Mathematics Modelling of Nitrogen Mass Balance at the Rembangan River with Plug flow System Approach Using Finite Difference Methods

Abstract

Fertilization of nitrogen for the crop has purpose to optimized of crop farm and minimized damage of environment, actually most additions of nitrogen caused releasing of nitrate. Nitrate from nitrogen compound able to release passing the ground water. Contaminated of nitrate at the river water made the river water became very underprivileged of oxygen ( hypoxic) and depressed life of biota river water at the downstream area. Aim the research was to know mass balance of nitrogen at the Rembangan river affected from input run off which entered into the river that contained waste from nitrogen fertilization. This research was built nitrogen mass balance model using Plug Flow System equation with Streeter-Phelps equation approach. This equation was finished by mathematics modelling finite difference method with Leapfrog schema. Result this research was value of output model for nitrate concentration equal to 0,728 mg/litre, but actually in the case average concentration of nitrate was equal to 0,6723 mg/litre for before fertilization and 0,8307 mg/litre for after fertilization . Value of plug flow system mass balance modelling was equal to 1,66 mg/sec of nitrate that dissolved at the Rembangan river. This result was shown that contribution of nitrate compound at Rembangan river still could be categorized as good based on the Indonesian Government Regulation number 20 Year 1990 with a maximum standard parameter of nitrate was 5 mg/liter.