Short notes on ecosystem services and on the water cycle

The question asks for any two of the three notes. Notes (a) and (b) are answered.

(a) Ecosystem services

Meaning. Ecosystem services are the benefits people obtain from the working of ecosystems; they are the products of ecosystem processes, like the cleaning of air and water by a forest.

Kinds, as grouped in the DU syllabus:

• Provisioning services: goods taken directly from nature, such as fruit, fodder, firewood, timber, fish and medicinal plants.
• Regulating services: control of natural processes: climate moderation, flood control, pollination and pest control, and prevention of soil erosion.
• Cultural services: non-material benefits such as scientific study, bird-watching and ecotourism, and the religious value of rivers and sacred groves.
• Supporting services: the basic processes such as photosynthesis and nutrient cycling on which all the others depend.

Why they matter. Most of these services are free and unnoticed, so they are easily lost. Overuse and misuse of land and resources disturbs processes such as photosynthesis, climate control and erosion control. When the hills above a town are cleared, for example, the town loses both its fuelwood and its protection from landslides and floods.

(b) The water cycle

Meaning. The water cycle (hydrological cycle) is the endless movement of water between the land, the oceans and the atmosphere, driven by the sun's energy.

Steps

1. Evaporation and transpiration. The sun's heat turns water from seas, lakes, rivers and soil into water vapour, and plants release more vapour through their leaves.
2. Cloud formation. Being lighter than air, the vapour rises and forms clouds, which winds carry over long distances.
3. Condensation and precipitation. As the clouds rise higher, the vapour cools, condenses into droplets and falls as rain (or snow).
4. Run-off. Rainwater flows over the ground into rivers, or falls directly into the sea.
5. Infiltration. Part of the rain soaks into the ground and is stored underground as groundwater, which later feeds wells, springs and rivers.

Importance. The cycle supplies the rain that plants and animals need, refills rivers, lakes and aquifers, and spreads heat around the globe.

Human impact. Pollution that changes the atmosphere is altering rainfall patterns, bringing long droughts in some regions and floods in others. Paving over cities and cutting forests also reduce infiltration, so more water runs off quickly and less recharges the ground, as seen in the falling water tables of many Indian cities.