Evaluation of the trophic diatom index for assessing water quality in River Gharasou, western Iran

Water quality, diatom species composition and biomass estimates were performed in the Gharasou River in western Iran. Five sites along the River Gharasou were sampled every month from April to September 2005. Physical and chemical factors (pH, NO3-N, PO4-P, dissolved oxygen, total suspend solids, total dissolved solids, conductivity, turbidity, chemical oxygen demand and biological oxygen demand) were measured along with biological properties of the periphyton including biomass, ash-free dry mass, chlorophyll-a concentration and the taxonomic composition diatom assemblages. Information from the diatom assemblage was used to calculate the Trophic Diatom Index and biovolume. The TDI was significantly correlated with measures of human disturbance at the sites (e.g. PO4-P, NO3-N and dissolved oxygen) as well as to biomass measures (chlorophyll a, ash-free dry mass and biovolume). The sensitivity of the TDI and its component metrics to environmental stressors supports the use of this index for monitoring ecological conditions in streams in Iran and to aid diagnosis of the cause of their impairment.