Colored dissolved organic matter
Encyclopedia
Colored dissolved organic matter (CDOM) is the optically measurable component of the dissolved organic matter in water. Also known as chromophoric dissolved organic matter, yellow substance, and gelbstoff, CDOM occurs naturally in aquatic environments primarily as a result of tannins released from decaying detritus
. CDOM most strongly absorbs short wavelength light ranging from blue to ultraviolet
, whereas pure water absorbs longer wavelength red light. Therefore, non-turbid water with little or no CDOM appears blue. The color of water
will range through green, yellow-green, and brown as CDOM increases.
and can inhibit the growth of phytoplankton
populations, which form the basis of oceanic food chains and are a primary source of atmospheric oxygen
. CDOM also absorbs harmful UVA/B radiation, protecting organisms from DNA damage.
Absorption of UV radiation causes CDOM to "bleach", reducing its optical density and absorptive capacity. This bleaching (photodegradation) of CDOM produces both low-molecular-weight organic compounds which may be utilized by microbes, and reactive oxygen species, which may damage tissues and alter the bioavailability of limiting trace metals.
CDOM also interferes with the use of satellite spectrometer
s to remotely estimate phytoplankton population distribution. As a byproduct of photosynthesis, chlorophyll
is a key indicator of phytoplankton activity. However, CDOM and chlorophyll both absorb in the same spectral range so it is difficult to differentiate between the two.
Although variations in CDOM are primarily the result of natural processes, human activities such as logging, agriculture, effluent discharge, and wetland drainage can affect CDOM levels in fresh water and estuarine systems. In general, CDOM concentrations are much higher in fresh waters and estuaries than in the open ocean, though concentrations are highly variable.
Detritus
Detritus is a biological term used to describe dead or waste organic material.Detritus may also refer to:* Detritus , a geological term used to describe the particles of rock produced by weathering...
. CDOM most strongly absorbs short wavelength light ranging from blue to ultraviolet
Ultraviolet
Ultraviolet light is electromagnetic radiation with a wavelength shorter than that of visible light, but longer than X-rays, in the range 10 nm to 400 nm, and energies from 3 eV to 124 eV...
, whereas pure water absorbs longer wavelength red light. Therefore, non-turbid water with little or no CDOM appears blue. The color of water
Color of water
The color of water is a subject of both scientific study and popular misconception. While relatively small quantities of water are observed by humans to be colorless, pure water has a slight blue color that becomes a deeper blue as the thickness of the observed sample increases...
will range through green, yellow-green, and brown as CDOM increases.
Significance of CDOM
CDOM can have a significant effect on biological activity in aquatic systems. CDOM diminishes light as it penetrates water. This has a limiting effect on photosynthesisPhotosynthesis
Photosynthesis is a chemical process that converts carbon dioxide into organic compounds, especially sugars, using the energy from sunlight. Photosynthesis occurs in plants, algae, and many species of bacteria, but not in archaea. Photosynthetic organisms are called photoautotrophs, since they can...
and can inhibit the growth of phytoplankton
Phytoplankton
Phytoplankton are the autotrophic component of the plankton community. The name comes from the Greek words φυτόν , meaning "plant", and πλαγκτός , meaning "wanderer" or "drifter". Most phytoplankton are too small to be individually seen with the unaided eye...
populations, which form the basis of oceanic food chains and are a primary source of atmospheric oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
. CDOM also absorbs harmful UVA/B radiation, protecting organisms from DNA damage.
Absorption of UV radiation causes CDOM to "bleach", reducing its optical density and absorptive capacity. This bleaching (photodegradation) of CDOM produces both low-molecular-weight organic compounds which may be utilized by microbes, and reactive oxygen species, which may damage tissues and alter the bioavailability of limiting trace metals.
CDOM also interferes with the use of satellite spectrometer
Spectrometer
A spectrometer is an instrument used to measure properties of light over a specific portion of the electromagnetic spectrum, typically used in spectroscopic analysis to identify materials. The variable measured is most often the light's intensity but could also, for instance, be the polarization...
s to remotely estimate phytoplankton population distribution. As a byproduct of photosynthesis, chlorophyll
Chlorophyll
Chlorophyll is a green pigment found in almost all plants, algae, and cyanobacteria. Its name is derived from the Greek words χλωρος, chloros and φύλλον, phyllon . Chlorophyll is an extremely important biomolecule, critical in photosynthesis, which allows plants to obtain energy from light...
is a key indicator of phytoplankton activity. However, CDOM and chlorophyll both absorb in the same spectral range so it is difficult to differentiate between the two.
Although variations in CDOM are primarily the result of natural processes, human activities such as logging, agriculture, effluent discharge, and wetland drainage can affect CDOM levels in fresh water and estuarine systems. In general, CDOM concentrations are much higher in fresh waters and estuaries than in the open ocean, though concentrations are highly variable.
See also
- Blackwater riverBlackwater riverA blackwater river is a river with a deep, slow-moving channel that flows through forested swamps and wetlands. As vegetation decays in the water, tannins are leached out, resulting in transparent, acidic water that is darkly stained, resembling tea or coffee. Most major blackwater rivers are in...
- Color of waterColor of waterThe color of water is a subject of both scientific study and popular misconception. While relatively small quantities of water are observed by humans to be colorless, pure water has a slight blue color that becomes a deeper blue as the thickness of the observed sample increases...
- Dissolved organic carbon (DOC)
- Ocean turbidityOcean turbidityOcean turbidity is a measure of the amount of cloudiness or haziness in sea water caused by individual particles that are too small to be seen without magnification. Highly turbid ocean waters are those with a large number of scattering particulates in them. In both highly absorbing and highly...
- Secchi diskSecchi diskThe Secchi disk, created in 1865 by Pietro Angelo Secchi SJ, is a circular disk used to measure water transparency in oceans and lakes. The disc is mounted on a pole or line, and lowered slowly down in the water. The depth at which the pattern on the disk is no longer visible is taken as a measure...
External links
- The Color of the Ocean from science@NASANASAThe National Aeronautics and Space Administration is the agency of the United States government that is responsible for the nation's civilian space program and for aeronautics and aerospace research...