DIEL CHANGES IK PHYSICAL AND CHEMICAL CHARACTERISTICS OF THE WATER IN A NORTH IBERIAN STREAM The importance of diel variability in the physical and chemical characteristics of the water has been investigated in three different reaches of the Agüera stream (Northern Spain). The changes in insolation and temperature, the rhythm of human caused discharges and the variations in the metabolic activity of the stream community interact to produce different diel dynamics for each reach studied. Ranges

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... f variation are lowest in headwaters and highest in midreaches affected by urban ninoff. There, diel variability can be most important, specially for variables related to the activity of the benthic community: percentage of oxygen saturation, inorganic nutrient concentrations or ])H. The removal of riparian vegetation enhances the biological activity of the stream, producing a shift to diel pattems more typical of rivers of greater order. To improve the design of sampling strategies in streams, it is necessary to take into account the intensity of diel changes in the different reaches under study. AGRADECIMIENTOS Este trabajo está basado en el proyecto de investigación PIGV 8924, financiado por el Gobierno Vasco. APHA. 1980. Standard methods for examination of water and wastewater. 151h edition. American Public Health Association, Washington.