Single and Combined Effects of Metals (Fe, Hg) on Periphytic Diatom Community: A Non-Taxonomic Approach for Fluvial Ecosystem Biomonitoring

Fluvial ecosystems face contamination of multiple metals together which impose great deal of stress on the diatoms inhabiting in such ecosystems. This study uniquely presents cumulative effect of Fe and Hg on periphytic diatom community ( Gomphonema, Nitzschia, Achnanthidium, Rhopalodia ). Assessment was mainly based on non-taxonomical metrices of diatom such as motility, protoplasmic content, lipid bodies, pigment and deformities in frustules, along with this one traditional endpoint- community analysis, was also incorporated, for the study diatoms were treated with Fe and Hg, in single and combination. Motility of diatom community acted as early warning tool for biomonitoring and motility decreased for all four genera, effect was more severe in combination. Protoplasmic content assessed gave similar effect as motility and contraction was seen in all three treatments. Lipid bodies which act as good indicator of stress also showed a pattern of increment and reduction in biovolume and numbers. Deformities in frustules increased as the time and concentration of metals increased, were more profound in combination and Hg. Based on the assessment of parameters, trend of toxicity is: Fe + Hg > Hg > Fe, effect was dose and time dependent. Possible explanation of outcomes was ROS generation and membrane solubilization by Hg. Non taxonomical parameters can be incorporated in biomonitoring, among these parameters, motility is unique feature of diatoms and hence can be used as early warning tool for biomonitoring while protoplasmic contraction and deformities can be incorporated as alarming parameters. This suggests that incorporation of these parameters for study of cumulative metal effect would be a significant aid for biomonitoring of fluvial ecosystem.