Materials and Methods
Varthur Lake (12.9407° to 12.9566° N and 77.67189° to 77.7476° E) is the second largest lake in Bangalore (Fig. 1) and has an average depth of 1.05 m. The lake is located in Varthur ward with a spatial extent of 180.8 ha and spreads across Amanikere Bellandur Khane village. Varthur Lake has a catchment area of nearly 279 km2 with 96 cascad- ing interlinked lakes. Land use analyses in Varthur using temporal (1970 to 2016) remote sensing data shows an increase in built-up (paved surfaces: buildings, roads, etc.) from 3.8% (1973) to 89% (2016), with a sharp decline in vegetation (58.7% to 6.1%), water bodies (4.5% to 1.2%) and other (open lands, agriculture) land uses (33.1% to 5.0%) (Ramachandra et al. 2017).
Macrophytes and sediments were collected from inlet to outlet following random method. A total of 45 macrophyte and sediment samples were collected from the lake (Fig. 2). Eichhornia crassipes and Alternanthera philoxe- roides were the dominant species of macrophytes. Collected< macrophytes were stored in polythene bags after species identification using taxonomic literature (Cook 1996). Approximately 1 kg of sediment was collected through a cylindrical PVC cores with 5 cm of internal diameter at a depth of 0–20 cm (root growing zone) from each sampling location. Collected macrophytes were washed to eliminate sediments and epiphytes and separated by species. Above ground and belowground parts were then separated and oven dried at 60°C for 2–3 days until constant weight. Sediments were air dried and sieved (1 mm) to remove coarse debris. Samples were powdered using a mortar and sieved (1 mm) to get fine powders. Powdered samples (0.5 g; macrophyte and sediment) were subjected to acid digestion according to established protocols (APHA 1995). Digested samples were filtered using 0.45 µm filter paper and made up to 50 mL using double distilled water for further analyses. Digested samples were analysed for six metals (Cd, Cr, Cu, Ni, Pb, and Zn) with reagent blanks and standards using Flame Atomic Absorption Spectrophotometry (GBC Avanta ver- sion 1.31).
Bioconcentration factor (BCF) is the ratio of metal concentration in the plant to that in sediment. The larger the factor, the more easily the plant absorbs the metal from the sediment and the higher possibility of redistribution for the metal (Zhang et al. 2009). A BCF value higher than one may indicate that a plant species could act as a hyperaccumulator of trace elements (Zhang et al. 2002). Translocation factor (TF) describes the efficiency of a plant to translocate metal from its root to shoot. It is calculated as the ratio of concentration (mg kg−1) of metal in plant shoot to the concentration of the same metal in plant root. TF provides information
Fig. 1 Map of India showing location of Bangalore and Varthur Lake
Fig. 2 Sampling locations of macrophytes and sediments in Varthur Lake
about the mobility of a given element from roots to leaves, and higher TF values result in greater mobility (Deng et al. 2004).