Kamis, 03 Februari 2011 | 17.19 | 11 Comments

Water Quality Monitoring : Biochemical Oxygen Demand

When organic matter decomposes, microorganisms (such as bacteria and fungi) feed upon it and eventually it becomes oxidized (combined with oxygen). Biochemical oxygen demand is a measure of the quantity of oxygen used by these microorganisms in the aerobic oxidation of organic matter.

When aquatic plants die, aerobic bacteria feed upon them and nutrients, such as nitrates and phosphates, are released into the body of water, stimulating plant growth. Eventually, more plant growth leads to more plant decay. Nutrients can be a prime contributor to high biochemical oxygen demand in rivers.

Impounded rivers also collect organic wastes from upriver that settle in the quieter water. The bacteria that feed on this organic waste consume oxygen. With much plant growth, the percentage of saturation (dissolved oxygen) often falls below 50 percent. Large daily fluctuations in dissolved oxygen levels are characteristic of bodies of water with extensive plant growth. Dissolved oxygen levels rise from morning through the afternoon as a result of photosynthesis, reaching a peak in the late afternoon. Photosynthesis stops at night, but plants and animals continue to respire and consume oxygen. As a result, dissolved oxygen levels fall to a low point just before dawn.

In rivers with high BOD levels, aerobic bacteria consume much of the available dissolved oxygen, robbing other aquatic organisms of the oxygen they need to live. Organisms that are more tolerant of lower dissolved oxygen levels may appear and become numerous, such as carp, midge larvae and sewage worms. Organisms that are intolerant of low oxygen levels, such as caddisfly larvae and mayfly and stonefly nymphs, will not survive. As organic pollution increases, the ecologically stable and complex relationships present in waters containing a high diversity of organisms is replaced by a low diversity of pollution-tolerant organisms with increasing populations.

Why is the biochemical oxygen demand in water so high?

Check out your local watershed - can you find organic matter (such as leaves) entering the lake or river from swamps, bogs or vegetation in the watershed?

What is the difference between point source and nonpoint source pollution?

Are there any pulp or paper mills, meat-packing plants, food processing industries or wastewater treatment plants on your local river?

If you live in a city or suburb - do you have a separate or combined sewer system? Check it out with your local government!

If you live in a rural setting - do you have septic systems near the river or lake? Are these systems properly maintained?

Can you find any cattle feedlots, dairies or barnyards in the watershed? Is the waste from these feedlots properly contained?

What is the cause(s) of your problem? What did you find that led you to this conclusion?

11 komentar:

TUKANG CoLoNG mengatakan...

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iip albanjary mengatakan...

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Vulkanisir mengatakan...

Organisms that are more tolerant of lower dissolved oxygen levels may appear and become numerous, such as carp, midge larvae and sewage worms

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Jasa Seo mengatakan...

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nicki minaj mengatakan...

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