Wetlands refer to lowlands covered with shallow and sometimes temporary or intermittent waters. Wetlands include marshes, swamps, bogs, wet meadows, potholes, shallow lakes and ponds.
However deep lakes, reservoir and permanent waters of streams are not considered as Wetlands. Hence we can say wetlands are transitional lands between terrestrial and aquatic systems where the water table is usually at or near the surface.
Importance of wetlands
Wetlands posses a great ecological significance in terms of, net primary production, micro-climatic control, ground water recharge and habitat to large number of flora and fauna.
It also plays a vital role in nutrient recycling and storage as well as biodiversity conservation. Wetlands help to retain water during dry periods, thus keeping the water table high and relatively stable.
Threats to Wetlands
Rapidly expanding human population, large scale changes in land use, different development projects and improper use of watersheds have caused the decline in wetland resources of the country.
The encroachment of wetlands leading to the extinction of rare aquatic species. The negative impacts on wetlands are mainly caused due to sediment load, pollution, aquaculture development and weed infestation.
The suspended micro particles along with toxic substances are transported from agricultural lands and effectively interface with the incoming solar radiation. This result in reduced photosynthetic activity and lowering of redox potential, causing impeded respiration to heterotrophs as well as degraded spawning habitat.
Finally it promotes over growth of algae and aquatic plants (eutrophication), which depletes oxygen, creates turbid condition, reduce species diversity (as sensitive species are replaced by lower number of less desirable species).
In addition decrease in primary production is associated with increase in sedimentation and turbidity and produce negative cascading effects through depleted food availability to zooplanktons, insects, fresh water mollusks, and fishes.
Hence there is a need to create inventory of various wetlands and their periodic assessment in terms of aquatic conditions.
For wetland management, the first and foremost task is to make its inventory and distribution. Remote Sensing data by virtue of its synoptic, multi-spectral and repetitive capability can be used suitably to demarcate the wetlands, changes in wetlands spread and time varying wetland profile.
High resolution satellite data with multi-spectral capability helps to accurately identify even the smallest wetlands, their turbidity level and the aquatic vegetation.
Turbidity level can be examined by selective use of satellite bands as turbidity is directly related to optical density of the medium, however aquatic vegetation could be identified through band combination because red band absorbed by the vegetation and infrared is reflected depending upon the vigor and pigment concentration.