Laboratory analysis
Homogenized samples (0.5 g of clay bottom and about 2 g of
sandy bottom) were treated with concentrated nitric and
sulphuric acids, heated until all organic matter oxidized. The
samples were washed and concentrated. For living cells; samples
were vigorously stirred for few minutes in a 500-ml beaker
after tap water was added. After stirring, the samples were left
for a few seconds to allow heavier clay and sand particles to
settle, whereas suspended microalgae were poured into a 1 L
glass cylinder. This process was repeated (at least 6–8 times).
Acidic Lugol’s Iodine solution was added. The samples were
concentrated and completed to 100-ml in plastic bottles.
Utermo¨ hl (1958) method was applied for counting and identification
of both digested diatom and living cells using an
inverted microscope (Zeiss, Model, Axiovert 25C). The main
references used for identification of epipelic cyanobacteria
were Starmach (1968) and Wehr and Sheath (2004), and diatoms
were, Cleve-Euler (1953) Patrick and Reimer (1975)
and Krammer and Lange-Bertalot (1986, 1988 and 1991),
and Chlorococcales were Tikkanen (1986) and Dillard (1991).