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International audience; Littoral benthic diatom communities are pivotal indicators which react to coastline sources of pollution. Littoral communities, however, may be also strongly influenced by other environmental factors: we assumed that even in lakes without anthropogenic pressure, communities could be heterogeneous. To investigate the natural causes of community heterogeneity along shoreline, we sampled 58 pristine high-altitude lakes in the French Alps. Inside each lake, three different littoral stations were sampled. Water chemical composition was measured with major environmental settings. Lakes with homogeneous communities along their shoreline were dominated by pioneer species adapted to strong physical disturbances. The water renewal time in these lakes was short (a few days) and this conveyed strong turbulences. Lakes with heterogeneous communities along their shore had longer water renewal time and were dominated by high-profile diatoms that were able to compete for light and nutrients. The within-lake heterogeneity could be explained by the variability in coastline terrestrial habitats. This study illustrates how water turbulences can limit the expression of some ecological processes like interspecific competition and reduce heterogeneity when it is an overriding stressor. Finally, implications for lake managers are given in terms of monitoring efforts.

Natural organic matter in soils contains stable semiquinone radicals, the nature of which depends on their origin and their maturation state. The relative proportions of these radicals, deduced from simulations of the EPR spectrum, constitute a signature which can be used to differentiate soils and even their horizons. It allows us to monitor the transfer of organic matter in a drainage basin from the soil to the hydrological systems, from the systems to their spillways and right up to the natural recorders (sediments, speleothems). The power of this tracing method is clearly illustrated by the determination of the catchment area and the residence time for drinking water in karst formations.

International audience; Mountain lakes are integrated sentinels of changes in the terrestrial environment, where these changes threaten the quality of the ecosystem services these lakes provide, including high biodiversity, economic and leisure activities. Few evidentiary records exist of the long-term relationships between human pressure and observed impacts. Multiproxy analyses of the Lake Bénit sediment sequence, including dating, grain-size, geochemistry, pollen, non-pollen palynomorphs and chironomid assemblage reconstructions, allowed reconstruction of past environmental evolution and lake trophic changes. Combined with soil analyses of the catchment, these data provide a record of the relationships between human activities and the lake-catchment ecosystem, and show the effect of inundation of the shore previously used as pasture. From 2100 to 1100 yrs cal. BP, the catchment was forested. During the Middle Ages, grazing deforested the catchment, triggering an increase in erosion and a change in sediment sources. The lake remained oligotrophic over most of the last millennia. The trophic state changed abruptly in the 20th century with intensification and multiplication of tourist activities in the catchment, i.e., fishing, hiking, while pastoral activities decreased. The sudden eutrophication coincides with an artificial increase of the lake water level in AD 1964 to improve fishing activities. A release of phosphorus (P) from the flooded soils was observed, which may be responsible for the current eutrophication. One thousand years of grazing practices would have led to the observed P concentrations in the soils of the lake shore, transferred by the cattle to this area. Our study highlights the combined effects of past and recent activities on the current eutrophication process, and the legacy of both soils and early anthropogenic activities.

International audience; Excessive nutrient delivery into freshwater bodies results in increased eutrophication risk worldwide. Because high-frequency monitoring cannot be generalised to all rivers, methods are needed to assess eutrophication risk in contexts with scarce data. To this end, we present an assessment framework which includes: (i) a mass-balance model to estimate diffuse N and P transfer/retention in unmonitored catchments and (ii) a set of indicators based on N:P:Si molar ratios to assess the risk of eutrophication in freshwaters. The model, called Nutting, integrates variables that describe both agricultural pressures and physical attributes of catchments (climate, topography, soil). Nutting refines previous mass-balance models by describing nutrient pressures with soil N surplus and soil P content instead of N and P inputs, and by considering physical attributes not only as lumped variables over the entire area but also within river corridors. The model was calibrated on a set of 160 independent catchments across France and applied to all headwater catchments. We found that apparent N and P retention represented 53 +/- 24% and 95 +/- 29% of soil N and P surplus, respectively, and was mainly controlled by the climate and a hydrology-related connectivity index. The spatial organisation of the landscape was of secondary importance compared to the refined description of agricultural pressures. Estimated eutrophication risk was highly sensitive to assumptions about P bioavailability, hence the potential range of headwaters at risk of eutrophication spanned 26-63% of the catchments, depending on assumptions. This framework provides a generic method to assess the relative contribution of agriculture to nutrient loads and the subsequent risk of eutrophication. (V) 2014 Elsevier Ltd. All rights reserved.

The Anthropocene is characterized by a worldwide spread of hypoxia, among other manifestations, which threatens aquatic ecosystem functions, services, and biodiversity. The primary cause of hypoxia onset in recent decades is human-triggered eutrophication. Global warming has also been demonstrated to contribute to the increase of hypoxic conditions. However, the precise role of both environmental forcings on hypoxia dynamics over the long term remains mainly unknown due to a lack of historical monitoring. In this study, we used an innovative paleolimnological approach on three large European lakes to quantify past hypoxia dynamics and to hierarchies the contributions of climate and nutrients. Even for lake ecosystems that have been well oxygenated over a millennia-long period, and regardless of past climatic fluctuations, a shift to hypoxic conditions occurred in the 1950s in response to an unprecedented rise in total phosphorus concentrations above 105 mu g P L-1. Following this shift, hypoxia never disappeared despite the fact that environmental policies succeeded in drastically reducing lake phosphorus concentrations. During that period, decadal fluctuations in hypoxic volume were great, ranging between 0.5 and 8% of the total lake volumes. We demonstrate, through statistical modeling, that these fluctuations were essentially driven by climatic factors, such as river discharge and air temperature. In lakes Geneva and Bourget, which are fed by large river systems, fluctuations in hypoxic volume were negatively correlated with river discharge. In contrast, the expansion of hypoxia has been related only to warmer air temperatures at Annecy, which is fed by small river systems. Hence, we outline a theoretical framework assuming that restored lake ecosystems have inherited hypoxia from the eutrophication period and have shifted to a new stable state with new key controls of water and ecosystem quality. We suggest that controlling river discharge may be a complementary strategy for local management of lakes fed by large river systems.

International audience; An essential aspect of eutrophication studies is to trace the ultimate origin of phosphate ions (P-PO4) associated with the solid phase of river sediments, as certain processes can make these ions available for algae. However, this is not a straightforward task because of the diversity of allochthonous and autochthonous sources that can supply P-PO4 to river sediments as well as the existence of in-stream processes that can change the speciation of these inputs and obscure the original sources. Here, we present the results of a study designed to explore the potentials, limitations and conditions for the use of the oxygen isotope composition of phosphate (δ18Op) extracted from river sediments for this type of tracing. We first tested if the method commonly applied to soils to purify P-PO4 and to measure their δ18Op concentrations could be adapted to sediments. We then applied this method to a set of sediments collected in a river along a gradient of anthropogenic pressure and compared their isotopic signatures with those from samples that are representative of the potential P-PO4 inputs to the river system (soils and riverbank material).The results showed that following some adaptations, the purification method could be successfully transposed to river sediments with a high level of P-PO4 purification (>97%) and high δ18Op measurement repeatability and accuracy (3‰) in the sediment δ18Op value immediately downstream from the discharge point revealed the strong impact of municipal wastewater. The calculation of the theoretical equilibrium δ18Op values using the river water temperature and δ18Ow showed that the downstream sediments were in equilibrium, which was not the case for the upstream sediments. This difference could be related to the contrast between the short residence time of the transfer system in the catchment head, which can preserve the isotopic variability of the source materials, and the longer residence times and higher P bioavailability in the lower catchment, possibly fostering the recycling of P-PO4 by the biota and the equilibration of the oxygen isotope signature in P-PO4. These results demonstrate the potential of the isotopic approach to assess the sources and in-stream turnover of sedimentary P in river systems.

International audience; Agricultural pesticide use has increased worldwide during the last several decades, but the long-term fate, storage, and transfer dynamics of pesticides in a changing environment are poorly understood. Many pesticides have been progressively banned, but in numerous cases, these molecules are stable and may persist in soils, sediments, and ice. Many studies have addressed the question of their possible remobilization as a result of global change. In this article, we present a retro-observation approach based on lake sediment records to monitor micropollutants and to evaluate the long-term succession and diffuse transfer of herbicides, fungicides, and insecticide treatments in a vineyard catchment in France. The sediment allows for a reliable reconstruction of past pesticide use through time, validated by the historical introduction, use, and banning of these organic and inorganic pesticides in local vineyards. Our results also revealed how changes in these practices affect storage conditions and, consequently, the pesticides' transfer dynamics. For example, the use of postemergence herbicides (glyphosate), which induce an increase in soil erosion, led to a release of a banned remnant pesticide (dichlorodiphenyltrichloroethane, DDT), which had been previously stored in vineyard soil, back into the environment. Management strategies of ecotoxicological risk would be well served by recognition of the diversity of compounds stored in various environmental sinks, such as agriculture soil, and their capability to become sources when environmental conditions change.

International audience; Enhanced phosphorus (P) export from land into streams and lakes is a primary factor driving the expansion of deep-water hypoxia in lakes during the Anthropocene. However, the interplay of regional scale environmental stressors and the lack of long-term instrumental data often impede analyses attempting to associate changes in land cover with downstream aquatic responses. Herein, we performed a synthesis of data that link paleolimnological reconstructions of lake bottom-water oxygenation to changes in land cover/use and climate over the past 300 years to evaluate whether the spread of hypoxia in European lakes was primarily associated with enhanced P exports from growing urbanization, intensified agriculture, or climatic change. We showed that hypoxia started spreading in European lakes around CE 1850 and was greatly accelerated after CE 1900. Socioeconomic changes in Europe beginning in CE 1850 resulted in widespread urbanization, as well as a larger and more intensively cultivated surface area. However, our analysis of temporal trends demonstrated that the onset and intensification of lacustrine hypoxia were more strongly related to the growth of urban areas than to changes in agricultural areas and the application of fertilizers. These results suggest that anthropogenically triggered hypoxia in European lakes was primarily caused by enhanced P discharges from urban point sources. To date, there have been no signs of sustained recovery of bottom-water oxygenation in lakes following the enactment of European water legislation in the 1970s to 1980s, and the subsequent decrease in domestic P consumption.

International audience; Watershed losses of phosphorus (P) have been a topic of concern for water resource managers over recent decades. To evaluate environmental policies or before implementing mitigation options at the watershed (catchment area) scale, stakeholders often need to analyze the patterns of point and diffuse sources of phosphorus. This information is often not easy to obtain in field conditions. Several statistical modeling approaches have been developed in recent years to respond to this basic operational demand. Point and diffuse sources are often evaluated from power functions established between phosphorus concentration and water discharge. Such models do not explicitly account for in-stream processes which control P concentrations in the hydrographic network and differentiate the P export dynamics of the various forms and inputs of P. To identify the phosphorus sources and evaluate their change in response to environmental policies, we developed a simple and loaded-oriented model (POPEYE - PhOsPhorus, Evaluation of the efficiencY of Environmental policy measures) that computes retention, settling and re-suspension rates of fine and coarse P fractions and their relation to P concentration of bed sediments. The model is calibrated to a long-term database (25 years), and describes the weekly water and chemical fluxes of a tributary of Lac Leman (Lake Geneva, Venoge river watershed, 240 km(2)). It adequately predicts observed values of fine and particulate phosphorus and reflects the gradual decrease of point and diffuse inputs over the studied period due to agricultural and sewage treatment policies implemented for the control of lake pollution. (c) 2012 Elsevier B.V. All rights reserved.

International audience; The impact particulate-phosphorus (particulate-P) has on eutrophication of aquatic systems that greatly depends on its composition. As a result, analysis methods for evaluating particulate-P speciation must be capable of identifying and/or quantifying the wide range of forms particulate-P can take. In the present study, we compare the particulate P speciation of the fine and colloidal fractions of riverbed sediment and suspended matter from two rivers in the Lake Geneva basin (French Alps) as determined with chemical extractions to results of a combined Transmission Electron Microscopy and Energy Dispersive Detection (TEM–EDS) analysis of the same samples. TEM–EDS provides semi-quantitative information about the distribution of P throughout the solid fraction of a sample and on the diversity of carrier phases, which are identified by their morphology and stochiometry. EDS-detectable quantities of phosphorus were found in 15–35% of the particles in the samples analyzed. As expected, particulate-P existed in a wide variety of forms, mostly associated with Al, Fe, Ca and Si. Some types of particles, often well-crystallized phosphate minerals, had high P contents (10–30%), but the dominant carrier phases of P were diffuse matrices of particles with low P contents (

Les impacts des eaux pluviales urbaines sur les milieux recepteurs sont encore mal connus. Notre recherche vise a evaluer l'impact des micropolluants des eaux pluviales urbaines sur un milieu aquatique via l'analyse de ses sediments. Le principal site d'etude est le lac du Bourget pour lequel l'analyse de carottes datees est mise en relation avec l'evolution de l'urbanisation sur le bassin-versant au cours des 100 dernieres annees. Ce papier presente dans un premier temps les elements bibliographiques ayant conduit a l'elaboration du projet et a la mise en place de la strategie d'echantillonnage et d'analyse. Puis dans une deuxieme partie, les premiers resultats sur les profils verticaux de concentrations en HAP et en PCB dans les carottes de sediments du lac du Bourget sont presentes.

Garnier, Josette ... et. al.-- 21 pages, 5 figures, 2 tables, Phosphorus (P) plays a strategic role in agricultural production as well as in the occurrence of freshwater and marine eutrophication episodes throughout the world. Moreover, the scarcity and uneven distribution of minable P resources is raising concerns about the sustainability of long-term exploitation. In this paper we analyze the P cycle in anthropic systems with an original multiscale approach (world region, country, and large basin scales) in two contrasting world regions representative of different trajectories in socioeconomic development for the 1961–2009 period: Europe (EU-27)/France and the Seine River Basin, and Asia (ASEAN-8)/Vietnam and the Red River Basin. Our approach highlights different trends in the agricultural and food production systems of the two regions. Whereas crop production increased until the 1980s in Europe and France and has stabilized thereafter, in ASEAN-8 and Vietnam it began to increase in the 1980s and it is still rising today. These trends are related to the increasing use of fertilizers, although in European countries the amount of fertilizers sharply decreased after the 1980s. On average, the total P delivered from rivers to the sea is 3 times higher for ASEAN-8 (300 kg P km−2 yr−1) than for EU-27 countries (100 kg P km−2 yr−1) and is twice as high in the Red River (200 kg P km−2 yr−1) than in the Seine River (110 kg P km−2 yr−1), with agricultural losses to water in ASEAN-8 3 times higher than in EU-27. Based on the P flux budgets, this study discusses early warnings and management options according to the particularities of the two world regions, newly integrating the perspective of surface water quality with agricultural issues (fertilizers, crop production, and surplus), food/feed exchanges, and diet, defining the so-called water-agro-food system, The FIRE-FR3020 research federation is gratefully acknowledged for the organization of an interdisciplinary workshop during which the paper emerged. Estela Romero was funded by a Research Fellowship from the Iberdrola Foundation, and Najla Aissa-Grouz and Lauriane Vilmin were granted by a R2DS-Ile-de-France Region scholarship

Both particulate phosphorus (PP) and soluble phosphorus (SP) contribute to the eutrophication of water bodies. This research focuses on the mechanisms and factors controlling SP exports at the watershed scale in a case study located in Southern France. Variability in the P concentrations and fluxes was analysed over a period of 6 years in a 302-ha rural watershed. During most of the hydrological periods, reservoirs and pathways for PP and SP seemed to be different both in time and space; differences were greatest during storm flows of the early wet season. Their high SP fluxes and concentrations were due to the P released from agricultural soils as shown by a P mass balance downstream/upstream. During these flushing periods, soluble forms of P follow a hydrochemical behaviour quite similar to solutes and are transferred in relationship to subsurface flows, as shown by a detailed monitoring of the transition from dry to wet season on an agricultural sub-watershed.

International audience; Recent improvements in the Soil and Water Assessment Tool (SWAT) model take account of hydrological processes controlling a variable source area (VSA). This model, SWAT-VSA, accounts for changes in the nature and extent of the VSA over the course of a hydrological cycle by considering global catchment storage capacity, which varies with soil moisture between threshold values whose spatial distribution is determined by topography. The objective of this work is to evaluate the contribution of several aquifers with specific storage capacities to global catchment storage, its dynamics; and subsequent effects on VSA and non-point-source pollution. For this purpose, a method called SWAT-mVSA (SWAT-multi VSA) was used in a catchment representative of the agricultural conditions of large perialpine lakes to calculate soluble reactive phosphorus (SRP) fluxes because SRP has a major influence on receiving waters. SWAT-mVSA predicted components of the hydrological balance and SRP fluxes more accurately than SWAT-VSA. This underlines the importance of VSAs in mobilizing and transporting non-point-source pollutants such as nutrients, pesticides, or bacteria.

Resume Une crue artificielle est realisee sur un troncon de ruisseau du bassin versant du Mercube (Haute-Savoie, France) afin de rendre compte du role du reseau hydrographique dans la transmission et l’emission de particules et de phosphore. Seul le phosphore d’origine diffuse est concerne. Cette experimentation se deroule en injectant de l’eau naturellement marquee par une teneur elevee en sulfates et chargee de suspensions. Elle met en evidence (1) les zones de stockage et de relargage des matieres en suspension dans le reseau hydrographique, (2) l’importance de l’effet piston sur le renouvellement des eaux en crue et (3) la capture du phosphore soluble au cours du transfert. L’augmentation du debit liee a l’onde de pression met en mouvement les sediments deposes au fond du lit. De ce fait, le phosphore est emis a l’exutoire d’abord lieaux particules remises en suspension, puis associea l’eau injectee. La contribution du reseau hydrographique a l’emission de phosphore n’est pas negligeable. Le meme phenomene se retrouve dans une crue reelle d’intensitecomparable.

Phosphorus is an important pollutant leading to lake eutrophication. Diffuse pollution accounts for a substancial share of the total phosphorus load. To improve our knowledge of this pollution, we conducted a watershed study in a small, rural, 302-ha watershed (Lake Léman area). To study the spatial distribution and temporal dynamics of phosphorus in the watershed and the corresponding variation in phosphorus speciation, 40 stormflow events over a 4- year period were analysed. We began by defining the ’state’ of the watershed using a) periodic field surveys of signs of erosion, b) the length of the flowing ditches and streams (active hydrological network) and the waterpathways on the fields, c) the overall water budget, and d) grab samples of stream water from a network of subwatersheds. Four states that reflected contrasting watershed conditions were identified. Analysis of the data on phosphorus flux at the outlet of the watershed, in conjunction with the observations on the state of the watershed, allowed us to develop a conceptual model of phosphorus export from the watershed and several hypotheses about phosphorus transfer. (© Inra/Elsevier, Paris.), On cherche, à travers l’étude d’un bassin versant rural, à identifier les mécanismes de la pollution diffuse phosphorée, ses modalités d’émission et de transport et ses impacts potentiels sur les milieux récepteurs. Les exportations de phosphore ont été étudiées pendant 4 ans sur le Mercube, bassin versant rural de 302 ha sans pollution ponctuelle, situé sur la rive française du Léman. Le principe de l’étude consiste à comparer des « états de bassin » avec des flux et des spéciations mesurés à son exutoire. La définition de l’état de bassin repose sur des campagnes d’observation et de mesures des écoulements présents sur le bassin versant. Quatre états reflétant des situations hydriques contrastées ont été définis. Ils se distinguent par la diversité spatiale des différents stocks de phosphore mis en jeu. Leur succession saisonnière décrit un cycle étroitement lié aux cycles culturaux et météorologiques. Afin de comprendre l’influence de ces états sur les quantités de phosphore émises vers le lac et sur sa spéciation, une quarantaine de crues ont été échantillonnées à l’exutoire du bassin.Cette analyse des transferts diffus de phosphore nous amène à proposer un modèle typologique des exportations de phosphore. Elle aboutit aussi à renouveler les conceptions concernant les processus de transfert des formes solubles et particulaires de phosphore. (© Inra/Elsevier, Paris.)

International audience; The aim of this study is to investigate phosphorus (P) species modifications triggered by soil genesis and mountain ecosystem development after glacial retreat using a lake sediment archive (Lake Anterne, North French Alps). Five lake sediment samples, representative of different stages of soil and ecosystem development, were selected for P speciation analyses. Furthermore, a sequence of current soils from the catchment was analyzed to better constrain our interpretations of the lacustrine archive. Synchrotron techniques (X-Ray Fluorescence (XRF) mapping and P K-edge X-ray absorption near edge structure (XANES) spectroscopy) were applied to lake sediments, soils, and standards (mineral and organic) to distinguish between different P species. The results show that soil development during the first millennia of the Holocene triggered increased P species diversity. At the onset of the Holocene, P was present as apatite when rocks and leptosols dominated the catchment. Pedogenic processes then led to apatite dissolution and the formation of large amounts of P on metal/clay-organic complexes. P geochemistry during the main step of soil genesis (early leptosols dominated by apatite, low weathered cambisols with P mainly adsorbed on iron oxides, highly weathered podzols with large amounts of P on Al/Fe/clay organic complexes) is thus clearly recorded in lake sediments. P K-edge XANES spectroscopy is particularly relevant as qualitative method to study P species in soils and lake sediments at high spatial resolution. Such resolution is needed to reveal the diversity of small P particles and like this better characterize the P cycle and improve our understanding of ecosystem evolution.

International audience; The spatiotemporal distribution of biochemical varves spanning the last 150 yr was investigated using 40 cores collected over a depth gradient in a large subalpine lake--Lake Bourget--in the French Alps. Four-dimensional sedimentological, biological, and geochemical analyses show that varve preservation can be used as a reliable proxy to reconstruct annual-to-decadal oscillations of hypoxia in large lakes. The volume of hypoxic waters was calculated by integrating the volume between the lake bottom and the depth of the shallowest varve-bearing core for each year. Although Lake Bourget bottom waters have been oxic over the last 9000 yr, severe hypoxia has occurred only since 1933 ± 1. The volume of hypoxic waters showed, thereafter, a succession of pronounced fluctuations, leading to an increase of 8% of the total lake volume in the 1960s, a decline in the 1980s, and a second, ongoing increase since 1990. Whereas the initial onset of persistent hypoxic conditions could be attributed to eutrophication due to nutrient-rich inputs from sewage water and/or diffuse contamination, the later fluctuations were also driven by climatic factors, i.e., flooding, rising air temperatures, and phosphorus-independent changes in primary production. Hence, cumulative effects related to global warming seem to have driven hypolimnetic hypoxic conditions since equilibrium was initially disrupted due to a drastic shift in the trophic state.

Resume Ce papier presente les resultats d'une etude sur les transferts des nutriments (P, N) et la qualite de l'eau, menee sur un petit bassin versant (14 ha) en milieu rural, situe en bordure du Lac Leman. L'etude du bilan annuel et de la variabilite des concentrations en N et P permet d'evaluer les risques de degradation des eaux lies aux pratiques agricoles. L'analyse d'une vingtaine de crues nous a permis de degager 3 types d'evenements: (1) les crues liees surtout a une mise en charge de la nappe et caracterisees par des exportations limitees de N et de P; (2) les crues a forte composante de ruissellement qui exportent surtout de grandes quantites de P sous forme particulaire; (3) les crues a ecoulement hypodermique important qui exportent beaucoup de N mais aussi de P sous forme soluble. Les flux sortant du bassin experimental s'ecoulent vers un marecage et a l'exutoire de ce marais, on constate une nette amelioration de la qualite de l'eau par denitrification et par insolubilisation et decantation de P. La gestion et la lutte contre la pollution diffuse agricole passe ainsi par un amenagement a la fois de la zone agricole elle-meme et des differentes zones tampons le long du parcours des eaux. Le type d'amenagement n'est pas forcement le meme pour N et pour P. Dans certains cas, il peut meme apparaitre des effets contraires.

Un projet multipartenarial de plus de 3 ans a été conduit sur les «diagnostics et solutions pour limiter les transferts de phosphore agricole vers le milieu aquatique ». Des bilans agronomiques de phosphore ont été calculés au niveau départemental, puis cantonal en Bretagne où les sols continuent de s’enrichir en phosphore. A l’échelle des exploitations d’élevage, deux principaux leviers de réduction des excédents sont pertinents : maîtrise de la fertilisation minérale et amélioration de l’alimentation (en diminuant lephosphore dans la complémentation minérale et en utilisant des phytases). A l’échelle de la parcelle, les données de dispositifs expérimentaux ont montré que (i) les transferts de phosphore par ruissellement et drainage sont augmentés dans les sols enrichis en phosphore et/ou les situations de fertilisation organique, (ii) dans les parcelles drainées, la suppression du labour aggrave les pertes dephosphore par le drainage en préservant les voies de circulation préférentielle de l’eau (galeries de lombrics par exemple). Enfin, la comparaison de deux bassins versants a permis notamment de souligner l’importance de la protection des berges dans la réduction des émissions de phosphore. A ces différents niveaux, des solutions ont été proposées pour réduire les « sources » de phosphore et les « transferts » diffus associés., A joint project was conducted for over three years on the diagnostics and solutions for limiting the transfer of agricultural phosphorous to water bodies. Agronomic phosphorous balances were calculated at the departemental level, and in Brittany where soils keep accumulating phosphorous, at the canton level too. At the livestock farm level, two main means of reducing excess phosphorous were demonstrated as being relevant: reducing mineral fertilization and improving feeding (particularly by decreasing the amount of phosphorous in mineral complements and providing phytases). At the plot level, data from field stations showed that (i) the transfer of phosphorous by runoff and drainage increased in soils enriched in phosphorous and/or when organic fertilization was applied, (ii) in drained plots, more phosphorous was lost when tillage was suppressed because of the preservation of preferential drainage channels such as worm burrows. Finally, the comparison between two watersheds highlighted the importance of protecting riverbanks for reducing the loss of phosphorous. Solutions were proposed at each level for reducing the sources of phosphorous and associated diffuse transfers.

National audience; Beaucoup de lacs en Europe ont développé un faciès laminé dans leurs sédiments ces dernières décennies (lamines claires d’été correspondant à de la calcite bio-précipitée et lamines sombres d’hiver riches en matière organique) en raison du manque d’oxygène biodisponible dans l’hypolimnion. Trois paramètres peuvent être à l’origine de la dégradation des conditions d’oxygénation dans l’hypolimnion : l’élévation du niveau trophique du lac, le retournement incomplet de la colonne d’eau et l’absence de courants de densité provenant des crues. Dans le lac périalpin du Bourget (Savoie), l’analyse géochimique des sédiments nous a permis de reconstituer les conditions d’oxygénation de l’hypolimnion des 150 dernières années. Dans le but d’étudier les variations spatio-temporelles de l’oxygénation et les processus impliqués dans la régulation de l’O2 nous avons réalisé un transect de 10 carottes dans l’axe des apports des crues Rhodaniennes et un deuxième, transversal, constitué de 4 carottes. Dans le bassin Nord l’intensité de l’anoxie a été évaluée spatialement et temporellement en fonction de la présence plus ou moins marquée des lamines saisonnières, de la préservation de la matière organique mesurée en spectrocolorimétrie, et du rapport Mn/Fe. Ces résultats ont été comparés aux flux de phosphore dans les sédiments ainsi qu’aux mesures des concentrations en Ptotal, Portho et oxygène de la colonne d’eau à partir des données INRA-CISALBa (Jacquet et al. 2008). Les résultats permettent de modéliser l’étendue des dépôts rhodaniens à différentes époques, ainsi que l’étendue des sédiments hypoxiques à partir des années 1930-40. Le retour d’un faciès non laminé sur deux carottes disposées dans l’alignement des crues du Rhône, entre 1976 et 1986, indique une période de réoxygénation du fond. Cette période de temps sans lamine correspond à une période plus intense de détritisme du Rhône (Giguet-Covex et al. 2010), ceci nous laisse supposer que le processus responsable localement de l’oxygénation du fond pourrait être attribué aux crues, favorisant ainsi le retour de la vie benthique. Une étude en cours sur l’oxygénation du fond du lac à partir de l’analyse des assemblages de chironomes devrait permettre d’affiner ces résultats.

Microbial contamination of surface waters frequently occurs on permanent natural grasslands subject to extensive grazing. Management of these problems requires developing methods to identify critical source areas that are responsible of significant losses of fecal microorganisms. In this study, GIS analysis of watersheds was used to calculate the flow of fecal bacteria (Escherichia coli) to the outflow of a watershed by summing bacterial flows in runoff from pixels containing cowpats. Calculations were performed in two steps: (i) identification of pixels with bacteria and runoff by modeling the distribution of cowpats and variable sources of surface runoff, and (ii) parameterization by inverse analysis of deterministic and stochastic functions for bacterial emission from cowpats and for retention during their transmission to the watershed outflow. During bacterial transport in water flow, bacterial retention on the soil surface has a large influence. Despite this effect, bacterial concentration in runoff remains high. In general, cowpat age, runoff volumes and the location and proportions of bacteria-emitting and non-emitting surfaces determine critical source areas and bacterial flows at the watershed outflow. These data are discussed in terms of feasibility of solutions for management of watercourses and grazing practices.

Les écosystèmes aquatiques reçoivent des apports conséquents de matière organique d'origine terrestre qui pourraient, lorsqu'ils sont intégrés dans les réseaux trophiques, soutenir une part significative de la production secondaire et piscicole de ces écosystèmes ou modifier la structure des communautés. Les études relatives à l'impact fonctionnel des apports d'origine terrestre aux écosystèmes lacustres sont, jusqu'à présent, essentiellement centrées sur les lacs peu profonds des boucliers scandinaves et Nord-américains. Les connaissances sont encore sporadiques en ce qui concerne les lacs profonds, dans lesquels la contribution du carbone d'origine terrestre n'a encore été que peu quantifiée. L'étude de la part prise par les apports allochtones dans le fonctionnement du système semble plus particulièrement pertinente dans les milieux en voie de réoligotrophisation, milieux dont ils pourraient maintenir la productivité. Dans le cadre d'une étude préalable sur les possibilités de distinguer les matières organiques d'origine terrestre dans les écosystèmes lacustres, un suivi mensuel des caractéristiques des MOD aquatiques dans la masse d'eau lacustre et dans les affluents a été mis en place. Des échantillons du niveau 0-20 m ont été prélevés dans le centre des lacs d'Annecy et du Léman de mars 2007 à mars 2008. Parallèlement des échantillons ont été prélevés dans la zone littorale du lac Léman et dans un certain nombre d'affluent des deux lacs. Les échantillons prélevés et filtrés à 0.2μm ont été analysés en utilisant les outils suivants : analyseur de DOC, spectrométre UV-visible, spectroscope de fluorescences 3D, chromatographie d'exclusion stérique. Les résultats mettent en évidence que les spectres de fluorométrie 3D peuvent constituer des signatures des différentes eaux. Les caractéristiques des MO fluorescentes apparaissent en effets bien distinctes : - prédominance des substances humiques dans les apports (indice HIX élevé) - importance des pics liés à la production récente de MO (pic γ de fluorescence) dans les eaux du centre des lacs - importance de l'activité biologique dans les zones littorales directement sous l'influence d'une rivière On constate par ailleurs une très nette évolution de la taille moyenne et de la distribution des familles de tailles de molécules au cours de la saison dans les eaux des lacs (diminution de la taille moyenne lors des pics de production printanier et estivaux) mais également dans les eaux des affluents). Ces résultats préliminaires mettent enfin en évidence le besoin d'études intégrées des matières organiques dans les écosystèmes lacustres avec une nécessaire combinaison d'approches analytiques diverses (spectroscopique, chromatographique mais aussi biomarqueurs) pour comprendre les interactions entre matières organiques autochtones et allochtones dans ces écosystèmes.

L'originalite de la pedogenese sur calschistes sedimentaires, en altitude (etage subalpin), reside dans l'homogeneite du residu de decarbonatation (plaquettes de micas de taille limons fins). Au sein des sols developpes en place, la principale evolution qui se manifeste entre l'alterite et la surface du sol, est une microdivision de ces particules limoneuses. Celle-ci s'accompagne d'une disparition du systeme de macroporosite herite de la decarbonatation de la roche et de l'apparition, dans l'horizon (B), d'un systeme de micropores (.)

En altitude, l'alteration des calcschistes sedimentaires (calcshales) conduit a des sols contenant une teneur elevee en limon fin, de composition mineralogique essentiellement micacee. La pedogenese se caracterise sur ce type de roche, par une argilisation importante due a une microdivision des micas, vers la surface du sol. Ce phenomene entraine une profonde reorganisation de la phase solide, de l'espace solide, de l'espace poral et en fin de compte, conditionne les proprietes hydriques des sols. Dans ce premier texte, un ensemble de methodes de mesure et d'observation est employe pour decrire l'evolution de la geometrie du systeme de porosite herite de la roche, apres sa decarbonatation (...)

International audience; The present article describes a first attempt to use infrared spectroscopy to trace the origin of suspended river sediments. Fifty samples of the main potential sediment sources within a small catchment area (990 ha) in the French Alps were collected and compared with samples of suspended sediment from the river, collected on various dates during 2006 and 2007 using sediment traps. Two major categories of sediment source were identified: topsoils and river channel sediments. For the qualitative part of the study, each of these two main categories was divided into two sub-categories, that is to say, cultivated and pastureland topsoils, and riverbed and riverbank sediments. Discriminant analysis on the source samples showed that Diffuse Reflectance Infrared Fourier Transform (DRIFT) spectroscopy can be used to differentiate between the four potential source materials. To determine whether or not immersion in the river altered the infrared spectra of these source materials, we measured the infrared spectra of samples that had been immersed in the river, in litter bags, for periods of up to 24 days. Immersion did not cause any major changes in the infrared spectra. The contribution of each type of source material to the suspended sediment in the river was quantified using partial least squares (PLS) analyses of DRIFT spectra to compare actual river sediment samples with an experimental model. This model was produced from the DRIFT spectra of a range of calibration samples produced by mixing source material samples in different ratios. The predictions of the model were valid and fell within the confidence interval calculated for the calibration set. Comparisons between suspended sediment samples and the model indicate that the predominant source of the sediment is riverbank erosion, which, in this case, is probably due to trampling by cattle.

International audience; Our knowledge of Escherichia coli (E. coli) ecology in the field is very limited in the case of dairy alpine grassland soils. Here, our objective was to monitor field survival of E. coli in cow pats and underlying soils in four different alpine pasture units, and to determine whether the soil could constitute an environmental reservoir. E. coli was enumerated by MPN using a selective medium. E. coli survived well in cow pats (10(7) to 10(8) cells g(-1) dry pat), but cow pats disappeared within about 2 mo. In each pasture unit, constant levels of E. coli (10(3) to 10(4) cells g(-1) dry soil) were recovered from all topsoil (0-5 cm) samples regardless of the sampling date, that is, under the snow cover, immediately after snow melting, or during the pasture season (during and after the decomposition of pats). In deeper soil layers below the root zone (5-25 cm), E. coli persistence varied according to soil type, with higher numbers recovered in poorly-drained soils (10(3) to 10(4) cells g(-1) dry soil) than in well-drained soils (< 10(2) cells g(-1) dry soil). A preliminary analysis of 38 partial uidA sequences of E. coli from pat and soils highlighted a cluster containing sequences only found in this work. Overall, this study raises the possibility that fecal E. coli could have formed a naturalized (sub)population, which is now part of the indigenous soil community of alpine pasture grasslands, the soil thus representing an environmental reservoir of E. coli.

Recommending the use of ‘‘grass buffer strips’’ to control diffuse P transfer has become well accepted among extension advisors, agricultural consultants, planners, and other practitioners that influence the structure of the agricultural landscape. These grassed areas are put in place to capture the P contained in runoff from source fields. They are designed to function as a filter and a sediment trap although it is often unclear what the long-term disposition of the accumulated P may be. The objective of this work was to determine if the available scientific literature justifies the continued recommendation of this approach in the prevention of phosphorus movement from agricultural soils to surface waters. We employed a theoretical analysis of the mechanisms of the buffering effect and the specific behaviour of phosphorus in typical grass buffer strips to establish the critical set of literature applicable to this question. An adequate body of literature exists describing many aspects of P dynamics and the short-term functioning of grass buffer strips over their seasonal cycles. Despite variable results in a diversity of landscape contexts, overall, the use of grass buffer strips appears to provide useful short-term functions in the reduction of P transport to surface waters. Long-term benefits remain questionable given the relatively short-term use of this approach in P reduction and the lack of long-term experimental results, but this current lack of data is not sufficient to deter the continued incorporation of grass buffer strips in the landscape of French agricultural. Additionally, a more comprehensive conceptual model integrating the shortterm functioning of grass buffer strips with seasonal cycles and the long-term consequences of cumulative storage emerged from our synthesis.

National audience

Diffuse pollution should be recognized as a landscape-level phenomenon. As such, it requires an observational approach consistent with the complex structure and function of the landscape system. We developed a landscape-level approach to study the transfer of phosphorus in rural areas of the Lake Champlain and Lac Leman basins. We began by developing a concept of P dynamics that captured some of the diversity and complexity of P movement through the land (transfer system). Given this initial concept of the diffuse pollution in the landscape, we adopted a synoptic watershed sampling strategy to begin the quantitative description of diffuse P pollution. Data from these types of studies were then analyzed using multiple regression to infer connections between activities on the land and phosphorus flux to surface waters. Our inferences include: 1) land cover determines phosphorus flux during high flow but not during low flows periods, 2) during high flow events, natural wetlands are a significant sink for diffuse phosphorus in surface waters, 3) fluxes and concentrations are higher when the basins are intensively plowed, 4) in the context of plowed areas, agricultural practices as opposed to land cover is a more important determinant of phosphorus flux in watersheds, and 5) the position of elements in the landscape is an important factor controlling diffuse phosphorus pollution. The method and basis for arriving at these conclusions are discussed. We suggest that synoptic sampling of water quality over extensive areas in a landscape, coupled with multiple regression to analyze relationships among P fluxes and landscape variables, is an appropriate tool for determining driving factors, analyzing the diversity of processes, and finding generality in complex landscape systems.

The aim of this work is to achieve a better understanding of the behavior of fecal coliform populations on the vegetation and in the soil after slurry spreading in environmental conditions, typical of vegetative growth period in mountain hay meadows. Changes in fecal coliform populations on the vegetation and in the soil were monitored in situ for 3 months after slurry spreading on 9 plots. The variations found in populations are related to the agricultural, soil. and climatic characteristics of plots and to the moisture regime of soils. These observations are compared with laboratory experiments on undisturbed soil microcosms. In absence of water flux, survival durations recorded in the laboratory and in the field are of the same order of magnitude. The data enable us to pinpoint the influence of various factors affecting the decline and transfer of fecal bacteria in the plant-soil system and consequently to discuss the risk management of water contamination by agriculture.

Small mountain lakes represent interesting ecosystems particularly from the point of view of their biodiversity. This article examines the environmental changes that can threaten the water quality of such lakes. A limnological survey was conducted in summer on Lake Bénit (4 ha) in the French Alps with a view to identifying its main chemical and biological characteristics. Numerous parameters indicate that the main threat for the lake is eutrophication (phosphorus in water, summer depletion of hypolimnetic water, blue green algae). The excess of phosphorus arises from flooded soils. A general management strategy for such a lake is discussed., Un lac à protéger : le lac Bénit (Haute-Savoie) A lake in need of protection : Lake Bénit (Haute Savoie, France) Jean-Claude Druart et al. Résumé : Le lac Bénit représente une ressource biologique et touristique de valeur. Son état a été évalué à partir de quelques suivis réalisés en été et en automne. Les paramètres physico-chimiques ont été complétés par l'analyse de la diversité spécifique du phytoplancton. Le diagnostic révèle un lac fragile en raison d'une nette tendance à l'eutrophisation causée par les apports exogènes en provenance du bassin versant., Druart Jean-Claude, Dorioz Jean-Marcel, Blanc Paul, Balvay Gérard. Un lac à protéger : le lac Bénit (Haute-Savoie). In: Revue de géographie alpine, tome 87, n°3, 1999. pp. 87-99.

Le recours à l’irrigation des prairies permanentes du val d’Aoste (Alpes italiennes) s’explique par la faible pluviosité estivale et la forte demande d’évapotranspiration. Pour étudier la satisfaction des besoins en eau de divers types de prairies irriguées, nous avons utilisé un modèle simplifié de calcul des variations de la teneur en eau du sol. Il s’agit du module bilan hydrique de CREAMS (chemical, runoff, and erosion from agricultural management systems). Dans un premier temps, nous caractérisons la variabilité des différentes variables entrées dans le modèle : propriétés hydriques des sols, fréquences, dates et doses d’irrigation. Nous évaluons par ailleurs la valeur d’un paramètre de calage décrivant la répartition du système racinaire avec la profondeur. Dans un deuxième temps, nous simulons les variations de la teneur en eau du sol sur un réseau de 8 parcelles dont nous suivons l’humidité volumique et la production de matière sèche. Les calculs donnent des résultats comparables aux humidités observées et le rendement en matière sèche est corrélé significativement aux déficits hydriques moyens calculés. Le modèle ainsi validé nous permet de simuler le comportement hydrique de différentes parcelles représentatives de la variabilité régionale des sols et des pratiques d’irrigation., Irrigation of permanent meadows in Val d’Aosta (inner Italian Alps) is rendered necessary by low summer precipitations and by a high evapotranspiration demand. To study the satisfaction of the water requirement of vegetation, a simple model of water balance calculation was used. This is the ’hydrology’ module of CREAMS (chemical, runoff, and erosion from agricultural management systems). We first characterized the variability of the different input variables: hydric properties of the soils, dates and frequencies of irrigation, and doses of water supplied. We also assessed the value of a parameter that relates root distribution with depth. We noticed a great variability of soil properties and irrigation practices. We then ran a simulation of water balance on 8 plots where soil moisture and dry-matter yield were monitored. The results of the calculations were comparable to the observed soil moisture values. Moreover, the dry-matter yields were correlated with the calculated mean water deficit. Simulations run with the model provide a framework adapted to the regional variability of soil properties and agricultural practices, which can be used to analyse interaction of the factors involved in the water balance.

Enzymatic liberation of molybdate reactive phosphorus (MRP) (equivalent to orthophosphate) from sediment extracts, obtained from sediments sampled from different parts of a subwatershed of Lake Leman, was investigated. Several hydrolytic enzymes; alkaline phosphatase, phosphodiesterase, RNase, DNase and phytase were used alone or in combination. As expected the release of MRP by combination of alkaline phosphatase with the other enzymes was more efficient than by alkaline phosphatase alone. In all cases, MRP enzymatically released accounted for less than 4% of the total phosphorus in the sediment but represented between 5 and 23% of the organic phosphorus. The highest percentage was obtained with the sediments polluted by domestic sewage. Traces of MRP were liberated by phytase only with the sediment of forest and agricultural origin. Phosphomonoesters were detected in each sediment as well as nucleic acids (except in the natural sediment). This study has shown that it seems possible to characterize organic phosphorus of sediments using this procedure.

Colloque « Eaux et milieux aquatiques continentaux » à Rennes le 2 octobre 2012.; National audience; Alpine lakes are influenced by multiple forcing factors acting at global or local scale. Ecological responses, changes in biodiversity, community structure reflect their interactions. Their understanding requires approaches that are spatially and temporally nested. In particular, highlighting the long-term trend requires physico-chemical and biological surveys organized in the frame of Observatory, including paleolimnological approaches and more specific studies to identify short-term ecological dynamics. The Alpine Lakes Observatory (SOERE) enables to trace the evolution of the major lakes of the French Alps, showing that the effects of global warming on biodiversity are lake declined locally, depending on the local characteristics.; Les lacs alpins sont sous influence de facteurs de forçage multiples, agissant à l’échelle globale ou locale. Les réponses écologiques, les changements de biodiversité, de structure de communautés traduisent ces interactions. Leur compréhension nécessite des approches emboîtées, spatialement et temporellement. En particulier, la mise en évidence de tendance sur le long terme nécessite des suivis physico-chimiques et biologiques pérennes dans le cadre d’Observatoire, incluant des approches de paléolimnologie et des études plus ponctuelles permettant de préciser des dynamiques écologiques à court terme. L’Observatoire des Lacs Alpins (SOERE) permet ainsi de retracer les évolutions des principaux lacs des alpes françaises, en montrant que les conséquences du réchauffement climatique sur la biodiversité lacustre sont déclinées localement, en fonction des caractéristiques locales.

This research project entitled « Pastor » is devoted to the study of the survival and dissemination of fecal bacteria contaminants originated from cattle, in soil and surface water. It focuses on microbial contamination by Escherichia coli in relationship with dairy grazing of alpine rangelands. E. coli is considered as a global indicator of fecal contaminations. Studies have been carried both at the plot and at the watershed scale. They deal with : 1) the dynamics of E. coli populations, including pathogenic STEC (Shiga-toxin producing E. coli) strains, released in the mountain environment ; the objective is to characterize survival and storage ompartments of E. coli in soil following their release by cattle feces ; the population dynamics of E. coli in soils is compared with dynamics of typical soil inhabitants (the fluorescent Pseudomonas spp.), in order to reveal specific adaptive strategies of E. coli ;2) the identification and characterization of the grazing areas providing specifically a high contribution to fecal contamination of surface water ; this was carried out by quantifying and modeling E. coli transfers from soil to water, with the aim to link together E. coli fluxes monitored at the watershed outlet, grazing conditions and hydrologic properties of the watershed. The output of the model is of interest to identify the critical source areas. Further assessment of the groundwater compartment is needed to improve our understanding of E. coli ecology especially with regards to the outlet peaks unrelated to stromflows. The operational interest of « Pastor » concerns the prevention of fecal pollution of surface water and the relevance of E. coli as an indicator of fecal contamination. The knowledge of critical source areas is an important information for management of pastured watersheds., L’objectif de ce projet mené dans le cadre du programme GESSOL 2 est de comprendre et modéliser la survie et la dynamique de transfert dans les déjections, les sols et les eaux, de contaminants fécaux bovins, en relation avec les pratiques pastorales et la variabilité des milieux. Les suivis sont centrés sur Escherichia coli et incluent des données sur les souches pathogènes STEC (Shiga-toxin producing E. coli). Des suivis complémentaires portant sur Pseudomonas spp fluorescents, populations typiques des sols, fournissent des éléments de comparaison importants. Les recherches sont réalisées dans un alpage des Alpes du nord, à l’échelle station-parcelle et bassin versant. L’article présente une vue d’ensemble de la démarche d’étude, des méthodologies et des résultats obtenus, puis se focalise sur les acquis concernant le comportement de E. coli dans les sols et sur les apports de la modélisation des transferts à l’échelle bassin versant. Les résultats sont discutés dans une double perspective, celle d’une synthèse présentant le fonctionnement du bassin versant pâturé comme un système de transfert de contaminants fécaux et celle de réflexions opérationnelles relatives à la gestion pastorale., El proyecto “Pastor” trata de la supervivencia y de la diseminación de los contaminantes microbianos del suelo hacia las aguas. Apunta la contaminación microbiana del agua por E. coli (indicador de la contaminación fecal) en los prados alpestres en relación con los pastos de lechera. La demanda social en términos de calidad microbiana del agua está importante, incluyendo los Alpes norteños franceses, región de reserva de agua. Las contaminaciones se deben en parte a las prácticas de pastizales. Un inquietante desenlace está la ocurrencia de animales portadores sanos de E. coli potencialmente patogénicos para los humanos y cuya diseminación por los animales de granja está posible. La calidad del agua en las zonas de pastizales entra en debates más amplios sobre la gestión sostenible de los recursos de aguas subterráneas bajo pastos. Las investigaciones desarrollas en el proyecto “Pastor” tratan de : 1) la dinámica de las populaciones de E. coli, incluyendo las tensiones debidas a las STEC patogénicas, una vez liberadas en el medio ambiente montañoso ; el objetivo está caracterizar los compartimentos de supervivencia y de almacenamiento de E. coli en los suelos después de su depósito por las deyecciones del ganado, y comparar con la dinámica de las populaciones típicas del suelo (Pseudomonas spp. fluorecens) para la evaluación de las estrategias adaptivas de E. coli. 2) la identificación y la caracterización de las zonas de pastos que contribuyen a la contaminación fecal de las aguas de superficie en una cuenca vertiente alpestre ; Se midió la cuantidad de E. coli que está transferida de las diferentes zonas de pastos hacia el agua, con la finalidad de ligar el stock de E. coli y el flujo a la salida de la cuenca vertiente, al funcionamiento del pasto y a las propiedades hidrológicas de la cuenca vertiente. “Pastor” incluye también un análisis del funcionamiento de la cuenca vertiente en términos de transferencia de los contaminantes fecales y de modelización del flujo bacteriano. La información necesaria para la modelización incluye los regímenes de exportación a la salida de la cuenca vertiente, condición de transferencia en la cuenca vertiente, y el potencial de liberación de las diferentes unidades de pastos. El rendimiento del modelo estará importante para la gestión mejorada de los recursos en agua en los pastos alpestres. La significación práctica de “Pastor” concierne la prevención de la contaminación fecal del agua y la pertinencia de E. coli como indicador de la contaminación fecal. Es necesario tener una evaluación más precisa del compartimento del agua subterránea para mejorar nuestro conocimiento de la ecología de E. coli especialmente para los picos de salida no ligados a los flujos. El conocimiento de las zonas de contaminación activa está importante para la gestión de los circuitos de pastos, de las zonas de abrevadero del ganado, de los pasos de arroyos, así como el cierre de las zonas de riesgo. Estas medidas de protección están más bien costosas a aplicar. Sin embargo, a pesar del hecho que una proporción muy pequeña de contaminantes microbianos llega al agua de superficie, pueden tener consecuencias muy significativas en términos de salud humana y animal.