Watersheds
How Can A Watershed Become Un-Healthy?
If a part of a watershed or factory fails to function, the entire production begins to fail. A healthy watershed may fail from excess fine materials (sediment or silt), loss of riparian areas, channelization or straightening, blockage of fish passage, loss of water quality or quantity, and combined or cumulative effects.
Excess fine material smothers fish food organisms and incubating eggs, restricts vision, and may irritate fish gills. Fine materials come from damaged riparian areas and various community, mining, forestry, and road construction activities, which may waste topsoil. When riparian areas are damaged, siltation often increases and woody debris is lost, which causes a loss of escape and overwintering habitats. Disturbed riparian areas often include loss of wetlands and fish rearing habitat, birds and wildlife. It also means loss of connectivity between habitats in the watershed. Riparian areas may be lost because of some forestry practices, human use of streambanks, clearing streambank vegetation and many community activities.
Channelization and straightening mean loss of irregular, complex shoreline that provide overhanging banks and deep hiding pools for rearing and refuge habitat. Usually, riparian habitat is also lost and water velocity increases. Fish passage for some species or life stages may be hampered when water becomes faster or shallower. Channelization and straightening are often by-products of road building, mining activities, and community development.
Blockage of fish passage means isolation of parts of the watershed and the watershed becomes under utilized. Fish passage may be damaged by culverts that are poorly designed, improperly installed, or that fail to operate as well as by anything that may increase water velocity, such as channelization, culverts, or jetties. Man-made dams may have severe effects on fish passage, but beaver dams rarely are a complete blockage.
Poor water quality may cause direct mortality or it may have long-term sublethal effects. Water quality is lost when petroleum products or fertilizers are washed from community or industrial sites or when mine tailings leach into streams. Loss of water quantity (i.e., "instream flow") may affect all or part of a watershed fish factory through reduced water volume, which may eliminate part or all of a particular fish habitat; e.g., spawning, rearing, or passage. Instream flow may be lost by stream diversion; e.g., by mining or construction activities or by diverting water for community or industrial uses.
Community development often causes combined or cumulative watershed losses; e.g., parking lots may cover riparian wetlands and drain petroleum products and fine material to streams, streams may be straightened and woody debris removed, and communities often have many culverts, which can hinder fish passage. Rapid runoff from paved surfaces can disturb spawning gravels and displace juvenile fish during rainstorms. Straightened sections without woody debris provide no refuges. Runoff from communities is the greatest source of pollution in many areas.
If you would like more information concerning Watersheds, please email DFG.DSF.StreambankRehab@alaska.gov.