Marine pollution can be defined as the introduction
of substances to the marine environment
directly or indirectly by man resulting in
adverse effects such as hazards to human health,
obstruction of marine activities and
lowering the quality of sea water.
The most obvious inputs of waste is through pipes directly discharging wastes into the sea . Very often municipal waste and sewage from residences and hotels in coastal towns are directly discharged into the sea.
Pesticides and fertilizers from agriculture which are washed off the land by rain, enter water courses and eventually reach the sea.
Petroleum and oils washed off from the roads enter the stormwater overflows carry these materials into rivers and eventually into the seas.
Ship accidents and accidental spillages of oil, pesticides, industrial chemicals, etc. in huge quantities at sea therefore can be very damaging to the marine environment.
Offshore oil exploration and extraction also pollute the seawater to a large extent.
Dry docking : All ships periodic dry docking servicing; cleaning the hulls etc. during this period when cargo compartments are emptied, residual oil goes into sea.
Deep sea mining is a relatively new mineral retrieval process that takes place on the ocean floor . Ocean mining sites are usually done at about 1,400 - 3,700
meters below the ocean’s surface. The vents create sulfide deposits, which contain precious metals such as silver, gold, copper, manganese, cobalt, and zinc.
These raises questions about environment damage to surrounding areas. Removal of parts of the sea floor will result in disturbances to the benthic layer, and habitat of benthic organisms.
Beside from direct impact of mining the area, leakage, spills and corrosion would alter the mining area’s chemical makeup.
Effects of Marine Pollution
Apart from causing Eutrophication a large amount of organic wastes can also result in the development of red tides . These are phytoplankton blooms of such intensity that the area is discolored.
Many important commercially important marine species are also killed due to clogging of gills or other structures.
When liquid oil is spilled on the sea it spreads over the surface of the water to form a thin film called an oil slick.
Oil slicks damage marine life to a large extent.
Salt marshes, mangrove swamps are likely to
trap oil and the plants, which form the basis for
these ecosystems thus suffer.
For salt marsh plants, oil slicks can affect the flowering, fruiting and germination.
Oil is also harmful for sea birds and fishes - clogging of gills and other structures
The most important commercial damage can however also come from tainting which imparts an unpleasant flavour to fish and seafood and is detectable at extremely low levels of contamination. This reduces the market value of seafood.
Control measures of marine pollution
1) Introduction of sewage treatment plants to reduce BOD of final product before discharging into sea.
2) Cleaning oil from surface waters and contaminated beaches can be accelerated
through the use of chemical dispersants which can be sprayed on the oil.
3) Load on top system reduce oil pollution cleaned with high pressures jets of water .