The spreading presence of Cabomba, a fast-growing submerged aquatic weed species, along the Aranmula Sathram Kadavu stretch of river Pampa has evoked serious concern among environmentalists as well as local population.

The Pampa Parirkashana Samiti (PPS), a Kozhencherry-based eco group, has recently conducted a study on the fast-spreading Cabomba weeds, posing threat to river Pampa, as part of its year-long 'Pampa Darshan' programme.

According to Mr. N.K. Sukumaran Nair, PPS general secretary, the study was conducted in association with the Kottayam Nature Society (KNS). Dr. N. Unnikrishnan, Reader in Botany at Vazhoor NSS College and KNS secretary, led the technical study team.

Cabomba (Cabomba Caroliniana), also known as the Fanwort plant, is said to be a native of north and south America. It grows in stagnant or slow flowing water bodies to a depth of about 12 ft. Mr. Nair said this aquatic weed is found to have been fast spreading in the wetlands of Kerala, especially in the Vembanad region.

The PPS study on the taxonomy and distribution of aquatic plants in Kuttanad showed that Cabomba is growing in all types of water bodies. Dense growth of this dangerous weed was found in canals, rivers, Vembanad lake and even in paddy fields, he said.

Dr. Unnikrishnan told The Hindu that Cabomba is a popular aquarium plant and its natural population in our wetlands might have been from aquarium escapes.

Threat to the river system

He said the fast spreading growth of this disastrous weed along the Pampa river course at Aranmula should be taken as an alarming threat to the river system as a whole.

According to him, Cabomba with its extremely dense strands which obstruct the free flow of water is a serious threat to the water bodies. 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 degradation of the river system, he said.

A dense population of this plant in the river further reduces the water flow and increases siltation. Excessive exploitation of sand has exposed the clayey bottom of the river which has become ideal for the growth of this weed.

Dr. Unnikrishnan said this weed contains a high degree of allelopathic chemicals which influence the growth and survival of other species of flora and fauna. The weed has very few natural enemies due to the presence of these chemicals. Moreover, its intense growth blocks the entry of light into water, badly affecting the diversity of indigenous fish varieties and other vertebrate and invertebrate fauna, he added.

Dr. Unnikrishnan said studies have found that the high nutrient content of water, due to flow of sewage, agrochemicals and land washouts into it, was another major factor contributing to the fast growth of this dangerous weed.

Mr. Nair says this alien weed has the capacity to change the entire ecology of the water bodies in the State. Unfortunately, the Government as well as the scientific community were yet to take note of this serious issue, he added.