Influence of aerosol on clouds over the Indo-Gangetic Plain, India

Using Total Ozone Mapping Spectrometer Aerosol Index (AI) and NCEP/NCAR reanalysis clouds data for the period 1979–1992, the influence of aerosol on the clouds (low and high cloud cover) over the Indo-Gangetic Plain (IGP) in India has been brought out for the first time in the present study. AI shows increasing tendency over the IGP suggesting that aerosol loading over this region increased significantly during the study period. In our analysis, High Cloud Cover (HCC) shows increasing trend and Low Cloud Cover (LCC) shows decreasing trend over the IGP during the same period. During pre-monsoon season when aerosol loading is more, HCC increases in positive correlation with AI. On the other hand, LCC show decreasing trend and is anti-correlated with AI. During summer monsoon, aerosol shows increasing trend but their effect on HCC and LCC is not seen to be significant. Similarly, the role of humidity on aerosol induced changes in HCC and LCC over the IGP region was also analyzed. In the low to moderate humid areas of IGP region (western and middle IGP), increasing AI leads to increase in HCC and decrease in LCC. On the other hand, in high humid areas (eastern IGP), increase in AI does not show any significant effect on HCC, but LCC shows positive trend. Therefore, we strongly argue that increasing aerosol loading enhances Cloud Condensation Nuclei over the region which in turn, alters the microphysical properties of clouds by reducing the size of cloud droplets, and atmospheric humidity controls the aerosol effect on clouds. During the recent period (2005–2010), similar features have also been observed over the IGP region.     

Very high 18o enrichment in Archean cherts from South India: implications for Archean ocean temperature

Stable carbon and oxygen isotopic compositions of essentially unmetamorphosed Archean (> 2.6 Gyr old) cherts and carbonates of the Dharwar Sequence of southern India, from the northernmost part of the Dharwar-Shimoga supracrustal belt (Kalche and Nagargali), have been determined. The cherts from the Nagargali area, which preserve oolitic texture and cryptocrystalline silica, show highly enriched δ¹⁸O values ranging from 28 to 31.4%o relative to SMOW. Such values are the highest yet reported from Archean nondetrital sediments, but are similar to those of modern marine cherts. On the assumption of a seawater δ¹⁸O of 0%₀, calculation of temperature based on the maximum δ¹⁸O value of 31.4%₀ yields a value of 40°C. This is significantly less than 70–80°C reported for the Archean oceans based on cherts and chert-phosphate pairs. Diagenetically recrystallized microcrystalline chert-dolomite pairs of Kalche area exhibit a range of oxygen isotopic ratios similar to those reported for Archean cherts and carbonates from other parts of the world. The temperature of diagenesis is estimated to be about 68°C.     

Input data measurement-induced uncertainty in watershed modelling

Abstract

This study presents a new methodology for estimation of input data measurement-induced uncertainty in simulated dissolved oxygen (DO) and nitrate-nitrogen (NO₃-N) concentrations using the Hydrological Simulation Program–FORTRAN (HSPF) model and data from the Amite River, USA. Simulation results show that: (1) a multiplying factor of 1.3 can be used to describe the maximum error in temperature measurements; similarly, a multiplying factor of 1.9 was estimated to accommodate the maximum of ±5% error in rainfall measurements; (2) the uncertainty in simulated DO concentration due to positive temperature measurement errors can be described with a normal distribution, N(0.062, 0.567); (3) the uncertainty in simulated NO₃-N concentration due to rainfall measurement errors follows a generalized extreme value distribution; and (4) the probability density functions can be utilized to determine the measurement-induced uncertainty in simulated DO and NO₃-N concentrations according to the risk level acceptable in water quality management.

Editor D. Koutsoyiannis

Citation Patil, A. and Deng, Z.-Q., 2012. Input data measurement-induced uncertainty in watershed modelling. Hydrological Sciences Journal, 57 (1), 118–133.     

Geo-microbial prospecting studies of surface sediments from petroliferous region of the Mehsana Block,North Cambay Basin

Surface adsorbed gas surveys and geo-microbiological surveys are well known techniques of petroleum exploration and aim towards risk reduction in exploration by way of identifying the areas warm with hydrocarbons and to establish inter-se exploration priorities amongst the identified warm areas. The thermogenic surface adsorbed gaseous hydrocarbons distribution patterns in petroliferous areas are considered to be a credible evidence for the upward migration of hydrocarbons. The present investigation aims to explore correlation between the adsorbed gas distribution pattern and microbial oxidizers in identifying the upward migration of hydrocarbons especially in the tropical black soil terrain of known petroliferous Mehsana Block of North Cambay Basin, India. A set of 135 sub-soil samples collected, were analyzed for indicator hydrocarbon oxidizing bacteria, adsorbed light gaseous hydrocarbons and carbon isotope ratios (¹³C_methane and δ¹³C_ethane). The microbial prospecting studies showed the presence of high bacterial population for methane (5.4 × 10⁶ cfu/gm), ethane (5.5 × 10⁶ cfu/gm), propane (4.6 × 10⁶ cfu/gm) and butane oxidizing bacteria (4.6 × 10⁶ cfu/gm) in soil samples. The light gaseous hydrocarbon analysis showed that the concentration ranges of C₁, C₂, C₃, iC₄ and nC₄ are 402 ppb, 135 ppb, 70 ppb, 9 ppb and 18 ppb, respectively, and the value of carbon isotope ranges of methane ?29.5 to ?43.0‰ (V-PDB) and ethane ?19.1 to ?20.9‰ (V-PDB). The existence of un-altered petroliferous microseep (δ¹³C, ?43‰) of catagenetic origin is observed in the study area. Geo-microbial prospecting method and adsorbed soil gas and carbon isotope studies have shown good correlation with existing oil/gas fields of Mehsana. Microbial surveys can independently precede other geochemical and geophysical surveys to delineate area warm with hydrocarbons, and mapped microbiological anomalies may provide focus for locales of hydrocarbon accumulation in the Mehsana Block of Cambay Basin.     

Precipitation induced stream flow: An event based chemical and isotopic study of a small stream in the Great Plains region of the USA

A small stream in the Great Plains of USA was sampled to understand the streamflow components following intense precipitation and the influence of water storage structures in the drainage basin. Precipitation, stream, ponds, ground-water and soil moisture were sampled for determination of isotopic (D, ¹⁸O) and chemical (Cl, SO₄) composition before and after two intense rain events. Following the first storm event, flow at the downstream locations was generated primarily through shallow subsurface flow and runoff whereas in the headwaters region – where a pond is located in the stream channel – shallow ground-water and pond outflow contributed to the flow. The distinct isotopic signatures of precipitation and the evaporated pond water allowed separation of the event water from the other sources that contributed to the flow. Similarly, variations in the Cl and SO₄ concentrations helped identify the relative contributions of ground-water and soil moisture to the streamflow. The relationship between deuterium excess and Cl or SO₄ content reveals that the early contributions from a rain event to streamflow depend upon the antecedent climatic conditions and the position along the stream channel within the watershed. The design of this study, in which data from several locations within a watershed were collected, shows that in small streams changes in relative contributions from ground water and soil moisture complicate hydrograph separation, with surface-water bodies providing additional complexity. It also demonstrates the usefulness of combined chemical and isotopic methods in hydrologic investigations, especially the utility of the deuterium excess parameter in quantifying the relative contributions of various source components to the stream flow.     

Shallow groundwater in a middle mountain catchment of Nepal: quantity and quality issues

The use of shallow groundwater in middle mountain catchments of Nepal is a recent development. It was only in early 1998 that a number of dug wells had been constructed in the Jhikhu Khola catchment. But their numbers are rapidly increasing. While it seems to be a good way of accessing additional water resources both for domestic (current) and agricultural purposes (future), it is very important that the groundwater resources are not overexploited. Current dug wells are used to abstract groundwater, which is seasonally being recharged by the abundant monsoon rainfall. The water levels responded rapidly to the rainfall and differed according to the location of the well. The water quality parameters indicated that the water of most of the wells was not suitable for drinking purposes without prior treatment. Microbiological contamination is of particular concern, in addition to the high nitrate and phosphate levels. Some wells show elevated turbidity levels, indicating that there is an interaction between the muddy surface water and the water in the well.