Nutrient cycling and sediment budgets of the River Adour in southwest France
Rivers are dynamic entities with variable catchment inputs while floodplains play an essential role in the functioning of these aquatic systems by regulating the transfer of material between terrestrial and aquatic ecosystems. Wetlands on large floodplains have a major impact on riverine nutrient loads as they flow through the system since the interaction between the wetland and the river allows a direct exchange of matter and energy. Seasonal flooding not only increases the productivity of these wetland areas but also provides a mechanism for the return of nutrients to the aquatic system. Examination of sediment and nutrient fluxes within a catchment therefore affords opportunities for the evaluation of the ecological status of aquatic systems.
In a number of studies, Dr Brian Astin, in association with a French scientist, Dr Rene-Claude Brunet has investigated the retention capacity of the flood zone of a 25 km stretch of the River Adour in southwest France. This zone consists of ca. 1 km2 of riparian vegetative strips (rvs) and ca. 16 km2 of floodplains. A novel method of sediment collection was used in both sectors of the floodplain to determine the quantities of sediment, together with concentrations of organic nitrogen, organic carbon, mineral nitrogen and dissolved phosphate. The research showed that the riparian vegetative strips accumulated large quantities of sediment with the distribution organic material varying with micro-topography and vegetation. The floodplains received much less sediment but, since the sediment that they did receive was finer, the associated organic matter concentrations were generally higher. Variations of inorganic nitrogen indicated that the rvs are subject to successive gains and losses according to the magnitude of the river borne flux. Gains of inorganic nitrogen are noted during periods of low flow, with significant losses during major flood events. In winter, losses due to denitrification are small rising to much higher values in summer. Additions of fertiliser during spring and summer have a major impact on the fluxes exiting the zone studied, varying with the growth cycle of the maize crop within the zone.
For more details contact Dr Brian Astin
Selected Publications
BRUNET, R C, & ASTIN, K B, 1996, Variations in Mineral Nitrogen levels: The River Adour. Hydrobiologia, 335, 159.
BRUNET, R C, & ASTIN, K B, 1997, Spatio-temporal Variations in Sediment Nutrient Levels: The River Adour. Landscape Ecology, 12, 171.
BRUNET, R C, & ASTIN, K B, 1998, Variations in Phosphorous Flux during a Hydrological Season: The River Adour. Water Research, 32(3), 547.
BRUNET, R C, & ASTIN, K B, 1999, Spatio-temporal variations in some physical and chemical parameters over a 25 year period in the catchment of the river Adour. Journal of Hydrology, 209.
BRUNET, R C, & ASTIN, K B, 2000, Role d'une zone inondable, filtre sélectif pour quelques éléments dissous ou particulaires issus d'un bassin versant in L'eau, de la cellule au paysage (ed. S. Wicherek), Elsevier, pp157-170.
BRUNET, R C, & ASTIN, K B, 2000, A 12 month sediment and nutrient budget in the floodplain of the River Adour, Southwest France. Regulated Rivers: Research and Management, 16, 267.
