Yvon Lapaquellerie

Ten-year observation of the Gironde tributary fluvial system: fluxes of suspended matter, particulate organic carbon and cadmium

A program of long-term observation of suspended solids (TSS), particulate organic carbon (POC) and cadmium transported into the Gironde estuary (France) by its major tributaries has been carried out between 1990 and 1999. This decade included contrasting hydrologic cycles and appears representative of a much longer period (1959-1999). The Garonne and the Dordogne river systems are the main tributaries of the Gironde estuary and derive their waters from drainage basins with different geological, industrial and agricultural features. To better understand their respective contributions, they have been observed separately and compared. Water and TSS fluxes of the Garonne River show greater temporal variations and discharge is more related to the hydrology of the drainage basin (e.g. wet/dry years, local flood events etc.). As POC and particulate Cd concentrations in suspended matter are much less variable than turbidity, their fluxes are mainly controlled by the TSS transport. A major part of annual fluxes of TSS and associated pollutants may occur within few flood days (depending on various parameters, e.g. intensity, duration, season, etc.), and also the succession of dry and wet years has an important influence on annual fluxes. The presented data allow calculating fluvial inputs into the Gironde as the sum of fluxes transported by its major tributaries, the Garonne and the Dordogne river systems. Mean annual fluxes into the Gironde observed in 1990-1999 are about 34 x 10 9 m 3 year -1 for river water, 3.24 x 10 6 t year -1 for suspended solids (TSS) and 9.88 × 10 9 mol year -1 for particulate organic carbon (POC). Generally, these fluxes are dominated by the contributions of the Garonne River. However, in dry years, the mean contribution of the Dordogne river system (including Dronne and Isle rivers) to the POC input into the estuary exceeded that of the Garonne. This reflects significant differences in vegetation and soil due to natural properties and land management of the basins. Mean Cd fluxes into the estuary are about 110 x 10 3 mol year -1 of which 19.6 × 10 3 mol year -1 are transported in the dissolved and 90.8 x 10 3 mol year -1 in the particulate phases, respectively. In 1991 (dry year), the net (dissolved) Cd flux towards the ocean exceeded the gross fluvial input of total Cd, suggesting the release of Cd from an important stock in the maximum turbidity zone (MTZ) or the fluid mud of the Gironde estuary.

A cadmium budget for the Lot-Garonne fluvial system (France)

Routine measurements of river discharge and total suspended sediment concentration (TSS) are combined with regular analyses for particulate and dissolved cadmium to produce a box model that allows us to propose a cadmium mass balance for the Lot-Garonne man-influenced river system (8400 km2). Nearly half the cadmium in the Garonne river is supplied by the tributary Lot river. Cadmium input onto the Lot river comprises wet deposition from the atmosphere, molecular diffusion at the sediment-water interface, surface-water runoff and discharge from the leaching of waste at a zinc refining plant. Approximately 85% of the cadmium in the Lot river is derived from anthropogenic origin. Cadmium in the industrial discharge is 80% dissolved and 20% in the particulate phase (4.2 and 1.1 t yr−1, respectively). Total inputs are estimated at 4.81 t yr−1 and 1.54 t yr−1 for the dissolved cadmium and for the particulate phase, respectively. Budgeting estimates an output onto the Garonne river of 0.54 t yr−1 for the dissolved cadmium (about 8%) and 6.13 t yr−1 for the particulate cadmium (about 92%) indicating that downstream sediment-associated cadmium fluxes are enhanced by the 4.27 t yr−1 removed from solution and the 0.32 t yr−1 remobilized by the erosion of sediment blanketing the Lot river bed. These figures are found to be comparable with those generated by a dilution model which suggests that 97% of dissolved cadmium is taken up by the particulate phase over 0.5 km downstream from the primary anthropogenic source.

Heavy metal pollution in the Arcachon Basin (France): Bonding states

Abstract Information available (since 1977) from a great many recent surveys on the Arcachon Basin has enabled us to determine three characteristic environments and study the behaviour of heavy metals (Ni, Cu, Zn, Pb, Cd, Hg). The relationship between heavy metals and grain-size fractions has been determined after having specified whether metals were preferentially organically or inorganically bound. This study has allowed us to establish the origin (natural or anthropogenic) of metallic enrichment and assess the extent of pollution.

Role of the dams on the River Lot on two types of pollution:point-sources (cadmium) and non-point sources (phosphorus)

The concentrations of cadmium and bioavailable phosphorus were determined in sediments samples of a large section of the River Lot (a 248-km section of 57 artificial stretches and dams). Phosphorus inputs include an important agricultural watershed (diffuse sources) and main point-sources such as towns. Cadmium pollution is mainly due to an industrial activity in the upper reach: high concentrations existed some years ago, the pollution is now lower. The concentration data related to a lithological cartography of the river bottom (sand/gravels/mud) and of the thickness of soft deposits, provide a longitudinal assessment of Cd and P storage in the whole river. The results show the location in the river where the two elements are associated to the sediment muds which are mainly stored in the largest dams situated in the lower section of the river. The sedimentary amounts represent potential sources (i) of metallic pollution in case of river flood or dam emptying (e.g. 69 tons of Cd in the last lower dam), (ii) for eutrophication processes in the lower course (near 10 000 tons of bioavailable-P in the last five dams). The cadmium flux leaving the watershed of river Lot is still important and remains greater than the industrial source (strongly reduced since 1986) of the pollutant located in the upper part of the river.

Origin and pathways of Cadmium Contamination in the Gironde estuary, Garonne river and tributaries.

Publisher Summary This chapter investigates the characteristics, effects on biota, origin, and transfer processes of Cd pollution in the Gironde estuary. Cd mainly originates from a former industrial zone of the drainage basin localized about 400 km upstream to the inlet. At the estuary mouth, a major cadmium contamination of mollusks was first recognized in 1979 in the framework of the National Observation Network, the office in charge of the monitoring of the quality of the French marine environment. Detailed studies were then undertaken on biota and on solid and dissolved media. Biota was investigated by monitoring the populations of oysters and mussels transplanted from uncontaminated areas into the inlet of Gironde. Cd concentrations in oysters reached high levels in only six months. The kinetics of Cd accumulation appeared higher in summer than winter. Downstream, suspended matter (SM) undergoes major changes facilitated by a long residence time of SM within the brackish waters of the estuary. Cd and many other associated metals pass, for a large part, into solution under the effects of macrotidal-type estuarine processes. After solubilization, the metals are concentrated by mollusks of the estuary mouth according to the kinetics of accumulation studied on the basis of an in situ experiment.

Arsenic et iode des Algues et des Zostères de l'environnement laguno-marin d'Arcachon (France)

Abstract Sargassum from Arcachon Basin concentrate As much more (factor 9) than other Algae and even more than Zostera . Antagonism between As and I is taken into consideration. Origins and forms of As are examined because of their possible consequences for oyster-farming.

Evolution du Pb, Zn, Cu, Ni et As dans le Bassin d'Arcachon (France). Impact de la biomasse végétale sur la géochimie d'un environment lagunaire

Abstract The concentration of metals as Pb, Cu, Ni and As in suspended matters and sediments during 14 years shows for suspended matters and sediments that: Zn and Cu are increasing, Pb and As decreasing and Ni is stabilised. The evolution of the suspended matter can be explained by the quantitative evolution of algae and phanerogams during these last 14 years. The biomass evolution, which resulted in environmental nutrient contribution, intensifies the exchange factors of Pb and As in the lagoon. These remarks, beyond their local interests, provide notions of sedimentary environment model opposed to a polluting environment constituted by nautic tourism and a large area of monoculture (corn).