Influence of watershed physiography on water qualities in conservation areas
1993
Auayporn Sangtian
Influence of watershed physiography on water qualities were carried out in 17 watersheds. Stream-water granitic watersheds have higher dissolved oxygen, phosphate-phos-phorous, potassium and total coliform, the sandstone watersheds produce higher dissolved oxygen, color, turbidity, pH, nitrate-nitrogen and fecal coliform. While limestone watersheds yield higher temperature, electrical conductivity and total solids. Most of water qualities are, however, within the water surface water standard level, except the color for sandstone, the electrical conductivity of water for limestone watershed and total coliform for all watersheds. The watershed physiography have effect on water temperature, pH, phosphate-phosphorus and potassium content. The effect of forest area on water color is accounted for 33.35 %, turbidity 28.81 % and nitrate-nitrogen 26.77 %. The stream density has 36.71 % effect on dissolved oxygen. The drainage density has 44.61 % effect on total solids and 51.75 % on electrical conductivity. The drainage density and the stream density have effects on electrical conductivity 62.06 % and on total solid 55.64 %. Other factors have no effect on water quality. Water qualities from conservation area are still in the standard of surface water. However, some of them are under standard. In order to control all values within the standard, it should have the policy to control and management of conservation area. Especially for limestone and sandstone watersheds, chemical solutions and suspended substances should be controlled. For head watersheds area, soil and water conservation should be practiced together with reforestation and pretreatment of stream water should be done before using.
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