UPSC Prelims 2011 Q47: Environment & Ecology – Water & Wetland Conservation
There is a concern over the increase in harmful algal blooms in the seawaters of India. What
could be the causative factors for this phenomenon?
1. Discharge of nutrients from the estuaries.
2. Run - off from the land during the monsoon.
3. Upwelling in the seas.
Select the correct answer from the codes given below:
- (a) 1 only
- (b) 1 and 2 only
- (c) 2 and 3 only
- (d) 1, 2 and 3
Answer: (d) 1, 2 and 3
Explanation
Causes of harmful algal blooms in Indian seawaters
Harmful algal blooms (HABs) are driven by excess nutrients reaching coastal waters, which fuel explosive algae growth.
| Factor | Verdict | Reason |
|---|---|---|
| 1. Discharge of nutrients from estuaries | Correct | Nutrient-rich discharge (from rivers/estuaries) is a classic driver of eutrophication and algal blooms |
| 2. Run-off from land during monsoon | Correct | Monsoon run-off carries fertilizers, sewage and nutrients into coastal waters, triggering blooms |
| 3. Upwelling in the seas | Correct | Upwelling brings nutrient-rich deep water to the surface, which can also fuel algal blooms |
HAB drivers at a glance:
| Point | Detail |
|---|---|
| Core trigger | Excess nutrients (nitrogen, phosphorus) in surface waters |
| Sources | Estuarine discharge, land run-off, upwelling |
| Effect | Explosive algae growth, sometimes toxic, depleting oxygen |
Answer: (d) 1, 2 and 3.
Why each option is right or wrong
- (a) Incorrect. Factors 2 and 3 (run-off, upwelling) are also real causes, so '1 only' is too narrow.
- (b) Incorrect. Factor 3 (upwelling) is also a recognized cause, so this combination is incomplete.
- (c) Incorrect. Factor 1 (estuarine nutrient discharge) is also a cause, so leaving it out is wrong.
- (d) CORRECT. All three — estuarine discharge, monsoon run-off, and upwelling — bring nutrients that trigger algal blooms.
Key point
Harmful algal blooms are driven by nutrient enrichment from ALL THREE sources: estuarine discharge, monsoon land run-off, and upwelling of nutrient-rich deep water.
Remember
Algal bloom causes: estuarine nutrient discharge + monsoon run-off + upwelling — all three contribute nutrients.
Common mistakes
- Thinking only one pathway (e.g., just run-off) can deliver nutrients to coastal waters.
- Not knowing upwelling also brings nutrients, not just pollution-linked sources.
- Underestimating how multi-causal eutrophication-driven blooms really are.
Exam tip
Any pathway that brings extra nutrients to seawater — rivers, run-off, or upwelling — can trigger algal blooms. Don't assume only pollution-linked sources count.
Sources
- Donald M. Anderson, Patricia M. Glibert and Joann M. Burkholder — "Harmful Algal Blooms and Eutrophication: Nutrient Sources, Composition, and Consequences", Estuaries, vol. 25 (2002)
- UNESCO Intergovernmental Oceanographic Commission — Harmful Algal Bloom Programme