Urbanization and seasonal effects on the lake ecosystem dynamics from 2002 to 2022 in Bengaluru, South India

The paper cites research from 2016 to note that 98 per cent of lakes in Bengaluru are encroached. Moreover, pollution by untreated sewage, industrial effluents and dumping of solid waste and construction debris affects as many as 90 per cent of lakes in the city.

Aquatic macrophytes (aquatic plants) play an important role in the ecological functioning of a wetland, aiding in the stabilisation of sediment. However, almost a quarter of the lakes in Bengaluru are covered in macrophytes which are exotic invasive species, pointing to a degradation of the wetland ecosystem.

The climate of Bengaluru ranges from monsoonal summers to dry winters. During the dry season, the vegetation in all lakes was seen to be highly dynamic. The macrophyte and algal cover could vary significantly due to the fast growth rate of macrophytes and frequent harvests for fodder by farmers as well as dredging undertaken by lake governing authorities.

Both urban lakes (Dodda Bommassandra and Bellandur) saw an increase in water levels as well as macrophytes between 2002 and 2022. In the former, the change was likely due to a rise in runoff flow and in the latter due to the changes in its immediate surroundings which became partly silted. The two rural lakes (Vrishabhavathi and Chudahalli) saw a negative correlation between water surface area and macrophytes. The paper posits this may be due to their interconnection along a stream.

The urban lakes were more affected by the growth of built-up areas than peri-urban or rural ones, the paper notes on reviewing around 300 metres of land around each lake. More than 60 per cent of such land around Dodda Bommassandra had been built up by 2022, compared to only 15 per cent around Bellandur. The area around Bellandur has historically been used for paddy and vegetable cultivation, the paper adds.

The peri-urban lake Attur saw a steep rise in built-up area from two per cent in 2004 to 38 per cent in 2021. The paper notes that the lake’s connectedness to rail and metro lines as well as the airport could be an important contributing factor for this change.

Of the two lakes in rural areas, Vrishabhavathi saw an increase in built up area from 6.5 per cent in 2015 to 16 per cent in 2019. This is in part due to the establishment of steel and auto-parts plants in the vicinity since 2007-08. In addition to this, engineering colleges and residences have also been set up in the surrounding areas. Conversely, the Chudahalli lake, which is known for its picnic sports, has seen a fairly unchanged built-up area during the study period.

The paper concludes that the urbanisation has not affected the lakes uniformly. Rather, the effects witnessed are more site-specific. It adds that while considering the wet surface areas, rural lakes showed a negative correlation with amount of rainfall received whereas urban and peri-urban lakes showed a positive correlation.

Focus and Factoids by Radhika Gupta.