SEASONAL-VARIATIONS IN THE PHYSICAL AND CHEMICAL CHARACTERISTICS OF ASHALLOW-WATER ECOSYSTEM, THE RICEFIELDS OF VALENCIA, SPAIN

A study was made of the physical and chemical features of the ricefiel ds from ''La Albufera'' (East Spain) with a view to improving the unde rstanding of this complex ecosystem. The results show the association of the measured variables in 3 factors: water mineralization, biologic al (photosynthetically) related variables, and the nutritional factor, including P and N concentrations. Water mineralization variables were the most descriptive for each type of system. Calcium concentration c an discriminate groups of water qualities in this system. Mineralizati on variables increased through the crop. On the other hand the biologi cal factor showed a very close relationship with photon flux density v ariation along the crop; dissolved O-2 and pH decreased, but CO2 incre ased. The nutritional factor indicated elevated mean values for nutrie nts (N and P), but did not show an unique pattern of variation, indica ting the strong influence of agricultural fertilization on the physico chemical features.