River Ecology is a system comprising of the river itself and the land alongside it. It's the zone where the non-living components of the river like water, rocks, sediment etc are intrinsically connected to living organisms like fish, plants, microbes etc. The river ecology comprises of four dimensions namely the Length, Width, Depth and Time of the river flow.
The physical characteristics of the river changes as it flows from mountain to ocean. The characteristics are depicted below:
With change in physical characteristics of river along its length, the biota (living organisms) changes too. The River Continuum Concept (RCC), attempts to generalize and explain observed longitudinal changes in stream ecosystems.
The ecosystem of River width wise can be categorized in two main components:
Unlike along the length of River, the ecosystem along the width of the river cannot be generalised. The flora of a floodplain vegetation can be approximately classified as shown below :
However, the stream bank vegetation plays a very important ecological function listed below:
The seasonal increase of water level has an important role in supporting river ecosystems. Rivers often link to adjacent wetlands only at high water level, which is often the only possibility for fish populations to migrate.
Apart from this, the depth of flow also affects the Groundwater level of the adjacent aquifers.
The volume of water flowing in a river at a particular point (runoff) varies with time.The increase in runoff leads to flooding which provides very important ecosystem service.
The processes of erosion, sediment transport, and deposition interacting with vegetation make river corridors very dynamic ecosystems.
The discussion on River Ecology would be incomplete without the discussion on Minimum Environmental Flow.
However, there are more than 200 methodologies for determining the Minimum Environmental Flow depending upon the purpose of such determination. Few examples are as follows :
Wetlands are areas where water is the primary factor controlling the environment and the associated plant and animal life. They occur where the water table is at or near the surface of the land, or where the land is covered by water. There are several types of wetlands like Swamps, Marsh, Bogs and Fens etc.
Wetlands are often called the "kidneys of the landscape" since, like kidneys, they filter out harmful materials.
Wetlands support a rich food web, from Microscopic algae and submerged vascular plants to great blue herons and otters.
Coastal zones are terrestrial areas dominated by oceanic influences and marine aerosols & marine area where light penetrates throughout.
The coastal ecosystem comprises of several entities like life on rocky coasts, life in sediments, Mangroves, Estuaries, Seagrass bed, kelp forest, coral reef etc. Few of them are discussed below :
Mangrove swamps are found in tropical and subtropical tidal areas. Mangrove forests consist of diverse, salt-tolerant tree and other plant species, ranging from small shrubs to tall trees.
Sunderban Mangroves : home to the Majestic Bengal Tigers
They are important to man as a source of timber, charcoal and tannin, their stabilizing properties protect coastlines from major erosional damage by tropical storms and they provide an important nursery ground for many commercially important fish and shellfish. Apart from this it also provides important ecosystem services like :
Estuaries can be defined as semi-enclosed bodies of coastal water which retain a free connection with the open sea and within which sea water is measurably mixed with fresh water of terrestrial origin (Pritchard, 1967).
Sketch of an Estuary
The biota in the Estuaries is sparse because of highly stressful environment due to salinity. However, it still provides very important ecosystem services like :
Coral reefs are large underwater structures composed of the skeletons of coral, which are marine invertebrate animals.
The Coral Reefs provide following ecosystem services :