City lakes support 333 types of flora and fauna

This is the second and final part of a two-part series that looks at the draft report presented by Environmental Management & Policy Research Institute (EMPRI). For the first time ever, almost every water body in the city has been studied rather comprehensively. And the news is not good, this time for denizens of an inter-connected lake system

In an increasingly concretised city, where space for trees is at a premium, lakes are not only a critical link in the everyday lives of humans around it, but also for over 333 types of flora and fauna in the eco-system.

Despite the severe pollution that is choking the lakes — 85% are categorised in the lowest water quality grade with none in the top two grades — a draft report by Environmental Management & Policy Research Institute (EMPRI) shows that trees, herbs, insects, amphibians, reptiles and birds depend on the eco-system provided by the lake. The report, which is in the final stages of completion, is a two-year comprehensive inventory of 1,518 water bodies.

“Existence of water bodies is not only based on the presence of the water, but also depends on the presence of biota (flora and fauna). Pollution, encroachment and urbanisation have extremely impacted the biota in terms of density and diversity,” notes the report.

The lake ecosystem

Each and every species plays a ‘critical role’, one that is endangered by Bengaluru’s rapid urbanisation, flow of toxic chemicals and sewage. “When there is no control on biota of water bodies, it will bring the nuisance, such as growth of vegetation (weeds), breeding place for mosquito (vector-borne disease), bad odour (decomposition of rapid grown biota), among other things. Few biota also act as a bio-indicator to show the status of water quality and some help in the cleaning process of water bodies,” states the draft report.

Unlike manicured parks, the periphery of lakes has provided the ideal zone for native trees to be grown. Trees not only harbour bird life, but also prevent soil erosion.

Shrubs, similarly, harbour insect life and filter silt while macrophytes (on the surface of water) provide a habitat for aquatic life and are excellent indicators of the health of water. Insects sustain the bird population while amphibians and reptiles control the insect population.

Islands bring in new life

While bird population and density have reduced due to lack of roosting places, the incorporation of islands in rejuvenation has provided a new home for numerous birds. EMPRI researchers have found bird islands (holms) in 66 lakes of which 41 are rejuvenated ones. Three lakes — Ulsoor, Gangondanahalli and Sonnenahalli — have six islands.

“(There have been) steps to conserve the aquatic biota, such as construction of islands, to conserve avifauna, introduce fingerlings in the rejuvenated water bodies and construct wetland ... but it needs a lot of improvement in the conservation of water bodies using native biota,” states the report.

Weeds over-running

However, the report reveals the danger to the last remaining biodiversity from pollution, which encourages the rapid growth of weeds. Of the existing 680 water bodies, weeds are seen in a staggering 89% of the water bodies. Of this, 11% are completely covered by weeds.

EMPRI estimates 22 types of aquatic or shrub weeds in and around lakes. The report notes the devastating impact of these weeds: “Aquatic weeds reduce the effectiveness of water bodies for fish production by reduction of light transparency and cause depletion of DO concentration...which impacts biodiversity...Dense growth provides an ideal habitat for mosquitoes and vector borne diseases.”

Humans and lakes

During their study, EMPRI found 773 water bodies (lakes, gokattes and kuntes) in the 1,300-sq-km Bengaluru Metropolitan Area, and has become an integral part of life, particularly in areas that still harbour vestiges of a rural lifestyle. As many as 580 water bodies are used for fishing, agriculture, cleaning as well as animal husbandry activities, notes the report.

However, the usage can be unsustainable, and a cause of further pollution. Direct idol immersion and waste from religious activity in 26 lakes leads to leeching of toxic metals, paints and increase eutrophication (algal blooms). Washing of vehicles, animals, clothes or mass bathing in 56 lakes have led to increase in oils and grease, microbial pollution, phosphates, among others.

To ensure that these lakes do not deteriorate with unsustainable use by humans, the EMPRI report advices: “Rejuvenation and maintenance based on the services delivered or various uses is required. That is, if a water body is rich in bird diversity, than it should be rejuvenated and maintained such that there is minimal public interference. Similarly, if a water body has very less biodiversity, then it should be developed for recreational purposes.”