Inland Waters
Aquatic Environments
Inland Waters
Of all the water in the world, a mere 2.5% is fresh water. Most fresh water is contained in polar ice caps, or stored underground in aquifers and soil moisture, leaving only 0.01% of the world’s inland waters available as habitat for aquatic life. Yet a quarter of the world’s vertebrates and nearly half of its fishes live in these fragile “islands” of water—water that must also supply human needs for irrigation, drinking water, hydroelectric power, and waste disposal.
Inland waters are divided broadly into running-water, or lotic (L. lotus, action of washing) habitats, and standing-water, or lentic (L. lentus, slow) habitats. Lotic habitats follow a gradient from mountain brooks to streams and rivers. Brooks and streams with high-velocity water flow are high in dissolved oxygen because of their turbulence. Energy input is chiefly in the form of organic detritus washed from adjacent terrestrial areas. More slowly moving rivers have less dissolved oxygen and more floating algae and plants. Their fauna is tolerant of lower oxygen concentration.
Lentic habitats, such as ponds and lakes, tend to have still lower concentrations concentrations of oxygen, particularly in the deeper areas. Animals living on the bottom or on submerged vegetation (benthos) include snails and mussels, crustaceans, and a wide variety of insects. Many swimming forms, called nekton, are found in lakes and larger ponds. Depending on the nutrients available, a large contingent of small floating or weakly swimming plants and animals (plankton) may occur. Ponds and lakes have short lifespans— a few hundred to many thousands of years depending on size and rate of sedimentation—and undergo great physical change as they age. The Great Lakes of North America, which occupy depressions gouged out by the glacial advances of the Pleistocene epoch, became ice free about 5000 years ago.
Many freshwater habitats have been severely damaged by human pollution such as dumping of toxic industrial wastes and enormous quantities of sewage. Of the Great Lakes, Lake Erie has been the most seriously affected by the inflow of large amounts of nitrates and phosphates. These nutrients fertilize the lake, creating huge blooms of algae that die and sink to the bottom to decompose and rob the lake of oxygen. As a result, all levels of aquatic life are adversely affected.
Inland Waters
Of all the water in the world, a mere 2.5% is fresh water. Most fresh water is contained in polar ice caps, or stored underground in aquifers and soil moisture, leaving only 0.01% of the world’s inland waters available as habitat for aquatic life. Yet a quarter of the world’s vertebrates and nearly half of its fishes live in these fragile “islands” of water—water that must also supply human needs for irrigation, drinking water, hydroelectric power, and waste disposal.
Inland waters are divided broadly into running-water, or lotic (L. lotus, action of washing) habitats, and standing-water, or lentic (L. lentus, slow) habitats. Lotic habitats follow a gradient from mountain brooks to streams and rivers. Brooks and streams with high-velocity water flow are high in dissolved oxygen because of their turbulence. Energy input is chiefly in the form of organic detritus washed from adjacent terrestrial areas. More slowly moving rivers have less dissolved oxygen and more floating algae and plants. Their fauna is tolerant of lower oxygen concentration.
Lentic habitats, such as ponds and lakes, tend to have still lower concentrations concentrations of oxygen, particularly in the deeper areas. Animals living on the bottom or on submerged vegetation (benthos) include snails and mussels, crustaceans, and a wide variety of insects. Many swimming forms, called nekton, are found in lakes and larger ponds. Depending on the nutrients available, a large contingent of small floating or weakly swimming plants and animals (plankton) may occur. Ponds and lakes have short lifespans— a few hundred to many thousands of years depending on size and rate of sedimentation—and undergo great physical change as they age. The Great Lakes of North America, which occupy depressions gouged out by the glacial advances of the Pleistocene epoch, became ice free about 5000 years ago.
Many freshwater habitats have been severely damaged by human pollution such as dumping of toxic industrial wastes and enormous quantities of sewage. Of the Great Lakes, Lake Erie has been the most seriously affected by the inflow of large amounts of nitrates and phosphates. These nutrients fertilize the lake, creating huge blooms of algae that die and sink to the bottom to decompose and rob the lake of oxygen. As a result, all levels of aquatic life are adversely affected.
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