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Land-use and water quality : a GIS evaluation of the problems, interaction, and initiatives, in the Pampanga River Basin, Central Luzon, Philippines Mapili, Mariano Cadanilla


Agricultural activities in the Pampanga river Basin (PRB) are threatened by the increasing population and development thrusts of the Philippine government. This study was conducted to develop a framework by which problems, initiatives, and interactions among land-use changes, water quality and governance issues may be assessed employing Geographic Information Systems (GIS) techniques. Stream stations were sampled for nitrate, phosphate, temperature, dissolved oxygen, total dissolved solids, chemical oxygen demand and pH. Land-use changes were analyzed through GIS, while land-use planning was investigated through workshop participation and review of government plans. Agricultural land increased 0.6% annually from 1953 to 1980 due to conversion of grasslands, wetlands and forests to agriculture, and declined 0.5 % annually from 1980 to 1993 due to expansion of settlements. A provincial land-use plan would accelerate conversion rather than protect agricultural lands. Water quality in the Pampanga river and its tributaries is deteriorating in both the spatial and temporal dimensions. The eruption of Mt. Pinatubo was responsible for increased levels of ortho-phosphate, TDS, and temperature in streams, but the low DO during the start of the rainy season and the high nitrate-N concentrations are indicators of human influence on water quality. Streams with catchments having the same predominant land-use classification exhibited similar trends in water quality. Animal species in different area classifications also affected water quality at different flow periods. Buffer analysis on 500 metre zone along the streams gave best values. The effect of runoff is altered by the type of land-use, specifically the presence of rice fields. The management of nitrate-N based on a nitrogen budget revealed that animal manure and inorganic fertilizer are major sources of nitrogen in the basin. The hotspot areas are catchments with large settlement areas, and/or with a very high animal population. Alternative scenarios revealed no significant changes in water quality even with a three-fold increase in animal production or 10 % agricultural land conversion. A cautious optimism is anticipated in involving the barangay captains in the overall management of the environment, in particular, the control of stream pollution that endangers the fishing industry.

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