MATERIALS AND METHODS

The field study was conducted in Varthur lake (12°57’24.98” - 12°56’31.24” N, 77°43’03.02” - 77°44’51.1”E) situated in the south of Bangalore, [Figure-1] which is the second largest lake  in the city. It covers a water-spread area of 220 ha (maximum depth 2 m) and has a varying extent of floating macrophytes during different seasons. It is a part of a series of interconnected and cascading waterbodies. The Varthur lake catchment has seen large scale land use changes after 2000, following rapid urbanization.

Water samples were collected at 10-15 cm from the surface (to avoid floatables and also macrophyte debris), every month over a period of twelve months and analyzed for various physico-chemical parameters - pH, water and air temperature, conductivity, turbidity, redox potential and dissolved oxygen (DO), BOD, COD and inorganic nutrient as per standard protocol of APHA [22]. The biomass/macrophyte coverage over the lake surface was also monitored with the help of GPS and remote sensing data. For macrophyte biomass estimation, 1 m² quadrate sampling method was adopted [23]. C and N contents were determined using CHN analyser. The algal community structures at various sampling sites were also investigated. The nutrient content in water and biomass were analyzed. The pattern of the wind induced drift resulting in the movement of macrophyte population and the accumulation at different extremes of the lake was studied. Changes in the dissolved oxygen concentration and other water quality parameters were investigated with the macrophyte cover and resultant oxidizing reducing environment.

Figure: 1. Varthur lake, Greater Bangalore, India with sampling locations