Biomass of Fast-Growing Weeds in a Tropical Lake: An Assessment of the Extent and the Impact with Remote Sensing and GIS

The Oussudu watershed is situated at 11°57' North and 77°45 ' East on either side of the border separating the Union Territory of Puducherry and the Indian state of Tamil Nadu (Figure 1). Apart from playing a crucial role in recharging the ground water aquifers, the Oussudu watershed also harbors rich flora and fauna (Chari and Abbasi, 2000; 2002; 2005). This watershed supports Puducherry's largest inland lake Oussudu which is also called Ousteri (a Tamil language hybrid of Oussudu and eri, meaning Oussudu lake) with a surface area of 8.026 Km2 and shore line length of 14.71 Km2. Oussudu lake is such an important wintering ground for migratory birds that it has been identified as one of the heritage sites by IUCN (Interactional Union for Conservation of Nature) and has been ranked among the most important wetlands of Asia (Scott 1989). In the recent past, Oussudu lake and its watershed have been subject to enormous pressures due to the increasing population, industrialization and urbanization. The resultant inputs of pollutants – rich in nitrogen and phosphorous – has provided aquatic weeds an opportunity to grow uncontrollably in the lake to the exclusion of other flora. This has led to a defacing of the lake by large patches of ipomoea (Ipomoea carnia) and other weeds.