Increased concentrations of phosphates and nitrates from industries, residential wastes as well as from agricultural run off water into the water bodies result in excessive growth of algae which form a mat on the surface of water. This phenomenon is called algal bloom or eutrophication.
It affects the ecosystem in following ways:
(i) It decreases light penetration thus affecting photosynthesis.
(ii)  It result in depletion of dissolved oxygen resulting in death of  aquatic life.
(iii) Nitrates contaminate drinking water leading to decrease in  oxygen capacity of haemoglobin in human beings.

The species that inhabit polluted water in highest concentration

Ecological role of biodiversity:
1. Biodiversity provides plant pollinators, predators, decomposers and contributed to soil fertility.
2. It helps in the purification of air and water, management of flood, drought and other environmental disasters.
3. Ecosystems with more diversity can withstand the environmental challenges better because genetically diverse species present in the ecosystem will have different tolerance ranges for a given environmental stress, hence they cannot be easily eliminated by any single stress at a time. However, if the ecosystem contains only few species, it will become a fragile or unstable ecosystem.
4. The species with high genetic diversity and the ecosystem with high biodiversity have greater capacity for adaptation against environmental perturbations.

Sacred groves are found in
(i) Khasi and Jaintia Hills in Meghalaya
(ii) Aravalli Hills of Rajasthan.
(iii) Western Ghat regions in Karnataka and Maharashtra
(iv) Sarguja, chanda and bastar areas of mathaya pradesh.

(i) Species richness
(ii) Species eveness ( in distribution) are the two measures of species diversity.

The human activities like deforestation, over-cultivation, unrestricted grazing, poor irrigation practices, result in arid patches of land (deforestation). When these large barren patches extend and remain unattended for long, a desert is created. Because the formation of fertile top layer of soil takes millions of years, desertification easily takes over.

Biomagnification or biological magnification.

Photochemical smog is grey or yellowish brown, opaque smog formed at high temperature over cities and towns due to still air, emission of nitrogen oxides and volatile hydrocarbons from automobile exhausts and solar energy.It contains secondary pollutants. It is having oxidizing environment.

1. The world summit on sustainable development was held in 2002, in Johannesburg, south Africa.
2. 190 countries signed the convention.
3. Its objective was achive by 2010, a significant reduction in the current rate of biodiversity loss at global, regional and local levels.

Co-extinction is a phenomenon in which when a species becomes extinct, the plant and animal species associated with it, in an obligatory manner, also become extinct.
e.g. (i) In case of a co-evolved plant and its pollinator, if one of them becomes extinct, invariably the other one becomes extinct.
(ii) If a host fish becomes extinct, the unique parasites depending on it would also become extinct.
The three other causes are:
(i) Habitat loss and fragmentation
(ii) Over-exploitation and
(iii) Invasion of alien species

Uses of biodiversity.
1. As source of food and improved varieties.
2. As source of drugs and medicines.
3. Aesthetic and cultural benefits.
Examples of aesthetic rewards include ecotourism, bird watching, wildlife, pet keeping, gardening, etc. Throughout human history, people have related biodiversity to the very existence of human race through cultural and religious beliefs.
4. Biodiversity is essential for the maintenance and sustainable utilization of goods and services from ecological system as well as from individual species.

Species-Area Relationship
1. Alexander Von Humboldt has observed that within a region, species richness increases with increased explored area, but only upto a limit.
2. The relationship between species richness and area for a number of taxa like angiospermic plants, freshwater fishes and birds is found to be a rectangular hyperbola.
3. On a log scale, the relationship becomes linear (straight line) and is described by the equation:
log S = log C + Z log A, where
S = Species Richness
Z = Slope of the line (regression coefficient)
A = Area and C = Y - intercept
4. Ecologists have found that the value of Z-line ranges between 0.1 and 0.2 irrespective of the taxonomic group of the region.
5. But in very large areas, like a continent, the Z value ranges between 0.6 and 1.2 and indicate species richness.