Colored Dissolved Organic Matter (CDOM), also known as gelbstoff or yellow substance, refers to organic molecules dissolved in water that can absorb light, especially in the ultraviolet (UV) and blue portions of the spectrum. CDOM plays a crucial role in aquatic systems because it influences the color of water, affects light penetration, and is part of the carbon cycle.
Key Characteristics of CDOM
- Source:
- Terrestrial Origin: CDOM often originates from the breakdown of plant material, such as leaves and wood, and is carried into aquatic systems via rivers and streams.
- Aquatic Production: It can also be produced within water bodies by decaying phytoplankton, bacteria, and organic detritus.
- Optical Properties:
- Light Absorption: CDOM absorbs UV and blue light strongly, which reduces the penetration of these wavelengths into the water column. This is why water with high CDOM concentrations appears brownish or tea-colored.
- Spectral Slope: CDOM’s absorption decreases exponentially with increasing wavelength, which is often used to characterize its properties.
- Chemical Composition:
- CDOM is a complex mixture of organic molecules, including humic substances (from plant decay) and fulvic acids. Its exact composition varies depending on its source and the aquatic environment.
Role and Importance of CDOM
- Impact on Light Penetration:
- CDOM controls how light penetrates through water. In areas with high CDOM, the light available for photosynthesis (especially for phytoplankton) can be limited, influencing primary production.
- Carbon Cycle:
- CDOM represents a pool of dissolved organic carbon (DOC). It plays a role in the aquatic carbon cycle by acting as a source of food for microorganisms or undergoing photodegradation, which releases carbon dioxide into the atmosphere.
- Remote Sensing and Water Quality Monitoring:
- Satellite sensors detect the color of water, and CDOM is one of the key components affecting these measurements. By analyzing light absorption, scientists can estimate CDOM concentration and monitor water quality.
- UV Radiation Protection:
- CDOM acts as a natural sunscreen for aquatic ecosystems, absorbing harmful UV radiation and protecting organisms that are sensitive to UV exposure.
Applications
- Environmental Monitoring: Understanding CDOM helps in tracking water quality, eutrophication, and pollution.
- Climate Studies: Since CDOM affects the carbon cycle and influences heat absorption in water, it has implications for global climate models.
- Marine and Freshwater Research: CDOM is essential for studying the dynamics of aquatic ecosystems and biogeochemical processes.