Phase 1: Establishment of PIREN-Seine (1989-1992)
Phase 2 : GDR “man-made fluvial systems” (1993-1996)
Phases 3 and 4 : The Seine, its drainage basin and its history (1998-2006)
Phase 5 : Health risks, landscapes, territories (2007-2010)
Phase 6 : (2011-2014)
In the mid-80s, CNRS launched the first of the PIRENs – Interdisciplinary Environmental Research Programmes. Several PIREN projects focusing on major rivers subsequently emerged, including on the Rhône, Garonne, and the Plain of Alsace. In the Seine basin, where the technical and political chessboard in terms of water resource management is particularly complex and confrontational, it took until 1989 before Ghislain de Marsily succeeded in setting up the necessary dialogue between all of the institutional partners in the basin and the research organisations. In a very pragmatic way, the research axes were set up from the very start by combining the skills of the immediately mobilisable scientific teams with the need expressed by the operators. Four relatively independent workshops were therefore set up, with foci on the impact of the Achères wastewater treatment plant in terms of the ecological function of the downstream areas of the river, on the evaluation of urban rainwater discharges, on the distribution and fate of water discharges from reservoir dams, and on the erosion of agricultural soil.
These initial objectives have widened considerably since the first years of the programme. It quickly became apparent, for example, that the operation of the downstream reaches of the Seine could not be understood without incorporating this into the operation of the fluvial continuum as a whole. An original approach to model the hydrographic network in its entirety was developed based on the notion of drainage order, and served as the basis for the study of planktonic development and the transfer of nutrients to the upstream areas of the basin. The study of urban rainwater discharges required an overall vision of the operation of the sewerage networks and their impact on the environment. It proved impossible to limit the work performed on water discharges from the reservoir dams solely to their hydraulic aspects, in the same way that work on the interaction of rain-drainage-agricultural soil, for which heavy field devices had been installed, could not take place without at the same time measuring the effects of pesticides and nitrates.
At the same time, relationships between the programme’s researchers and the water management institutions also expanded. The preparation of the new Water Act and the implementation of the Schéma Directeur d’Aménagement et de Gestion des Eaux (SDAGE – Outline for the Organisation of the Development and Management of Water Resources) raised specific questions regarding the overall management of the basin.
Against this background, the scientific objectives of the second phase of the programme were required to cover all of the processes associated with water quality in the basin in a much more global manner. Whereas the focus during the first phase of the programme had been on the longitudinal dimension of the aquatic continuum (the upstream-downstream gradient), most of the effort this time was focused on the transversal interactions of the watercourses with their riparian areas (wetlands, hydraulic annexes). The role of the wetlands in the retention of nutrients from the drainage basin or the waterways themselves, the role of floodplains in pike breeding, the role of the reservoir dams as a source of organisms or as wells for nutrients and suspended matter, the role of the hydraulic annexes as areas for fish nutrition and breeding, inter alia, were thus studied in detail. We also focused on developing a better understanding of the urban cycle of water and its associated pollutants, and of the fate of these pollutants in the fluvial environment. Collectively, the results achieved by the end of this 2nd phase on these different topics provide an overall vision of the biogeochemical operation of the ‘Seine system’, seen in terms of the circulation of matter (suspended matter, nutrients, organic matter, oxygen, micro-pollutants) and trophic equilibria throughout the hydrographic network.
The uniform approach which underlies most of the work of the programme lies in the use of an original form of modelling, which is employed both as a tool for understanding as well as a means for decision-making. In this case, understanding means to establish a link between the kinetics of these processes and the macroscopic operation of the ecosystem, as manifested by the flows of matter between its main constituents and their variation over space and time. These models, as we see them, enable us to establish this link. Once validated, these models also allow us to simulate a system response to a change in the constraints to which they are subjected. Although they are reworked and expanded on an ongoing basis, these models are now perfectly operational and have already been used to simulate precise planning scenarios and to optimise the design thereof (improvements to the sanitation infrastructure in the Ile de France region, application of various European directives, etc.). These comprise the most tangible and most immediately useful product of the PIREN-Seine programme.
In January 1998, after drafting a summary work, “La Seine en son Bassin: Fonctionnement écologique d’un système fluvial anthropisé” (The Seine and its Basin: Ecological Operation of an Anthropised Fluvial System; Meybeck, et al. 1998), a third PIREN-Seine phase was established, under the direction of Gilles Billen, focus on two unified axes:
– The first of these axes was the result of a desire to better position the hydrographic network within the complex operation of its drainage basin. This involved, for example, recognising nitric contamination as a manifestation of the emergence of the Earth’s nitrogen cycle associated with the development of modern agriculture and agri-food chain; analysing the flows of heavy-metals transferred by the fluvial network as an aspect of the ‘industrial metabolism’, i.e. as a consequence of production and consumption flows of these metals in industrial and domestic activities. It was therefore necessary to make space for the industrial ecology of the ‘Seine system’ within our work on the ecology of the aquatic environment.
– The second unifying axis consisted of taking the longer term into account. Taking time into account is to recognise the dynamic nature of the hydrosystem, i.e. its present operation as the result of a history which must be pieced together, not only in a narrative or descriptive manner, but in terms of the details of the mechanisms involved. The models established to take this present operation into account must also be applicable to previous states of the hydrosystem, and enable the evolution of human activity along the basin to be linked with that of the operation of the ecosystem and of water quality. This increase in the ‘depth of field’ of the models needed also to enable their use in an exploratory manner in order to determine the state of the hydrosystem corresponding to various future evolutionary scenarios in the socio-system which the basin sustains.
A special issue of the journal Science of the Total Environment (Human Activity and Material Fluxes in a regional River Basin: The Seine River watershed , 375, 1-292) made it possible to take stock of the achievements of these 8 years of research for the international scientific community.
Jean Marie Mouchel took over the leadership role in 2007. The 5th phase of the programme which he established revolves around 3 components which expand the programme with new issues.
During this phase, a number of projects have thus focused on emerging micro-pollutants: new molecules with as-yet little-known effects, medications, pathogens. The risks which these substances may potentially pose to public health form the core of the questions under consideration.
On the landscape axis, it was a question of analysing not only the operation and quality of the environments (water courses, with a special emphasis on minor periurban rivers, wetlands, watersheds) but also the perception of riverside dwellers, and the social organisation which support its uses. Ecological engineering concerns are given full voice here.
The territories, carbon, nitrogen and global change component provides a new dimension to the previous programme initiatives on the linked cycles formed by carbon and nutrients in the basin. At the time of CAP reform and the rise in cereal and agri-fuel prices, the future of the Seine basin and the quality of its water necessarily underwent an analysis into which were integrated these multiple challenges connected with global change.
For its 6th phase, the PIREN-Seine programme proposed structuring its initiatives around 5 main research axes. These were drawn up to Answer the majority of the questions from our partners, and of course ensure a high level of consistency with the major challenges facing the Seine basin identified by its main stakeholders.
These were translated into objectives for our research, which can be summed up as follows:
– Propose scenarios for agriculture which are compatible with water quality requirements for the Seine basin;
– Identify the role of the wetlands, moving from localised studies to a functional overall vision on the scale of the Seine basin, including its emblematic wetland, the Bassée;
– Further define our understanding of the water quality in the fluvial axes, against a background of a very significant improvement while faced with the challenge of stricter good condition requirements;
– Understand the relationship between the chemical pressures and the ecological conditions in the basin where the impact of human activity is at its strongest, and evaluate the pressure/condition relationship over time;
– understand the chemical pressure and its dynamics over extended periods of time while differentiating between different factors, both human and linked to the physical environments which constitute the basin.
In support of these structural initiatives, and also because of their innate relevance, several transversal themes (represented by the steps in the figure below) were also developed. These were both standard bearers for specific scientific and technical developments as well as supports for the development of the aforementioned research axes:
Modelling which remains a major programme tool, supported by a dedicated research theme, particularly to coordinate common developments.
A special effort was made to develop databases structured in a more homogeneous manner for the programme as a whole, including for cartographic data. These have enabled the storage and retrieval of large quantities of new data to be acquired, as well as the results of the models, and enable the sharing of information, both internally and externally.
Historical cartography, which is also a research theme, was a particularly useful tool during this phase in terms of understanding the context and the meaning of the maps.
Finally, the transversal theme of change of scale was the subject of particular mention since a portion of the developed initiatives provided no support function for the research axes. The change of scale theme focuses on both the physical as well as the modelling, and the inhabitants of the basin.
Phase 7 (2015-2020)