Sediment and nutrient export by water from an agricultural catchment: An analysis of hysteresis patterns in the Upper Relau River, Penang

Eksport Sedimen dan Nutrien dari Kawasan Tadahan Pertanian: Satu Analisis Pola Histeresis di Ulu Sungai Relau, Pulau Pinang

Abstract

A small drainage basin (0.5 km2) was selected on the Relau hill to evaluate sediment and nutrient export. Stream flow gauging, water depth and gulp water samples were collected manually on a weekly basis between November 2001 to October 2002 with additional gauging and water samples taken during storm events. The concentrations of sediment and nutrient were analysed to determine the quality of the river water and the health of the catchment. The highest
suspended sediment concentrations and nutrients concentration in upper Relau catchment are, in most cases, associated with periods of high discharge during the monitoring period. Hysteresis relationships between SSC, NO3-N, TN, orthophosphate and TP concentration with discharge (Q) shows some form of pattern of variation during the monitoring period. The hysteresis approach was used to identify the sources of SSC, NO3-N and orthophosphate in streams. The findings from this study are common to most drainage systems having seasonal bimodal discharge. We describe the mechanisms of SSC, NO3-N and orthophosphate, TN and TP concentrations generation with discharge magnitudes, highlighting the importance of storm events in the transportation of pollutants from this small hill-land catchment where agriculture is the dominant land use.

Satu penilaian eksport sedimen dan nutrien telah dijalankan di satu kawasan tadahan kecil (0.5 km2) di atas bukit Relau. Pengukuran aliran sungai, kedalaman, dan sampel air dikutip secara manual setiap minggu antara November 2001 dan Oktober 2002 dengan sampel air dan pengukuran semasa musim ribut. Kepekatan sedimen dan nutrien dianalisis untuk menentukan kualiti air sungai dan kesihatan kawasan tadahan. Kepekatan sedimen dan nutrien yang paling tinggi di Ulu Sg. Relau dalam banyak kes ialah berkait dengan kadar luahan tinggi sepanjang masa pemonitoran. Pertalian histeresis antara SSC, NO3-N, TN, ortofosfat dan TP dengan luahan (Q) mempamerkan beberapa bentuk pertalian sepanjang masa pemonitoran. Pendekatan histeresis digunakan untuk menentukan sumber pencemar sediment (SSC), NO3-N, dan ortofosfat di dalam sungai. Dapatan kajian ini adalah hampir serupa dengan dapatan lain yang mengalami luahan bermusim dwi-mod. Kami menjelaskan mekanisme penjanaan kepekatan sedimen (SSC), NO3-N, ortofosfat, TN dan TP dengan perubahan magnitud luahan, dan menunjukkan kepentingan kejadian hujan ribut dalam mengangkut bahan pencemar dari kawasan tadahan kecil ini yang didominasi oleh pertanian.