Chemical composition of rain water and influence of airmass trajectories at a rural site in an ecological sensitive area of Western Ghats (India)

Samples of rain water were collected during monsoon season (June to September) of 2006 and 2007 at Hudegadde, a rural site located in an ecological sensitive area of Western Ghats. The collected samples were analyzed for pH, conductivity and major ions. At this site, rainwater pH varied from 4.20 to 7.39 with 5.65 as volume weighed mean. The observed mean was slightly lower than the average pH reported at most of the Indian continental sites. Monthly variation showed that average pH of rain water was the lowest during September (end of monsoon) and the highest during July (peak of monsoon). Overall, marine sources had dominating influence at this site. However, significant influence of anthropogenic and crustal sources from local as well as inter-continental regions was also noticed. As compared to NO₃⁻, higher concentration of SO₄²⁻ was noticed which might be due to contribution from industrial activities responsible for SO₂ emission. At this site, influence of five types of airmass trajectories was noticed i.e. i) C.I.O. (Central part of Indian Ocean)-when air masses blown from Maldives and nearby region of central Indian ocean. These airmasses had higher concentrations of nss Ca²⁺ which did not show any adverse impact on the pH; ii) N.W.I.O.(North-West Indian Ocean)-when airmasses travelled from oceanic region close to north-east Africa. These airmassses had higher concentrations of nss sulphate and nitrate and gave rise to acid rain; iii) S.W.I.O. (South -West Indian Ocean)- when airmasses came from southern part of Indian ocean (close to Mauritius). During these airmasses, rain water samples had almost equal ratio of nss SO₄²⁻ and nss Ca²⁺ similar to N.W.I.O but very low NO₃⁻ ; iv) Gulf-when airmasses were observed coming from Gulf region. Although these airmasses contributed only 2% of the total number of samples but carried high amount of nss SO₄²⁻ which gave rise to acid rain. The second lowest pH was observed during these airmasses which might be due to very high nssSO₄²⁻/nssCa²⁺ ratios; v) N.W.I.O. + S.W.I.C. (North-West Indian Ocean+South-West Indian Continental)- when airmasses originated from north-west Indian Ocean travelling towards south continental part of India and then arriving to the site. During these airmasses, samples showed typical influence of urban activities having high concentrations of nss SO₄²⁻ and NO₃⁻ leading to the lowest pH of rain water.     

Role of sediment in solute acquisition in the Himalayan glacier meltwater stream,Gangotri glacier,Uttarakhand, India

Low temperature in-stream solute acquisition in a glacial environment with very high suspended sediment is critical for downstream evolution of water chemistry. Present work is carried out on 18 km headwater reach from Gomukh (snout of the Gangotri glacier) to Gangotri along River Bhagirathi, India for understanding the hydrological processes controlling the solute acquisition in the glacial environment. This is the first attempt to conduct dissolution experiments with river bed sediments and meltwater considering different operating variables namely; contact time, seasonality, different sediment particle sizes, different sediment dose, effect of pH, wetting and crushing of bed sediments of the glacial stream. The role of sediment in low temperature solute acquisition process is characterized by sudden release of ions from the sediment in initial few seconds. Equilibrium time was observed to be 600 s (10 min). Further progressive increase in EC was observed from Gomukh to Gangotri, suggesting change in sediment surface characteristics/or source. Higher dissolution was observed from the bed sediments collected in June. It is found that the dissolution increases with increase in sediment doses but decreases with an increase in sediment particle size fraction. Higher solute acquisition was observed from crushed sediment because of an abundance of very fine particles having fresh, aggressive/reactive mineral surfaces which are capable of dissolution. The solute released from wetted sediment is significantly lower than the fresh sediment, which may be attributed to the destruction of microparticles adhering to mineral grains, the removal of fresh reactive surface sites, dissolution of rapidly weathered minerals such as calcite and evolution towards to equilibrium of the solution. Further, higher dissolution was observed with decrease in pH, which may be attributed to the availability of more hydrogen ion concentration of the solution, which favours more solute acquisition from sediment into meltwater.     

Investigation of two coronal mass ejections from circular ribbon source region:Origin,Sun-Earth propagation and Geoeffectiveness

In this article,we compare the properties of two coronal mass ejections(CMEs)that show similar source region characteristics but different evolutionary behavior...     

Mortality risk from heat stress expected to hit poorest nations the hardest

Climatic Change - Anthropogenic climate warming has increased the likelihood of extreme hot summers. To facilitate mitigation and adaptation planning, it is essential to quantify and synthesize...