Dissolved Organic Matter

Definition

Dissolved organic matter (DOM) refers to a complex mixture of organic molecules that are soluble in water and derived from the decomposition of plant and animal material, as well as microbial activity. DOM plays a crucial role in biogeochemical cycles, influencing nutrient availability, carbon cycling, and the overall health of aquatic ecosystems. It serves as a food source for microorganisms, facilitating the breakdown of organic materials and contributing to nutrient regeneration in the environment.

5 Must Know Facts For Your Next Test

1. Dissolved organic matter can account for a significant portion of the total organic carbon in aquatic systems, affecting water quality and ecosystem functioning.
2. The composition of DOM varies depending on the source of organic matter, environmental conditions, and microbial processing, which can influence its reactivity and bioavailability.
3. DOM can influence light penetration in water bodies, affecting photosynthesis in aquatic plants and phytoplankton by absorbing UV and visible light.
4. The decomposition of DOM by microorganisms leads to the release of nutrients such as nitrogen and phosphorus, which are essential for primary production in aquatic environments.
5. Changes in land use and climate can alter the quantity and quality of DOM entering water systems, impacting overall ecosystem health and functioning.

Review Questions

• How does dissolved organic matter impact microbial communities in aquatic ecosystems?
  • Dissolved organic matter serves as a critical food source for microbial communities in aquatic ecosystems. When organic materials decompose, they release DOM, which is rich in carbon and other nutrients that microorganisms utilize for growth and metabolism. The presence of DOM can enhance microbial diversity and activity, promoting nutrient cycling and energy flow within these ecosystems.
• Discuss the relationship between dissolved organic matter and carbon cycling within freshwater systems.
  • Dissolved organic matter plays a vital role in carbon cycling by transporting organic carbon through freshwater systems. It acts as both a substrate for microbial decomposition and a means of sequestering carbon. As microbes break down DOM, they convert it into CO2 through respiration, which then returns to the atmosphere. This process links terrestrial ecosystems to aquatic environments and contributes to global carbon dynamics.
• Evaluate the potential ecological consequences of altered dissolved organic matter concentrations due to climate change.
  • Altered concentrations of dissolved organic matter due to climate change could have significant ecological consequences. Increased rainfall or changes in land use might lead to higher inputs of DOM into aquatic systems, potentially causing eutrophication through nutrient overload. Conversely, reduced DOM concentrations could impair microbial communities and disrupt nutrient cycling. Overall, these shifts can impact primary productivity, water quality, and biodiversity within affected ecosystems.

Related terms

Humic Substances: Humic substances are a major component of DOM, consisting of humic acid, fulvic acid, and humin, which result from the decomposition of organic matter and contribute to soil fertility and water quality.

Microbial Decomposition: Microbial decomposition is the process by which microorganisms break down dead organic matter into simpler compounds, ultimately leading to the formation of DOM and nutrients that are available to other organisms.

Carbon Cycling: Carbon cycling is the process through which carbon is exchanged between the atmosphere, land, and water bodies, with DOM acting as a key player in this cycle by transporting carbon within aquatic systems.