Heavy metal distribution and environmental status of Doon Valley soils, Outer Himalaya, India

 Doon Valley is surrounded by two major river systems (Ganga and Yamuna) on either side, with a water divide passing nearly across the centre of the valley, and is sandwiched between two mountain ranges in the fragile ecological systems of the Himalayan foothills. In total 398 soil samples were collected from the valley in a grid pattern (∼1 sample per 2 km²) and investigated for their heavy metal (Cr, Cu, Ni, Pb and Zn) abundances that are environmentally sensitive. Comparison of the heavy metal abundances with the contamination threshold values (CTV) revealed that most of these elemental abundances in Doon Valley soils fall well within the range of the uncontaminated to slightly contaminated category. In the case of Cr and Ni, a sizeable number of samples exceeded the CTV (250 and 100 mg kg^–1 respectively) with an overall background value of 109 and 52 mg kg^–1 respectively. Sites of high Cr and Ni mostly occur in the Ganga Catchment (GC) sector that includes even relatively undisturbed forestland. The source of this contamination is attributed to geological factors which indicate contribution from the mafic volcanics of the Lesser Himalaya. This is also consistent with the distribution pattern of Mn and Fe, though their abundance levels are not alarming. The background concentration of Pb is low (22 mg kg^–1) in Doon Valley soils; however, signs of gradual Pb contamination are palpable in and around the centre of the Dehra Dun city and along the highways. Aluminium normalized heavy metal ratios were found to exhibit narrow variability in the case of Cu, Ni and Cr and had good correlation with Al, indicating their affinity and association with the clay minerals. On the other hand, Pb and Zn seem to be associated with non-silicate sources. Received: 7 January 2000 · Accepted: 30 July 2000     

Identifying potential sites for artificial groundwater recharge in sub-watershed of River Kanhan,India

Groundwater is an important decentralized source of drinking water. Being underground, it is relatively less susceptible to contamination. In addition to domestic needs, it is extensively used for irrigation and industrial purposes. It is therefore necessary to implement groundwater recharge systems by capturing the rainwater runoff. In the present study, GIS-based hydrological assessment of watershed has been used to identify the potential sites for locating the groundwater recharge structures. Based on land use, soil and topography, rainfall runoff modelling was carried out in GIS for a sub-watershed of River Kanhan, in Nagpur District, Maharashtra State, India. Five potential sites with maximum flow accumulation were delineated using the rational method for peak runoff estimation. As the groundwater recharge potential also depends on the geological and geomorphological characteristics of land, analytic hierarchy process (AHP) with expert’s judgement was used for ranking the sites. The criteria considered in AHP were geological features, i.e. lineament density, depth to bedrock and soil cover; geomorphological features, i.e. drainage density, slope, landforms and land use/land cover; and water table level fluctuation. The site P5 with maximum flow accumulation and sandstone rock formation was ranked first. The site P1, where catchment has well-developed drainage and geological formation shows rock with secondary porosity, was ranked second.     

Changes in the concentration of mesospheric ozone during the total solar eclipse

Measurements of dayglow radiance of $\text{O}{}_2\text{(}{}^1\text{Δ}{}_{\mathrm{g}}\text{)}$ and OH(7,2) bands are reported. Ground based photometers were used to monitor zenith radiance of 1270 and 694 nm emissions during the total solar eclipse of 16 February 1980. Altitude distribution of 1270 nm intensity was derived from ground based observations. A set of altitude distributions of $\text{O}{}_2\text{(}{}^1\text{Δ}{}_{\mathrm{g}}\text{)}$ were thus obtained throughout the eclipse. These altitude distributions were converted into ozone distributions using the rate equations for formation and loss of ozone and $\text{O}{}_2\text{(}{}^1\text{Δ}{}_{\mathrm{g}}\text{)}$ molecules. Results indicate an increase in the ozone concentration at mid-eclipse. OH(7,2) emission did not show enhancement during totality. This may mean that there was no increase in OH concentration during the eclipse.