The song of the river ends not at her banks but in the hearts of those who have loved her. The once-prolific and vibrant rivers Pampa, Achenkovil and Manimala as well as their tributaries in the Central Travancore region are facing an alarming degradation threat from certain invasive aquatic species. Thanks to man’s neglect of nature coupled with the over-exploitation of the river resources over the past few decades.

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

The study team comprised of 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 PPS team has found spreading presence of Cabomba, a fast-growing submerged aquatic weed species, along many stretches of the river Pampa and its tributaries.

Pampa is considered as the lifeline of Pathanamthitta, Kottayam and Alappuzha districts and about four million people depend on it for their daily water needs. Biodiversity depletion of the riverine system of Pampa is a matter of serious concern, says Mr Nair.

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 feet. The PPS study team has found this aquatic weed spreading fast in the rivers and wetlands of Kerala.

According to Mr Nair, Cabomba is an aquarium plant introduced into the riverine system by mistake and all the other natural inhabitants are suffered by it.

The dense growth of this invasive species has already reduced the water flow and increased siltation in many reaches of Pampa. The plant is rooted in the clayey bed at the bottom from where the sand. Mr Nair has attributed this foreign weed menace in Pampa and its tributaries to the uncontrolled human interference, mainly sand mining.

The spreading presence of these invasive species along the Aranmula stretch of Pampa has evoked serious concern among the local population as it has already started creating problems to the riverine ecology. Thannermukkom bund

Mr Nair says the salinity of the Vembanad lake has been highly reduced with the construction of the Thanneerkumukkom salt water regulator (bund), leaving the lake almost a fresh water system, leaving a conducive atmosphere for Cabomba and other aquatic weeds to flourish in it and other connected water bodies. It is also observed that this species disappear 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 properly regulated.

N. Unnikrishnan, Reader in Botany at NSS College, Vazhoor near Kottayam, who has guided the PPS study team said that Cabomba with its extremely dense strands which obstruct the free flow of water is a undoubtedly a threat to the water body. The dense growth of this aquatic weed promotes increased silting of the river, gradually making it shallow and dry. The Cabomba presence in Pampa is an indication of the fast decreasing river flow and alarming rate of river degradation, he said.

Dr Unnikrishnan says Cabomba contains high degree of allelopathic chemicals which influence the growth and survival of various other species of flora and fauna. Moreover, this weed has very few natural enemies due to the presence of these chemicals.

The intensity of its growth blocks entry of light into water, badly affecting the diversity of indigenous fish varieties and other vertebrate and invertebrate fauna.

The high nutrient content of water, due to flow of sewage, agrochemicals and land washouts into the river, was another major factor contributing to the fast growth of this dangerous weed.

The PPS study has stressed the need to implement the key recommendation in the Kuttanad Package prepared by the M.S. Swaminathan Committee to ensure proper regulation of the Thanneermukkom bund, facilitating salinity intrusion into the Vembanad lake as and when necessary.

Biological control

Salvenia (African Payal) was once a major menace of the Vembanad system and it was successfully managed by the Kerala Agriculture University by introducing its natural enemies.

PPS is of the opinion that the Government may engage a scientific institution with the task of developing suitable natural enemies which can be effectively utilized for managing the Cabomba menace too.

Experts say that Cabomba has the capacity to change the entire ecology of various water bodies in the State, if the authorities failed to launch effective de-weeding drive with out any further delay.

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