Yelahanka Puttenahalli Lake and Bird Conservation Trust


Balance between hydrophytes & phytoplankton was attempted by deweeding for the first time after the rejuvenation was undertaken

De-weeding methods, types of weeds and quantity.

In most of the Lake deweeding efforts this far, as there have been no prior art or quantification, it has always been difficult to decide upon the simplest and most effective method to remove weeds from the Lake on the one side and on the other assess the quantum and nature of weeds that need to be removed from the water body (Lake).

During the first manual weeding approach involving about 60 college students, we learnt the following lessons.

  1. The lake water when filled with floating and emergent weeds gives rashes to a few and the reason for this form of rashes is not clear from the water quality parameters that have been measured.  Thus not everyone can enter the water body to remove weeds.
  2. Most floating water weeds are generally enmeshed to such an extent that it is necessary to cut them to separate them in 50-150m2 rafts for floating weeds.  This can be done by wading along the lakebed when the depth is less than 1.5m and separating it with by hand or a strong stick.  
  3. In deeper regions one needs to use a coracle in which the person in the front uses the paddle to separate a chunk from the main body of floating weed mass.  
  4. A weighted rope, weighted in three points can be pushed into the middle of separated raft of weed mat and can easily be pulled to the shore along with the coracle.  When the weed raft reaches the shore, the coracle then is paddled back to where the next weed raft needs to be separated from the larger weed mat.
  5. When two teams work in tandem with two coracles and two ropes or when one team cuts the weed mats into smaller rafts and other hauls it to the shore, there will adequate extent of work to lift the weeds out of water and place it on the shore.  
  6. It is better to deploy a power shovel and backhoe (JCB) to lift the hauled weed rafts out of water and pile it on the shore.  
  7. g) The piled weeds rapidly dry and become compost in about 30-45d.  

When such weed growth occurs in our case dominated by Alternanthera species, the weight of the weed mat will reach and saturate around 35-55kg wet mass /m2 at around 10-15% dry matter.  For reasons not available it appears that partially rooted plants in shallows have lower dry matter (10%) compared to completely floating plant mass (~15% dry matter).  This turns out to be between 350-550t of wet weeds/ha.