Effects of Substrate Type on Benthic Diatom Assemblages of a Masooleh Rud River - Guilan

The present study was conducted to evaluate the effects of some physical and chemical parameters of water e. g. pH, temperature, electron conductivity (EC), Fe, silicate, orthophosphate, Nitrate on diversity and abundance of periphyton diatoms in a tributary of the Masooleh River (located 37o 22’ to 37o 23’ northern latitude and 49o17’- 49o19’ eastern longitude in Guilan Province, north of Iran) in summer, autumn and winter, 2011. The study area was 15 km in area, and 5 sites were chosen for diatom sampling. The average depth of the river was 0.5 m with temperature ranging from 14 to 31 0C. Elevation from the sea level and all parameters mentioned above were measured for each sampling site. The samples were collected from surface layer of Epilithon, Epidendron, Epipssamon and Epipelon as natural substrates. The results showed the following ranges: EC: 617-1370 S.cm.-1; pH: 7.82- 8.81; and nutrients: PO43-: 0.02- 0.21mg.l-1, NO3: 1.2- 3.5 mg.l-1, SiO2: 0.02- 6.5 mg.l-1and Fe2+ < 0.02- 0.1 mg.l-1 as an indicator of trophic status of the river. The collected samples were processed and slides were prepared for LM examination. In this study, 23 genera of diatoms were identified. The least and most abundant diatoms were observed on muddy (12.52) and stony (30.86) substrates, respectively. Comparison of mean abundance of diatom population on different substrates (muddy: 23.95± 4.08, gravel: 15.52± 0.97, woody: 17.71± 0.62 and stony: 23.95± 4.08) revealed statistically significant differences between stony, gravel, muddy, and woody substrates (P<0.05). The distribution of diatoms on coarser substrates (wood, stone and gravel) was higher than on softer ones (muddy). Based on the obtained results, woody and stony substrates seem to be more suitable for ecological monitoring of streams than muddy and gravel substrates.