Impact of sediments resuspension on metal solubilization and water quality during recurrent reservoir sluicing management.
In dam contexts, sluicing operations can be performed to reestablish sediments continuity, as proposed by the EU Water Framework Directive, as well as to preserve the reservoirs' water storage capacity. Such management permits the rapid release of high quantities of reservoir sediments through the opening of dam bottom valves. This work aims to study the impact of such operation on the evolution of environmental physicochemical conditions notably changes in dissolved metallic elements concentrations (Al, As, Cd, Cr, Cu, Fe, Mn, Ni, Pb, Zn) through field and laboratory investigations. Results were interpreted in terms of concentrations and fluxes, and compared with data collected on an annual basis regarding both suspended matter and metallic elements. The release of high quantities of sediments (4,500tons dry weight in 24h), with concentrations representing up to 300 times the inter-annual mean suspended sediments discharge, significantly modified water parameters, notably solid/liquid (S/L) ratio, pH and redox conditions. Despite the fact that they are mainly trapped in stable phases, a clear increase of the solubilized metals content was measured, representing up to 60 times the maximum values of current exploitation. This solubilization is related to desorption phenomena from sediments through changes in chemical equilibriums as highlighted by laboratory characterizations and experiments. These chemical modifications are mainly attributed to S/L ratio variations. Indeed, the low S/L ratios (≤1.3g·L(-1)) measured in situ are typically the ones for which metals solubilization is the highest, as shown by laboratory experiments. Additional thermodynamic modeling highlighted that the decrease in pH measured during the operation favors the release of the free forms of metallic elements (Al and Cu), and decreases the OM complexation influence. These changes, either in term of physical conditions or speciation, increasing metals long term bioavailability notably during redeposition phase, may have adverse effects on aquatic biota.
Groupement de Recherche Eau Sol Environnement, Université de Limoges, 123 avenue Albert Thomas, 87060 Limoges Cedex, France.
Franck
F
Frémion
Groupement de Recherche Eau Sol Environnement, Université de Limoges, 123 avenue Albert Thomas, 87060 Limoges Cedex, France.
Alexandra
A
Courtin-Nomade
Groupement de Recherche Eau Sol Environnement, Université de Limoges, 123 avenue Albert Thomas, 87060 Limoges Cedex, France. Electronic address: francois.bordas@unilim.fr.
François
F
Bordas
Groupement de Recherche Eau Sol Environnement, Université de Limoges, 123 avenue Albert Thomas, 87060 Limoges Cedex, France.
Jean-François
JF
Lenain
CETU - ELMIS Ingénieries, Université François Rabelais, , 60 Rue du Plat d'Étain, 37000 Tours, France.
Philippe
P
Jugé
EDF - DPIH, Unité de Production Centre, 19 bis avenue de la Révolution, BP 406, 87012 Limoges Cedex, France.
Tim
T
Kestens
Groupement de Recherche Eau Sol Environnement, Université de Limoges, 123 avenue Albert Thomas, 87060 Limoges Cedex, France.
Brice
B
Mourier
D004784:Environmental Monitoring; D019015:Geologic Sediments / Q000737:chemistry*; D008670:Metals / Q000032:analysis*; D014874:Water Pollutants, Chemical / Q000032:analysis*
D008670:Metals; D014874:Water Pollutants, Chemical
Metallic solubilization; Reservoir Sluicing; Sediments; Speciation; Water quality