EPD - Marine Water Quality in Hong Kong

The development of the marine monitoring programme

Scope of the monitoring programme

The EPD monitors the entire breadth of Hong Kong's marine waters, collecting water and sediment samples from a number of designated locations (monitoring stations) in the sea that are identifiable by specific longitude and latitude co-ordinates. In 2005, it collected samples once a month from each of the 76 water quality monitoring stations and twice a year from the 45 bottom sediment sampling stations. In addition, it took further samples from 18 water and 15 sediment stations covering the Government Dockyard and 16 typhoon shelters and marinas across Hong Kong. At 25 of the water quality monitoring stations in nine Water Control Zones, the EPD also carried out monthly phytoplankton monitoring.

The 76 marine monitoring stations in Hong Kong

The number of stations used to monitor water quality has remained fairly stable since 1986, when there were 77 stations in use. However, in 1986 the EPD only had 19 bottom sediment sampling stations, and has added a further 26 over the following two decades. It also only monitored 13 typhoon shelters in 1986, against the current total of 17 including the Government Dockyard. The increases arose because two typhoon shelters (To Kwa Wan and Hebe Haven) were added to the monitoring programme, as was a brand new typhoon shelter at Hei Ling Chau and the new Government Dockyard which were commissioned in 2000. The EPD collects water samples bimonthly from the water quality monitoring stations in typhoon shelters and the Government Dockyard, and twice a year from the sediment stations.

Resources and equipment

The general-purpose vessel "Chop Yat" used in the early years

Aside from the typhoon shelters, almost all the monitoring stations are sited away from shore. This means that the EPD relies on a dedicated monitoring vessel to access the stations and obtain samples. From 1986 to 1992 it used a small general-purpose vessel named the 'Chop Yat', supplemented as necessary by hired boats and a Police Boat for sampling in the Deep Bay area. As a general-purpose vessel, the 'Chop Yat' suffered from having limited deck space, no cold room for storing samples, and no on-board facilities for on-site analysis of samples. In 1993, the EPD built a new vessel called the 'Dr. Catherine Lam' especially designed for monitoring in Hong Kong waters. Its namesake Dr. Catherine Lam was active in the early years of setting up the EPD's marine monitoring programme, and carried out valuable work on phytoplankton and red tides. She was also instrumental in the acquisition of the new monitoring vessel. Sadly, in 1990 Dr. Lam passed away without seeing the project's completion, and the vessel was named in her memory.

The EPD's dedicated marine monitoring vessel "Dr. Catherine Lam"

The 'Dr. Catherine Lam' is operated and maintained by the Marine Department, which also supplies its crew. The vessel comes with adequate deck space, a built-in cold room and in-house laboratory, and an inflatable boat for special operations. The vessel was fitted with Global Positioning System (GPS) technology, which was later upgraded to Differential Global Positioning System (DGPS), allowing highly accurate positional readings for locating monitoring stations. On deck, CCTV cameras are installed to provide staff working on board with extra safety and security. Electronically controlled cranes/winches have been installed on the sides of the vessel to lower the heavy water/sediment sampler and instruments into the water.

Water monitoring in the 1980s

In 1986 and right through to 1993, EPD personnel took water samples manually by lowering a Van Dorn sampler into the water at each monitoring station. These samples were then measured by individual meters on deck for parameters such as temperature, salinity and dissolved oxygen. The data was recorded by hand onto paper forms

From 1994, the meters for in situ measurements were replaced by a multiparameter "conductivity-temperature-depth" (CTD) water quality profiler. As they were lowered into the water, these new instruments measured parameters such as temperature, salinity, dissolved oxygen and turbidity at different depths, thus obtaining a vertical profile of the water column. The data from these instruments was stored directly into a computer. These advanced pieces of equipment enabled measurements to be made more quickly, efficiently and accurately. In 1999, the EPD also replaced its hand-held Van Dorn water samplers with a computer-controlled rosette water sampler. This new equipment collects up to 12 water samples at once, and takes measurements of physico-chemical parameters the same time as it collects the samples. Today, the sampling procedure involves both the rosette sampler and the CTD profiler being lowered into the water together by electronic winch.

A CTD meter and a water quality profiler housed within the rosette sampler

Since 1995, all the data collected from water sampling has been entered into the EPD's comprehensive Water Quality and Pollution Load Information System (WQPLIS). This compact but high-performing computer database system allows multiple modes of data storage organisation and analysis, and makes data and trends quickly available as required.

Trialled equipment

The EPD has always been ready to embrace new technology that can help streamline and improve its water quality monitoring programme. However, some promising new technology has not been adopted, following trials to see how well it would suit Hong Kong conditions.

One such piece of new technology was remote sensing using telemetric monitoring. This was a development that could allow for continuous monitoring of marine water quality by stationing instruments at fixed marine sites. The instrument buoys could electronically transmit data back to a base site, continuously. By contrast, the EPD's existing programme required monthly visits by staff to take individual samples.

Telemetry Marine Water Quality
Monitoring System

In 1996, the EPD began a seven-month trial of an experimental Telemetry Marine Water Quality Monitoring System (TMWQMS), to see how feasible it would be to deploy telemetric monitoring in Hong Kong's marine waters. The trial certainly indicated that the equipment was accurate in its readings. Problems, however, were manifold. Costs of installing and maintaining the system were high, but the system could only be placed at one or two sampling locations and could not provide the territory-wide coverage required by a comprehensive monitoring programme. It was prone to malfunction, requiring regular repairs in addition to standard maintenance work. In particular, it was quickly affected by biofouling (e.g. growth of marine organisms on the equipment), which affected the functioning of the sensors. Because it was left unattended for long periods in the sea, the system was also vulnerable to vandalism, theft, or the effects of storms or large waves. Finally, the system only measured a limited number of parameters, reducing its effectiveness. For reasons of usefulness and cost, therefore, the EPD decided not to pursue telemetry for routine marine monitoring.

Sampling techniques

To collect water samples, EPD staff aboard the monitoring vessel first have to locate the position of each sampling station. In the 1980s, the positioning was determined visually by reference to distinctive objects such as prominent landmarks or nearby buoys. With the arrival of the new vessel 'Dr. Catherine Lam' in 1993, the exact positions of monitoring stations could be determined using the Global Positioning System aboard, later upgraded to the even more precise Differential Global Positioning System (DGPS). This system enables the vessel to be brought to within one metre of the designated station position on every visit.

EPD staff collecting water samples

As mentioned above, in the early years individual water samples were collected manually. Samples from different depths would thus have to be taken separately, with one sample taken at each depth. To obtain a comprehensive picture of the water body, water samples at each station are generally collected from three depths: one from one metre below the surface of the water ('Surface'), one from midway between the surface and the sea bed ('Middle'), and one from one metre above the sea bed ('Bottom'). With the introduction of the rosette sampler in 1999, samples could be taken by a single piece of equipment from all three depths in one haul.

For sediment sampling, EPD staff use sampling grabs to collect sediment from the top 10cm of the seabed. The kind of sediment grab used at each station depends on the depth of the seabed there and the amount of sediment needing to be collected. The EPD uses three different types of sediment grabs: a Birge-Ekman grab (0.023sq.m.) for swallow water, a Van Veen grab (0.1sq.m.), and a Smith-Mcintyre grab (0.1 sq.m.) for deeper water.