agricultural practice changes (decrease of N-fertiliser input, grass-band set up) and discharge increase, especially in the last years of the period. On the other hand, K and DOC increased over the 15-year period. This increase might result from both 1) organic matter eroded from the soil surface by runoff during flood events and 2) an increase in mineralisation with increasing temperature. Seasonal variations and nycthemeral cycles indicated either calcite precipitation and nitrification processes and/or evapotranspiration, water and/or vegetation uptake during the day with increasing temperature. This paper highlights that the hydrochemical parameters measured at various time scales and frequencies can be used as powerful indicators of catchment internal processes, and of changes in agricultural management and climate change. Particularly, the multivariate high-resolution survey has shown its ability to evidence very tenuous processes not detectable by discrete sampling. The recent observed changes in hydrology argue for the need to continue the hydrochemical survey over decades