NEET Biology question
Not in NEET syllabus
A large quantity of urban sewage is drained into a nearby village river. Which among the given conditions would happen after mixing of sewage into the river? 1. Biochemical oxygen demand (BOD) of the receiving water body increases. 2. Dissolved oxygen of the receiving water body decreases. 3. It will not cause mortality among fishes and other aquatic creatures. 4. It will lead to nutrient enrichment of the receiving water body. **[NEET 2014]**
Solution
Sewage introduces a heavy biodegradable organic load, which increases BOD (1) as microorganisms consume dissolved oxygen for decomposition, lowering dissolved oxygen levels (2), while also enriching the water with nutrients like nitrates and phosphates
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