Materials and Methods

Study Area
The study area comprises of the two major water bodies - Bellandur lake and Varthur lake  which are situated in the south of Greater Bangalore as depicted in Figure 1.  Bellandur Lake is the largest lake in the Bangalore city and spreads across an area of 365ha [Figure 1 a)]. Sewage from residential areas near the old Bangalore International Airport, regions around Challaghata and Koramangla is directly fed into the lake through the storm water drains.

Varthur Lake is the second largest fresh water body in Bangalore built by the Ganga Kings over a thousand years ago [Figure 1. b)] for domestic and agricultural uses. It is 5 km downstream of Bellandur lake receiving the discharge from Bellandur lake and an additional sewage from inflows from near by areas. The Varthur lake catchment has seen large scale land use changes after 2000, consequent to the rapid urbanization in the region. The lake receives 595 million liters per day (MLD) of sewage. The sampling locations are shown in the Figure 1. Table 1 shows the characteristics of the studied lakes.

Figure 1. Study Area: Bangalore city, Greater Bangalore; 2 lakes of Bangalore.

 Table 1. Characteristics of the Study area

Experimental Design

Water samples from 10cm below the surface were collected from the inlet, middle and outlets representing the inflow and the outflows of the lake. Parameters like pH, temperature, electric conductivity were analysed on-site with appropriate probes. Dissolved Oxygen, free Carbon dioxide and other physico-chemical analyses were carried out following standard methods (APHA, 1995). Algal samples from water were collected with the help of Planktonic net in 100 ml polythene bottles and were preserved in 70% alcohol. Algae attached to aquatic plants and stones (biofilms) were also collected in separate containers. With the help of a pipette, samples were mounted on the slide and observed under the microscope for enumeration. Images were captured using Caliper pro software and DIP microscope. Algae were identified till genus level following Taylor et al., 2006 and 2007 and their community structure were observed. The relative abundance of algal communities was examined. The bacterial count and density were analysed by Flow Cytometer (FACS Caliber) and were verified with microscopy. The bacterioplankton population was analysed by first filtering the lake samples with 40 μm and 2.5 μm sieve and then by the FSC (forward scatter) plots. The nutrient content (C and N) of the phytoplankton, bacterioplankton and macrophytes were measured with CHN analyzer (TRUE SPEC CHN, 1.9X, LECO).