An ecological and floristic study of the diatoms in Babolrud river

Epilithic diatoms are a division of Bacillariophyceae which live on stone and hard surfaces. This study was aimed to investigate the population dynamics of diatoms in Babolrud river. Samples were collected from 5 stations from May 2012 through September 2012 in a monthly interval. Temperature، pH، NO3-، PO4- and (EC) were measured for each sampling. Samples were prepared using Patrick and Reimer procedure. 72 taxa were identified، among which 33 taxa (46%) were cosmopolitan or widely distributed. The genera with the highest species were Navicula (12)، Nitzschia (9)، Achnanthes (9)، Cymbella (8) and Gomphonema (6). The decrease in diatoms diversity from upstream toward downstream can be regarded as an indicator of increasing water pollution. Trends in distribution of diatom species in the sampling sites were explained by variations in environmental parameters such as conductivity، pH، temperature، nitrate and phosphate. In highly contaminated sites of the Babolrud River، species such as Gomphonema olivaceum، Navicula pupula، Nitzschia flexa and Pinnularia major were observed، while individuals of Achnanthes clevei، Achnanthes deflexa، Cymbella affinis and Fragilaria virescens were found in sampling sites with relatively less environmental perturbation. We concluded that diatoms can be used as quantitative indicators of environmental conditions in lotic systems.