Seasonal hydrobiological characterization of the Bizerte Lagoon (Tunisia)
The purpose of this study was the hydrobiological characterization of a Mediterranean lagoon (Bizerte Lagoon, North Tunisia) based on ten sampling campaigns carried out during the year 2004, from January to December, on a roughly monthly frequency. Two of these ten campaigns were subject to a high spatial coverage with 118 stations in May and 40 stations in September; the eight remaining campaigns covered only ten stations. During these campaigns, physicochemical parameters were measured (temperature, salinity, dissolved oxygen) and laboratory analyses were performed for chemical and biological parameters (ammonium, nitrate, phosphate, total nitrogen, total phosphorus, chlorophyll-a and pheopigments). A multivariate analysis distinguished two principal functioning hydrobiologic modes. The first mode, explaining 26.3% of the total variance, shows a North-South contrast reflecting the relative effect of the Mediterranean Sea and the catchment area. The second mode, explaining 18.2% of the total variance, shows an East-West contrast that reflects the effect of Lake Ichkeul. The parameters that contribute significantly to the first mode are temperature, salinity, absolute and relative transparency, whereas those that contribute to the second mode are absolute and relative transparency as well as chlorophyll-a and pheopigments. However, parameters for which the average weights were not significant showed important spatial oscillations according to seasons, in relation with terrestrial discharges.