ASSESSING THE EFFECTS OF LAND USE CONVERSION ON RUNOFF AND NUTRIENT LOAD

Abstract

An agricultural land with intensive cultivation, large catchments with extended rivers and agricultural population of high-density are the primary reasons for higher pollutant loads in freshwater. However, there are problems in pursuing nutrient losses since several parameters, such as variability in soils and climate are associated with heavy rainfall, especially in tropic regions; plant management, limited resources, and insufficient technical support are not consistent in every crop management. Changes in agricultural practices and unmonitored point sources discharge from watershed, have led to algal bloom in abundance, and thus generated eutrophication at the downstream. The complex watershed processes and forecasting the effects of land use change on water quality can be determined by using tools of watershed models. The Hydrological Simulation Programme-FORTRAN (HSPF) uses lumped parameters, continuous model to predict the long-term evaluation, and deterministic for simulating the water quality and quantity process that occur at the watershed. Pervious land segments (PERLND), impervious land segments (IMPLND), and channel reach (RCHRES) modules were used to determine the general water quality and quantity on Johor watershed. Based on calibration and validation, the HSPF model was capable of simulating different runoff seasons. An increment of 60% in agricultural land had increased the annual mean total phosphorus (TP) load and total nitrogen (TN) load by 3.82% and 5.34%, respectively. A 2-fold increase in agricultural land would result in an approximately 2-fold increase in the quantity of annual TN and TP loads. Between TN and TP loads, TP load has potentially increased more than TN load during the dry, wet, and base-flow years. Upon the long-term of water quality and quantity simulation, this study provides essential knowledge for a method-based runoff and nutrient management plan for the Johor watershed.