Relative Importance of the Free and Fixed Bacterial Community in Three Lacustrine Ecosystems having Different Trophic Status

Raoui Sidi Mohammed, Rachiq Saad , Bouayad Kenza, Chadli Nourddine

The present work consists in determining the total bacterial densities and biomasses and the relative importance of free and fixed bacterioplankton in three lacustrine environments with different trophic status: Pavin lake, oligomesotrophe, and the Villerest reservoir, eutrophe (two French ecosystems) and the dam Allal Fassi, mesotrophe (Morocco). Along the water column, the results obtained showed bacterial densities that ranged from 0.60 to 7 x 105 cells.ml-1 at Pavin Lake, from 1.01 to 9.86 x 106 cells.ml-1 in the Allal Fassi dam reservoir and from 0.70 to 12.90 x 106 cells.ml-1 in the Villerest reservoir. The average recorded bacterial biomass ranged from 0.73 to 1.92 μgC.l-1 in Pavin Lake, from 10.50 to 81.10 μgC.l-1 in the Allal Fassi dam and from 29.40 to 60.52 μgC.l-1 in the Villerest reservoir. Seasonal variations show fluctuations in bacterial densities for the three environments. The proportion of free and fixed bacteria revealed high percentages of the fraction of free bacteria with 96.10% ; 90.50% ; 87.90% at the surface layers respectively at Pavin Lake, Villerest Reservoir and Allal Fassi Reservoir. Mean recorded values ​​of fixed bacteria at all depths were 4.26% ; 10.35% ; 17.13% of the total bacterial density respectively in Pavin Lake, Villerest Reservoir and Allal Fassi Reservoir.