Groundwater depletion and its adverse impacts
Expansion of agricultural field and decreasing pattern of usage of surface water, accelerates the over exploitation of groundwater.
Groundwater is the water found under ground in the cracks and spaces in soil, sand and rock. It is stored in and moves slowly through geologic formations of soils, sand and rocks called aquifers. It is one of the Nation’s most important natural resources. It plays a major role in ensuring livelihood security across the world, especially in economies. Groundwater contains mineral ions which slowly dissolved from soil particles, sediments and rocks named as dissolved solids.
Continuous discharge of industrial effluents, domestic sewage, use of fertilizers and pesticides, waste dump and over exploitation of the resources have badly impact on groundwater sustainability. Though over utilisation of groundwater is the key factor for groundwater depletion but there are other factors which have negative impacts on groundwater sustainability. The most important impact on groundwater depletion is loss of base flow; other impact being severe crisis of safe drinking water and irrigated water.
Groundwater is one of the extremely valuable renewable resources. Now a day’s pollution of groundwater resources is a matter of serious concern. Groundwater quality comprises the physical, chemical and biological qualities of water. Temperature, turbidity, color, taste and odor are the physical quality of water. pH, E.C, N,P,K ,organic carbon etc. represent the chemical quality and total microbiological count etc. stand for biological quality of groundwater. Microbial components are also available in groundwater. There are different forms where groundwater is stored and human can withdrawal from there namely aquifers, wells etc. Manmade activities play a key role for depletion of natural composition of groundwater through disposal or dissemination of toxic chemicals and microbial matter at the land surface and into soils, or through waste water. In India most of the population is dependent on groundwater as the only source of much clean drinking water supply than surface water. Sustainable groundwater management is a burning challenge for the 21st century because it ensured livelihood security across the world. Agriculture dependent countries like India are most relied on groundwater. Although groundwater is mentioned as renewable resource but it does not recycle rapidly. The groundwater recycling depends on aquifers depth, type, location and connectivity etc. Generally the average time of renewal of groundwater is 1,400 years as per World water Balance, 1978. Significantly renewal rate of shallow groundwater are about 15 times less than deep groundwater (Jones-1997). Of all the Earth’s water, fresh water is very limited (three per cent) compare to saline water (97 per cent). Of all the limited and valuable fresh water, a huge amount of water (68.7 per cent) is permanently stored in icecap and glaciers and other huge amount of fresh water is stored as groundwater. Approximately out of 37 million cubic kilometers of total fresh water about 8 million cubic kilometers of fresh water is stored as groundwater. So groundwater is a key source of fresh water.
Fresh water demand rise day by day, especially for irrigation purpose. The percentage of total irrigation water increased 23 per cent in 1950 to 42 per cent in 2000. Water shortage increased dramatically and it is projected that around 3 billion people will be water stressed by 2025. Increasing demand of water and decreasing availability of water create a significant pressure on groundwater and this ultimately depleted the groundwater quality. At present, approximately 61 per cent of total irrigation water has come from groundwater. Expansion of agricultural field and decreasing pattern of usage of surface water, accelerates the over exploitation of groundwater. Though over utilisation of groundwater is the key factor for groundwater depletion but there are also other important factors those have negative impact on groundwater sustainability. Contamination or presumption contamination also has adverse impact on groundwater. Agricultural chemicals like N, P, K, pesticides etc. percolate through soil and contaminate the groundwater. Naturally occurring constituents like arsenic fluoride, chloride etc. contaminate the groundwater and made the water unsafe.
The most important impact of groundwater depletion is loss of base flow. If the base flow is reduced then there are different crucial additional impacts take place. These are: increased magnitude and frequency of floods; loss of wetland and riparian vegetation; changes in channel morphology; accelerates erosion; increased frequency of drought and loss of biodiversity. Groundwater, as a valuable resource, we should meet its sustainability for our basic needs. Firstly, we should not exploit in an unsustainable manner. Groundwater use policy should be sustainable and depends on basin’s recharge capacity. We should follow the groundwater basin mass balance equation P-E-T-S-G-D= 0, where P= precipitation, E = Evaporation, T= Evapotranspiration, S= Surface runoff, G= groundwater runoff, D= Deep percolation. In rural areas where groundwater is the main source for drinking, implementation of well-head protection is necessity and secondly must control the waste water to percolating through soil and disposing of waste water to neighboring septic system. Tapping primary deep percolation and secondary shallow percolation are important measures for maintaining groundwater sustainability. Baseline and time dependent hydrological studies are necessary to monitor the groundwater. Conjunctive use of surface water and groundwater, desalination, recycling and waste water reuse, water harvesting, increase recharge to the groundwater system are also effective measures to promote sustainable groundwater supply. Protection of the water resource from depletion is not possible unless the users agree to cooperate and manage the resource themselves in a sustainable manner. Moreover state also needs to play a key role of facilitating and fostering community action for sustainable management. Lastly awareness should be raised towards groundwater sustainability.