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Essay on Bio-Drainage
Essay Contents:
- Essay on the Definition of Bio-Drainage
- Essay on the Concept of Bio-Drainage
- Essay on the Bio-Drainage Tree Species
- Essay on the Limitations of Bio-Drainage
Essay # 1. Definition of Bio-Drainage:
Bio-drainage may be defined as “pumping of excess soil water by deep-rooted plants using their bio-energy”. The bio-drainage system consists of fast growing tree species, which absorb water from the capillary fringe located above the groundwater table. Absorbed water is translocated to different parts of plants and finally more than 98 per cent of the absorbed water is transpired into the atmosphere mainly through the stomata.
This combined process of absorption, translocation and transpiration of excess groundwater into the atmosphere by the deep rooted vegetation conceptualises bio-drainage. Fast growing Eucalyptus species, known for luxurious water consumption under excess soil moisture condition, are suitable for bio-drainage.
These species can be planted in blocks in the form of farm forestry or along the field boundary in the form of agroforestry. Other suitable species for bio-drainage may be Casuarina glauca, Terminalia arjuna, Pongamia pinnata, Syzygium cuminii etc.
Essay # 2. Concept of Bio-Drainage:
In natural environments, components of hydrological system, i.e. rainfall, evapotranspiration, change in soil-water storage and drainage, are (on average) in balance. Periods of high rainfall might temporarily result in increased drainage flows, a rise in the groundwater table and/or soil moisture storage, then over a period of about 5-10 years equilibrium is established.
Vegetation plays a vital role in the evapotranspiration and soil- water storage components of this balance. When natural vegetation is cleared and replaced by crops or tree plantations, the seepage losses to the groundwater table under the new land use system are either higher or lower than under the pre-clearing situation.
Plantations of fast growing tree species such as Eucalyptus, when grown on previously cleared land, could also result in strongly reduced accessions to the groundwater and in the drying-up of wells and springs. The driving force behind the bio-drainage concept is the consumptive water use of plants.
Deep-rooting characteristics of trees make them extremely efficient users of water. While shallow-rooted grasses and crops have limited access to underlying water tables, deep rooted trees can access water tables down to several meters.
Essay # 3. Bio-Drainage Tree Species:
Eucalyptus species are generally considered to be effective for bio-drainage purposes. Acacia nilotica, Dalbergia sissoo, Tecomella undulata and Ziziphus mauritiana are other species that have performed quite well in plantations along leaking canals in arid conditions. Species suitable for non-irrigated conditions are Acacia tortilis, Prosopis cineraria, Prosopis juliflora and Parkinsonia.
Suitable Eucalyptus species for different areas of India are given below:
Essay # 4. Limitations of Bio-Drainage:
i. Bio-drainage can be practised with certain limitations. The transpiring capacity of trees reduces progressively as the groundwater salinity increases. When the groundwater salinity is about 8 dS m-1, Eucalyptus trees may transpire only one-half as much water as they do under non-saline conditions.
ii. Long term sustainability of non-irrigated bio-drainage tree plantations growing in shallow saline water table areas may be questionable. At some stage in their commercial life, their growth performance could be affected by increasing root- zone salinity. After the trees are harvested, in the absence of sub-surface drainage to provide salt balance, the accumulated salts in the root zone will move to the surface by capillarity and impact on successive land use.
iii. No biological system is sustainable without salt balance. Salt balance is one of the most important issues to be addressed before bio-drainage can be promoted as an appropriate drainage management technology.
iv. Planting large areas of new crops, especially tree crops, will have significant impact on regional economies and social structures.
v. Release of toxic chemicals from leaf, stem and roots extracts of Eucalyptus may inhibit the germination and seedling growth of some crops.
vi. Bio-drainage occupies potentially valuable land thereby decreasing the availability of area for commercial/food crops.