Trend study and assessment of surface water quality in the Ebro River (Spain)

Thirty-four Physical–chemical and chemical variables were analysed in surface water samples collected every month over a period of 24 years. They were determined from thirteen sampling stations located along the Spanish Ebro River affected by anthropogenic and seasonal influences. The trend study was performed using the Mann–Kendall Seasonal Test and the Sen′s Slope estimator. Results revealed parameter variation over time due mainly to the reduction in phosphate concentration and increasing pH levels at the Ebro Basin during the 1981–2004 period. Exploratory analysis of data was also carried out by display methods (cluster analysis), and unsupervised pattern recognition (principal component analysis) in an attempt to differentiate between sources of variation in the water quality. PCA has allowed the identification of the following factors: geologic, climatic and anthropogenic. Spatial and seasonal sources of variation were identified that affect the quality and hydrochemistry of river water.