Re ECF Project: 7/2006

Project Title: Mechanism of the elevated algal proliferation in intertidal shrimp ponds (gei wais) of the Mai Po Nature Reserve

Applicant: University of Hong Kong

Project Proponent: Dr. Ji-Dong Gu

Total Approved Grant: $145,256.50 (ECF & WWGF: 50/50)

Duration: 1/3/2007 to 29/2/2008

Project Status/Remarks: Completed

The purposes of this project are:

  1. to conduct an intensive on-site investigation to identify the environmental condition(s) responsible for the active algal proliferation and elevation of organic contents in gei wais as compared with open marine and fresh waters;
  2. to investigate the potential effect of suspended solids on algal growth in gei wais with matrix experiments; and
  3. to substantiate the role of sediments as a sink-and-source of pollutants in association with the water quality of gei wais with simulation experiments.

Summary of Findings/Outcomes:
In line with previous findings, difference in physicochemical parameters between the two ends of gei wais 8, 13 and 18 were observed during the 12-month monitoring period. The flow rate and nutrient levels (e.g. nitrate-N, nitrite-N, ammoniacal-N, total Kjeldahl-N, orthophosphate and total-P) were higher in water at the seaward side. Moreover, this is the first report that chlorophyll a (24.5%) and dissolved oxygen (67.9%) were higher at the seaward end. This is important in demonstrating the need to investigate the causation of elevated algal growth from both ends (instead of gei wai as a whole) for future studies. Matrix experiment showed that the level of suspended solids was a critical factor to algal growth in gei wai. Algal growth in water sample freshly collected from gei wai with suspended solids settled was 57.1% higher than that with suspended solids maintained in the aliquot. In microcosm, sediments were demonstrated to be an important sink-and-source of nutrients (nitrogen and phosphorus) affecting water quality. In conclusion, alteration in the level of suspended solids may help controlling active algal proliferation in gei wai; future studies should also take into account the difference in environmental conditions at both ends of gei wai.