Nutrient transport from various agricultural sources in the Pagsanjan-Lumban watershed in Laguna de Bay, Philippines

摘要

The off-site transport of nutrients can have detrimental effects on waterways hence this study was conducted to monitor the sources and quantify the amount and form of transported nutrients in order to identify strategies that can minimise their impact. Four sites representing various land uses were selected and installed with automated water samplers and Odyssey water level loggers to measure water flow. Total suspended solids (TSS), total Kjeldahl nitrogen (TKN) and total phosphorus (TP) were determined in both unfiltered and filtered (<1.2 mu m) samples. Agriculture is the major source of nitrogen (N) and phosphorus (P) transported in the Pagsanjan-Lumban watershed and the dominant land use upstream of the sampling sites greatly influenced the parameters measured. The effluent from the piggery farm had the highest TSS, TKN and TP concentrations. Among the cropped lands, higher concentrations of suspended sediments and nutrients were found in Pagsanjan (rice site). A positive linear relationshipbetween TSS and TKN was noted in Pagsanjan and Lumban (vegetable site). The colloidal fraction dominated the transport process of N and P in the same sites. Nitrogen transport in Cavinti was mostly colloidal (>1.2 mu m)-bound, although in some instancesthe soluble (<1.2 mu m) fraction dominated. In Majayjay (piggery site), the soluble fraction dominated P transport.