Review of water quality monitoring programme and water quality index (WQI) for inland waters of Hong Kong

Abstract

Hong Kong has over 200 of rivers, streams and open channels, forming parts of inland water resources. The Environmental Protection Department (EPD) conducts regular water quality monitoring programme, in order to obtain long-term data for improving and maintaining water quality in rivers and streams. Water Quality Index (WQI) is a tool used by EPD to transform complex scientific data into easy and understandable water quality information to the general public. The Existing Water Quality Index (EWQI) in Hong Kong was developed by integrating three parameters: Dissolved Oxygen (DO), 5-days Biochemical Oxygen Demand (BOD5) and ammonia-nitrogen (NH3-N). EWQI and water monitoring programme for river waters in Hong Kong has been set up and used since the mid-1980s. The purpose of this study is to review the river monitoring programme and EWQI in Hong Kong. A Proposed Water Quality Index (PWQI) is suggested. It is derived from Canadian Council of Ministers of the Environment Water Quality Index (CCME WQI), to include 7 parameters: E. coli, pH, suspended solids, DO, BOD5, Chemical Oxygen Demand (COD) and NH3-N (or unionized ammoniacal nitrogen (UIA-N)) and incorporate the Water Quality Objectives (WQOs) into the calculation. 17 EPD’s river monitoring stations in 10 rivers were studied to compare PWQI with EWQI. In general, both PWQI and EWQI provide similar water quality trends. PWQI produces worse water quality classification rank. It is mainly due to the deviation of exceedances of E. coli from its WQO as E. coli is a determining parameter in PWQI. Recommendations to improve EWQI and river water quality monitoring programme are suggested such as inclusion of ecological parameters, extension of the existing monitoring network to the rivers in Mirs Bay Water Control Zone (WCZ) and establishing a set of WQOs for ecological sensitive areas. It is recommended that a more comprehensive water quality index should be used by increasing the numbers of parameters in the (EWQI) and refining the calculation methods relate to WQOs.