Change In Land Use Pattern Causing Recharge Variability As Derived By Isotopic Technique In Delhi Region

摘要

National capital territory of Delhi is experiencing the exponential growth in population resulting in more demand of water from different sources for different purposes like domestic, agricultural and industrial activities. As the other sources are diminishing hence putting pressure to the renewable but exhaustable resource called groundwater. Moreover, the population growth and industrial development are inducing unplanned use as well as misuse of the land leading to conversion of useful land into wasteland. This is evident by the fact that the total cropped area in 1980-81 was 87599 ha as compared to 48917 ha in 1996-97, a reduction of 44%. In Delhi region the process of change in land use pattern linked with water scarcity started in late eighties. An isotopic study during 1990-92 showed wide range of δ~(18)O values (-2.8 per thousand to -8.6 per thousand), indicated the spatial inhomogenity in the groundwater aquifer system in its lateral extent. The small isotopic gradients in groundwater suggested the occurrence of high permeability and potential recharge zones in the study area. In the highly polulated blocks of Delhi viz. Najafgarh, Alipur and Nangloi where demand of groundwater is more, indiscriminate pumping of groundwater which allowed forceful mixing of highly saline groundwater to the good quality groundwater, as visualized by the δ~(18)O-Cl relationships. These relationships showed different flow path ways of intermixing in different years in the over exploited, region. While fluoride contaminated area was around 52% in Alipur Block, 80% in Najafgarh and Nangloi blocks. The nitrate contaminated area was 42% in Najafgarh Block and 15% in Nangloi block. As compared to the decade back situation, the 1999-2000 study for the same region showed that the fluoride contaminated area is 27% in Najafgarh block, 42% in Nangloi block and 33% in Alipur block. And the nitrate contamination is 9% in Najafgarh block , 28% in Nangloi block and 11% in Alipur block. The decadal change in land use and water use induced the variability in the chemical composition of groundwater in the area. Although, the groundwater quality and quantity in an area is controlled by many factors, yet in Delhi area the changes in water use induced by land use pattern changes are governing the groundwater rechargability and quality. The main reasons for this change are tremendous increase in urban as well as rural population, causing spreading of urbanization and the important one is low crop yield or less economic return compelling the people for occupational shift. Therefore, sustainable water management demands precise information on fast changing land utilization, rechargability conditions and accurate and more reliable estimation of groundwater extraction as linked to short-term and long-term developmental activities.