What are diatoms?

Diatoms are one of the main groups of algae found in our oceans, rivers, lakes, and soils. Algae are organisms living in aquatic environments that photosynthesise, similar to plants. Diatoms are far too tiny to see with the naked eye, but they are everywhere, in our waterways and seas making up a significant share of the earth’s living biomass.

They are an important part of our global ecosystem. Collectively, they are responsible for generating up to 50% of the oxygen produced globally each year.

Globally, they also take in over 6.7 billion metric tons of silicon each year from the aquatic environments where they live. Diatoms make up nearly half of all the organic material found in the oceans. The silica shells of dead diatoms can reach as deep as half a mile on the seafloor.

What can they tell us?

We can discover all kinds of information about water bodies from the populations of diatoms we find within them.

Diatoms are collected in benthic samples (from the sea or riverbed) from freshwater or marine sites. These samples are put through a series of processes to remove the organic matter from the algal cells, leaving behind a silica skeleton. The species of diatom can then be identified from this skeleton (the frustule) to provide an assessment of the water quality conditions over time.

This data can be analysed using several tools to determine the nutrient load, acidity and more, allowing different sites to be compared. The effects of any inputs into the watercourse can be assessed. This is especially useful for understanding the effects of storm outflows from sewage works or the impact of an accidental discharge.

Diatom species vary in their sensitivity to inorganic nutrient concentrations in the water, so each species has been assigned sensitivity scores. The most numerous species found in the sample count will be given more weighting. For example, the species Gyrosigma acuminatum is more likely to be present than Diatoma mesodon under nutrient-rich conditions.

With this data the Trophic Diatom Index (TDI) for a site can be calculated. Higher scores indicate higher nutrient levels in the river or lake. This is useful when looking for evidence of nutrient enrichment which can occur due to runoff from agricultural land or wastewater discharge.

For sites where acidification may be an issue, for example, upland areas, there is a different index based on sensitivity to changes in pH value, the Diatom Acidification Metric (DAM).

How can diatoms help you?

Analysing diatoms can tell us a variety of things about a particular site. Diatoms are used to inform reporting under the Water Framework Directive (WFD), pollution incident assessment, baseline surveys, general water quality monitoring and more.

By collecting paleo core samples, diatoms can even be used to gather information about historic conditions hundreds or thousands of years ago. This can aid paleolimnology studies, revealing mysteries from the past.

Whatever your water quality needs, APEM can support you with our diatom services. APEM has experience delivering a wide range of projects from the very small scale to extremely large scale (over 1000 samples) from a wide range of geographical areas.

We have one of the largest diatom processing and analysing capabilities in the UK. All our analysts have over 10 years’ experience in the identification of freshwater or marine diatoms. They all take part in the UK diatom ringtest programme run by Bowburn Consultancy.

Our quality control systems are extremely robust, ensuring consistent quality and proven contamination control. If required, our labs have access to quality control data across several years.

We manage and deliver the whole process, from sampling to processing to identification to data analysis and finally providing a written report.

Over the years, APEM has introduced new processing methods to ensure we get the best result for each sample type. This willingness to adapt means that we can get the best results possible for any sample type that we are provided with.

If you are interested in using our diatom services for your water quality project, get in touch.


Check out our infographic!

Our infographic sets out the complex process of collecting and analysing diatoms undertaken by our specialists.