A 12‐month sediment and nutrient budget in a floodplain reach of the River Adour, southwest France

The sediment and nutrient budget in the floodplain reach of the River Adour in southwest France has been examined over a 1-year period (1991-1992). Outputs of total suspended matter, dissolved inorganic nitrogen (i.e. nitrate + ammonium ions) and dissolved inorganic phosphorus (DIP) and particulate phosphorus (PP) have been compared with inputs. Alternating phases of mobilization and retention are observed for all the elements considered. Low water periods in summer allowed retention of both soluble material (24-26% for inorganic nitrogen) and suspended matter (9-19%). However, mobilization of PP associated with suspended matter transport during these periods. Elevated discharges associated with increased rainfall during the autumn period induced significant mobilization for all elements. In contrast, the winter flood event gave rise to a retention of particulate material (i.e. suspended matter and PP, 11% and 26%, respectively), but a loss of soluble materials (5% for inorganic nitrogen and 186% for DIP). The spring flood event produced retention for particulate materials (26%) while inducing losses of inorganic nitrogen (9%) and gains of DIP (7.4%). These results are related to riparian vegetation and the dynamics of nutrient cycling within the floodplain.