EarthArXiv (California Digital Library), Jun 27, 2019
Mountain areas provide disproportionally high runoff in many parts of the world, but their import... more Mountain areas provide disproportionally high runoff in many parts of the world, but their importance for lowland water resources and food production has not been clarified so far. Here we quantify for the first time the extent to which lowland inhabitants potentially depend on runoff contributions from mountain areas (39% of land mass). We show that ~1.4 billion people (23% of world's lowland population) are projected to depend critically on runoff contributions from mountains by mid-21 st century under a 'middle of the road' scenario, compared to ~0.2 B (8%) in the 1960s. This striking rise is mainly due to increased local water consumption in the lowlands, whereas changes in mountain and lowland runoff play a minor role only. We furthermore show that one third of global lowland area equipped for irrigation is currently located in regions that both depend heavily on runoff contributions from mountains and make unsustainable use of local blue water resources, a figure that is likely to rise to well over 50% in the coming decades. Our findings imply that mountain areas should receive particular attention in water resources management and underscore the protection they deserve in efforts towards sustainable development. Water is a key resource for the 21 st century: Mainly due to population growth and associated food production, global water consumption has increased almost four-fold over the past 100 years 1 and water demand is approaching the total renewable freshwater available today 2 . The importance of water for environmental, economic and social aspects places it at the heart of the UN Sustainable Development Goals (SDGs) 3 . Mountain areas, in turn, play an important role in water resources in that they often deliver disproportionally high runoff to the subjacent lowlands that is crucial for irrigation, industry, drinking, domestic use, hydropower and ecosystems [4][5][6][7] . In this context of superior runoff contributions, "mountain area" and "mountains" are used here in a broad definition that also includes hills and elevated plateaux 4,5 (Methods). Because of their importance in water resources, the contributions of mountain areas need to be understood much better yet. In particular, demographic, socio-economic and environmental changes affecting mountain water resources must be viewed in the larger picture of global development planning and policy making 8 . The large lead times required for implementing adaptation measures, such as reservoirs and water transfer systems, emphasise the urgency of a solid basis for long-term management of water resources originating in mountain areas 9 . Moreover, sharpening the picture of increasing pressure imposed on mountain areas through rapidly growing water demand both in mountains and lowlands is a key ingredient to sustainable mountain development 10 . benefiting from essential but insufficient contributions in the 1960s, ~0.8 B (17%) in the 2000s, and a projected ~1.4 B (23%) in the 2040s under SSP2-RCP6.0 (SSP1-RCP4.5: ~1.2 B / 21%; SSP3-RCP6.0: ~1.5 B / 23%). A complete lack of runoff surplus from mountain areas is found in various regions, caused by low runoff (e.g., parts of the Rocky Mountains and South Africa), high water consumption (e.g., parts of China and India), or both (e.g., parts of the Yellow River catchment) (Supplementary Fig. ). In the lowlands, such a lack is especially grave if a deficit prevails there (Supplementary Fig. ). In this case, the lowlands must be expected to resort to other options 21 , including dams, desalination, water recycling, use of fossil groundwater and interbasin transfers (such as in California and China) 22 . Our analysis suggests that a number of catchments have already moved into this situation in the past decades or will do so until mid-21 st century (e.g., on the Indian Peninsula 23 ) (Supplementary Fig. , Supplementary Tables ). These figures, however, only paint part of the picture since the dependence of lowland inhabitants on mountain runoff strongly depends on the climate zone in focus, and global averages thus tend to underrate this dependence in individual regions. Especially in dryer climate zones, mountains provide important runoff that is distributed downstream via the river systems . In these cases, mountains are elevated humid islands within an arid region and thus match the original concept of "water towers" 5 . Therefore, we further analyse our results by hydrobelts, i.e. hydrological basins aggregated to regions with similar hydroclimatic characteristics 24 (Methods) (Figs. , Supplementary Figs. ). The most notable changes are found in the North mid-latitude hydrobelt, where the lowland population depending on essential mountain contributions increases by almost a billion from ~0.4 B (26% of this hydrobelt's lowland population; 16% of world total lowland population) to ~1.4 B (45%; 22%) in the same time (Fig. ). Further notable increases are found in the North dry, North subtropical, Boreal and Equator hydrobelts (Fig. ). The global picture shows a number of 'hot spot' regions where the dependence of lowlands on mountain runoff was high already in the past, is today or is projected to become so in the future (Fig. , Box 1). South and East Asia are of particular relevance, especially the Ganges-Brahmaputra-Meghna catchment that hosts the largest number of lowland people depending on essential mountain contributions, namely 94 M in 1961-1970, 391 M in 2001-2010 and 570 M in 2041-2050 under SSP2-RCP6.0 (Table ). It is worth noting that this sixfold increase (+476 M) also represents the major part of population growth in this catchment from 1961 to 2050 (+639 M). Another vast growth of lowland population depending on mountain contributions is found in the
SUMMARYThe determination of the natural radioelements in suspended matter in rivers and estuaries... more SUMMARYThe determination of the natural radioelements in suspended matter in rivers and estuaries, lead to a simple relation between gamma activity and turbidity T, such as Nt=aTb (Nt counting rate caused by turbidity, a and b experimental coefficients). A new turbidimetry method is based on this relation and discussed here. In situ measurements have been conducted with field gamma scintillometers and compared with different turbidimetry methods, such as nephelometry, gravi‐metry and gamma ray absorptiometry. This method has been particularly convenient to continuous in situ measurements of turbidity from 0.5 g to several hundreds of g/1. This broad range is very well adapted to turbidity studies in estuaries.The new method has been applied to study suspended matter dynamics in the Gironde estuary (France) during November 1968, as a part of a more general study of natural radioactivity in terrigenous sediments brought into the ocean.
A briefly review on the current knowledge of the influence of the terrestrial vegetation and soil... more A briefly review on the current knowledge of the influence of the terrestrial vegetation and soils within the climate system, especially the interactions between the terrestrial biosphere and atmosphere via the hydrological cycle
Martin Jean-Marie, Meybeck Michel. Transports dissous et particulaire de quelques éléments chimiq... more Martin Jean-Marie, Meybeck Michel. Transports dissous et particulaire de quelques éléments chimiques par les rivières en milieu tempéré. In: Phénomènes de transport de matière dans l'écorce terrestre. ATP - CNRS. Action thématique Programmée du Centre National de la Recherche Scientifique. Résultats scientifiques. Strasbourg : Institut de Géologie – Université Louis-Pasteur, 1979. pp. 45-48. (Sciences Géologiques. Mémoire, 53
WIT Transactions on Ecology and the Environment, 1970
Mass budgets of chemical species or suspended sediments are often needed in hydrology The importa... more Mass budgets of chemical species or suspended sediments are often needed in hydrology The importance of computing mass budgets is detailed in ( OKane*; Meybeck"; Bellamie et al.'; Walling^; Littlewood?)-Without entering into details we can name some domains where the knowlege of mass budgets and their confidence limits is usefull: -River, lake and marine eutrophisation, ecological modelling and corresponding decision making ( P, N, SiCb) -Erosion and sedimentation phenomena ( suspended sediments) -Assessment and quantification of long term trends Typically, daily water discharge and sparse concentration data are available. According to Walling^ or Littlewood\ three types of methods are described in the literature for estimating global budgets using such data: a) Interpolation methods, based on weighted mean computation. b) Extrapolation methods, using a concentration -discharge relationship. c) Mixed methods, trying to take advantage of both types of information: concentration covariance and cross covariance between concentration and dis-In any case, the obtained result is an estimate of the real budget, estimate which is subject to different kinds of uncertainties, including a possible systematic biais. The purpose of the present study is to estimate the bias and the precision for methods belonging to the interpolation class. We use a large data base of daily concentration ( e.g. Cl ) and water discharge, measured in various French rivers and described in §4. Sampling simulations ( §3) are applied to daily data in order to obtain sparse series of concentration. The methods described in §2 are applied to the sparse series in order to obtain approximate budgets, and the statistics of these estimates are explained as functions of time series characteristics. Finally ( §6), practical recommandations are given in order to appreciate the reliability of suspended or dissolved river loads estimates .
In water quality monitoring programs, standard sampling frequency schemes tend to be applied thro... more In water quality monitoring programs, standard sampling frequency schemes tend to be applied throughout entire regions or states. Ideally, the common standard among monitoring stations ought not to be the sampling frequency but instead the level of uncertainty of the estimated water quality indicators. Until now, there was no obvious way of doing this. This article proposes, for the first time, guidelines to select appropriate sampling frequencies to harmonize the level of uncertainty in the case of yearly nitrate indicators for the regional river water quality monitoring network in Brittany, France. A database of 50 watershed-year datasets (nine watersheds of 4 to 252 km 2 in size) was used for which high temporal resolution data (hourly and daily) were available for flow and nitrate concentrations. For each dataset, the uncertainty levels were calculated by numerically simulating sampling intervals varying from 2 to 60 days. The precision limits of the uncertainties were successfully correlated to a hydrological reactivity index. The correlations were used to derive sampling frequency charts. These charts can be used by watershed managers to optimize the sampling frequency scheme for any watershed for a desired uncertainty level, provided that the dimensionless local hydrological reactivity can be calculated from previous records of continuous flow rates. The sampling frequency charts also suggest that, depending on the hydrological reactivity, expected uncertainties generated by monthly sampling range between ±6% and ±14% for the annual load and between -5% and +2.5% to +7.2% for the annual concentration average.
Algal and bacterial biomass and activities have been studied in the Loire estuary (France) by mea... more Algal and bacterial biomass and activities have been studied in the Loire estuary (France) by means of particulate organic matter proteins and chlorophyll pigments détermination, électron transport system activity measurement, '''Cbicarbonate incorporation and tritiated thymidine incorporation détermination. Thèse data coUected throughout the estuary in varions hydrological conditions allow to characterize two opposite typical situations: (i) During winter and early spring, when discharge increases beyond lOOOm^s"', heterotrophic activity always dominâtes over primary production but remains moderate because of low température and non-biodegradable quaUty of organic carbon; (ii) at drought situations, phytoplankton production develops in the river causing increases of pH and oxygen concentration. In thèse situations, accumulation of phytoplanktonic material in the highly turbid inner estuary results in very high heterotrophic activities causing pH decrease and complète depletion ofdissolved oxygen. Budgets of POC show that the anthropogenic inputs contribute only for less than 5 °'o to the organic load of the inner estuary.
Uncertainty upon the physico-chemical quality state of surface water using the 90% percentile of ... more Uncertainty upon the physico-chemical quality state of surface water using the 90% percentile of concentrations, as a function of annual monitoring frequency; application to nutrients. In France, the studies carried out to assess the status of the aquatic environment from monitoring programs (RNB, annual complementary networks) still use some previously validated official methods : “SEQ Eau” for the physico-chemistry, or standardized/ officially validated biologic indicators (document “Circulaire DCE 2005/ 12”). Regarding the physico-chemistry, it is then of interest to question the reliability of the quality assessment methods that use the 90% annual percentile, especially nowadays as a new water status evaluation system (SEEE) is being elaborated, attached to the DCE supervision program. We present a new methodology to quantify the uncertainty in determining the SEQ-Eau quality state of surface water, as a function of the annual monitoring frequency. We focus on nutrient parameters (phosphorus and nitrogen, dissolved and total fractions). As an example we show that for the Total Phosphorus fraction, the uncertainty upon the “Green/Yellow” class transition, which corresponds to the “Good Status” threshold as defined by the European Water Framework Directive, can be evaluated to range between 7% and 15% wit monthly records, whereas it is broken down by a factor of 2 using weekly monitoring.En France, les études réalisées pour évaluer l’état des milieux aquatiques à partir des réseaux actuels (RNB, réseaux annuels complémentaires) continuent d’utiliser les méthodes officiellement validées : SEQ Eau pour la physico-chimie, indicateurs biologiques (circulaire DCE 2005/12). Pour la physico-chimie, il est donc intéressant de s’interroger sur la fiabilité des évaluations des classes de qualité à partir du quantile 90% annuel, notamment à l’heure de la réflexion sur la mise en place du nouveau système d’évaluation de l’état des eaux (SEEE) concernant le programme de surveillance DCE. Dans ce travail, une méthodologie de quantification de l’incertitude associée à la détermination des classes de qualité SEQ-Cours d’eau à partir du quantile C90 annuel est proposée, en fonction de la fréquence des prélèvements des paramètres mesurés. Elle est illustrée par des résultats sur les nutriments (phosphore, azote, constituants dissous et totaux). On montre par exemple pour le Phosphore total que l’indétermination sur la classe SEQ-Eau à la transition «Jaune/Vert» qui matérialise le seuil du Bon Etat peut être évaluée entre 7% et 15% pour un suivi mensuel, et être réduite d’un facteur 2 en passant à des suivis hebdomadaires.Staub P., Audet J., Raymond Sébastien, Moatar-Bertrand Florentina, Meybeck Michel, Sarraza M. Incertitudes sur l’attribution de l’état de qualité physico-chimique des cours d’eau par le quantile 90% des concentrations en fonction de la fréquence des suivis annuels : cas des nutriments. In: Mesures Hydrologiques et Incertitudes en Hydrométrie et Qualité de l’eau. Paris, 1 et 2 avril 2008. 2008
EarthArXiv (California Digital Library), Jun 27, 2019
Mountain areas provide disproportionally high runoff in many parts of the world, but their import... more Mountain areas provide disproportionally high runoff in many parts of the world, but their importance for lowland water resources and food production has not been clarified so far. Here we quantify for the first time the extent to which lowland inhabitants potentially depend on runoff contributions from mountain areas (39% of land mass). We show that ~1.4 billion people (23% of world's lowland population) are projected to depend critically on runoff contributions from mountains by mid-21 st century under a 'middle of the road' scenario, compared to ~0.2 B (8%) in the 1960s. This striking rise is mainly due to increased local water consumption in the lowlands, whereas changes in mountain and lowland runoff play a minor role only. We furthermore show that one third of global lowland area equipped for irrigation is currently located in regions that both depend heavily on runoff contributions from mountains and make unsustainable use of local blue water resources, a figure that is likely to rise to well over 50% in the coming decades. Our findings imply that mountain areas should receive particular attention in water resources management and underscore the protection they deserve in efforts towards sustainable development. Water is a key resource for the 21 st century: Mainly due to population growth and associated food production, global water consumption has increased almost four-fold over the past 100 years 1 and water demand is approaching the total renewable freshwater available today 2 . The importance of water for environmental, economic and social aspects places it at the heart of the UN Sustainable Development Goals (SDGs) 3 . Mountain areas, in turn, play an important role in water resources in that they often deliver disproportionally high runoff to the subjacent lowlands that is crucial for irrigation, industry, drinking, domestic use, hydropower and ecosystems [4][5][6][7] . In this context of superior runoff contributions, "mountain area" and "mountains" are used here in a broad definition that also includes hills and elevated plateaux 4,5 (Methods). Because of their importance in water resources, the contributions of mountain areas need to be understood much better yet. In particular, demographic, socio-economic and environmental changes affecting mountain water resources must be viewed in the larger picture of global development planning and policy making 8 . The large lead times required for implementing adaptation measures, such as reservoirs and water transfer systems, emphasise the urgency of a solid basis for long-term management of water resources originating in mountain areas 9 . Moreover, sharpening the picture of increasing pressure imposed on mountain areas through rapidly growing water demand both in mountains and lowlands is a key ingredient to sustainable mountain development 10 . benefiting from essential but insufficient contributions in the 1960s, ~0.8 B (17%) in the 2000s, and a projected ~1.4 B (23%) in the 2040s under SSP2-RCP6.0 (SSP1-RCP4.5: ~1.2 B / 21%; SSP3-RCP6.0: ~1.5 B / 23%). A complete lack of runoff surplus from mountain areas is found in various regions, caused by low runoff (e.g., parts of the Rocky Mountains and South Africa), high water consumption (e.g., parts of China and India), or both (e.g., parts of the Yellow River catchment) (Supplementary Fig. ). In the lowlands, such a lack is especially grave if a deficit prevails there (Supplementary Fig. ). In this case, the lowlands must be expected to resort to other options 21 , including dams, desalination, water recycling, use of fossil groundwater and interbasin transfers (such as in California and China) 22 . Our analysis suggests that a number of catchments have already moved into this situation in the past decades or will do so until mid-21 st century (e.g., on the Indian Peninsula 23 ) (Supplementary Fig. , Supplementary Tables ). These figures, however, only paint part of the picture since the dependence of lowland inhabitants on mountain runoff strongly depends on the climate zone in focus, and global averages thus tend to underrate this dependence in individual regions. Especially in dryer climate zones, mountains provide important runoff that is distributed downstream via the river systems . In these cases, mountains are elevated humid islands within an arid region and thus match the original concept of "water towers" 5 . Therefore, we further analyse our results by hydrobelts, i.e. hydrological basins aggregated to regions with similar hydroclimatic characteristics 24 (Methods) (Figs. , Supplementary Figs. ). The most notable changes are found in the North mid-latitude hydrobelt, where the lowland population depending on essential mountain contributions increases by almost a billion from ~0.4 B (26% of this hydrobelt's lowland population; 16% of world total lowland population) to ~1.4 B (45%; 22%) in the same time (Fig. ). Further notable increases are found in the North dry, North subtropical, Boreal and Equator hydrobelts (Fig. ). The global picture shows a number of 'hot spot' regions where the dependence of lowlands on mountain runoff was high already in the past, is today or is projected to become so in the future (Fig. , Box 1). South and East Asia are of particular relevance, especially the Ganges-Brahmaputra-Meghna catchment that hosts the largest number of lowland people depending on essential mountain contributions, namely 94 M in 1961-1970, 391 M in 2001-2010 and 570 M in 2041-2050 under SSP2-RCP6.0 (Table ). It is worth noting that this sixfold increase (+476 M) also represents the major part of population growth in this catchment from 1961 to 2050 (+639 M). Another vast growth of lowland population depending on mountain contributions is found in the
SUMMARYThe determination of the natural radioelements in suspended matter in rivers and estuaries... more SUMMARYThe determination of the natural radioelements in suspended matter in rivers and estuaries, lead to a simple relation between gamma activity and turbidity T, such as Nt=aTb (Nt counting rate caused by turbidity, a and b experimental coefficients). A new turbidimetry method is based on this relation and discussed here. In situ measurements have been conducted with field gamma scintillometers and compared with different turbidimetry methods, such as nephelometry, gravi‐metry and gamma ray absorptiometry. This method has been particularly convenient to continuous in situ measurements of turbidity from 0.5 g to several hundreds of g/1. This broad range is very well adapted to turbidity studies in estuaries.The new method has been applied to study suspended matter dynamics in the Gironde estuary (France) during November 1968, as a part of a more general study of natural radioactivity in terrigenous sediments brought into the ocean.
A briefly review on the current knowledge of the influence of the terrestrial vegetation and soil... more A briefly review on the current knowledge of the influence of the terrestrial vegetation and soils within the climate system, especially the interactions between the terrestrial biosphere and atmosphere via the hydrological cycle
Martin Jean-Marie, Meybeck Michel. Transports dissous et particulaire de quelques éléments chimiq... more Martin Jean-Marie, Meybeck Michel. Transports dissous et particulaire de quelques éléments chimiques par les rivières en milieu tempéré. In: Phénomènes de transport de matière dans l'écorce terrestre. ATP - CNRS. Action thématique Programmée du Centre National de la Recherche Scientifique. Résultats scientifiques. Strasbourg : Institut de Géologie – Université Louis-Pasteur, 1979. pp. 45-48. (Sciences Géologiques. Mémoire, 53
WIT Transactions on Ecology and the Environment, 1970
Mass budgets of chemical species or suspended sediments are often needed in hydrology The importa... more Mass budgets of chemical species or suspended sediments are often needed in hydrology The importance of computing mass budgets is detailed in ( OKane*; Meybeck"; Bellamie et al.'; Walling^; Littlewood?)-Without entering into details we can name some domains where the knowlege of mass budgets and their confidence limits is usefull: -River, lake and marine eutrophisation, ecological modelling and corresponding decision making ( P, N, SiCb) -Erosion and sedimentation phenomena ( suspended sediments) -Assessment and quantification of long term trends Typically, daily water discharge and sparse concentration data are available. According to Walling^ or Littlewood\ three types of methods are described in the literature for estimating global budgets using such data: a) Interpolation methods, based on weighted mean computation. b) Extrapolation methods, using a concentration -discharge relationship. c) Mixed methods, trying to take advantage of both types of information: concentration covariance and cross covariance between concentration and dis-In any case, the obtained result is an estimate of the real budget, estimate which is subject to different kinds of uncertainties, including a possible systematic biais. The purpose of the present study is to estimate the bias and the precision for methods belonging to the interpolation class. We use a large data base of daily concentration ( e.g. Cl ) and water discharge, measured in various French rivers and described in §4. Sampling simulations ( §3) are applied to daily data in order to obtain sparse series of concentration. The methods described in §2 are applied to the sparse series in order to obtain approximate budgets, and the statistics of these estimates are explained as functions of time series characteristics. Finally ( §6), practical recommandations are given in order to appreciate the reliability of suspended or dissolved river loads estimates .
In water quality monitoring programs, standard sampling frequency schemes tend to be applied thro... more In water quality monitoring programs, standard sampling frequency schemes tend to be applied throughout entire regions or states. Ideally, the common standard among monitoring stations ought not to be the sampling frequency but instead the level of uncertainty of the estimated water quality indicators. Until now, there was no obvious way of doing this. This article proposes, for the first time, guidelines to select appropriate sampling frequencies to harmonize the level of uncertainty in the case of yearly nitrate indicators for the regional river water quality monitoring network in Brittany, France. A database of 50 watershed-year datasets (nine watersheds of 4 to 252 km 2 in size) was used for which high temporal resolution data (hourly and daily) were available for flow and nitrate concentrations. For each dataset, the uncertainty levels were calculated by numerically simulating sampling intervals varying from 2 to 60 days. The precision limits of the uncertainties were successfully correlated to a hydrological reactivity index. The correlations were used to derive sampling frequency charts. These charts can be used by watershed managers to optimize the sampling frequency scheme for any watershed for a desired uncertainty level, provided that the dimensionless local hydrological reactivity can be calculated from previous records of continuous flow rates. The sampling frequency charts also suggest that, depending on the hydrological reactivity, expected uncertainties generated by monthly sampling range between ±6% and ±14% for the annual load and between -5% and +2.5% to +7.2% for the annual concentration average.
Algal and bacterial biomass and activities have been studied in the Loire estuary (France) by mea... more Algal and bacterial biomass and activities have been studied in the Loire estuary (France) by means of particulate organic matter proteins and chlorophyll pigments détermination, électron transport system activity measurement, '''Cbicarbonate incorporation and tritiated thymidine incorporation détermination. Thèse data coUected throughout the estuary in varions hydrological conditions allow to characterize two opposite typical situations: (i) During winter and early spring, when discharge increases beyond lOOOm^s"', heterotrophic activity always dominâtes over primary production but remains moderate because of low température and non-biodegradable quaUty of organic carbon; (ii) at drought situations, phytoplankton production develops in the river causing increases of pH and oxygen concentration. In thèse situations, accumulation of phytoplanktonic material in the highly turbid inner estuary results in very high heterotrophic activities causing pH decrease and complète depletion ofdissolved oxygen. Budgets of POC show that the anthropogenic inputs contribute only for less than 5 °'o to the organic load of the inner estuary.
Uncertainty upon the physico-chemical quality state of surface water using the 90% percentile of ... more Uncertainty upon the physico-chemical quality state of surface water using the 90% percentile of concentrations, as a function of annual monitoring frequency; application to nutrients. In France, the studies carried out to assess the status of the aquatic environment from monitoring programs (RNB, annual complementary networks) still use some previously validated official methods : “SEQ Eau” for the physico-chemistry, or standardized/ officially validated biologic indicators (document “Circulaire DCE 2005/ 12”). Regarding the physico-chemistry, it is then of interest to question the reliability of the quality assessment methods that use the 90% annual percentile, especially nowadays as a new water status evaluation system (SEEE) is being elaborated, attached to the DCE supervision program. We present a new methodology to quantify the uncertainty in determining the SEQ-Eau quality state of surface water, as a function of the annual monitoring frequency. We focus on nutrient parameters (phosphorus and nitrogen, dissolved and total fractions). As an example we show that for the Total Phosphorus fraction, the uncertainty upon the “Green/Yellow” class transition, which corresponds to the “Good Status” threshold as defined by the European Water Framework Directive, can be evaluated to range between 7% and 15% wit monthly records, whereas it is broken down by a factor of 2 using weekly monitoring.En France, les études réalisées pour évaluer l’état des milieux aquatiques à partir des réseaux actuels (RNB, réseaux annuels complémentaires) continuent d’utiliser les méthodes officiellement validées : SEQ Eau pour la physico-chimie, indicateurs biologiques (circulaire DCE 2005/12). Pour la physico-chimie, il est donc intéressant de s’interroger sur la fiabilité des évaluations des classes de qualité à partir du quantile 90% annuel, notamment à l’heure de la réflexion sur la mise en place du nouveau système d’évaluation de l’état des eaux (SEEE) concernant le programme de surveillance DCE. Dans ce travail, une méthodologie de quantification de l’incertitude associée à la détermination des classes de qualité SEQ-Cours d’eau à partir du quantile C90 annuel est proposée, en fonction de la fréquence des prélèvements des paramètres mesurés. Elle est illustrée par des résultats sur les nutriments (phosphore, azote, constituants dissous et totaux). On montre par exemple pour le Phosphore total que l’indétermination sur la classe SEQ-Eau à la transition «Jaune/Vert» qui matérialise le seuil du Bon Etat peut être évaluée entre 7% et 15% pour un suivi mensuel, et être réduite d’un facteur 2 en passant à des suivis hebdomadaires.Staub P., Audet J., Raymond Sébastien, Moatar-Bertrand Florentina, Meybeck Michel, Sarraza M. Incertitudes sur l’attribution de l’état de qualité physico-chimique des cours d’eau par le quantile 90% des concentrations en fonction de la fréquence des suivis annuels : cas des nutriments. In: Mesures Hydrologiques et Incertitudes en Hydrométrie et Qualité de l’eau. Paris, 1 et 2 avril 2008. 2008
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Papers by Michel Meybeck