Nutrient and faecal contamination and retention in wetland enclosures (gei wais) in the Mai Po Marshes, Hong Kong

摘要

Nurient and faecal contamination is an increasing problem to the shrimp productivity and wildife conservation at the internationally important wetland ecosystems of the Mai Po Marshes (Hong Kong, P.R.China). The present study examined the nutrient status and faecal bacteria loading and potential retention capacity of contaminants of two wetland enclosures. Water in the wetland enclosures was eutrophicated with high concentratios of dissolved inorganic nitrogen (inorg-N_(diss)=15.0 mg l~(-1)) and orthophosphate phosphorus (o-P=1.89 mg l~(-1)) and was loaded with high levels of faecal coliforms (172 X 10~3 cfu in 100 ml) and faecal streptococci (1.94 X 10~3 cfu in 100 ml). The pattern of nutrient enrichment of two wetland enclosures is related to a north-to-sourth pollution gradient from the Shenzhen River to the wetlands. By retaining tidal water in the wetland for an 8-day period, water quality was greatly improved; NH_4-N was removed by 83%, o-P by 45% and faecal bacteria by 100%. This implies a self-purfication capability of the wetland enclosures and a potentiality of using them as an alternative sewage treatment.