Eutrophication is often seen in [2011]

Biochemical Oxygen Demand (BOD) in a river water [2009]

DDT residues are rapidly passed through food chain causing biomagnifications because DDT is [2009]

A lake near a village suffered heavy mortality of fishes within a few days. Consider the following reasons for this? [2008]
(1) Lots of urea and phosphate fertilizer were used in the crops in the vicinity
(2) The area was sprayed with DDT by an aircraft
(3) The lake water turned green and stinky
(4) Phytoplankton populations in the lake declined initially thereby greatly reducing photosynthesis.
Which two of the above were the main causes of fish mortality in the lake?

In which one of the following the BOD (Biochemical Oxygen Demand) of sewage (s), distillery effluent (DE), paper mill effluent (PE) and sugar mill effluent (SE) have been arranged in ascending order ? [2007]

Which one of the following is not a bio-indicator of water pollution? [2007]

Limit of BOD prescribed by Central Pollution Control Board for the discharge of industrial and municipal waste waters into natural surface waters, is [2006]

Prolonged liberal irrigation of agricultural fields is likely to create the problem of [2005]

Which of the following is not used for disinfection of drinking water? [2005]

More than 70% of world’s freshwater is contained in: [2005]