VARIABILITY OF ABIOTIC CHARACTERISTICS IN THE WATER OF A MEDITERRANEAN LAGOON, THE ETANG DE CANET (PYRENEES-ORIENTALES, FRANCE)

The Mediterranean lagoon of Canet was studied between october 1994 and september 1997. Over 180 visits were made with over 5,000 measurement s of physico-chemical parameters (temperature, pH, dissolved oxygen, o xygen saturation, salinity, conductivity, redox potential, affluent wa ter flow and water level) and about 500 chemical analyses of the main nutrients. The physico-chemical parameters were found to follow a well -specified seasonal rhythm in spite of very large absolute variations and interannual differences. Because of the little depth of the lagoon , the water body reacts very rapidly to climate influences. The lagoon receives an important annual nutrient input of about 160 tons of nitr ogen and more than 26 tons of phosphorus causing very high water conce ntrations of these elements. The exchange with the sea is nearly entir ely controlled by man and only the opening of the sluices on the chann el of communication provides the lagoon with salt water. In this way, man largely influences negatively the physico-chemical, chemical and b iological environment of the lagoon.