Monday, January 31, 2011

The things that nobody told you about Pasir Ris

The water quality off Pasir Ris Park has piqued my interest since it has been in the limelight for failing the Enterococcus test for primary contact activities (e.g. swimming) for 3 years in a row (2008 - 2010) and the mass fish kill in Dec 09/ Jan 10 (see previous posts). I also found out that further back in Dec 06/ Jan 07 (1, 2, 3), another mass die-off has been observed and the reason was suggested to be a sharp drop in salinity (Update: In her blog, Ria Tan questioned whether Chek Jawa will survive the incessant rain in Jan 2011). Therefore in 2010, I decided to get my team to test out the water quality off Pasir Ris at 2 patches of seagrasses - 1 close to Sg Loyang and the other close to Sg Tampines.

Figure: Patch of seagrass near Sg Loyang

Figure: Another patch of seagrasses near Sg Tampines

Fast forward to the present, and we have some interesting results to share, not just on Pasir Ris but also on the other 2 locations we monitored. Evidently, Enterococcus is not the only thing we have to worry about.

Data were obtained from sampling seawater and sediments in three selected seagrass areas, namely Chek Jawa (CJ), Pasir Ris (PR) Park and Pulau Semakau (PS) from June to December 2010. Sampling dates and times corresponded to tide levels of 0 to 0.5m for safety reasons and ease of seagrass observation. Our team made 6 visits to Chek Jawa (2 sites), 6 visits to Pasir Ris Park (2 sites) and 2 visits to Pulau Semakau (3 sites) during the monitoring period. (The smaller number of trips to Pulau Semakau was due to logistical constraints hence the team could only head there together with Team Seagrass on their routine seagrass monitoring sessions.)

Our on-site tests include air temperature, water temperature, pH, dissolved oxygen (DO), electrical conductivity (EC), turbidity and nutrients in water - ammonia (NH3), nitrate (NO3-) and phosphate (PO43-). Laboratory testing of water samples involves Escherichia coli (E. coli), chemical oxygen demand (COD), total alkalinity, total hardness, calcium and magnesium hardness, metal ions (aluminium, copper, iron and lead) and chlorophyll a. Sediment samples were also brought back to the laboratory to analyse for nutrient content - ammonia (NH3), nitrate (NO3-) and phosphate (PO43-).

Summary of results

The values below were obtained by averaging all the results for each location. For ease of reading, only the notable water quality parameters are highlighted.

* ND = not detected

DO (mg/L) 10.5 (CJ), 8.79 (PS), 5.85 (PR)
DO is significantly lower at Pasir Ris. While considered acceptable compared to waters elsewhere in Singapore, these DO levels were relatively low for a seagrass area which is supposed to photosynthesise and produce oxygen in the day.

EC (mS/cm) 43.9 (CJ), 46.0 (PS), 42.7 (PR)
The average EC appeared consistently healthy for all 3 areas except for Chek Jawa in November 2010 for which the EC plummeted to 24.67 mS/cm at site 2.

Turbidity (NTU) 30.6 (CJ), 18.9 (PS), 262 (PR)
The water at Pasir Ris is significantly more turbid. Turbidity measures the loss in transparency in water due to the presence of suspended particles such as phytoplankton and silt. Fishes start to experience stress when exposed to a turbidity of 10-100 NTU for several hours.

E. coli (CFU/ml) 17.3 (CJ), 2.17 (PS), 23.4 (PR)
Though E. coli is a different bacterium from Enteroccus, it too indicates the presence of faecal contamination, just like Enteroccus.

Pasir Ris and Chek Jawa are significantly higher in E. coli count compared to Pulau Semakau.

E. coli has the highest count at 76 CFU (colony forming unit)/mL in November for Pasir Ris site 2. United States Environmental Protection Agency (USEPA) standards provide a maximum of 10 CFU/mL faecal coliforms for primary contact activities e.g. swimming, and a maximum of 50 CFU/mL for secondary contact activities e.g. boating.

COD (mg/L) 135 (CJ), 136 (PS), 132 (PR)
Surprisingly, the organic matter content in all 3 areas was rather similar and compares well with values obtained in our coastal areas in 2009.

Iron (mg/L) 0.998 (CJ), 0.314 (PS), 1.34 (PR)
Though not considered a threat to marine life, Pasir Ris has the highest iron concentration.

Aluminium (mg/L) 0.612 (CJ), 0.0148 (PS), 1.64 (PR)
Pasir Ris has significantly higher concentration of aluminium. The toxicity of aluminium depends to a large extent on the water pH, with the most toxic aluminium compound forming at pH 5.2-5.8. At pH 7.0, a concentration as low as 0.52 mg/L was found to reduce the growth of rainbow trout. In another example, a mass kill of maraena and peled fry occurred at 0.3 mg/L at a pH of 7.0-7.5. Seawater contains an average of 0.01 mg/L aluminium.

Lead (mg/L) 0.181 (CJ), 0.0428 (PS), ND* (PR)
Superb! Pasir Ris water has no lead detected!

Chlorophyll a (µg/L) No data (CJ), No data (PS), 7.59 (PR)
Though not shown in the averaged result above, chlorophyll a concentrations peaked at 25.1 µg/L at site 2 and 19.2 µg/L at site 1 for Pasir Ris in December. This placed the water within eutrophic condition as given under the guidelines for USA (10-500 µg/L). Eutrophic water has excessive nutrients which support an abundance of algae releasing chlorophyll a.

Nutrient in Water

Ammonia (mg/L-N) 0.174 (CJ), 0.178 (PS), 0.345 (PR)
Pasir Ris has significantly higher concentration of ammonia. Ammonia is toxic by itself. It can also contribute to eutrophication.

Nitrate (mg/L-N) 0.103 (CJ), 0.0875 (PS), 0.242 (PR)
Pasir Ris has significantly higher concentration of nitrate. Nitrate can contribute to eutrophication. Concentrations of 0.1-0.75 mg/L nitrate + ammonia N in fresh waters or even less in saline waters have been enough for a bloom.

Phosphate (mg/L-P) ND* (CJ), ND* (PS), 0.103 (PR)
Pasir Ris has significantly higher concentration of phosphate-phosphorus. Like nitrogen, phosphorus can contribute to eutrophication. A level of 0.005-0.5 mg/L P is already enough to cause phytoplankton blooms.

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