Abstract
Batticaloa lagoon occupies an area of 168 km 2 in the eastern coast of Sri Lanka. Change in lagoon water salinity is an important aspect that affects the availability and composition of aquatic resources and the livelihoods of the people who are depending on these resources. In this view, lagoon water level, electrical conductivity (EC), salinity, pH and temperature were continuously monitored at two locations, namely Kallady and Manmunaithurai, which are located 7.5 km apart. Readings were taken at weekly intervals during the wet season between September 2012 to March 2013. The lagoon water levels varied between 0.01 and 1.32 m above mean sea level (AMSL) at Kallady, which is located near the barmouth, whereas the variation at Manmunalthurai was between 0.15 and 1.54 m. Corresponding salinity variation was from 37.5 to 3.5 ppt and 31.0 to 4.5 ppt at Kallady and Manmunaithurai, respectively. Surface water temperature at these two locations varied between 25.1 o C to 30.6 o C and the pH varied between a narrow range of 7.7 and 8.7. Salinity showed a highly significant decreasing trend with time (r=-0.693 and -0.71, p0.01 at Kallady and Manmunai area, respectively) during the rainy season. Similarly, a significant positive correlation was observed between the rainfall amount and the lagoon water height (r=0.782 and r=0.853, p0.01 at Kallady and Manmunai area, respectively). However, salinity showed no significant correlation with lagoon water height and the amount of rainfall. This may be due to the influence of tidal action on lagoon water salinity. The study revealed that a substantial variation in salinity occurs during a short period during the wet season and warrants further investigation on its influence on ecosystem and livelihoods. Tropical Agricultural Research Vol. 25 (3): 403-411 (2014)
Highlights
The city of Batticaloa is located between the lagoon and the Indian Ocean in the east cost of Sri Lanka
Lagoon water height from MSL was recorded during the rainy season to find the relation of lagoon water height and the critical point for flood occurrence
It was observed that, during the heavy rain that occurred during 15.12.2012 to 18.12.2012, the lagoon water entered the adjacent land upto 48 m (West side), 30 m (East side) at Kallady and 56 m (East) 45 m (West) from the lagoon border at Manmunai thurai when the lagoon water height of 1.32 m and 1.54 m above MSL at the flood gauges fixed at Kallady and Manmunai thurai area, respectively
Summary
Batticaloa lagoon is the largest coastal water body in the District and it is a long and narrow lagoon and occupies an area of 168 km (Santharuban & Manobawan, 2005). This lagoon is surrounded by a densely populated region used for cultivating rice, coconut and other field crops. The system of lagoon is likely to consist various elements such as catchment area, ocean conditions and lagoon mouth characteristics The effects of these various factors surrounding a lagoon would influence mixing processes. Depending on the local climatic conditions, lagoons which exhibit salinities may be changed from completely fresh to hypersaline. This is true for the type of coastal lagoon, where the lagoon is connected to the coastal sea, at least intermittently, via a single channel and the tidal variability is largely filtered out during propagation of the tidal wave into the lagoon (Knoppers et al, 1991)
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