Fe-P-phyte (EPOC / Irstea)
Role of aquatic macrophytes on iron-phosphorus
Knowledge on phosphorus (P) and nitrogen (N) cycles is vital to resolve or prevent eutrophication problems. One of the practice suggested for P and N retention is the use of vegetated ditches and artificial wetlands, which have been demonstrated to remove large proportion of nutrient through plant uptake, sedimentation and transformation. Despite the numerous literature on nutrient removal, previous studies have rarely considered the indirect role of plant on iron-geochemistry. Indeed, coupling between iron (Fe) and P geochemistry is one of the main processes that control P availability in aquatic system. One of the aspect that remains to be addressed is how plants may influence Fe geochemistry, and therefore, the speciation of P. This has been extensively studied in marine seagrasses rhizosphere and in soil science, but interactions between plant activity and Fe-P coupling in the surface freshwater is poorly documented. The objective of our project is to gain better insight into complex interactions between macrophytes and Fe and P geochemistry in the Leyre watershed. For that, the project brings together specialists of P and Fe biogeochemistry in sediments and water column, and of aquatic plants, from two Labex-COTE teams. We will monitor the evolution of geochemical, physical, and vegetal parameters during the day-night and the seasonal cycles in streams colonized by different communities of plants, from the headwater part of the drainage basin. We will select streams that drain pine forest and crop fields, which are the two main land use of the Leyre catchment (83 and 14%, respectively). Assumptions are that freshwater aquatic macrophytes and associated biofilms are hotspots of sequestration of P as Fe-ox bound P due to increasing kinetics of dissolved Fe oxidation during photosynthetic activity. These particles could be dissolved through redox processes in the river bed below plant canopy. These feedback processes will be studied too.
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