Monitoring water quality in estuarine environments: lessons from the MAGEST monitoring program in the Gironde fluvial-estuarine system

Abstract

Abstract. The Gironde Estuary, one of the largest European ones, presents temporary low dissolved oxygen content in its fluvial section close to the Bordeaux urban area. In a context of population growth and of long-term environmental changes, the development of a high-frequency monitoring programme of the fluvial-estuarine system of the Gironde, called MAGEST (MArel Gironde ESTuary), had appeared essential to address current and future water-quality issues/evaluations. The objectives of the MAGEST survey program are to establish a reference database to improve the knowledge of the Gironde Estuary functioning, encompassing the aspects of hydrology, sediment dynamics and biogeochemistry. Through examples of results from intratidal to seasonal time scales, we demonstrate how such a long-term, high-frequency monitoring of a fluvio-estuarine system is of valuable interest to extract the main trends of its functioning and of the water quality in relation to external forcings (climatology, urban wastes, land use, . . . ) and to predict the future evolution of an estuary with global and environmental changes.

Toward Sentinel-2 High Resolution Remote Sensing of Suspended Particulate Matter in Very Turbid Waters: SPOT4 (Take5) Experiment in the Loire and Gironde Estuaries

“…Turbidity measurements, given in Nephelometric Turbidity Unit (NTU), were automatically performed using commercial sensors (Turbimax CUS31, Endress & Hauser, Reinach, Switzerland) covering the range 0-9999 NTU range. Data were qualitycontrolled and validated following a protocol adapted to the estuarine environment [6], including a regular calibration of the turbidity sensors. Turbidity measurements were used to estimate SPM concentration using a regional empirical relationships derived from laboratory calibration.…”

“…Direct effects mainly concern the modification of river morphology due to erosion and sedimentation, locally resulting in bed sediment washout, mudflat and sandbar moves, or silting-up of harbours and navigation channels [4]. Indirect effects include changes in light attenuation and primary production [5], oxygen saturation [6], alteration of fish nursery function [7], transport of SPM-attached pollutants [8], modification of nutrients pathways [9] and biogeochemical cycles [10].…”

“…Measurement is needed at high temporal and high spatial resolution to accurately document SPM variation. Though the deployment of automated sensors makes it possible to study SPM temporal variation over a range of scales from hours to years [14], it is restricted to the geographical location of the instrumented stations in instrumented estuaries, and most estuaries are not instrumented [6]. Due to its global coverage and ability to zoom in specific areas, satellite remote sensing provides synoptic observations of water reflectance in the visible and near infrared (NIR) spectral regions, which in turn can be used to map SPM surface concentration in turbid waters [15] at worldwide scale.…”

Turbidity in the fluvial Gironde Estuary (southwest France) based on 10-year continuous monitoring: sensitivity to hydrological conditions

“…The saturation value (9999 NTU) of turbidity sensor corresponds to about 6 g L −1 (Schmidt et al, 2014). One may refer to Etcheber et al (2011) for a description of the MAGEST survey programme, for the technical features of monitoring system and for examples of the trends in measured parameters; and to Lanoux et al (2013) (Fig. 1).…”

Atmospheric Corrections and Multi-Conditional Algorithm for Multi-Sensor Remote Sensing of Suspended Particulate Matter in Low-to-High Turbidity Levels Coastal Waters

“…The Gironde Estuary includes an automated continuous monitoring network, called MAGEST (MArel Gironde ESTuary), [56] comprising four sites ( Figure 2): Pauillac in the central Estuary (52 km upstream the mouth); Libourne in the Dordogne tidal river (115 km upstream the mouth), and Bordeaux and Portets in the Garonne river (100 and 140 km upstream the mouth, respectively). The automated stations record dissolved oxygen, temperature, turbidity and salinity every ten minutes at 1 m below the surface.…”