The most abundant and frequent epipelic diatoms and 8 environmental
factors were applied to the CCA analysis (Table 3
and Fig. 4). The correlation coefficient between the first environmental
factors axis and species axis was 0.61, while that
for the second axes was 0.65, indicating a close relationship
between epipelic diatoms and environmental variables. Two
canonical roots were extracted explaining 54.8% of the variance
observed. The first two species axes have correlation
coefficient of 0.01. Eight environmental factors affected epipelon
distribution with different degrees. Transparency, temperature,
pH, PO4, and SiO2 had great influence on epipelon as
indicated by their high correlation with the two significant
canonical roots. Most species were marginally affected by
transparency except species of group D and two species of
group B (Melosira varians and Fragilaria acus). Species of
group D and majority of groups C and B were positively
affected by eutrophication, PO4 and NH4 and temperature,
whereas they were negatively affected by pH and SiO2