a1 Scheme of Research on the Ecology of Aquatic Weeds of Kerala; Professor, Department of Botany, Mar Ivanios College, Trivandrum 15, India.
A comparative study of the floristic composition of aquatic vegetation growing in certain ponds in parts of Kerala, and those recorded as growing in the same ponds more than 20 years ago, reveals changes that are often extreme. Thus many of the once-dominant species have either dwindled or disappeared. In some ponds, most of the components of the original flora of only a quarter-of-a-century ago have been completely replaced by thick mats of Salvinia over the past two decades. Salvinia multiplies vegetatively very rapidly (cf. Mitchell et al., 1980), forming mats on which secondary colonists grow. This commonly leads to a gradual filling of the pond. Besides, Salvinia infestations also cause considerable loss of water from water-bodies through increased evapotranspiration. If these ecological processes are allowed to continue, many of our water-bodies seem sure to dry up in due course.
A well-planned and systematic method of control, involving physical removal—either through manual labour or specially-designed machines—to be followed by biological control (for example by grazing vertebrates or invertebrates), would keep the explosive spread of the weed under check. The huge mass of harvested weed could be utilized for production of organic manure, cooking gas, or hard-boards, or could be dried as packing material. There should also be vigilance by a surveillance squad of experts in the scientific disciplines concerned, which would be effective in preventing further spread of the weed—much as is already being practised with good results for the hydroelectric reservoirs of Kerala.