Rapport de stage - DREAL Languedoc-Roussillon

Mémoire de Travail de Fin d’Etude ENGEES – UDS – DREAL LR
Abstract
Dystrophic processes measurement network construction study for
evaluation in the Languedoc-Roussillon rivers
Eutrophication is a natural phenomenon characterized by a vegetal proliferation due to
high nutrients levels. Human activities can speed up the phenomenon or make it worse. In this
way, eutrophication becomes a dystrophic process: it leads to a river imbalance and be the
reason of the death of aquatic populations.
In 1991, two European directives have been enacted in order to protect the environment.
They impose restrictions more severe in areas where there is an eutrophication potential as
sensitive areas (Urban Waste Water Directive) and vulnerable areas (Nitrates Directive). The
application of these two directives needs the definition of the areas where there is a risk or a
presence of the eutrophication phenomenon to limit the most severe restrictions to theses areas.
The definition of these areas must be realised/reviewed every 4 years by the State
Administration Services (DREAL)
Currently, classification measurement networks are those created to respond to the
Water Framework Directive (WFD), called monitoring networks. The problem is that the
structure of these networks, adapted to the WFD demands, is not compatible with
eutrophication phenomenon diagnostic. We studied the available data and concluded that, even
if a lot of biological or physical and chemical parameters are measured, no eutrophication
information can be produced. The only biological compartment that produces relevant
information is the macrophytes one but there is still an uncertainty on the reliability of the data
when no other parameter is measured. The conclusion is we have to review the current
networks in order to produce indisputable cartographic data.
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The following study led to two ways of improvement:
- Current networks data can be studied more precisely. It’s especially true for
diatoms.
- Measurement of oxygen dial variations is necessary, as some practical details
measurement changes: networks screenplays are presented with their financial
valuation.