The plankton diversity and density in the Iranamadu tank in the wet season

Abstract

The Iranamadu tank is one of the largest surface aquifer found in Northern Sri Lanka. The capacity to harvest large amount of rainwater makes this reservoir a potential source for drinking water supplies. A study was conducted to determine the diversity and density of the planktons from October to December 2005, from the start till the end of the wet season in the Northern Sri Lanka. Samples were collected using Plankton nets once a week from 0500 hrs onwards along the two selected sub sampling areas (SS); one from the outlet sluice (SS I) and the other from the catchments aren (SS II). Onboard sampling was carried out too. The samples consisted of major phytoplankton like the Microcystis sp (29%), Microspora sp (26%). Chlorococcum sp (15%). Pediastrum sp (6%), Volvox sp (6%), Gleocapsa sp (6%), Nostoc sp (3%). Spirulina sp (3%). Chlamydomonas sp (3%). Sorastrum sp (2%), Spheaerocystis sp (2%) and Scenedesmus sp (2%). The zooplanktons consisted of Cyclops sp (4%), Brachiomus sp (3%). Lecane sp (3%), and a species of water mite (1%) with various density levels. The Microcystis sp was the dominant phytoplankton (1423 x10/1 at SSI and 1363 x10/1 at SS II) followed closely by Microspora sp (1288 x10/1 at SSI and 1274 10/1). The Cyclops sp (249 x10/1 at SS 1 and 229 10/1 at SS II) was the dominant zooplankton followed by the rotifers Lecane sp (152 x10/1 at SSI and 205 10/1 at SS II) and Brachionus sp (160 x10/1 at SS 1 and 187x101 at SS II). The phytoplankton density was high which indicates the need for a better filtration process in any drinking water supplying unit when this tank is considered for that purpose.