Seasonal dynamics of phytoplankton community in a tropical wetland

Phytoplankton species composition and seasonal changes were investigated in the Bhoj wetland Bhopal. Taxonomic composition, diversity, and abundance of phytoplankton were studied at nine stations from March 2008 to February 2010, in relation to various physico-chemical factors. Total phytoplankton species composition in the Bhoj wetland was represented by 360 species. Among phytoplankton, diversity belonged to seven groups. Chlorophyceae was the dominant group (48 %) followed by Bacillariophyceae (26 %), Cyanophyceae (15 %), and Euglenophyceae (9 %), while Pyrophyceae, Chrysophyceae, and Xanthophyceae contributed 2 % of the population. Phytoplankton on the basis of seasonal studies recorded 1651 units l(-1) during summer season which was contributed mainly by Chlorophyceae (39.3 %), with Spirogyra sp. (14.2 %) and Closteriopsis sp. (9.1 %) contributing maximum to the total group in the first year, while during the second year of summer period, a total of 2095 units l-1 was recorded which was contributed mainly by group Pyrophyceae (51 %) with the main dominant species represented by Ceratium hirundinella (98.46 %). The highest Shannon-Wiener diversity index (H') value (4.27) was recorded. Simpson values are approaching 1, signifying that sites have high relative diversity due to its supporting surrounding components. The trend of variation in evenness values was more or less the same as Shannon diversity index. Thus, the highest diversity indices recoded at all the stations in the present study justify the diverse nature of species inhabiting the different ecological niches in the ecosystem. The very high phosphate and nitrate concentrations in the wetland are indicators of pollution which may be due to the discharge of agricultural and sewage wastes enriched with nutrients as well as the human activities there. Our recommendation is to avoid as far as possible the discharge of sewage and agriculture wastes into the Bhoj wetland. The effects of various physicochemical water quality parameters on the seasonal distribution and succession of the above mentioned phytoplankton population as well as the interaction and eutrophication are discussed.