Microbiological indicators of freshwater pollution in Hong Kong

Abstract

Freshwater quality has been assessed using a number of lines of investigation, namely chemical, biological and micro-biological. Each approach has its uses and yields different information; each also has limitations. Microbiological indicators are particularly useful in that they respond directly and rapidly to environmental changes and, bacteria in particular, offer an immediate bioindicator system for both sewage (and animal manure) and chemical pollutants.

Organic pollution of Hong Kong streams has been assessed using a number of techniques and this paper reviews the results obtained using these different methods. Thus, the results provided by the enumeration of bacterial indicator species are compared with the results provided by various methods of algal (particularly diatom) community structure analysis. The results from these microbiological indexes of pollution are then compared with the results obtained from two extensively used chemical indexes of pollution, namely Biochemical Oxygen Demand (BOD₅) and ammoniacal nitrogen (NH₃-N) content, which are the methods currently used by the Hong Kong Government Environmental Protection Department to prepare a water quality index for Hong Kong streams.

Of the four algal indexes of pollution used, only the algal genus pollution index (AGPI) showed significant correlation with both chemical and bacteriological indicators. Faecal coliform counts showed significant correlations both with BOD₅ and NH₃-N content (as did total coliform counts with the latter). Although both the AGPI and bacterial count methods of biological assessment showed correlation with chemical methods of assessment, the relative ease of use, simplicity and speed of results of the bacterial indicator enumeration technique compared with the algal community structure analysis required in the AGPI, makes the former method particularly useful where fast results are essential or where non-ecologists are involved in environmental studies. Furthermore, and of great advantage, using bacterial counts, the faecal coliform to faecal streptococcal ratio indicates the origin of the pollution and its significance (human or animal wastes and possible disease potential).