Water quality of tropical reservoir based on spatio-temporal variation in phytoplankton composition and physico-chemical analysis

Abstract

This study assessed the water quality of Mengkuang Reservoir, Penang, Malaysia, by its trophic status according to a Carlson Modified Trophic Index (CMTSI) and by its biological parameters using Shannon–Wiener diversity index (H′) and saprobic index. The study conducted from August 2005 to July 2006 showed that mean values of CMTSI (nutrients), CMTSI (chlorophyll a) and CMTSI (Secchi depth) were 27.18 ± 8.73, 40.63 ± 7.12 and 41.74 ± 6.38, respectively. The mean values of CMTSI indicated that the reservoir was oligotrophic. Mean value of H′ was 2.15 bits/individual, showing that the water quality based on H′ value was in class III (slightly polluted). Saprobic index value (2.24) also revealed that the reservoir was moderately polluted (class II). The occurrence of Anabaena, Microcystis, Oscillatoria, Nostoc, Dinobryon, Chroococcus, Staurastrum paradoxum and Mallomonas which are indicators of toxic and polluted waters was also recorded. This study therefore showed the importance of phytoplankton composition and community structure as a reliable and important tool to assess the degree of pollution in Mengkuang Reservoir. Long-term assessments of biological and chemical parameters in the reservoir are necessary, and phytoplankton community structure as bioindicator provides unique information about the ecosystem. This information is potentially useful as an early warning sign of deteriorating condition and thus gives insight into the overall ecology of lakes and will assist in the future conservation and management of this lentic ecosystem.