en
Doctoral thesis
French

Biodisponibilité du phosphore lié aux sédiments en suspension du Rhône et d’autres affluents du Léman

ContributorsSantiago, Sergio
Number of pagesXIII, 94
Imprimatur date1991-06-03
Abstract

Bioavailability of phosphorus (P) bound to river sediment has been assessed to date by chemical speciation analyses related to laboratory bioassays performed with monocultures of algae. These studies, simulating a maximum nutrient uptake in the environment by the algae, provided estimates on loadings of potentially bioavailable phosphorus for the tributary rivers of Lake Geneva (Burrus & al. 1990, Zhang 1988; tab. 1.1 ). To better determine the utilization of particulate phosphorus by the lake phytoplankton, the algal fractionation bioassay of Munawar & Munawar (1982) has been modified and adapted to allow direct contact with river suspended sediment. After a short incubation with radioactive labelled inorganic carbon, the carbon-14 uptake of microplankton (> 20 μm) and nanoplankton ( < 20 μm} fractions is measured by liquid scintillation, following filtration and an organic extraction with dimethyl sulfoxide (DMSO; fig. 4.3).

Suspended sediments were recovered in 1988 and 1989 by continuous flow centrifugation of water samples at the mouths of the Rhone, Venoge, Dranse and Aubonne rivers. ln addition the effluent of the sewage treatment plant {STP) at Lausanne-Vidy was sampled in each of the two years (fig. 4.1 ). The performance of the system using two centrifuges in parallel (a Westphalia and an Alfa-Laval) has been assessed (Santiago & al. 1989). Both centrifuges show good agreement for particle size and trace metal concentrations in suspended solids, providing the sediment trapped in the brass core of the Alfa-Laval is discarded.

Results indicate that primary production can be promoted in the short term by the suspended sediments, and that the bioassay is particulate specific and well adapted to determine the bioavailable proportion of the particulate phosphorus. Conditions of incubation (temperature, illumination, turbidity effect, length) and methodological procedures (filtration, DMSO extraction, liquid scintillation counting) have been assessed (figs. 4.5, 4.6, tabs. 4.1, 4.2). Addition of soluble nutrients, either in filtered river water or as a pure solution of orthophosphate, did not enhance growth before 15 hours of incubation (fig. 4.7). This lag is believed to be necessary to allow algal adaptation.

This being the case, our observations suggest that compounds associated with particulate macronutrients promote in the short term the productivity of naturally adapted phytoplankton. Determination of these unknown substances (phosphatase enzymes, organic compounds, aminoacids, vitamins, etc...) needs further research in biochemistry.

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freeng
Keywords
  • Eutrophisation
  • Phosphore
  • Sédiment
  • Biotest
  • Écotoxicité
  • Léman (lac)
Citation (ISO format)
SANTIAGO, Sergio. Biodisponibilité du phosphore lié aux sédiments en suspension du Rhône et d’autres affluents du Léman. 1991. doi: 10.13097/archive-ouverte/unige:177738
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