Abstract:
Chilaw Lagoon is an intermittently closed, shallow coastal lagoon located in the North Western
province of Sri Lanka. Excessive shrimp farm development has resulted in pollution of the
lagoon since the farms extract water from the lagoon and discharge the effluent to the same
lagoon.
This study investigated the seasonal and spatial variations of selected water quality parameters
at fifteen different locations situated between 7° 29' 17'' to 7° 36' 25'' N latitude and 79° 47' 19''
to 79° 49' 02'' E longitude in the Chilaw lagoon for a period of six months (from March to
August in 2016). Each water sample was analyzed at the sampling sites for pH, Electrical
Conductivity (EC), Salinity, Dissolved Oxygen (DO), Turbidity, Air Temperature and Water
Temperature as physical and chemical parameters. Nitrite Nitrogen, Nitrate Nitrogen,
Ammoniacal Nitrogen and Dissolved Phosphate were also analyzed.
According to the experimental results, pH values of water in the lagoon fluctuated from 6.7 to
9.3 and exceeded the proposed ambient water quality standards for fish and aquatic life. The
lagoon DO levels varied from 1.25 to 6. 79 mg/L and the lower limit does not comply with the
tolerance limit for fish and aquatic life. EC values ranged from 2.8 to 55.1 mS/cm and the
corresponding Salinity variation was 2 to 35 ppt (parts per thousand). The surface water
temperature and the turbidity of the water in the lagoon varied in the range of 27.4 to 33.9 ͦ C
and 0.96 to 50.3 NTU respectively. Ammoniacal Nitrogen was detected from 0.01 to 0.25 mg/L.
The maximum Nitrite Nitrogen value was 0.04 mg/L and it was 0.32 mg/L for Nitrate Nitrogen.
The maximum level of Orthophosphate was observed as 0.29 mg/L. Therefore, pH, EC, DO,
Salinity, Turbidity and nutrients showed a significant spatio-temporal variation that affects the
aquatic life in the lagoon critically.
