Organic Mattter

General Information: Natural organics consist of biodegradable organic matter such as wastes from biological material processing, human sewage, and animal feces. Microbes aerobically break down the complex organic molecules into simpler, more stable end-products. Microbial degradation yields end products such as carbon dioxide, water, phosphate and nitrate. General forms of these reactions are as follows:
Carbohydrates    /---> Carbon Dioxide
                               \---> Water

Proteins ---> Amino Acids --->Ammonia --->Nitrite ---> Nitrate
                                              \----> Sulfate		
                                               \----> Phosphate
Each step above results in consumption of dissolved oxygen (Dunne et al., 1978).

Numerical Categories:

No standard is currently established for natural organics. However, standards are set for dissolved oxygen, biological oxygen demand, and coliform bacteria, three parameters that may be directly influenced by the presence of natural organics. For more information, please refer to Bacteria and Dissolved Oxygen  sections.

Health Effects:

Organic particles in the water may harbor harmful bacteria and pathogens. Infection by the microorganisms may occur if the water is used for primary contact or as a raw drinking water source. Treated drinking water will not present the same health risks. In a potable drinking water plant, all organics should be removed from the water before distribution.

Environmental Effects:

High organic inputs trigger deoxygenation. If excess organics are introduced to the system, there is potential for complete depletion of dissolved oxygen. Without oxygen, the entire aquatic community is threatened. The only organisms present will be air- breathing insects and anaerobic bacteria (Gower, 1980).

If all oxygen is depleted, aerobic decomposition ceases and further organic breakdown is accomplished anaerobically. Anaerobic microbes obtain energy from oxygen bound to other molecules such as sulfate compounds. Thus, anoxic conditions result in the mobilization of many otherwise insoluble compounds.

In areas of high organics there is frequently evidence of rapid sewage fungus colonization. Sewage fungus appears as slimy or fluffy cottonwool-like growths of microorganisms which may include filamentous bacteria, fungi, and protozoa such as Sphaerotilus natans, Leptomitus lacteus, and Carchesium polypinuym, respectively. The various effects of the sewage fungus masses include silt and detritus entrapment, the smothering of aquatic macrophytes, and a decrease in water flow velocities. An accumulation of sediment allows a shift in the aquatic system structure as colonization by silt-loving organisms occur. In addition, masses of sewage fungus may break off and float away, causing localized areas of dissolved oxygen demand elsewhere in the water body.




Organic levels decrease with distance away from the source. In a standing water body such as a lake, currents are generally not powerful enough to transport large amounts of organics. In a moving water body, the saprotrophic organisms (organisms feeding on decaying organic matter) break down the organics during transportation away from the source. Hence, there is a decline in the oxygen demand and an increase of dissolved oxygen in the water. Community structure will gradually return to ambient with distance downstream from the source.


  1. Nonpoint source:
  2. Point source:

    Sewage treatment plants are the primary contributors of organics in many areas. Sewered communities may not have enough capacity to treat the extremely large volume of water resulting from large rainfalls. Periodically, treatment facilities may need to bypass treatment of their wastewater. Some areas encourage practices that may be harmful to estuarine systems, such as dumping untreated sewage sludge offshore or discharging treated water offshore (Kennish, 1992). Additional organics may be contributed by industries, such as the pulp and paper industry, that discharge organic-laden effluent.


Analytical Techniques:

(APHA, 1992)

  1. Five-Day Biochemical Oxygen Demand (BOD5): BOD5 is defined as the amount of oxygen required by bacteria to decompose organic matter for a specified time (usually 5 days) under aerobic conditions. The amount of oxygen reported with this method represents only the carbonaceous oxygen demand (CBOD) or the easily decomposed organic matter. BOD5 is commonly used to measure natural organic pollution.
  2. Chemical Oxygen Demand (COD): COD is defined as the oxygen equivalent of the organic portion of the sample that is susceptible to oxidation by a strong chemical oxidant. COD does not distinguish between refractory or "inert" organic matter. COD tests require approximately three hours.
  3. Total Organic Carbon (TOC): The TOC method converts organic carbon to carbon dioxide using a combination of heat and oxygen, ultraviolet radiation, and chemical oxidation. Once converted to carbon dioxide, the TOC can be quantitatively measured.
Mode of Transport: Natural organics can be directly discharged into a surface water systems or may be carried from an inland source by overland flow.