Spatial and temporal changes in water quality in a Spanish river

Spatial and temporal variation in the water quality of a Spanish river Alberche 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 general, the conservative parameters alkalinity, sulphate, calcium, and chloride. gradually increased in a downstream direction. However, nutrient variables showed marked differences depending on the location and the season. Two sections can be distinguished in the river. The first in an upstream zone with little human occupation, a siliceous substrate produces waters with low ionic composition and few nutrients. However, the second, downstream zone, featured high levels of phosphate and dissolved inorganic nitrogen in summer and to a lesser extent in spring. The variation in nutrient content in this section of the river can be attributed to anthropogenic sources since in these seasons the presence of holiday-makers leads to a high population density in the residential buildings and recreation areas. Thus, in this area, seasonal increases in human activities at some locations cause high levels of nutrients and may therefore be considered to be classed subject to spatio-temporal eutrophication