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What is CDOM/FDOM and why is it necessary?

Coloured, or chromophoric dissolved organic matter (CDOM), is a naturally occurring dissolved matter that absorbs UV light in water. It’s usually made up of tannins that are released from the breakdown of plant material. A fraction of CDOM fluoresces when it absorbs light of a certain spectrum, and is called fluorescent dissolved organic matter, or FDOM.

CDOM/FDOM is used to measure the relative amount of dissolved organic material (DOM) in the water. Although it is naturally occurring, human influence through aspects such as logging, agriculture, effluent discharge and wetland drainage can affect the levels of CDOM in freshwater and estuarine systems.


It is vital to measure the levels of CDOM/FDOM and understand their trends because they can have a significant effect on aquatic ecosystems. Raised levels of CDOM/FDOM can inhibit the growth of phytoplankton and limit photosynthesis, damaging the food chain and limiting the production of oxygen in water bodies.

Aquaread’s water quality monitoring equipment

Aquaread designs and manufactures highly scientific water testing equipment that is designed specifically for use in the field. The rugged instruments are used both by researchers and in related industries throughout the world.

We offer three Aquaprobes that have optical electrode ports suitable for the CDOM sensor. These are the Aquaprobe AP-2000, our portable multi-parameter probe, the Aquaprobe AP-5000, which is more versatile but still portable, and the Aquaprobe AP-7000, which is designed for unmanned deployment.

Our CDOM/FDOM sensor, as well as a full range of Aquaread’s water testing probes and accessories, are available from our dealers. Alternatively, for short term projects, we have packages available to rent.

Our CDOM/FDOM sensor measures levels of UV light in water. A common use for an FDOM sensor is the continuous monitoring of wastewater discharge. This is because FDOM corresponds to total organic carbon, which is an indicator of discharge water quality. The sensor can also be used for hydrological studies, monitoring the dispersion, transport and mixing of a water mass.

The CDOM sensor is also used to assess the human influence on rivers and streams. Used in long term deployment, CDOM measurements can be used to identify trends. Another application for these sensors is assessing the light availability in lakes. If there is a high amount of DOM it can affect how much light is available for photosynthesis and reduce the amount of vegetation able to grow in the lake. This can impact aquatic life, such as ducks and wading birds.

The CDOM sensor is an optical sensor that uses a fluorometer and a sapphire lens, which is highly scratch resistant. The sensor measures the fluorescence and uses this measurement to indicate the concentration of DOM in the water sample. The sensor has a range of 0 – 20,000µg/L, with 2 auto ranging scales for high resolution at low levels.


The new CDOM/FDOM sensor can be used with any Aquaprobe with an optical auxiliary port, although it is recommended for use with Aquaprobe AP-7000, which is designed for long term deployments.

Get into monitoring with Aquaread

If you would like any more information about TDS meters and other total dissolved solids testing equipment, or water quality monitoring in general, please Contact Us. Click here to see our product range.