16-A satellite imagery and GIS based study on the urbanization and the pollution of the Oussudu Lake as indicated by aquatic weed infestation

Abstract

The most evident, dramatic, and conclusive evidence of the gross pollution of any lake due to urbanization is provided by aquatic weeds. Whereas industrial pollution may or may not add plant nutrients to a lake, demographic pressure almost always does. The resulting excessive supply of nutrients enables the invasive plants to thrive and colonise the lake. Such colonization can provide almost graphic evidence of the severity of demographic pollution of a lake. In this paper we present a study of Oussudu lake which is the largest freshwater lake of Pondicherry as also a heritage site. We have conducted an assessment of the area covered by the amphibious weed Ipomoea carnia using the satellite imagery IRS — ID LISS III in conjunction with GIS. The infestation by submersed weeds was simultaneously studied by ground truth studies. The weed biomass density in each case was estimated at 5 sampling stations by biomass harvest method. The study reveals that almost a fifth of the lake area has been colonised by Ipomoea. The rest of the lake is heavily infested by submersed weeds, principally Ceratophyllum and Hydrilla. The implications of these findings and the measures necessary to reverse the trend of the demographic pollution of Oussudu are discussed in the paper