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Due to the unparalleled levels of population and economic growth which Hong Kong has experienced since the late 1960s, and the heavy reliance on marine waters as the receiving medium for liquid, and some solid, wastes, there has been a progressive deterioration in Hong Kong's marine water quality. This trend has been accompanied by an accelerating programme of water pollution and dumping control strategies and wastewater collection and treatment systems which has served to offset an otherwise widening gap between pollutant inputs and the marine environment's ability to accommodate these inputs. However, it is recognised that infrastructure to enhance assimilative capacity as a stand-alone solution to marine pollution may not be sufficient to maintain the natural capital stock without supporting measures to address the fundamental causes of pollution.
As the assimilative capacity of the marine environment in Hong Kong is not presently well-understood, it is not possible to quantitatively address whether the assimilative capacity has already been exceeded or the extent to which additional discharges can be absorbed. Nevertheless, using statutory Water Quality Objectives as a guideline, it is clear that the beneficial uses of certain waterbodies including Deep Bay, Victoria Harbour and Tolo Harbour have already been compromised by a surfeit of uncontrolled discharges.
Whilst acknowledging the progress and initiatives undertaken by EPD and other Government departments concerned to tackle water quality problems, greater action needs to be taken and alternatives are provided to address current and future pressures on marine assimilative capacity. There are two types of possible responses to address the problems. The first can be broadly characterised as "output" responses, or those which act on the wastes which are already captured by the existing system controlling collection and treatment of the wastestreams destined for marine waters. In Hong Kong there are many options for implementing improved "output" strategies including:
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improving the level of treatment, and the percentage treated, of collected flows through existing or new sewage treatment works;
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locating outfalls for marine discharges in areas of high dispersion capacity;
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ensuring that the natural flushing characteristics of receiving waterbodies are maintained by avoiding physical barriers to dispersion and excessive abstraction or diversion of clean, natural flows;
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maintaining standards for permitted marine discharges through monitoring of waterbodies to ensure unacceptable impacts are not occurring;
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ameliorating areas of extreme contamination through removal of sediment and diversion of inputs; and
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co-operating on a regional level to maintain and improve ambient marine water quality in areas bordering marine waters.
The second type of response is characterised by its focus on "inputs", ie reducing the flows and loads entering wastestreams destined for marine waters through waste reduction measures. Under this approach, incentives are provided to reduce contributions to the existing waste management system and/or to stem unauthorised use of marine waters for disposal. "Input" - focused options include:
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providing a more extensive sewerage network to collect a greater proportion of wastewaters;
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heightening enforcement of discharge licence conditions and prosecution of illegal disposal activities;
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promoting technologies which can reduce the load of pollutants generated through cleaner production processes;
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implementing full cost recovery for wastewater services as an extension of the polluter pays principle; and
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educating the public to cease illegal dumping of waste in marine waters and casual littering from vessels and in coastal areas such as beaches.
A sustainable approach to preserving the assimilative capacity of marine waters will require components of both "output" and "input" approaches and many initiatives of both types are currently underway. These initiatives will improve marine water quality but as they are addressed to specific sources rather than to cumulative impacts they will not guarantee that the benefits associated with marine waters, including assimilative capacity, ecological, natural resource, recreational, and landscape natural capital stock values, will be maintained. In the absence of the scientific information necessary to quantitatively apply the assimilative capacity concept as a water quality management tool, it will be necessary to continue to adopt a management approach based on in situ monitoring to assess trends in ambient conditions.
While EPD already use sophisticated water quality models to guide their decision making, the assimilative capacity of the marine environment is still not well-understood. To obtain a better understanding of the possible interactions between discharges and resulting quality of receivers, Hong Kong could pursue constructing an assimilative capacity model of all waterbodies which could be used to set permitting discharge limits for polluting activities. EPD has already successfully developed such an assimilative capacity model for Deep Bay and is now working to develop a similar model for Mirs Bay. When applied in conjunction with feedback from monitoring data, such a model would help to provide an explicit link between the levels of individual discharges and the resulting quality of the receiving waterbody, and allow for more proactive management.
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