In fits and starts and with a lot of pressure from the Courts, the community and the citizenry, the tank ecosystem is being revived in the city. In many tanks such as the one in Rachenahalli, Jakkur, Doddabommasandra or the one in Lower Ambalipura and in most of the tanks being rehabilitated by the BDA or the BBMP, a silt trap and artificial wetland is incorporated as part of the design of the lake itself. Storm-water entering the lake will go through this stilling basin and the plant ecosystem will further clean up the waters, thus ensuring cleaner water in the lakes or so is the theory.
Even treated waste-water from sewage treatment plants can be further cleaned and polished by these wetlands, thus enabling them to be sent to surface water bodies such as lakes and rivers safely. Basically of two types, surface flow and sub-surface flow, these wetlands try and mimic their natural cousins. A variety of plant types such as cat-tails, bulrushes, reeds and even water hyacinths can populate these places.
These plants provide a variety of functions such as reducing the turbidity of the water flowing in, removing nitrates and phosphates, supplying oxygen to the water, reducing and absorbing heavy metals and most importantly hosting a whole range of bio-diverse life.
Birds coming in Birds such as purple moorhen, cattle egrets, purple and grey heronare are often seen in these wetlands. Many amphibians and reptiles will also occupy this habitat. These are perfect grounds for students to learn the functioning of water and soil ecosystems.
With these constructed wetlands it would be essential to study and understand their functions better. There are very few centres of learning which are capable of training students in understanding, designing, building and managing constructed wetlands.
While Ecological Science studies do a thorough job in studying natural ones, it requires a multi-disciplinary approach to look at constructed ones and that so far seems to be missing in India. A wetland ecosystem is much more productive and much more diverse than a water ecosystem.
Right now in the city, tens of constructed wetlands have been created but unfortunately none of them are being maintained because the skill is simply not there with the institutions involved in redoing the lakes.
With time these wetlands will deteriorate and without management their functioning will be impaired because the dying plants need to be removed occasionally to help the system function better.
Karanji Lake next to the Mysore zoo is one such lake where a small experiment is going on to maintain the quality of lake water.
The cleaning of urban water bodies and rivers is now a national mission. Constructed wetlands would be a major weapon in the hands of designers to help improve water quality and thus clean rivers and lakes.
We need to include them as part of the process of rejuvenating lakes and also treating waste-water and build the capacity to be able to construct and maintain them. That would be water wisdom.
