Spatial and temporal changes in water quality in a Spanish river

Spatial and temporal variation in the water quality of a Spanish river (Alb erche River) were examined during 2 consecutive years. Principal component analysis was used to analyse the environmental factors associated with the physico-chemical variability. The first principal component corresponded to the variation of water solute content along the course of the river. In ge neral, the conservative parameters (alkalinity, sulphate, calcium, and chlo ride) gradually increased in a downstream direction. However, nutrient vari ables showed marked differences depending on the location and the season. T wo sections can be distinguished in the river. The first in an upstream zon e with little human occupation, a siliceous substrate produces waters with low ionic composition and few nutrients. However, the second, downstream zo ne, featured high levels of phosphate and dissolved inorganic nitrogen in s ummer and to a lesser extent in spring. The variation in nutrient content i n this section of the river can be attributed to anthropogenic sources sinc e in these seasons the presence of holiday-makers leads to a high populatio n density in the residential buildings and recreation areas. Thus, in this area, seasonal increases in human activities at some locations cause high l evels of nutrients and may therefore be considered to be classed subject to spatio-temporal eutrophication. (C) 1999 Elsevier Science B.V. All rights reserved.