Change in groundwater chemistry as a consequence of suppression of floods: the case of the Rhine floodplain

Spatio-temporal variations of nitrogen, phosphorus and base cation concentrations in groundwater were related to the drastic change in hydrological conditions of the Rhine alluvial floodplain (Eastern France), which has been disconnected from the river by canalisation. The Groundwater chemistry was studied in two alluvial forests with contrasting hydrological conditions: one in a sector unflooded for 30 years, the second one in a sector still subject to flooding. Nutrient concentrations were measured at two levels, in the root zone (1.5 m depth) and in the gravel below the root layer (4.5 m depth). In the unflooded sector, the average nitrate concentration was significantly lower in the shallow groundwater (2.06 mg l−1 NO3−) than in the deeper layer (5.84 mg l−1NO3−). In contrast, in the flooded sector the nitrate concentrations in the shallow groundwater (5.02 mg l−1 NO3−) were not significantly different from those in the deep groundwater (3.98 mg l−1 NO3−). The concentration of phosphate was similar in shallow and deep groundwater in the unflooded sector (46 and 35 μg l−1, respectively) but significantly lower in the deep groundwater of the flooded sector (47 μg l−1), than in the shallow groundwater (58 μg l−1). The major elements (cations: Ca2+, Mg2+, Na+ and associated anions: HCO3−, SO4−2, Cl−) concentrations were significantly higher in the groundwaters than in the surface water. The results are discussed in terms of changes that accompanied suppression of floods, and processes that take place during the transfer of nutrients through the groundwater–soil–plant compartments. The reduction of groundwater fluctuations in the unflooded sector modified the transfer of nitrate by reducing the resolubilisation of locally produced nitrate, and/or denitrification. The transfer of phosphate was affected to a lesser extent, because of precipitation and adsorption. Base cation concentrations reflect exchange between groundwater and the calcareous gravel

Nitrate elimination by denitrification in hardwood forest soils of the Upper Rhine floodplain – correlation with redox potential and organic matter

Denitrification in floodplains is a major issue for river- and groundwater quality. In the Upper Rhine valley, floodplain forests are about to be restored to serve as flood retention areas (polders). Besides flood attenuation in downstream areas, improvement of water quality became recently a major goal for polder construction. Redox potential monitoring was suggested as a means to support assessment of nitrogen elimination in future floodplains by denitrification during controlled flooding. To elucidate the relationship between redox potential and denitrification, experiments with floodplain soils and in situ measurements were done. Floodplain soil of two depth profiles from a hardwood forest of the Upper Rhine valley was incubated anaerobically with continuous nitrate supply. Reduction of nitrate was followed and compared with redox potential and organic matter content. The redox potential under denitrifying conditions ranged from 10 to 300 mV. Redox potential values decreased with increasing nitrate reduction rates and increasing organic matter content. Furthermore, a narrow correlation between organicmatter and nitrate reduction was observed. Experiments were intended to help interpreting redox potentials generated under in situ conditions as exemplified by in situ observations for the year 1999. Results obtained by experiments and in situ observations showed that monitoring of redox potential could support management of the flooding regime to optimize nitrogen retention by denitrification in future flood retention areas

Changes in foliar nutrient content and resorption in Fraxinus excelsior L., Ulmus minor Mill. and Clematis vitalba L. after prevention of floods

This paper focuses on the impact of flood on tree mineral nutrition through measurement of resorption (i.e. transfer of nutrients from leaves to perennial organs). Nutrient (N, P, K, Mg, Ca) concentrations in leaves of three representative species, Fraxinus excelsior L., Ulmus minor Mill. and Clematis vitalba L. were measured before and after abscission on flooded and unflooded hardwood forests of the upper Rhine plain. The nutrient concentrations in the soils, which were measured in the top layer of the study sites, were higher in the flooded sites for P but slightly lower for N and K, and identical at both types of site for Ca and Mg. The summer foliage concentrations were higher for N and P in the flooded areas, and probably related to the flooding process, which contributes to regular nutrient inputs in the flooded forest, causes high fluctuations of water level and increases bioavailability of certain nutrients. Resorption occurred for all nutrients in the three species, and was higher for N, P and K (40-70 %) than for Ca and Mg (0-45 %), but not significantly different at the two sites. This paper stresses the variability of the test species response (nutrient content and resorption) to the soil and flood water nutrient sources, and tries to specify parameters which control resorption, i.e. soil fertility, tree species or flood stress. © 1999 Inra/Éditions scientifiques et médicales Elsevier SAS

Impact of river management history on the community structure, species composition and nutrient status in the Rhine alluvial hardwood forest

The present-day Rhine alluvial hardwood forest (Querco-Ulmetum minoris, Issler 24) in the upper Rhine valley (France/Germany) is comprised of three vegetation units, one still flooded by calm waters (F) and the two others unflooded, one for 30 years (UF30) (after the river canalisation) and the other for about 130 years (UF130) (after river straightening and embankment work in the middle nineteenth century). In the three stands, species composition, structure and diversity of vegetation and nutrient content of mature leaf, leaf litter and soil have been studied. Fungi (Macromycetae) were only studied in two stands (F and UF130). The intensity of nutrient recycling was exemplified by comparing the chemical composition of rainwater, flood, throughfall, mature leaf, leaf litter, soil and groundwater in two of these stands (F and UF30). The elimination of floods has caused a change in floristic composition, tree density and plant diversity. Tree density was higher in the two unflooded stands and was related to a large increase in sapling (< 6 cm dbh) density more than to a change of stem (> 6 cm dbh) density. Sapling density increased 2 times and three times in the UF30 and the UF130 respectively, whereas the stem density increased only 12% in the first stand and decreased 29% in the second one. The saprophytic macromycete communities have been supplemented with mycorrhizal species

Impact of river management history on the community structure, species composition and nutrient status in the Rhine alluvial hardwood forest

The present-day Rhine alluvial hardwood forest (Querco-Ulmetum minoris, Issler 24) in the upper Rhine valley (France/Germany) is comprised of three vegetation units, one still flooded by calm waters (F) and the two others unflooded, one for 30 years (UF30) (after the river canalisation) and the other for about 130 years (UF130) (after river straightening and embankment work in the middle nineteenth century). In the three stands, species composition, structure and diversity of vegetation and nutrient content of mature leaf, leaf litter and soil have been studied. Fungi (Macromycetae) were only studied in two stands (F and UF130). The intensity of nutrient recycling was exemplified by comparing the chemical composition of rainwater, flood, throughfall, mature leaf, leaf litter, soil and groundwater in two of these stands (F and UF30). The elimination of floods has caused a change in floristic composition, tree density and plant diversity. Tree density was higher in the two unflooded stands and was related to a large increase in sapling (< 6 cm dbh) density more than to a change of stem (> 6 cm dbh) density. Sapling density increased 2 times and three times in the UF30 and the UF130 respectively, whereas the stem density increased only 12% in the first stand and decreased 29% in the second one. The saprophytic macromycete communities have been supplemented with mycorrhizal species

Introducing the Spatial Conflict Dynamics indicator of political violence

Modern armed conflicts have a tendency to cluster together and spread geographically. However, the geography of most conflicts remains under-studied. To fill this gap, this article presents a new indicator that measures two key geographical properties of subnational political violence: the conflict intensity within a region on the one hand, and the spatial distribution of conflict within a region on the other. We demonstrate the indicator in North and West Africa between 1997 to 2019 to show that it can clarify how conflicts can spread from place to place and how the geography of conflict changes over time

Quantification of nitrate removal by a flooded alluvial zone in the Ill floodplain (Eastern France)

The nitrate reducing capacity of a flooded system in the Ill floodplain (Eastern France) was investigated for a period of 2 years. The methodology used consisted of a spatio-temporal monitoring of stream flow and nitrate concentrations in the groundwater and surface water, calculation of input and output fluxes and modelling of groundwater fluxes and nitrate transfer through the alluvial area. A comparison of chloride flux (used as hydrological tracer) and nitrate flux was done to determine a floodplain effect on the retention of nitrate. We show that up to 95% of the nitrate load in the groundwater is retained by the system, whereas the retention in the stream network is very low. Ammonium fluxes increased from inputs to outputs in the stream and in the groundwater. The chloride input in the groundwater is higher than the output, whereas in the surface water the output is higher than the input, the amount evacuated in streams corresponding to the losses from groundwater. The nitrate removal rate calculated for the whole modelized surface area (40 km2) represented 559 t N yr-1 or 1397.7 kg N ha-1 yr-1. The ammonium fluxes exported by the system represented 102 kg N ha-1 yr-1 A part of nitrate is reduced and exported by the groundwater and stream network in the form of ammonium. These results can be explained by the duration of floods which controls the equilibrium between the various forms of nitrogen. Thus, long watering periods favour nitrogen removal (denitrification and plant uptake) and limit nitrate production which compensates elimination during the dry period

La philosophie positiviste de Leszek Kołakowski

Kołakowski est l’auteur d’une présentation de La philosophie positiviste (1966), lorsqu’il enseignait encore à Varsovie, traduite en français dix ans plus tard (1976). L’ouvrage se donne comme une histoire du positivisme, depuis ses origines médiévales jusqu’à l’empirisme logique. Cette histoire est aussi un examen critique, le positivisme se définissant comme une théorie de la connaissance, mais cette théorie conduisant dans plusieurs cas, notamment le pragmatisme américain (William James), à une idéologie. Dans son analyse de l’œuvre d’Auguste Comte, Kołakowski montre la difficulté à dissocier les deux orientations. On a choisi, dans les limites du présent article, de privilégier ce chapitre et ceux consacrés, d’une part, aux versions antérieures du positivisme (Kołakowski saluant en David Hume « un des plus grands esprits que les Temps modernes aient produits ») ; d’autre part, au « conventionnalisme » (Édouard Le Roy notamment), ainsi qu’aux enjeux généraux de caractérisation et d’évaluation du positivisme.Kołakowski is the author of a Positivist philosophy (1966) presentation, while he was still teaching in Warsaw, translated in French ten years later (1976). This work is presented as a history of positivism, from its medieval origins up to logical empiricism. This history is also a critical evaluation, since positivism is defined as a theory of knowledge, but this theory leads in several cases, notably American pragmatism (William James), to ideology. In his analysis of the work of Auguste Comte, Kolakowski shows how difficult it is to dissociate the two orientations. Within the limits of this article, we have chosen to focus on this chapter and on those dealing with, on the one hand, the previous versions of positivism (Kolakowski recognizes David Hume as “one of the greatest minds the modern era has produced”); and on the other hand, “conventionalism” (in particular Edward The Roy), as well as the general issues of the characterization and evaluation of positivism.Kolakowski es el autor de una presentación de La filosofía positivista (1966), cuando aún enseñaba en Varsovia, traducida al francés diez años más tarde (1976). La obra se presenta como una historia del positivismo, desde sus orígenes medievales hasta el empirismo lógico. Esta historia es también un examen crítico, ya que el positivismo se define como una teoría del conocimiento, pero esta teoría conduce en varios casos, especialmente en el pragmatismo americano (William James) a una ideología. En su análisis de la obra de Augusto Comte, Kolakowski muestra la dificultad de disociar las dos orientaciones. Elegimos, en los límites del presente artículo, privilegiar aquel capítulo y aquellos consagrados, por un lado, a las versiones anteriores del positivismo (Kolakowski saluda en David Hume a “uno de los más grandes espíritus que los Tiempos modernos hayan producido”); por otro lado, al “convencionalismo” (Eduard Le Roy especialmente), así como a los desafíos generales de la caracterización y de la evaluación del positivismo

Agnès Desmazières, L’inconscient au paradis. Comment les catholiques ont reçu la psychanalyse (1920-1965)

Sous un titre discutable (on attendrait aussi bien l’enfer, et l’illustration de couverture qui dramatise l’opposition entre deux figures : Freud et Pie XII, ne laisse pas augurer une sanctification de la psychanalyse) se donne à lire ce que le sous-titre indique en effet, une étude de la réception de la psychanalyse au sein du catholicisme, sous forme de récit, qui va du contexte intransigeant de l’après-modernisme à l’aggiornamento conciliaire. Le rapport à la psychanalyse est l’une des mod..