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Erosion, Sediment Yield and Water Quality Assessment in a Subwatershed of Taal Lake, Philippines
Dissertation Abstract:
The study was conducted to assess the erosion-sedimentation system and its water quality implications in a sub-watershed of Taal Lake, Philippines.
Sheet and rill erosion from the 200-hectare Angasin watershed was estimated using a modified Universal Soil Loss Equation. The average and total soil losses were 45.72 tons/ha/yr and 9,144.61 tons/yr, respectively. Among the three types of land cover and for all slope ranges, soil loss per unit area was found highest from areas under diversified cropping followed by shrub lands. The least was from coconut areas.
Based on suspended load measurements conducted from July 1999 to July 2000, the suspended sediment yield of the Angasin River was estimated at 37.88 tons/ha/yr. The relation between sediment concentration in mg/L (Cs) and discharge in L/s (Q) was found highly significant (Cs = 0.0056Q2.1182, R2 = 0.732). The derived relation between sediment discharge in kg/hr (qs) and Q was expressed as qs = 0.00002Q 3.1182 with R2 = 0.8555.
Water quality sampling conducted during the same period revealed that temperature, total suspended solids, total dissolved solids, electrical conductivity, and iron concentration were statistically higher during the wet season; pH was found significantly higher during the dry season. In general, water quality deteriorated toward the downstream portion of the river.
Sedimentation is known to affect the quality of receiving waters. Cs was found to significantly affect turbidity and iron concentration (both quadratic), phosphate concentration (geometric), and nitrate concentration (linear).