ABSTRACT

Water quality inversion model based on satellite images could provide a good complement for coastal hydro-environment monitoring in the Hong Kong waters. However, previous studies attempted to establish a single inversion model for expressing the whole Hong Kong waters without considering the regional differences of water properties. In this study, the whole Hong Kong waters is firstly divided into 6 clusters for the inspection of their respective water quality characteristics. The local models for a specific cluster are then developed and compared with the original single model results for the Hong Kong water quality analysis. It shows that the results obtained by the cluster-based local inversion models are comparable to or even better than those by the original single models, thereby providing a more effective tool for the coastal water quality management in Hong Kong.

INTRODUCTION

Water quality deteriorations including hypoxia, nutrient enrichment, and harmful algal blooms events have been a worldwide concerned issue since last century. The Hong Kong waters are also one of the areas that has been severely threatened by water degradation events (Deng et al., 2021; Kwong et al., 2022). Hong Kong is located in the estuary area where the Pearl River meets South China Sea. Specifically, the water state in the northwestern areas is mainly affected by the inflow of fresh water from the Pearl River, while the hydrodynamics in the east and south are largely influenced by ocean circulation. The spatial variability in hydrological and geographical conditions and in the intensity of anthropogenic activities in this area makes the distribution and evolutions of Water Quality (WQ) indicators even more elusive. In order to effectively monitor and control the water quality conditions, the Environmental Protection Department (EPD) of Hong Kong government has launched the marine water quality monitoring programme since 1986. In this programme, 24 biophysical and biochemical parameters (Fig. S1) are monthly collected from 76 in-situ stations and published at the website (https://cd.epic.epd.gov.hk/EPICRIVER/marine/?lang=en) for free access. In addition, the government divided these 76 WQ stations into 10 Water Control Zones (WCZs) (Fig. 6) based on the accessible convenience of sampling for separate management (Nazeer, 2016). Although in-situ sampling data provides reliable WQ information, its low sampling frequency (once a month) and the sparsity of point-based sampling hinder a finer and continuous hydro-environment monitoring.

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