(a) Give a brief account of sources of groundwater pollution in India and discuss the management of groundwater resources. (20…

(a) Groundwater pollution in India and management of groundwater

Groundwater pollution is the contamination of aquifers that makes water unfit for use.

Natural (geogenic) sources: fluoride from fluoride-bearing minerals, serious in Rajasthan, Andhra Pradesh, Telangana, Karnataka and Gujarat; arsenic in the Ganga–Brahmaputra plains of West Bengal, Bihar, Uttar Pradesh and Assam; iron in the North-East and coast; uranium in Punjab and Haryana; and salinity in arid areas.

Human sources: nitrate and pesticides from heavy fertiliser use in Punjab and Haryana; untreated industrial effluent, as in Patancheru, Vapi and Ludhiana; sewage, leaking septic tanks and unlined landfills, whose leachate enters aquifers; mining effluents and acid mine drainage; leaking fuel tanks; and seawater intrusion in coastal aquifers (Gujarat, Tamil Nadu) caused by over-pumping.

Management:

• Monitoring through the Central Ground Water Board network and quality mapping, with aquifer mapping (NAQUIM) as a base for plans.
• Control of pollution at source: effluent treatment, sewage treatment, lined landfills, and Water and Environment Protection Acts, with regulation of extraction by the Central Ground Water Authority.
• Artificial recharge and rainwater harvesting to dilute contamination and raise levels.
• Demand management: micro-irrigation, crop change, efficient use, conjunctive use of surface water and groundwater, and the Atal Bhujal Yojana with community management.
• Treatment of contaminated water: community arsenic and fluoride removal plants, and safe-water supply through Jal Jeevan Mission.

(b) Microfossils and their use in petroleum exploration

Microfossils are fossils of microscopic size, studied only under a microscope: foraminifera, ostracods, radiolaria, calcareous nannofossils, diatoms, conodonts and pollen and spores (palynomorphs).

Application in petroleum exploration:

• Drilling produces only small cuttings and cores, which would crush larger fossils; microfossils survive them in large numbers.
• They give the age and allow correlation of subsurface beds between wells (biostratigraphy), so the extent of source, reservoir and cap rocks can be traced.
• They show the environment of deposition and water depth (benthic foraminifera, ostracods), which helps to find reservoir sandstones, and reefs and shelf margins.
• Colour change of spores and conodonts shows the thermal maturity of source rocks, thus whether oil or gas has been generated.
• They help in sequence stratigraphy and in identifying unconformities, and in wellsite decisions on when to stop drilling. Their use has been important in Indian basins such as Cambay, Bombay High and Assam.

(c) Mass extinctions and the Permian–Triassic event

A mass extinction is a short geological interval in which a very large share of species (over about 75 per cent) vanishes worldwide. The "Big Five" are the end-Ordovician, Late Devonian, end-Permian, end-Triassic and end-Cretaceous.

The Permian–Triassic extinction (about 252 million years ago) was the greatest, removing roughly 90 per cent of marine species and a large share of land animals.

Hypotheses for its cause:

• Volcanism: eruption of the Siberian Traps released huge amounts of carbon dioxide, sulphur dioxide and halogens, causing global warming, acid rain and ocean acidification. This is the leading hypothesis.
• Ocean anoxia and euxinia, with hydrogen sulphide poisoning, from warming and stagnation.
• Release of methane from hydrates and burning of coal and organic-rich rocks, adding to warming.
• Fall in sea level and loss of shelf habitat as Pangaea assembled, with extreme continental climates.
• Asteroid impact, proposed but not well supported. Most researchers favour a combination, driven by the Siberian eruptions.