Aladin Andrisoa (OT-Med PhD student)
Thomas Stieglitz, Valenti Rodellas (CEREGE)
P Raimbault (MIO)
F Lartaud (UPMC)
Coastal lagoons host some of the most dynamic, diverse and productive ecosystems on Earth, which are subject to significant pressure from human activities. Hydrological land-ocean connectivity is a universally accepted important driver of coastal ecosystems, but the ecological effects of groundwater and associated solute fluxes to coastal systems remain poorly understood for most of the world’s shores.
The overall goal of this project is to evaluate the role that groundwater flows to coastal Mediterranean lagoons play in the functioning and vulnerability of these ecologically and economically important ecosystems. This project encompasses a suite of interdisciplinary investigations aimed at (a) the quantification of groundwater and associated nutrient fluxes and (b) the evaluation of groundwater-derived effects on lagoon primary production. Two French lagoons with contrasting hydroecological conditions are investigated combining current methods to quantify groundwater discharge and associated nutrient inputs (use of tracers such as radioisotopes and salinity) with the evaluation of new tools (application of the stable isotope signature in primary producers). The novel understanding of groundwater-ecological interactions derived from this project will allow closing a current gap in the fundamental understanding of coastal processes, improving our capacity to sustainably manage hydrological and ecological resources in the coastal zone.
This project provides direct evidence for the role of groundwater processes in sustaining primary production in two French coastal lagoons (La Palme and Salses-Leucate). Our results show that:
- groundwater discharge, including both terrestrial and recirculation processes, is the main source of nutrients in the studied lagoons, well above the sewage effluent contribution. We found that the nitrogen isotopic signatures in macrophytes and phytoplankton reflect predominantly the nitrogen signatures of the terrestrial groundwater and recirculation sources, indicating that they must have sourced the majority of their nitrogen from terrestrial groundwater and/or recirculation sources, with only punctual contributions from sewage input.
- growth rates of Mediterranean mussels exposed to terrestrial groundwater discharge (near karstic springs) appear higher than those growing in more saline environment and are amongst the highest observed for this species along the Mediterranean coastline (preliminary results).
This figure illustrates the nitrogen isotopes signatures in water sources and primary productors. The closest the ratio between water sources and primary producers, the more uptake.