[Show abstract][Hide abstract] ABSTRACT: In 2011, the European Council stressed the significance of water quality for sustainable development in Europe and emphasized the need for better integration of the water policy objectives into the Common Agriculture Policy reform in rural areas. Since 2000, the Water Framework Directive (WFD) has required the EU Member States to target good ecological status for their water bodies. However, the implementation of the Directive for the numerous Mediterranean temporary streams has been delayed indicating the need for elaboration of the tools and methods that address the special characteristics of such water bodies. This requirement has been addressed by the recently completed MIRAGE project. In the context of the recent publication of the European Commission’s
Blueprint to Safeguard Europe’s Waters, the MIRAGE-proposed framework for the characterization of the ecohydrological dynamics and the systematic description of the measured impact for temporary rivers could bring considerable added value to the EU revision of all relevant water policies. The project recommends additions to WFD articles including an explicit definition of temporary rivers, adaptation of environmental objectives to
their peculiarities and establishment of a proper method to determine the initial status and specific actions in River Basin Management Plans.
Water Policy 09/2013; 15:830-849. DOI:10.2166/wp.2013.158 · 0.83 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: 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.
[Show abstract][Hide abstract] ABSTRACT: The aim of this study was to better understand the fate of nutrients discharged by sewage treatment plants into an intermittent Mediterranean river, during a low-flow period. Many pollutants stored in the riverbed during the low-flow period can be transferred to the downstream environments during flood events. The study focused on two processes that affect the fate and the transport of nutrients, a physical process (retention in the riverbed sediments) and a biological process (denitrification). A spatial campaign was carried out during a low-flow period to characterize the nutrient contents of both water and sediments in the Vène River. The results showed high nutrient concentrations in the water column downstream of the treated wastewater disposal (up to 13,315 μg N/L for ammonium and 2,901 μg P/L for total phosphorus). Nutrient concentrations decreased rapidly downstream of the disposal whereas nutrient contents in the sediments increased (up to 1,898 and 784 μg/g for total phosphorus and Kjeldahl nitrogen, respectively). According to an in situ experiment using sediment boxes placed in the riverbed for 85 days, we estimated that the proportion of nutrients trapped in the sediments represents 25% (respectively 10%) of phosphorus (respectively nitrogen) loads lost from the water column. In parallel, laboratory tests indicated that denitrification occurred in the Vène River, and we estimated that denitrification likely coupled to nitrification processes during the 85 days of the experiment was significantly involved in the removal of nitrogen loads (up to 38%) from the water column and was greater than accumulation processes.
[Show abstract][Hide abstract] 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.
[Show abstract][Hide abstract] ABSTRACT: The sanitary microbiological condition of Mediterranean coastal rivers is a growing concern because of its impacts on the compliance of receiving coastal and transitional waters which are of high recreational and economic values. Due to strong anthropogenic pressures, coastal rivers do not often meet the required standards and guidelines, expressed in terms of coliforms and streptococci abundances. These indicator bacteria themselves are usually not pathogenic, but they allow the tracking of recent faecal contamination and the possible presence of pathogenic micro-organisms in rivers, in an easier and less costly way. Mediterranean coastal rivers are subject to long dry periods cut by short duration flush flood events. During dry and low flow period, faecal bacteria often bound to particulate matter tend to settle in the riverbed and to constitute an in-stream store in which bacteria are able to survive for long durations and even to multiply. During intense rainfall events and floods, peaks of faecal contamination occur in rivers due to entrainment of stored bacteria in river channels by the flood. Modelling these intermittent rivers poses a numerical challenge due to the high spatial and temporal gradients and proximity of zero value. These conditions are not well handled or not simulated at all in most of the currently available watershed and rivers models. The objective of this work is to simulate the transfer and fate of faecal coliforms and faecal streptococci in an intermittent river, considering a dry period followed by a flash flood. The river considered is the French river "La Vène", close to Montpellier, for which data of several dry periods and floods are available. The model considered is Mohid River Network (MRN), (www.mohid.com). MRN is a 1D hydrodynamic model that considers a network of tributaries and allows for dynamic time step. It can also compute properties transport, such as faecal bacteria, and compute water storage in pools, transmission losses and evaporation fluxes with the fine spatial and temporal discretisation required by temporary waters. In a first step an analysis of sensibility has been performed to assess the effect of the uncertainties in the input data on the results of the model. These uncertainties can for example be due to insufficient temporal and/or spatial resolution. For dry periods, we have then adapted the decay laws of the bacteria in the bed and the surface water to better simulate the fate of the bacteria. During flash floods, the hypothesis that the bacteria will be transferred from the river bed to the surface water and from the surface water to the river bed according to the sediments erosion and deposition fluxes leds to relatively good results. An important parameter for the simulation is however the particular / dissolved ratio of CTT and SF in the surface water.
[Show abstract][Hide abstract] ABSTRACT: Organotins (OTs) are anthropogenic molecules used in many industrial applications for their thermoresistant and biocidal properties. Because of their toxicity and widespread use these molecules are on the EU water directive's list of prioritary substances. Organotins are prone to adsorption, can bond easily to particulate matter and "migrate" from the water column unto the sediments where their half-life can extend to a few decades. Recent surveys in various EU countries have indicated the presence of OTs in surface and sewage waters. The objective of this work is to study the temporal evolution of butyl, octyl and phenyl tins in contrasted flow conditions, in the sediments and water column of an intermittent river reach located to the right of an extensive sewage treatment plant (STP). The study zone is a reach of the Vène river located in southern France. The Vène is a major tributary of the Thau lagoon which is an important shellfish farming site and thus very vulnerable to OT contamination. Butyltin, trace metal and DOC concentrations were measured on water and sediment samples collected during two consecutive and contrasted hydrological years. The input and output of the STW was sampled in order to assess its impact on butyltin degradation and transformation. The results revealed the presence of butyltins at concentrations exceeding the EU and French pollution limits regularly. Very low concentrations of phenyltins were found in the water samples thus indicating that there is little use of OTs based pesticides in the area. The OTs concentrations were systematically higher during the wetter year, probably because of higher and more frequent wash off contribution to the reach and minimal dilution along the rivercourse. By contrast, the STW's impact in terms of OTs flux is more important during dry periods when there is less dilution in the river. Although the STW's outflows contained less OTs than the inputs, its efficiency in terms of OTs degradation could not be quantified from the available data as no information was available on the OTs concentrations in the deposited sediments of the lagoons. Future efforts will concentrate on a thorough analysis of OTs degradation within the STW.
[Show abstract][Hide abstract] ABSTRACT: Arid and semiarid areas where the temporary rivers and streams occur, account for one third of the earth's surface land area. However, little is known regarding their hydrologic and biogeochemical behaviour. In the European Community, all water resources have to be monitored following the requirements outlined in the Water Framework Directive (WFD-2000/60/EC). The temporary rivers provide a significant challenge in developing appropriate sampling strategy for their monitoring. The objective of this work is to characterize the nutrient dynamic on the Vène River for different hydrological conditions. To this aim, a strategic sampling was realized on this river. We selected key locations located upstream and downstream the most important point- and/or diffuse-pollution sources. 23 sampling stations were chosen: 13 sites are located in the main river and 10 sites concern direct inputs (including two sewage inputs). The spatial sampling realized all along the river was conducted on a one-day survey campaign for different hydrological conditions (including periods of very low flow and high flow). At each station, grab water samples were collected and were analysed for the different nitrogen (N) and phosphorus (P) forms. Additionally, automatic samplers coupled to three stream-gauges installed along the river permitted to collect water samples during flood events. The first results were obtained for two one-day survey campaigns which occurred in June and September 2009 at, respectively, the beginning and the end of the dry period. During these periods, the karstic spring was dry and the two wastewater inputs contributed to a great share of the flow discharge (up to 80 %). Concerning the water quality, a similar trend was observed for the evolution of N and P concentrations all along the river course, i.e., an increase was observed just after each sewage inputs (up to 2400 µg/l for ammonium and up to 4900 µg/l for total phosphorus), followed by a drop of concentrations. In comparison with concentrations obtained previously during high flow periods, these concentrations are 5 to 10 fold higher and overtook the environmental quality standards (EQS) proposed by the water framework directive. During the flood event that occurred after the dry period, high concentrations of particulate N and P, previously stored in the riverbed, were measured in water samples. These preliminary results highlight the difficulty of monitoring the temporary rivers, and the need to consider the different hydrological conditions.
[Show abstract][Hide abstract] ABSTRACT: This study aims to characterise and quantify the pollutant concentrations and fluxes in various locations of the Oued Fez hydrological network and assess their impact on the Sebou River, which is considered as a national priority zone in Morocco. Eight observation sites have been set up to quantify the temporal and spatial variability of pollutant fluxes in the river and to rank water and pollutant contributors. Water quality is evaluated through nutrients (total nitrogen and total phosphorus essentially) and heavy metals (essentially chromium). The results show that the river is highly polluted: the measured concentration values exceed international water quality standards for all the studied elements and indicate that the river is a possible threat to the downstream water bodies of high economic interest.
[Show abstract][Hide abstract] ABSTRACT: The hydrological behaviour of the River Vène (67 km, south of France) was assessed through a coupled approach based on field observations and modelling. The origins of runoff were identified by analysing discharge and water conductivity data. During rainfall events, natural areas did not contribute to runoff. In these areas, infiltration fed the karstic aquifer and contributed to spring discharges. Urban areas were characterized by a rather constant runoff coefficient whose value compares well with the extent of urbanisation and explains the total volume of small floods. Agricultural areas did not contribute directly to the flood peak, and subsurface flow in unsaturated areas was the major hydrological process during flood recession. A mathematical model, based on this “perceptual model”, confirmed the hydrological processes identified and helped quantify the functioning thresholds in this intermittent river.
[Show abstract][Hide abstract] ABSTRACT: Seven catchments of diverse size in Mediterranean Europe were investigated in order to understand the main aspects of their hydrological functioning. The methods included the analysis of daily and monthly precipitation, monthly potential evapotranspiration rates, flow duration curves, rainfall—runoff relationships and catchment internal data for the smaller and more instrumented catchments. The results showed that the catchments were less “dry” than initially considered. Only one of them was really semi-arid throughout the year. All the remaining catchments showed wet seasons when precipitation exceeded potential evapotrans-piration, allowing aquifer recharge, “wet” runoff generation mechanisms and relevant baseflow contribution. Nevertheless, local infiltration excess (Hortonian) overland flow was inferred during summer storms in some catchments and urban overland flow in some others. The roles of karstic groundwater, human disturbance and low winter temperatures were identified as having an important impact on the hydrological regime in some of the catchments.
[Show abstract][Hide abstract] ABSTRACT: Intermittent Mediterranean rivers show long draught periods interrupted by floods of high intensity and short duration. Their channel network structure is also highly variable in space and time. Water quality dynamics in these rivers is highly impacted by this specific hydrological behaviour. During the dry period, the river channel may dry up completely except in some reaches where anthropogenic point-source inputs (mainly waste water treatment plant effluents) contribute to maintain pools. Accumulation of pollutants is observed in these reaches. During the first floods, flow is rarely continuous all along the channel network, because of the existence of transmission losses. At the beginning of a storm, propagation of flood waves is limited by infiltration in the channel bed, but also by filling-up of localized storage zones. Total flood volumes therefore do not increase very much, and even decrease downstream. Some floods observed in the upstream part of the river are not transferred to the outlet. This, in turn, influences the spatial and temporal dynamics of pollutant fluxes. Along the river course, pollutograph shapes show significant differences. Intense autumn floods flush away suddenly the pollutants from the soils and the river bed, but large amounts of pollutants remain trapped in the riverbed, if transmission losses are significant. Due to this peculiar Mediterranean hydrological regime, specific observation networks must be set up to assess the temporal and spatial variability of pollutant fluxes in the river, the processes governing pollutant transport, as well as the ranking of the origins of the pollutants. All these phenomena are illustrated here on the case of the Vène River (67 km², South of France) over the observation period: from September 2003 to August 2006, on suspended solids, nutrients and faecal bacteria. The combination of continuous and event based monitoring coupled with the multi-scale sampling strategy allows a global understanding of the factors and processes influencing water quality at the catchment scale: concentration data are used to assess the contamination levels of the river and the bio-availability of pollutants, while by analysing the instantaneous fluxes the various contributions to the river might be established. Finally total flood loads are calculated in order to evaluate the exports at the catchment outlet. The multi-disciplinary approach followed herein improved our knowledge of the integrated catchment response and its impact for downstream environments.
[Show abstract][Hide abstract] ABSTRACT: Seven catchments of diverse size in Mediterranean Europe were investigated in order to understand the main aspects of their hydrological functioning. The methods included the analysis of daily and monthly precipitation, monthly potential evapotranspiration rates, flow duration curves, rainfallârunoff relationships and catchment internal data for the smaller and more instrumented catchments. The results showed that the catchments were less âdryâ than initially considered. Only one of them was really semi-arid throughout the year. All the remaining catchments showed wet seasons when precipitation exceeded potential evapotrans-piration, allowing aquifer recharge, âwetâ runoff generation mechanisms and relevant baseflow contribution. Nevertheless, local infiltration excess (Hortonian) overland flow was inferred during summer storms in some catchments and urban overland flow in some others. The roles of karstic groundwater, human disturbance and low winter temperatures were identified as having an important impact on the hydrological regime in some of the catchments.