INTRODUCTION

Wetlands are the areas inundated with water, where the water table is close to the land.   They constitute a vital ecosystem, which helps in maintaining the ecological balance, serving the various needs of the society by recycling nutrients, purifying water, attenuating floods, maintaining stream flow, recharging ground water, etc., making it one of the most productive ecosystems.

Societies depend on aquatic ecosystems for food, and for domestic, agricultural and industrial purposes. The economic benefits from wetlands to the society are in the form of water supply, commercial fisheries, agriculture, energy resource, wildlife resource, recreation, tourism, cultural heritage, biodiversity, etc.

The myriad ways, in which wetlands are used, along with the numerous anthropocentric activities, have stressed wetlands in diverse ways. This is causing impairment of wetlands quality and disrupting its natural functions, which have led to direct physical destruction (drained for agricultural and developmental activities), siltation (soil erosion and removal of vegetative cover) and pollution from both point sources (municipal sewage and industrial effluents) and non-point source degradation (urban and agricultural runoffs) within the watershed and from more insidious long-range atmospheric transport of contaminants. Pressures from burgeoning population and unplanned urbanisation have subjected these ecosystems to tremendous stress threatening their very existence. In Bangalore, as elsewhere, wetlands are being lost due to,

1. Population pressures and growing economies leading to unplanned urbanisation and expansion, exerting greater pressures on land resources.
2. Lack of governmental commitment in understanding the importance and essence of conservation and management of wetlands.
3. Lack of cohesive academic research centered on wetland per se for its protection, management owing to financial constraints and lack of infrastructure and required expertise.
4. Lack of proper stormwater management (source of non point sources) and unregulated land use management have also led to the persisting problems of pollution, eutrophication, invasion of exotic species, toxic contamination by heavy metals, pesticides and organic compounds.

Excessive nutrients and organic matters have led to eutrophication, siltation from erosion due to agricultural, construction, logging and mining activities, introduction of exotic species, acidification from atmospheric sources and contamination by toxic metals such as mercury and organic compounds (such as PCBs), and pesticides. In addition to physical alteration at the land-lake interface (e.g. draining) and hydrologic manipulations also (such as, damming outlets to stabilise water levels) affects the structure and functioning of the ecosystem.

The loss of wetlands has led to increased flooding in low lying areas, while degradation has resulted in decline in both surface and ground water quality, decrease in biological diversity, altered productivity of these ecosystems and its beneficial uses. Studies also show that about 40% of all waterbodies in Bangalore are mainly sewage fed [Krishna et al, 1996]. A broader definition of  "urban wetland" is used to highlight aquatic systems predominantly affected by urban population and their drainage basin dominated by urbanisation, rather than the geology, soils or plants.

Realizing the importance of wetlands and its role to the society, a study was undertaken to assess the spatial and temporal changes, and the present status of wetlands to identify the major problems and threats encountered by wetlands, and formulate suitable strategies for their restoration, conservation and management.