Figure 11 illustrates the habitat of diatoms – diatom colonies on stones, sand, etc. At each site, three to five stones were randomly selected across the stream and diatoms were scraped off the exposed surface of the stones using a tooth brush. Fresh samples were carefully checked to assure that majority of the diatom frustules were alive prior to acid combustion. A hot HCl and KMnO4 method was used to clean frustules of organic materials. The cleaned diatom samples were dried on 18x18 mm cover slips and mounted with Pleurax. A total of 400 frustules per sample were enumerated and identified using compound light microscope (Lawrence & Mayo LM-52-series, with 1000× magnification) following methods described by Taylor et al. (2005) and Karthick et al. (2010). Diatoms were identified primarily to the species level according to Gandhi, (1957a,b,c; 1958a,b; 1959a,b,c; 1960a,b,c); Krammer and Lange-Bertalot (1986–1991) and Taylor et al. (2007).