The HAIPHONG project is organized in 4 approaches (Fig. 3):
Figure 3: Diagram of the interactions between the 4 approaches within the project.
To improve comprehension of the physical operation of the estuary and to validate its modeling initially requires characterizing hydrodynamic functioning. Transects will be carried out across the river using a current meter adapted to measurement in shallow depths drawn by a boat. They will make it possible to quantify with precision flows for various flows regimes (dry season, wet season) and various tidal phases. The physical profiles of parameters (T, S, turbidity, in situ granulometry) will be carried out using an equipped CTD probe and a laser granulometer LISST. Sampling and filtrations will be carried out to determine the dry weight of the suspended matter. Sampling will include a transect upstream and extending down to the mouth, 2 transects starting from the mouth towards the sea (including one following a pseudo-Lagrangian trajectory determined following a surface buoy), and 2 stations of 24h in fixed points, one in the turbidity zone and one close to the mouth. The department of physical oceanography of the IMER (Haiphong) is specialized in the implementation of digital models. Delft3D, standard model adapted to simulate the hydrodynamics and particulate transport, is already established on the coastal zone including the island of Cat Ba, the Halong Bay and the mouth of Bach Dang. The data collected during field campaigns will make it possible to validate the model set up at IMER, and whose influence will go up sufficiently in the estuary to study the mechanisms occurring there. This model will constitute a support to analyze the processes of aggregation, disintegration and sedimentation occurring in the salt wedge and the salinity gradient of the estuary. (Persons in charge: S Ouillon, J-P Lefebvre, P Douillet, Do DC, Vu DV).
The microbial compartments considered will be the bacteria, the viruses and the phytoplankton. We will evaluate their structure in relation to environmental forcings. This will be carried out during 2 campaigns on an array of stations and during a monthly survey on a more reduced number of stations. This information will be compared later on with that obtained by means of experiments in controlled systems (see below).
Bioassays will aim at evaluating if it is possible to directly estimate the effect of the nutrients, TEP, and xenobiotics with the most critical concentrations in the estuary (those will be selected from the results of the 2 workshops). The responses of the phytoplankton, bacterioplankton and the viruses (biomass, activity, structure of the communities) to these contributions will be evaluated in microcosms incubated in illuminated cultures at IMER.
Structure of the phytoplanktonic communities: The submersible probe FluoroProbe will make it possible to quantify the algal biomass along vertical profiles and to provide the relative contribution of each group of phytoplankton (chlorophytes, cyanobacteria, bacillariophytes, dinophytes, cryptophytes) to the total biomass (Beutler et al. 2002, Leboulanger et al. 2002) during 2 field campaigns. The structure of the phytoplanktonic communities moreover will be evaluated by inverse microscopy, flow cytometry, and by analysis HPLC of the pigment contents during 2 field workshops and the monthly sampling. (Persons in charge: Chu VT, P Got, F Vidussi).
Structure of the bacterioplankton communities: The methods of molecular print based on the analysis of fragments of ADNr 16S amplified by PCR are semi-quantitative. The generated profiles give a representation of the structure of the bacterial communities very much used to follow its variations. Method FISH is an intracellular hybridization of specific fluorescent oligonucleotidic probes of the large bacterial phylogenetic groups (Alpha, Beta, Gamma, Delta, etc, limited information but quantitative estimate of diversity). The combination of the results of these methods makes it possible to compensate for the gaps within each one and to obtain a better image of bacterial diversity (Amann et al. 1995). (Persons in charge: T Bouvier, R Duran, O Pringault, Do MH).
The bacterial and phytoplanktonic functional potentialities will be measured by means of BIOLOG microplates (Ecoplates, Sala et al. 2006) and will be supplemented by measurements of bacterial production, primary production and community respiration during 2 campaigns and the monthly survey. (Persons in charge: M. Bouvy, J-P Torréton, O Pringault, E Rochelle-Newall)
The structure of the virioplanktonic communities will be evaluated starting from their morphological and genetic features. The distribution of the classes of size of the capsids and the classification of the viruses in morphological family will be given starting from observation in electronic transmission microscopy by distinguishing (I) the particles from sizes < 60 nm, 60-90 nm, and > 90 nm; and (II) tailed forms vs. not tailed forms (Wichels et al. 1998, Bettarel et al. 2006). Genetic diversity will be estimated by pulsated field gel electrophoresis (PFGE). The whole viral genomes of a population are separated according to their size under a multidirectional alternate electronic field. After migration, a coloring makes it possible to reveal “pulsotypes” in which each band represents a subpopulation of virus with a particular size of genome (Sandaa et al. 2003). This technique allows isolation and analysis of bands of ecological interest by cloning and sequencing. (Person in charge: Y Bettarel).
Distribution of the metal contaminants (Cd, Pb, Cu, Zn, etc…) and organometallic (compounds of Hg and Sn) in the water column will be studied by ultratrace sampling, followed by in situ filtrations in order to collect the aqueous (filtrate) and particulate (>0.45µm) fractions. The analysis of total metals (atomic absorption spectrometry) and of persistent organic pollutants (gas chromatography) will be carried out by the Vietnamese partner (IMER), and the analyzes of speciation of organometallic will be carried out by the French partner (IPREM, GC-ICPMS). This project will allow, in addition to the compilation of the existing data (often scattered, specific and most of the time published in the form of reports), to establish reference data both at the spatial scale (campaigns) and at the temporal scale (monitoring) allowing to compare contamination with the former states and to treat on a hierarchical basis the contaminants by order of potential impact. A series of intercomparisons and analyzes of reference material will be also set up during the first year in order to control the quality of measurements by the two partners. For the aqueous fraction no material of reference exists to validate the analysis of organometallic in natural water. The ECABIE team of the IPREM thus developed methods of absolute references using the isotopic dilution of the species of Hg and Sn (Monperrus et al. 2003) and a coupling GC-ICPMS allowing right and precise measurements for the levels of concentrations met in natural water (Monperrus et al. 2005). The nutrients (organic and inorganic) will be analyzed by IMER and DOC (Dissolved Organic Carbon) and cDOM will be determined by the UR103. (Persons in charge: Duong TN, D Amouroux, E Rochelle-Newall, Cao TTT, Nguyen XT).
Whereas the processes of aggregation and sedimentation partly control the fate of anthropogenic elements, the presence of these elements in the medium deteriorates these mechanisms. Aggregation and sedimentation are related to the adhesiveness of the particles and the density of the aggregates. The adhesiveness of the particles depends mainly on the presence of biological ‘glue’ (i.e., transparent exopolymeric particles, or TEP), of the age of the organic matter (Mari et al. 2007), of the presence of metals (Mari & Robert, submitted), of salinity, and the pH. The TEP having a positive buoyancy, the density of the formed aggregates depends mainly on the ratio between solid particles and TEP (Azetsu-Scott & Passow 2004). The factors influencing the properties of adhesion and the processes of sedimentation in the vary along the estuarine salinity gradient, these mechanisms will be studied in relation to the variations of metal concentration, pH, and salinity.
Spectrum size and sedimentation test of the aggregates. They will be studied in situ with to a submersible analyzer of particles (LISST). (Persons in charge: X Mari, S Ouillon, J-P Lefebvre).
Density of the aggregates. It will be evaluated on water taken along the salinity gradient, and placed in sediment chambers in the presence of microspheres of known density. The direction and the rate of vertical travel will be studied. Persons in charge: X Mari, S Ouillon, J-P Lefebvre).
Adhesiveness of the organic matter. The physicochemical properties of the organic matter will be studied by examining the adhesiveness of the TEP. The TEP will be formed starting from dissolved organic matter taken along the gradient of salinity, and the adhesiveness will be measured by studying the formation of aggregates of TEP-microspheres (Mari & Robert, 2008). Persons in charge: X Mari, Chu VT).