Marie-George Tournoud

Spatial and temporal trends in water quality in a Mediterranean temporary river impacted by sewage effluents

This paper analyzes how changes in hydrological conditions can affect the water quality of a temporary river that receives direct inputs of sewage effluents. Data from 12 spatial surveys of the Vène river were examined. Physico-chemical parameters, major ion, and nutrient concentrations were measured. Analyses of variance (ANOVA) and multivariate analyses were performed. ANOVA revealed significant spatial differences for conductivity and major ion but no significant spatial differences for nutrient concentrations even if higher average concentrations were observed at stations located downstream from sewage effluent discharge points. Significant temporal differences were observed among all the parameters. Karstic springs had a marked dilution effect on the direct disposal of sewage effluents. During high-flow periods, nutrient concentrations were high to moderate whereas nutrient concentrations ranged from moderate to bad at stations located downstream from the direct inputs of sewage effluents during low-flow periods. Principal component analysis showed that water quality parameters that explained the water quality of the Vène river were highly dependent on hydrological conditions. Cluster analysis showed that when the karstic springs were flowing, water quality was homogeneous all along the river, whereas when karstic springs were dry, water quality at the monitoring stations was more fragmented. These results underline the importance of considering hydrological conditions when monitoring the water quality of temporary rivers. In view of the pollution observed in the Vène river, “good water chemical status” can probably only be achieved by improving the management of sewage effluents during low-flow periods.

Flow and nutrient transport in intermittent rivers: a modelling case-study on the Vène River using SWAT 2005

Abstract Intermittent rivers have a specific hydrological behaviour which also influences water quality dynamics. The objective of this work was to model the flow and water quality dynamics of a coastal Mediterranean intermittent river using the Soil and Water Assessment Tool (SWAT 2005). Flow, sediment, nitrogen and phosphorus transport were simulated on the Vène experimental catchment, France. The model was sequentially calibrated at sub-catchment scale and validated both at sub-catchment and catchment scales. A procedure for building the data records for the point sources is presented. The results indicate that, while the model produces good results for flow simulation, its performance for sediment transport is less satisfactory. This in turn impacts on the nutrient transport module. The reasons behind these shortcomings are analysed, taking into account the length of the data records, their distribution and the equations used in the SWAT model. The need for a thorough multi-objective model validation is illustrated. Citation Chahinian, N., Tournoud, M.-G., Perrin, J.-L. & Picot, B. (2011) Flow and nutrient transport in intermittent rivers: a modelling case-study on the Vène River using SWAT 2005. Hydrol. Sci. J. 56(2), 268–287.

Nutrient load modelling during floods in intermittent rivers: An operational approach

In the Mediterranean area, lagoons and coastal waters are often under the influence of intermittent rivers that contribute the majority of pollutant loads during flood events. Reliable tools for evaluating pollutant loads from land sources are needed for managing the water quality of the receiving waters, but available water quality models are not suitable for simulating these flash flood events. An operational tool, D-PoL (Diffuse-Pollution Load), to estimate the pollutant loads transferred during rainfall events by small Mediterranean rivers is described. The tool is based on a rainfall-load semi-distributed approach and was developed with the aim of simulating temporal variations in fluxes of dissolved pollutants. The model simulates pollutographs at the outlet of the catchment during rainfall events: the rainfall triggers the processes. The model can be described as a rainfall-load model. Three parameters describe the processes involved: the initial stock of pollutants on the hillslopes, the production parameter (which is related to the lag time of the catchment) and the routing parameter (which is related to the lag time of a basic river reach). First, sensitivity analysis demonstrated that each of the parameters controlled one key-feature of the pollutograph. The initial stock of pollutants influenced the amplitude of the pollutograph, the production parameter controlled the recession period, and the routing parameter influenced the rising phase. Second, the model was calibrated for dissolved inorganic nitrogen and dissolved phosphorus on a 20-flood data set. The sets of optimal parameters were fitted to empirical relationships for both elements. On the 20-flood calibration data set, the simulated total loads with adjusted parameters compared well with the observed parameters, except for very small events. Finally, the D-PoL model was checked against a new set of data, a 10-flood validation data set. This final validation of the model showed that the dynamics of the pollutograph were not perfectly reproduced, but that simulated total loads agreed with the observed loads.

Sensitivity of effective rainfall amount to land use description using GIS tool. Case of a small mediterranean catchment

Abstract Distributed modelling in hydrology assess catchment subdivision to take into account physic characteristics. In this paper, we test the effect of land use aggregation scheme on catchment hydrological response. Evolution of intra-subcatchment land use is studied using statistic and entropy methods. The SCS-CN method is used to calculate effective rainfall which is here assimilated to hydrological response. Our purpose is to determine the existence of a critical threshold-area appropriate for the application of hydrological modelling. Land use aggregation effects on effective rainfall is assessed on small mediterranean catchment. The results show that land use aggregation and land use classification type have significant effects on hydrological modelling and in particular on effective rainfall modelling.

Occurrence and removal of butyltin compounds in a waste stabilisation pond of a domestic waste water treatment plant of a rural French town.

The aim of this study was to investigate the fate and behaviour of butyltin pollutants, including monobutyltin (MBT), dibutylin (DBT), and tributyltin (TBT), in waste stabilisation ponds (WSP). The study was conducted as part of a baseline survey and included five sampling campaigns comprising bottom sludge and the water column from each pond from a typical WSP in France. Butyltins were detected in all raw wastewater and effluents, reflecting their widespread use. Our results revealed high affinity between butyltins and particulate matter and high accumulation of butyltins in the sludge taken from anaerobic ponds. The dissolved butyltins in the influent ranged from 21.5 to 28.1 ng(Sn).L(-1) and in the effluent, from 8.8 to 29.3 ng(Sn).L(-1). The butyltin concentrations in the sludge ranged from 45.1 to 164 and 3.6-8.1 ng(Sn).g(-1) respectively in the first and last ponds. Our results showed an average treatment efficiency of 71% for MBT, 47% for DBT, 55% for TBT. Laboratory sorption experiments enabled the calculation of a distribution coefficient (Kd = 75,000 L.kg-1) between TBT and particulate matter from the WSPs. The Kd explained the accumulation and persistence of the TBT in the sludge after settling of particulate matter. The continuous supply of contaminated raw wastewater and the sorption-desorption processes in the ponds led to incomplete bio- and photolytic degradation and to the persistence of butyltins in dissolved and particulate matrices throughout the survey period. It is thus recommended to use shallow ponds and to pay particular attention when sludge is used for soil amendment.

Rapid Proliferation of Vibrio parahaemolyticus, Vibrio vulnificus, and Vibrio cholerae during Freshwater Flash Floods in French Mediterranean Coastal Lagoons

ABSTRACT Vibrio parahaemolyticus, Vibrio vulnificus, and Vibrio cholerae of the non-O1/non-O139 serotype are present in coastal lagoons of southern France. In these Mediterranean regions, the rivers have long low-flow periods followed by short-duration or flash floods during and after heavy intense rainstorms, particularly at the end of the summer and in autumn. These floods bring large volumes of freshwater into the lagoons, reducing their salinity. Water temperatures recorded during sampling (15 to 24°C) were favorable for the presence and multiplication of vibrios. In autumn 2011, before heavy rainfalls and flash floods, salinities ranged from 31.4 to 36.1‰ and concentrations of V. parahaemolyticus, V. vulnificus, and V. cholerae varied from 0 to 1.5 × 103 most probable number (MPN)/liter, 0.7 to 2.1 × 103 MPN/liter, and 0 to 93 MPN/liter, respectively. Following heavy rainstorms that generated severe flash flooding and heavy discharge of freshwater, salinity decreased, reaching 2.2 to 16.4‰ within 15 days, depending on the site, with a concomitant increase in Vibrio concentration to ca. 104 MPN/liter. The highest concentrations were reached with salinities between 10 and 20‰ for V. parahaemolyticus, 10 and 15‰ for V. vulnificus, and 5 and 12‰ for V. cholerae. Thus, an abrupt decrease in salinity caused by heavy rainfall and major flooding favored growth of human-pathogenic Vibrio spp. and their proliferation in the Languedocian lagoons. Based on these results, it is recommended that temperature and salinity monitoring be done to predict the presence of these Vibrio spp. in shellfish-harvesting areas of the lagoons.

Implementing the DPSIR framework to link water quality of rivers to land use: methodological issues and preliminary field test

ABSTRACT River functioning is closely influenced by land uses, along the stream itself and throughout the catchment. Land uses can be seen as both the expression of the natural environment and the result of increasing human activities. Land uses generate various pressures that affect river water quality at different scales of time and space. The assessment of multi-scale impacts of land use on river water quality is a major issue for scientists and for water managers who have to reach ambitious and rigorous legislative objectives. The ‘driving forces, pressures, state, impact, responses’ (DPSIR) conceptual framework is promoted by the European Environmental Agency for this purpose. A rigorous methodology, following a decision cycle-based approach, has been settled to help the implementation of the DPSIR on an environmental issue and its test on a field site. We develop a system of indicators based on the literature review and in accordance with water managers. The selected indicators are able to characterize the spatial and temporal evolution of water quality, land uses and their interactions. Pressure indicators are built according to the nature of the land use, the distance to rivers and the location in the watershed, at three spatial scales. We use two land-uses databases, the European Corine Land Cover database for macro-scale indicators and a high-resolution map for meso-scale and micro-scale indicators. Water quality status is characterized by a bioindicator based on population of invertebrates. The methodology is tested on the Ognon basin, which is a sub-catchment of Saône River (France). Results show that it is easy to implement the driving forces–pressures–state–impacts–responses for land use and river ecosystems framework on a medium-size catchment. But some limitations must be underlined: (1) the land-use data suffer from a lack of precision in their topological description and in the definition of the land-use nomenclature; (2) there was not enough bioindicators data to analyse, both the spatial and temporal variability of the bioindicators on the whole data set, but their spatial variability could be easily studied for a given year and (3) despite the difficulty to synthesize responses in a simple and unique indicator, the available data help to target areas for implementing actions. Lastly, this study leads us to work in close cooperation with water stakeholders, to share a common conceptual framework and to support their decision-making.

Comparison of index systems for rating water quality in intermittent rivers

Water quality indexes (WQI) are a practical way to evaluate and compare the level of chemical contamination of different water bodies and to spatially and temporally compare levels of pollution. The purpose of this study was to check if these indexes are appropriate for intermittent rivers under arid and semi-arid climates. A literature review enabled the comparison of 25 water quality indexes to discern their capability to evaluate spatial (inter and intra catchment) and temporal (high and low water flow conditions) variations in water quality in three Mediterranean intermittent rivers: the River Vène (France) and the Oued Fez and the River Sebou (Morocco). Hierarchical cluster analysis identified groups of WQI with similar behavior and brought to light the 6 most distinguishing indexes. Whatever the hydrological conditions at the two sites, both the ME-MCATUHE and NCS indexes, which were developed for Morocco and Greece, and the CCMEWQI and BCWQI indexes, which were developed for non-arid or semi-arid zones, gave appropriate water quality evaluations.