Biochemical Oxygen Demand

All waters of the world contain organic matter such as bits of old plants">

Biochemical Oxygen Demand All waters of the world contain organic matter such as bits of old plants, algae, expired organisms such as fish and plankton, etc. Without this organic material, aquatic life would suffer because as bacteria in the water break down this matter, many nutrients are released to the water column allowing the cycle of life to repeat. However, too much organic material can lead to problems because, as the bacteria are busy breaking down the material, they are consuming oxygen. When oxygen levels are depleted to very low levels, the fish and other animals find it difficult to breathe. This is why it is important not to have too much organic material in the water. Measurement:  Five-Day Biochemical Oxygen Demand--BOD(5):  BOD(5) is defined as the amount of oxygen required by bacteria to decompose organic matter for a specified time (usually 5 days) under aerobic (with oxygen) conditions.  The amount of oxygen reported with this method represents the easily decomposed organic matter.  BOD(5) is commonly used to measure organic pollution in surface waters. The BOD(5), as measured on the Lower Spanish River, averaged 1.22 mg/L and ranged from 0.5 to 2.6 mg/L in 1999 water quality sampling.  To put these values into perspective, the "Water Quality Sourcebook--A Guide to Water Quality Parameters", published by Environment Canada (1979) stated that: "No specific guidelines for BOD have been proposed, but waters with BOD levels of less than 4 mg/L are deemed reasonably clean.  Waters with levels greater than 10 mg/L thus are considered polluted since they contain large amounts of degradable organic material." Accordingly, the Spanish River is in good shape with respect to Biochemical Oxygen Demand.