Spatio-temporal variation in some physical and chemical parameters over a 25-year period in the catchment of the river Adour

The catchment of the river Adour (SW France) has been examined in order to analyse spatio-temporal variations in a number of key variables (flow, susp ended matter, nitrate and dissolved orthophosphate concentrations) over a 2 5-year period (1972-1996). Within the catchment area, it has been possible to discern how hydroclimati c fluctuations have affected the watershed, with dry periods in 1972-1976 a nd 1983-1993 alternating with wetter phases in 1977-1982 and 1994-1995. The anthropogenic activity, primarily, involving the use of water for agricult ural purposes, has also had a major impact during this period, particularly in the downstream areas of the catchment. Suspended matter fluxes display regular downstream increases with significa nt erosion being evident in the mountainous region contrasting with retenti on in the floodplains area downstream. These fluxes exhibit temporal and sp atial variations with peaks occurring every 3-5 years, 1975-1977, 1979, 198 2, 1985, 1987 and 1992. Some of these peaks are suggested to be related to anthropogenic activity involving river management, including the cutting of meanders and the construction of dykes for flood prevention. Nitrate concentrations evince a similar pattern to the suspended matter flu xes with enhanced levels of downstream. The confluence of the Adour with th e Midouze appears not to have any major impact on the nitrate concentration . In the downstream areas, an uptake of nitrate is registered indicating th e activity of the riparian vegetation. For the entire catchment, maximal ni trate concentrations are observed in 1979, 1982, 1987, 1991-1992 and 1995. (C) 1999 Elsevier Science B.V. All rights reserved.