WETLANDS SUCH AS RIVERS, LAKES, MARSHES, SWAMPS,SWAMP WOODLANDS, MANGROVES AND SHALLOW WATER ESTUARINE AND MARINE AREAS ARE AMONG THE MOST PRODUCTIVE HABITATS IN THE WORLD. THESE ECOSYSTEMS ARE THE PRIME TARGETS FOR HUMAN INTERFERENCE IN BUILDING RESERVOIRS AND HYDROELECTRIC DAMS, OR THEY ARE DRAINED FOR AGRICULTURAL ACTIVITIES AND FOR URBANIZATION OR FOR DEVELOPING HARBOURS AND MINING.
IN THE PHILIPPINES, MARI CULTURE WAS RESPONSIBLE FOR 80 PER CENT OF THE SUBSTANTIAL LOSS OF MANGROVES BETWEEN 1952 AND 1997;IN THAILAND THE MANGROVE AREA HAS DIMINISHED BY MORE THAN 40 PER CENT. IN OTHER PLACES CUTTING OF MANGROVE POLES AND RECLAMATION FOR URBAN OR INDUSTRIAL USES HAVE BEEN SIGNIFICANT. THE SUNDERBANS FOREST OF INDIA AND BANGLADESH ARE DECLINING DUE TO CONSTRUCTION OF IRRIGATION PROJECTS,BARRAGES AND OTHER USES OF THE FRESH WATERS OF GANGES. SIMILAR EXAMPLES IN MANY PARTS OF THE DEVELOPING WORLD HAS RESULTED IN SERIOUS CONSEQUENCES AS MANGROVE HABITATS PROTECT THE COASTS FROM STORM SURGES AND ARE ALSO MAJOR FISH NURSERIES.CLEAR FELLING ON A LARGE SCALE IS A MAJOR THREAT TO THE MANGROVES THROUGHOUT THE TROPICS. THIS BRINGS CONSEQUENCES RISK TO COASTLINES WHICH WILL BE AGGRAVATED IF SEA LEVEL RISES. DESPITE THE IMPORTANCE OF GOODS AND SERVICES WHICH WETLANDS PROVIDE THEY ARE CONSIDERED AS A HINDRANCE TO DEVELOPMENT. THEY LOST OR ALTERED BECAUSE OF THE DISRUPTION OF NATURAL PROCESS BY AGRICULTURAL INTESIFICATION , URBANIZATION, POLLUTION, DAM CONSTRUCTION, REGIONAL WATER TRANSFERS AND OTHER FORMS OF INTERVENTION IN THE ECOLOGICAL AND HYDROLOGICAL SYSTEM.
ENGINEERING THE LANDSCAPE HAS GREATLY DISRUPTED THE EARTH'S BALANCE. THE EARTH CONTAINS A HUGE RANGE OF MINERAL TREASURES SUCH AS COAL, OIL, URANIUM, IRON, ALUMINIUM ,RAW, MATERIALS FOR CONCRETE AND GLASS, ALL HAVE TO BE EXTRACTED FROM THE EARTH. MINING SPELLS DISASTER FOR THE SURROUNDING HABITAT, HUMANS AND MACHINES FELL TREES AND TEAR OPEN THE LAND USUALLY CAUSING LONG TERM DAMAGE. HUGE GAPING HOLES ARE DUG INTO THE GROUND' DISFIGURING THE LANDSCAPE FOR MANY YEARS. THE SURROUNDING AREA BECOMES DOTTED WITH UNSIGHTLY SLAG HEAPS, ARTIFICIAL HILLS MADE OF MUD AND CRUMBLING STONE.
IN SOUTH AND CENTRAL AMERICA THE RAIN FORESTS ARE BEING BURNED DOWN TO CREATE VAST CATTLE RANCHES. THIS IS GOING TO RESULT IN SOIL EROSION CAUSED BY HEAVY RAINS. EXPERTS BELIEVE THAT WITHIN 10 YEARS, NOT EVEN GRASS WILL GROW WHERE GIANT TREES ONCE STOOD. MANY SCIENTISTS FEAR THAT HUGE AREAS THAT HAVE ALREADY BEEN CLEARED WILL NEVER REGROW. THE AREA COULD BECOME A DESERT. THESE FORESTS CONTAIN HUGE MASSES OF PHOTOSYNTHETIC VEGETATION AND THEY RECYCLE THOUSANDS OF TONS OF CARBON DIOXIDE AND OXYGEN EVERY DAY. OVER 75 PER CENT OF THE RAIN THAT FALLS ON THESE FORESTS IS RETURNED TO THE ATMOSPHERE THROUGH EVAPO-TRANSPIRATION. PRESERVING THESE FORESTS IS NOT ONLY IMPORTANT FOR THE EARTH'S ECOLOGICAL BALANCE BUT ALSO FOR SAVING LIFE ON THE EARTH.
OVER FISHING AND EXCESSIVE HARVESTING OF WHALES, DOLPHINS, SEALS AND POLAR BEARS IS ONE OF THE CLEAREST EXAMPLES OF OVER-EXPLOITATION OF MARINE RESOURCES. MODERN FISHING METHODS ARE EXTREMELY EFFICIENT AND HARVESTING THE SEA IS NOW AS MECHANIZED AS HARVESTING THE LAND. THE CROP OF THE WILD FISHES IS ON THE DECLINE DUE TO OVER-FISHING, MOST OF THE FISH WE EAT COMES FROM FISH FARMS. TRAWLING AND SEINING ARE TWO MOST IMPORTANT FISHING TECHNIQUES. FISH ARE PURSUED OFTEN BY MEANS OF ECHO-LOCATION EQUIPMENT. A TAWL NET MAY BE DRAWN BY ONE OR TWO SHIPS. SINCE . SINCE, BOTH PELAGIC AND DEMERSAL FISH ARE CAUGHT BY TRAWLERS HUGE QUANTITIES ARE HARVESTED. OVER-FISHING IS NOT ONLY ABOUT NUMBERS OF FISH BUT CATCHING TOO MANY SMALL(YOUNG) FISH CAUSES THE POPULATION AS A HOLE TO DECLINE THUS UPSETTING THE BALANCE.
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