CHAPTER FIVE

SYSTEMATIC SAMPLING

5.1Collection of Diatom

In qualitative sampling, diatoms can be variously collected from different substrata. The substrata are rinsed carefully with the river/stream/lake water.

5.2Floatation Method

This is used in the collection of episamic and epipelic diatoms. These substrata provide very diverse assemblages of motile diatoms. Floatation method has a special advantage of extracting the motile living fraction of the diatom community (Taylor et al., 2007).

Phytoplankton: since diatoms are component of phytoplankton, they can also be obtained from collection of phytoplankton. Qualitative phytoplankton samples are collected by towing plankton nets of not more than 25 µm mesh size.

Diatom collection from phytoplankton in lentic water bodies (e.g., lakes, reservoirs, etc.) is done by vertical tows. In very deep-water bodies, vertical hauls with plankton net should be done in the euphotic zone, at least up to 5m depth.

5.3Sediments

The procedure of Round (1991) & (Taylor et al., 2007) is commonly used as follows:

5.3.1Deeper Water

This involves the use of 5 mm glass tube of about 1m length, attached to a rod (e.g., broomstick) at the river margin as follows:

  1. Over the top end of the tubing, place a finger and insert the bottom end under the water and allow it to rest on the sediment.

  2. Release the finger pressure while drawing the tube lightly over the sediment surface horizontally (for about one meter), gently scraping a line on the surface of the sediment.

  3. The pressure of the water pushes the sediment material (with diatoms) into the tube.

  4. The top of the tube is then sealed with the finger (to prevent sample loss)

  5. The tube is then carefully taken out and the collected material kept into a sample bottle.

5.3.2Shallow Waters

In shallow waters, an alternative approach to the above procedure can be used. It involves using a large syringe attached to the upper end of a flexible latex tube. The contact end of the latex tubing is cut at an angle to allow for oblique contact with the sediment containing the diatoms. Gradual sucking of water through the syringe ensures the collection of diatom material along with some surface sediment. The sample is then discharged into a sample bottle5.3.3 Rapid Sediment Samples

Scraping of damp sediment surface to a depth of 1 cm in several smaller areas in the stream bed and the material stored in a petri dish kept in a damp environment is also another collection method.

5.4Water surface/Column

Samples of diatoms can be collected from the surface/column of a water body by towing a plankton net. Such samples will contain a mixture of other algae other than diatoms though.

Quantitative samples of sediments are required for biomass measurement e.g., chlorophyll, diatom population like cell count, etc. The sediment is first moistened if it is dry. Take a glass tube of a known diameter, press it on the sediment or mud or sand 1 cm deep core. Push out sediment sample from the lower opening, using any extruder. This core sample should be taken randomly five times from each sampling area.

5.5Soil or Terrestrial Diatoms

Just like with sediments, soil diatoms are collected using a glass corer or a knife, or spoon, from 1 cm depth. This soil sample should be stored in a paper envelope to prevent moisture build-up. Sample should also be taken randomly for five times.

5.6Epilithon Diatoms

This is collection of diatoms growing on solid substrata such as pebbles, boulders, stones etc. They are collected by brushing the upper surface with a small (tooth) brush or scrapping with a spoon or a knife. The diatom samples are kept in sample bottles.

5.7Epiphytic Diatoms

These are diatoms attached to surfaces of other plants or algae or macrophytes, for example emergent macrophytes such as Typha and Phragmites, submerged macrophytes such as Potamogeton spp, Ceratophyllum spp. For collection, such surfaces are scrapped using hand, brush, etc. and stored in sample vials.