Dominique Trevisan

Infrared spectroscopy tracing of sediment sources in a small rural watershed (French Alps).

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.

Survival and leaching of fecal bacteria after slurry spreading on mountain hay meadows: consequences for the management of water contamination risk

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.

Persistence of culturable Escherichia coli fecal contaminants in dairy alpine grassland soils.

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.

Mapping of critical source areas for diffuse fecal bacterial pollution in extensively grazed watersheds.

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.

Tracing the sources and cycling of phosphorus in river sediments using oxygen isotopes: Methodological adaptations and first results from a case study in France

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 (<0.4‰). The values for the potential allochthonous sources varied from 11.8 to 18.3‰, while the δ18Op value for the river sediments ranged from 12.2 to 15.8‰. Moreover, a sharp increase (>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.

Using a Landscape Approach to Interpret Diffuse Phosphorus Pollution and Assist with Water Quality Management in the Basins of Lake Champlain (Vermont) and Lac Léman (France)

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.

Using SWAT-VSA to Predict Diffuse Phosphorus Pollution in an Agricultural Catchment with Several Aquifers

AbstractRecent 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 ...

Development and implementation of eco-genomic tools for aquatic ecosystem biomonitoring: the SYNAQUA French-Swiss program

The effectiveness of environmental protection measures is based on the early identification and diagnosis of anthropogenic pressures. Similarly, restoration actions require precise monitoring of changes in the ecological quality of ecosystems, in order to highlight their effectiveness. Monitoring the ecological quality relies on bioindicators, which are organisms revealing the pressures exerted on the environment through the composition of their communities. Their implementation, based on the morphological identification of species, is expensive because it requires time and experts in taxonomy. Recent genomic tools should provide access to reliable and high-throughput environmental monitoring by directly inferring the composition of bioindicators’ communities from their DNA (metabarcoding). The French-Swiss program SYNAQUA (INTERREG France-Switzerland 2017–2019) proposes to use and validate the tools of environmental genomic for biomonitoring and aims ultimately at their implementation in the regulatory bio-surveillance. SYNAQUA will test the metabarcoding approach focusing on two bioindicators, diatoms, and aquatic oligochaetes, which are used in freshwater biomonitoring in France and Switzerland. To go towards the renewal of current biomonitoring practices, SYNAQUA will (1) bring together different actors: scientists, environmental managers, consulting firms, and biotechnological companies, (2) apply this approach on a large scale to demonstrate its relevance, (3) propose robust and reliable tools, and (4) raise public awareness and train the various actors likely to use these new tools. Biomonitoring approaches based on such environmental genomic tools should address the European need for reliable, higher-throughput monitoring to improve the protection of aquatic environments under multiple pressures, guide their restoration, and follow their evolution.