Carbohydrates /---> Carbon Dioxide \---> Water Proteins ---> Amino Acids --->Ammonia --->Nitrite ---> Nitrate \----> Sulfate \----> PhosphateEach step above results in consumption of dissolved oxygen (Dunne et al., 1978).
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.
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.
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.
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.