UPSC Prelims 2022 Q43: Wetlands as Earth's 'Kidneys' — Explained
"If rainforests and tropical forests are the lungs of the Earth, then surely wetlands function as its kidneys." Which one of the following functions of wetlands best reflects the above statement?
- The water cycle in wetlands involves surface runoff, subsoil percolation and evaporation.
- Algae form the nutrient base upon which fish, crustaceans, molluscs, birds, reptiles and mammals thrive.
- Wetlands play a vital role in maintaining sedimentation balance and soil stabilization.
- Aquatic plants absorb heavy metals and excess nutrients.
Answer: (c) Wetlands play a vital role in maintaining sedimentation balance and soil stabilization.
Statement-wise explanation
- a: incorrect — This statement correctly describes how water moves through a wetland: surface runoff, percolation into the subsoil, and evaporation. But that is the hydrological cycle, and it happens in any land system. It says nothing about cleaning or balancing what passes through. A kidney's job is to filter and regulate, not to move water, so this does not fit the analogy.
- b: incorrect — Algae are primary producers that form the base of the wetland food web, and fish, crustaceans, molluscs, birds, reptiles and mammals depend on them. This describes the wetland's biological productivity, which is a feeding role rather than a cleansing one. It is closer to calling wetlands 'biological supermarkets', another common metaphor, than to calling them kidneys.
- c: correct — Vegetation slows the water entering a wetland, so suspended silt settles out and roots hold it in place. The water that leaves is clearer, and soil downstream is stabilised. Because the wetland traps what the water carries and keeps the system in balance, it acts like a kidney for the whole landscape. The official UPSC key marks this as the answer (see the dispute note).
- d: incorrect — The fact is true. A Ramsar water-purification sheet reports that Florida cypress swamps removed 98% of the nitrogen and 97% of the phosphorus entering from wastewater, and that some wetland plants have been used to treat mining effluent containing heavy metals. Most sources cite exactly this function for the 'kidney' analogy, so it is a very strong option. The key recorded for this page marks it as not the best fit, because it names one component (aquatic plants) rather than a function of the wetland as a whole.
How to eliminate
Two options go quickly. A kidney filters and regulates, so ask of each option whether it cleans or balances what flows through. The water cycle (runoff, percolation, evaporation) describes movement, not cleansing. The algae food base describes productivity. Neither is a kidney function, so both can be eliminated. Between sediment trapping/soil stabilisation and plants absorbing heavy metals and nutrients, there is no wording trick. Both are filtering functions, and the question cannot be cracked by elimination alone. Most coaching keys and candidates chose heavy-metal and nutrient absorption, because it maps most directly onto a kidney removing waste from blood. The key recorded here is sediment balance and soil stabilisation, which treats the wetland as a whole system that traps and balances what water carries. Fact to remember: wetlands are called 'kidneys of the landscape' because they trap sediment and absorb nutrients and pollutants before water reaches rivers, lakes and aquifers. Expect UPSC to test this filtering role in both forms.
Know more
Why wetlands are 'kidneys of the landscape'
Water from farms, towns and hill slopes carries silt, nutrients (nitrogen, phosphorus) and toxins. When it enters a wetland, dense vegetation slows it down. Three things then happen:
- Sediment trapping: suspended particles settle, and roots bind them. This clears the water and stabilises soil.
- Nutrient uptake and denitrification: plants and microbes take up nitrogen and phosphorus. Some nitrate is converted to nitrogen gas.
- Pollutant sequestration: plants and sediments bind heavy metals. This is phytoremediation, used in constructed wetlands to treat wastewater.
A Ramsar water-purification sheet reports that Florida cypress swamps removed 98% of the nitrogen and 97% of the phosphorus in incoming wastewater before it reached groundwater.
Organ metaphors used for ecosystems
| Metaphor | Ecosystem | Function behind it |
|---|---|---|
| Lungs of the Earth | Rainforests | Photosynthesis, oxygen release, carbon uptake |
| Kidneys of the landscape | Wetlands | Filtering sediment, nutrients and pollutants |
| Biological supermarkets | Wetlands | High productivity that supports large food webs |
| Sponges | Wetlands, peatlands | Storing floodwater and releasing it slowly; groundwater recharge |
Other wetland ecosystem services: flood control, groundwater recharge, shoreline protection (mangroves), carbon storage (peatlands), fisheries, and habitat for migratory birds.
Governance: The Ramsar Convention was signed at Ramsar, Iran, on 2 February 1971. 2 February is marked as World Wetlands Day. In India, wetlands are regulated under the Wetlands (Conservation and Management) Rules, 2017. A PIB backgrounder notes that nearly 90% of the world's wetlands have been degraded since the 1700s.
Limit: a wetland's filtering capacity is finite. Overloading it with nutrients causes eutrophication, and the wetland can become a pollution source.
In the news
On World Wetlands Day, 2 February 2022, the Environment Ministry added Khijadia (Gujarat) and Bakhira (Uttar Pradesh) to the Ramsar list, taking India to 49 sites, and released the National Wetland Decadal Change Atlas. The 2022 theme was 'Wetlands Action for People and Nature'. This put wetland functions in the news months before the June 2022 Prelims.
NCERT Concepts to Revise
- Wetland: The question asks which wetland function fits an analogy, so start with what counts as a wetland.
- Ecosystem services: Each option describes an ecosystem service; the question asks which one matches the 'kidney' role.
- Ramsar Convention: Wetland functions are the basis of the Ramsar Convention's 'wise use' idea, often paired with this topic.
- Ramsar sites of India: New Indian Ramsar sites announced on World Wetlands Day 2022 put wetlands in the news that year.