There are other linkages between freshwater assimilative capacity (and associated environmental quality) and other aspects of the natural capital stock (see Figure 5.3b for these linkages and sustainability issues generally for freshwater assimilative capacity). Land use and land use change has implications for water quality, particularly through changes in agricultural activity (Paragraph 5.3.3.2). Freshwater quality has direct implications for the renewable and non-renewable natural resources and ecological functions which may be supported within a water body. The sustainability of the fish and invertebrate community supported within rivers will depend on the level of pollution. Similarly, the diversity of habitats and species within and alongside rivers and streams will be influenced by their environmental quality.

The future sustainability of the freshwater resource therefore depends upon a range of measures to prevent polluting discharges, enforce regulation to protect watercourses from waste disposal and illegal pollution, and to consider rivers and streams as part of the natural and ecological capital stock. Despite reductions in pollutant loadings to Hong Kong's rivers, there are still many point source discharges of both treated and untreated wastewaters from domestic, commercial, industrial and agricultural activities. Given the low flows of most rivers in Hong Kong (aside from flooding events), it seems unlikely that there will be sufficient assimilative capacity to deal with discharges other than those from non-point sources (ie run-off). Future water quality and assimilative capacity will therefore rest with measures to close off point source discharges to rivers, and instead direct wastewater discharges to sewer for eventual treatment at STWs.

ThIn common with marine waters, further research into determining assimilative capacity of freshwaters may help to further understand assimilative capacities of river systems and provide a scientific foundation to establish the discharge loadings which could collectively be accommodated within the assimilative capacity of the waterbody, taking account of the level of pollution already being discharged. It is recognised, however, that this approach would require a different analysis of each individual watercourse and may be a more complex task than its equivalent for marine waters.