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Kedong is presently in Hong Kong

 


Kedong Yin | Research Associate

Estuarine Benthic Ecology: Long Term Response to Diversion of Sewage Treatment Plant Effluent at Iona and Sea Islands


The intertidal ecosystem off Iona Island, on Sturgeon Bank, was exposed to sewage pollution (estimated 23,000 kg of suspended solids per day) between 1962 and 1988. Beginning in 1989, the primary treated sewage was discharged through a pipe at a depth of 100 m which extends further out into the Strait of Georgia than the previous open ditch. This change in the discharge site offers an unique opportunity to study the recovery of the intertidal ecosystem on Sturgeon Bank. Our project is to study the estuarine benthic ecology: long term response to diversion of sewage treatment plant effluent at Iona and Sea Islands. This is the second year of the project. The data were collected during January-December, 1995 on the mudflats of Sturgeon Banks and Roberts Banks. The data include the measurements of physical parameters (salinity and temperature), chemical parameters (pH, and oxygen), nutrients (NO3, NO2, NH4 and PO4) in the water column during flood tides and ebb tides, benthic chl a, sediment pore water nutrients (nitrate, ammonium and phosphate), total sedimental organic carbon and nitrogen, and benthic invertebrates.

The objectives of this research are: 1) to determine changes in benthic invertebrate and algal community structure since the effluent from Iona Sewage Treatment Plant was diverted in 1988; 2) to estimate algal biomass and primary production so as to establish a long-term baseline for future comparisons; 3) to estimate secondary production of two important benthic invertebrates (a bivalve Macoma baltica and an amphipod Corophium salmonis using cohort analysis); 4) to identify and quantify processes controlling inorganic and organic nutrient cycling and utilization; 5) to determine if contaminants (metals, OC's and PAH's) in surface sediments are affecting the productivity or structure of the investigated benthic communities.

Ten stations were selected (Figure 1; W1 to W10) for water sampling. Five of them were at the 10 m depth contour further off shore and constantly under water. The other five were nearer the shoreline and covered by water during high tides and exposed to the air during low tides. The water was sampled during the late stage of a flood tide (assuming that water comes towards the Bank) and during the middle stage of the following ebb tide (water leaving the Bank).

The four stations (Figure 1: A0, A10, A12 and A14) were selected for sediment coring for benthic invertebrates on the mud flat of Sturgeon Bank and Roberts Bank. The samples were taken once every 2 weeks starting in May until August 19 and then once every 4 or 6 weeks until November 29, 1994.


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