SHAIJU

Water pollution
Water pollution has many sources and characteristics. Humans and other organisms produce bodily wastes which enter rivers, lakes, oceans and other surface waters; in high concentrations these wastes result in bacterial contamination and excessive nutrient loading (eutrophication). Industries discharge a variety of compounds such as heavy metals, and wastewater, sometimes in toxic concentrations, from industrial processes that may also be too hot or too low in dissolved oxygen to support life. Silt-bearing runoff from construction sites and farms can inhibit the penetration of sunlight through the water column, hampering water organisms in their ability to photosynthesize.
Groundwater pollution is much more difficult to clean up than surface pollution because groundwater can move hundreds of miles through unseen aquifers. Porous, fine-grained aquifers such as sands and sandstones naturally purify water of bacteria by simple filtration (adsorption and absorption), dilution, and, to lesser extent, chemical reactions and biological activity. Groundwater that moves through cracks and caverns is not filtered and can be polluted just as easily as surface water. In fact this can be aggravated by the human tendency to use sinkholes in areas of Karst topography as dumps.
1.Causes
Pumping of highly toxic (dark black) sludge, much seeps back into the ocean in the form of tiny particlesThe causes of water pollution can be divided into two groups: anthropogenic sources of pollution are those due to human choices, and natural sources are those resulting from forces intrinsic to the environment.

Anthropogenic sources include:
discharge of poorly-treated or untreated sewage;
runoff from construction sites, farms, or paved and other impervious surfaces e.g. silt
discharge of contaminated and/or heated water used for industrial processes
acid rain caused by industrial discharge of sulfur dioxide (by burning high-sulfur fossil fuels)
excess nutrients added by runoff containing large amounts of detergents or fertilizers

Natural sources include:
seasonal turnover of lakes and embayments;
siltation due to floods;
eutrophication of lakes due to seasonal changes
acid rain caused by natural volcanic discharges or smog from factories
acid pollution of rivers and lakes by runoff from naturally acid soils
carbon dioxide discharges and runoff, volcanic or mineral
Contaminants
Contaminants may include organic and inorganic substances. Some organic water pollutants include:
bacteria,that is from sewage or livestock operations;
fertilizers, in runoff from agricultural fields or forestry;
food processing waste;
tree and brush debris from logging operations
Inorganic pollutants include:

metals
acid mine drainage
acid rain caused by industrial or volcanic discharges
acid pollution of lakes by runoff from acid soils
carbon dioxide discharges and runoff, volcanic or mineral
chemical waste industrial byproducts
silt in stormwater runoff from cleared land

2.Consequences
Mercury in zooplankton (copepods) in the open ocean off New York and Atlantic City USA New Jersey
Oxygen depletion in the open oceanThe toxic chemicals and particles are carried out by the rivers into the ocean. In some areas of the world the influence can be traced hundred miles from the mouth, like in front of the Hudson river. As indicator filter feeding animals are used by the oceanographers, like copepods in the map of New York Bight. The highest toxin loads are not directly in front off New York but 100 km South, because it takes a few days to be incorporated in the tissue of the plankton. The Hudson water flows south along the coast due to the coriolis force. The second map shows areas of oxygen depletion, caused by chemicals using up oxygen and by heavy algae blooms, caused by too much nutrients, when the cells die, sink and decompose. Heavy fish and shellfish kills have been reported. The toxins make their way up the foodchain when small fish eat the copepods, then large fish, each step concentrating up ca. 10 times.