CDOM Colored Dissolved Organic Matter Sensors: Water Quality Monitoring

Why would I want to measure CDOM (Colored Dissolved Organic Matter)?

Dissolved Organic Material (DOM) exists in many forms ranging from naturally occurring humic acids, to by-products or secretions excreted from organisms.  DOM is a highly abundant form of organic matter and represents a major reservoir of reactive carbon.  It is also a dynamic substrate which can undergo reactions to become accessible to bacteria, plants, and animals as an energy source, or it can photodegrade resulting in the production of volatile compounds that can have adverse effects on organisms and the environment.  DOM typically contains chromophores that absorb UV and visible light, hence the term Chromophoric (or colored) Dissolved Organic Materials (CDOM).  CDOM will also fluoresce (hence the term FDOM) after light absorption, allowing researchers a way to detect and quantify its abundance in water systems using fluorometry.  

Detection of DOM levels in water systems greatly increases the power of monitoring efforts and helps explain events such as a sudden decrease in primary productivity, phytoplankton regime shifts, algal blooms, and changes in an environment.

How is CDOM Measured?

There are many methods for the detection of CDOM in water but the simplest and most cost efficient way, is in situ fluorescence. Eureka’s CDOM sensor from Turner Designs is a fluorometric sensor.  Fluorescence occurs when a molecule absorbs light energy at one wavelength and then emits that energy at a different wavelength.  Fluorometric sensors emit light at a certain wavelength, and look for a very specific, different wavelength in return.  Eureka’s CDOM fluorometer, uses ultraviolet (UV) excitation for CDOM detection. Realizing there are different CDOM sources that may emit a range of wavelengths, Turner chose a broad band emission filter that will detect various types of CDOM found in the natural environment. 

What should I know about CDOM (Colored Dissolved Organic Matter) measurement in the field?

Fluorescence detection of CDOM is the easiest and fastest means of estimating DOM by taking advantage of CDOM’s natural fluorescent property of absorbing UV light and fluorescing blue light. CDOM measurement is of interest to researchers due to its effect on light in surface waters. Fluorescence detection using Eureka’s CDOM fluorometer is more sensitive, faster and less expensive than other qualitative measures, and requires no sample handling. Natural water fluorescence data can be collected without the need to conduct extractions or other sample preparations. Although fluorescence data from natural water is a qualitative measurement, this data has been shown to correlate well with extracted DOM data. Due to the sensitivity and ease of use of the MantaPlus Multiprobe, data can be collected easily and quickly in virtually any environment. Monitoring of CDOM in a continuous, flow-through mode, using Eureka’s flow cell adapter, eliminates the problems associated with sample collection and storage, and allows for the automatic correction of temperature effects. Shipboard on-line monitoring permits the collection of large data sets along a ship’s track. Applications Include:

•  Continuous monitoring of wastewater discharge. CDOM fluorescence corresponds to total organic carbon (TOC), which is an indicator of discharge water quality.
•  Natural tracer of specific water bodies. CDOM concentration can indicate the dispersion, transport and mixing of a water mass.
•  Investigations of the magnitude of photosynthetically active radiation (PAR) and primary production due to its significant absorption of light in surface waters, especially in coastal and estuarine areas.
•  Ocean color research and the effect of CDOM on satellite imagery.
•  Investigations of DOM cycling and energy budgets.
•  Investigations on the effects of photochemical bleaching of DOM in surface waters.
•  The use of CDOM fluorescence data to calculate the fluorescent quantum yield that is then used to determine the CDOM absorption coefficient.