During the study period, the water depth varied
between 0.4 and 8.3 m due to changes in the total
water volume of the reservoir. One-litre samples
were collected in order to obtain for each site,
having a water depth greater than 1 m, a surface
water sample and a water column sample. This
last sample was positioned in the middle of the
water column. Water samples were not filtered.
The surface water samples were collected in clean
polyethylene vials. A two-step procedure for
cleaning vials included the washing in a neutral
detergent Extran, Merck. and a 24-h bath in a
10% nitric acid solution Analytical, Merck, vrv..