Materials and Methods
Bengaluru landscape with undulating terrain forms three major watersheds namely Koramangala and Challaghatta Valley, Vrishabhavathi Valley and Hebbal Valley. Bengaluru (Greater Bangalore or Bangalore) lies between the latitude 12°39’00” to 13°13’00” N and longitude 77°22’00” to 77°52’00” E, covering an area of 741 square kilometres and located at an altitude of 920 meters above mean sea level. The study involves monitoring of 40 lakes of Bengaluru spread over the 3 valleys (figure 2). The exploratory field survey was done for determining the location coordinates (longitudes and latitudes) and identifying the key issues in and around the lakes.
Sample collection and water quality analysis
Water samples for determining the physicochemical characteristics were collected from the forty lakes in the clean and sterile polypropylene bottles during the years 2016 - 2019. Various physicochemical analysis like water temperature (WT), dissolved oxygen (DO), pH, total dissolved solids (TDS), electrical conductivity (EC), total alkalinity (TA), chloride (Cl), total hardness (TH), calcium (Ca), magnesium (Mg), nitrate (Nit), ortho-phosphate (OP), chemical oxygen demand (COD) and biochemical oxygen demand (BOD) of lake water samples were analyzed using standard methods (APHA, 2005). Some parameters like water temperature, pH, total dissolved solids (TDS), electrical conductivity (EC), dissolved oxygen (DO) and turbidity (TB) were measured onsite while other chemical and nutrient parameters were estimated in laboratory. Each experiment was carried out in triplicates to determine the overall water quality.
Weighted arithmetic water quality index (WQI) was computed for the monitored forty lakes using ten key water quality parameters like total dissolved solids, electrical conductivity, dissolved oxygen, pH, calcium, magnesium, total hardness, chloride, total alkalinity and nitrate (Chaurasia et al., 2015; Sincy et al., 2016). Created distribution maps with water quality data using QGIS software.
Data analysis
Pearson’s correlation coefficient (r) was determined using data of physicochemical parameters of lakes. In order to identify the main factors responsible for variations in water quality, multivariate analysis like Principal Component Analysis (PCA) was done using PAST3 software.