Biomass of Ruppia cirrhosa and Potamogeton pectinatus in a Mediterranean brackish lagoon, Lake Ichkeul, Tunisia
Résumé
The biomass of the macrophytes Potamogeton pectinatus L. and Ruppia cirrhosa (Petagna) Grande and their energy input that is at the basis of the functioning of the Ichkeul wetland, northern Tunisia, which harbours a conspicuous population of wintering waterfowl, were investigated. The mean (above- and belowground) biomass of P. pectinatus from July 1993 - April 1994 was at a maximum in September and ranged between 340.9 +/- 38.4 and 480.6 +/- 91.8 g dry mass (DM)/m(2) depending on the area. Tubers represented 10-30 % of this biomass. In R. cirrhosa maximum biomass of 368.7 +/- 68.1 g DM/mn(2) was recorded in October. In both species about 40 % of the total biomass was allocated to the roots and rhizomes. The production estimates in the Ichkeul lagoon are within the same range as estimates for other Mediterranean lagoons. Other energy sources in the Ichkeul lagoon were litter (60.1 g DM/m(2)), the overwintered roots and rhizomes (61.4 g DM/m(2)) and the suspended particulate organic matter (7.64 g DM/m(2)). Total mean energy income from the macrophytes in the Ichkeul ecosystem during the study period is estimated at 5306 kJ/m(2).