Temporal and spatial distribution of diatom assemblages and their relationship with environmental factors in Balikhli River (NW Iran)

Benthic diatom assemblages on the natural substrata at Balikhli River (northwest Iran) were investigated monthly. A total of 96 samples were collected from epilithic and epipelic substrata. A total of 110 taxa from 49 genera were identified. The most abundant diatom species were Cyclotella meneghiniana, Diatoma moniliformis, Nitzschia inconspicua, Planothidium lanceolatum and Gomphonema olivaceum. Non-metric multidimensional scaling (nMDS) analyses revealed explicit differences between diatom communities of stony and sediment substrates. Although common diatom taxa were not restricted to single substrates, some taxa had higher tendencies to every substrate. The nMDS analysis also showed differences between summer and autumn samples. Canonical correspondence analysis (CCA) of groups resulted from cluster analysis, showed that the nutrient concentration gradient, pH were the most important factors affecting the composition of diatom assemblages and species distribution. In our study orthophosphates had greater effect than nitrates, and Gomphonem parvulum and Navicula recenswere found in phosphate rich samples. Anthropogenic input including agricultural and domestic wastes may be responsible for high levels of these parameters. Alkali volcanic rocks and limestone sediments underlying the watershed could explain the high pH in the Balikhli River. In total 67.5% of the identified species in the river are considered as alkaliphilous. The findings of this study denote that the main determinants of variation in benthic diatom communities of Balikhli River result from a combination of land use patterns caused by human activities, river hydrology and natural phenomena including geology.