Study of Pampa Parirakshana Samiti highlights threat posed by Cabomba

The once-prolific and vibrant rivers Pampa, Achencoil, and Manimala and their tributaries in Central Travancore are facing an alarming degradation threat from invasive aquatic species.

The Pampa Parirakshana Samiti (PPS), a Kozhencherry-based environmental organisation that has been campaigning for the conservation of the Pampa river for the past two decades, conducted a study with the support of the Kerala State Biodiversity Board on the management of various invasive aquatic species in the river, especially Cabomba, a fast-growing submerged weed.

The study team comprised T.N. Ramakrishna Kurup, former Head of the Department of Physics at the Birla Institute of Technology and Science, Pilani; N.K. Sukumaran Nair, environmentalist and PPS general secretary; and Anju Chandran, research fellow. The team found the spread of Cabomba along many stretches of the Pampa river and its tributaries.

Siltation

N. Unnikrishnan, Reader in Botany at NSS College, Vazhoor near Kottayam, who guided the team, says that the extremely dense strands of Cabomba obstructs the free flow of water and promotes increased siltation of the river, gradually making it shallow and dry. Cabomba (Cabomba caroliniana), also known as Fanwort plant, is a native of north and south America that grows in stagnant or slow-flowing water bodies to a depth of about 12 ft. According to Mr. Nair, Cabomba is an aquarium plant introduced into the riverine systems and wetlands in Kerala by mistake and it affects all other inhabitants in a water body.

Mr. Nair says uncontrolled human interference, mainly sand-mining, accounts for it.

Thanneermukkom bund

Mr. Nair says the salinity of the Vembanad Lake has been highly reduced with the construction of the Thanneermukkom salt water regulator (bund), leaving the lake almost a freshwater system. This creates a conducive atmosphere for Cabomba and other aquatic weeds to flourish. It is also observed that this species disappears completely during summer months when the barrage shutters remain open, he adds. This shows that Cabomba can be eradicated if the salt water flow into the Vembanad Lake is regulated.

Dr. Unnikrishnan says Cabomba contains a high degree of allelopathic factors that influence the growth and survival of other flora and fauna. Moreover, this weed has very few natural enemies owing to the presence of these chemicals. The thick weed blocks entry of light into water, badly affecting the diversity of indigenous fish varieties and other fauna.

The high nutrient content of water, owing to flow of sewage, agrochemicals, and land washouts into the river, is another major factor contributing to its growth.

Biological control

Salvenia (‘African Payal’) was once a major menace in the Vembanad system and it was successfully managed by Kerala Agricultural University by introducing its natural enemies. The PPS is of the opinion that the government may engage a scientific institution with the task of developing suitable natural enemies for managing Cabomba too. Experts say that Cabomba has the capacity to change the entire ecology of waterbodies in the State.