Physicochemical environment of Malala Lagoon in Southern Sri Lanka

Abstract

Malala Lagoon is the largest of the five enclosed shallow lagoons in Bundala National park, and is one of the most productive of the fifteen lagoons in the Hambantota district, Sri Lanka.  It has been vulnerable to human induced pollution for nearly three decades. This paper ascertains the status of physicochemical environment of the lagoon and its temporal variation from 1995 to 1997. During the study period physicochemical and biological parameters measured in Malala lagoon were water temperature, pH, conductivity, Secchi depth, dissolved oxygen, salinity, total alkalinity, dissolved phosphate, and chlorophyll-a, and their mean values were; 27.69 ± 1.62°C, 7.93±0.46, 5.14±3.88 mS/cm, 00.39 ± 00.19 m, 7.83±0.89 mg/L, 2.18±1.61‰, 2.14 ±0.59 mmol/L, 12.25±4.67 mg/L and 8.86 ± 4.62 mg/L respectively. Maximum depth of the lagoon rarely exceeded 2 m during the study period. Due to the shallowness of the lagoon, there were no significant differences (p>0.05) in physicochemical parameters of surface, middle and bottom layers of the water column. Water level of the lagoon showed a significant (p<0.01) negative correlation with electrical conductivity (r = 0.727) as well as with the salinity (r = 0.729). Water influx to the lagoon showed a significant (p < 0.05) negative correlation with conductivity (r = 0.454) and salinity of the lagoon (r = 0.406). Findings of the study are compared with those carried out over a decade to explore and elucidate the long term changes in the lagoon environment. When compared with the published data from preceding and subsequent studies, it confirmed that the brackish water characteristics of the lagoon are gradually degrading due to pollution caused by natural phenomena and anthropogenic activities adversely affecting the ecological balance and the productivity of the lagoon. These findings could be of great importance when studying long term changes in the coastal waters, which are essential for sustainable coastal planning, with respect to socioeconomic development programmes as well as to identify the impacts of Hambantota port and maritime activities in the area and to understand the trends related to global climate change.