Seasonal abudndance of planktonic diatoms in doon valley

Diatoms also known as “stick plants”, are a major group of algae. They belong to the kingdom Protista, the very first established. (Abdina 1948). Most diatoms are unicellular, although they can exist as colonies in the shape of filaments or ribbons (eg. Fragilaria), fans (eg. Meridian), zigzag (eg. Tabellaria) or satellite colonies (eg. Astreionella). They are essentially pinnate or centric. Diatoms are producers within the food chain. A characteristic feature of diatom cell is that they are encased within a unique cell will made of silica (hydrate silicon dioxide) called a frustules. These frustules show a wide diversity in form, but usually consists to two asymmetrical sides with a split between them, hence the group name. The two tests fit together like tow parts of a petriplate and the assembly is called a value. Diatom communities are popular tool for monitoring environmental conditions, past or present and are commonly used in studies of water quality. Diatom is a widespread group and can be found in the fresh water, in soil and on dam surfaces. Most live pelagic ally in open water, although some live as surface films at the water – sediment interface (benthic), or even under damp atmospheric conditions. Plank tonic diatoms in fresh water environments typically exhibit a ‘bloom and bus life style, when conditions in the upper missed layer are favorable their competitive edge allow them to quickly dominate phytoplankton communities. Living diatoms are often found in great numbers an compared to filamentous algae, or forming gelatinous masses on various submerged plants. Diatoms are eukaryotes, meaning that they have true cells with a defined nuclei enclosed in a nuclear membrane. Since they are algae, which are plants, they carry out photosynthesis in celluar “organelles” called chloroplast. Diatoms range considerably in sixe, the largest species being about 2mm and the smallest being only a few micrometers long, (Adhikary S.P. and Jaynati Sahn 1986). The “Pennate” diatom show below is a little over 200 micrometers long. Diatoms are equally common in gold or yellow colour. This is because they have a large amount of yellow carrotenoid pigment and xanthophylls pigment that masks the green colour of their chlorophyll.

Diatoms are often difficult to identify since their body plan is quite simple and they are usually of the same colour.