Financeur du programme

programme national
ISblue

Résumé

What is the socio-ecosystemic trajectory, or propagation of impacts along the land-sea continuum, in response to climate variability and direct anthropization? Can we understand human-environment interactions in a pilot site?

We will gather data from local observatory surveys (e.g. temperature, salinity, nutrient concentrations, dissolved oxygen, phytoplankton biomass; SNO-SOMLIT and SNO-PHYTOBS), participatory sciences (Ecoflux and Objectif Plancton), and national observatories (e.g. AELB, Banque Hydro, REPHY, SAFRAN). In addition to the regular methodologies deployed at the Lanvéoc-SOMLIT station, surface sediments will also be collected to investigate present-day microfossil deposits in the BoB and their evolution on several years. This will additionally allow us to accurately understand proxies used for BoB sediment reconstructions in sediment cores.

We also aim at producing a detailed chronicle of the evolution of human activities and modes of exploitation of natural systems over the two centuries around the BoB. This historical work will focus on maritime (i.e. mainly fisheries and aquaculture), fluvial, agricultural and industrial activities. In parallel, the historical research will document climate events (storms, extreme temperatures, floods), at regional and global scales, either because they are reported (press and various chronicles) or naturally recorded (e.g. dendrochronology, sclerochronology). This will consist in a chronological frieze of the BoB and its watersheds: a tool linking a database to its spatial representation. A series of hypotheses, confirmations, and refutations will be proposed to interpret human activities and natural systems, integrating feedback loops.

In the end, PACTE objective is the development of a land-sea continuum model adapted to the macrotidal estuarine-coastal site of the BoB, first by using current environmental data and second by running model-data intercomparisons with the paleo-reconstructions. Even if such modelling approaches have already been developed, the intercomparison between paleoreconstructions and modelling outputs is the most original and “risky part” of the project. A selection of model outputs will be studied along the land-sea continuum for the studied period: e.g. streamflow, water temperature, nutrient (N, P, Si) concentrations, ratios and fluxes, oxygen concentrations, suspended particulate matter, phytoplankton biomass (e.g. diatoms and dinoflagellates). New integrative indicators, such as the eutrophication index B_ICEP, will be tested and calculated from model outputs. Two main deliverables are: i) cross-validation of paleo-reconstructions and land-sea modelling indicators before and after WWII, ii) land-sea continuum trajectories after WWII with a retrospective analysis of river and estuarine ecosystem functioning and forcing drivers. If successful, these proxies have the potential of powerful tool to “validate models” in coastal systems over past periods with no instrumental datasets. After PACTE, the land-sea model may be used to simulate alternative scenarios of future socio-ecosystemic trajectories.