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Effect of Land Use Patterns on Runoff, Sediment Yield, and Pesticide Loading in Selected Microcatchments in Manupali Watershed, Lantapan, Bukidnon, Philippines
Thesis Abstract:
A study on the effect and relationship of land use patterns on runoff (average, peak,
and volume), sediment yield, and pesticide loading on a watershed scale was conducted on four selected upland microcatchments in Manupali Watershed in Lantapan, Bukidnon. Land use pattern was monitored based on land use (percentage cultivated area) and land treatment (percentage conserved area). The hydrometeorological data were monitored from January to December 2004. The runoff, sediment, and pesticide transport were measured using weir, graduated staff gauges, digital flow meter, and depth-integrating sediment sampler. The climatic data was monitored monthly from an automatic weather station at the study site. Information on tillage practices and pesticide use were gathered using the questionnaire-interview method with farmers as respondents. The variables were analyzed using F-test analysis of variance (ANOVA) and Duncan multiple range test (DMRT) at α = 0.05.
During the study period, the weekly average runoff (Qave), peak runoff (Qpeak), and runoff volume (Vq) per unit area of the catchments ranged from 0.0407 to 0.0512 lps/ha, 0.2531 to 0.3520 lps/ha, and 27.69 to 35.41 m3/ha, respectively. The range of mean weekly sediment yield was from 0.0089 to 0.0466 ton/ha while weekly pesticide loading ranged from 0.0031 to 0.0959 μg/s/ha.
Statistical analysis showed that on a per unit area basis, runoff variables (Qave, Qpeak, and Vq) were found to be not significantly different among the catchments while sediment yield and pesticide loading were significantly different between Kiluya and Kalainigon catchments. Results of statistical analysis also showed that runoff, sediment yield, and pesticide loading were directly proportional to the percentage cultivated area and inversely proportional to the percentage conserved area indicating that an increase in land use leads to the increase in runoff, soil erosion, and pesticide transport while increase in percentage conserved area lessens the detrimental effects of such variables.
Among the independent variables (rainfall, rainfall intensity, average runoff, cultivated area, and conserved area), rainfall was found to have the greatest contribution in runoff with partial R2 ranging from 0.206 (in Kiluya 2) to 0.830 (in Kalainigon 1), while average runoff had the greatest contribution on sediment yield with partial R2 ranging from 0.334 (in Kalainigon 1) to 0.692 (in Kalainigon 2). Moreover, the percentage cultivated area exhibited greater contribution on runoff, sediment yield, and pesticide loading than percentage conserved area as shown by its higher partial R2.
The prediction equations for the runoff, sediment yield, and pesticide concentration proved to be highly acceptable with model R2 ranging from 0.818 (in Kiluya 2) to 0.964 (in Kalainigon 2). Thus, the generated equations could be used for future prediction and estimation of runoff, sediment yield, and pesticide loading.