Diatoms are a group of algae characterised by a silica shell (frustule), which is essentially an ornate glass case surrounding the organism. They form an important part of both the phytoplankton (the community of algae growing in the water column) and the periphyton (the community of algae growing attached to surfaces, substrates and aquatic plants).

The beautifully patterned frustules, which can survive the death of the algae or the digestion of organic matter, have long held a particular fascination for microscopists. For this reason this group of algae has a history of extensive research and much information is available on the ecological requirements of different species.

Diatoms are therefore recognised as being particularly useful in the assessment of water quality and chemistry. Being the subject of various biotic indices, they are used as indicators of parameters such as trophic status and acidification of water bodies. They also form an important fossil record in the sediments of lakes and other waterbodies and have been used to measure past changes in climate and water chemistry.

As well as their use in wider aquatic ecological studies, diatoms are increasingly seen as a reliable indicator of nutrient status. With the implementation of the Water Framework Directive, biotic indices will play a key role in the determination of water quality. Diatom communities, analysed using the Trophic Diatom Index (TDI), will be central to this form of assessment.

APEM DIATOM SERVICES

With dedicated specialist laboratory staff, Biolabs offers diatom analysis services such as design and implementation of diatom sampling strategies and laboratory analysis including:

• Identification to lowest necessary taxonomic level
• Creation of permanent mounts of samples for future reference
• Analysis and calculation of biotic index values
• TDI - sampling, identification, counts and calculation of index. All work undergoes external AQC according to the standards set out in the TDI Users Manual.