Effect of arsenic contamination on microbial biomass and its activities in arsenic contaminated soils of Gangetic West Bengal, India

A study was conducted to see the effect of arsenic contamination on soil quality indicators, viz., microbial biomass, soil respiration, fluorescein diacetate and dehydrogenase (DHG) activity in arsenic contaminated soils of West Bengal. All the parameters were significantly and negatively correlated with all the form of arsenic (bioavailable and total) but the microbial metabolic quotient was significantly and positively correlated with all forms of arsenic, indicating arsenic induced stress to the soil microbial community. This may be due to part of the microbial biomass, which is located in the inner parts of the micro-aggregates of soil, which is affected by arsenic accumulates present in soil particles. Linear regression analysis revealed that the bioavailable arsenic exerted greater inhibitory effect on the soil microbial population than the total arsenic content of soils. Water-soluble arsenic showed more inhibitory effect than NaHCO(3) extractable form, in their association with biological properties of the contaminated soils. Water-soluble form of arsenic was much more toxic than insoluble forms. This signified that with increase in bioavailability, the arsenic exerted more inhibitory effect on these parameters. It is thus suggested that the microbial biomass, fluorescein diacetate and dehydrogenase activity alone and expressed on a soil organic matter basis along with the soil respiration parameters can be helpful in assessing the effects of arsenic on the size and activity of microbial biomass in soils.     

Appraisal of stormwater-induced runoff quality influenced by site-specific land use patterns in the south-eastern region of Bangladesh

Environmental Science and Pollution Research - Urban stormwater runoff is considered as one of the major contributors to nonpoint source that contributes to the pollution of all water resources in...     

Active carbon-pools in rhizosphere of wheat (Triticum aestivum L.) grown under elevated atmospheric carbon dioxide concentration in a Typic Haplustept in sub-tropical India

Study on active and labile carbon-pools can serve as a clue for soil organic carbon dynamics on exposure to elevated level of CO2. Therefore, an experimental study was conducted in a Typic Haplustept in sub-tropical semi-arid India with wheat grown in open top chambers at ambient (370 micromol mol-1) and elevated (600 micromol mol-1) concentrations of atmospheric CO2. Elevated atmospheric CO2 caused increase in yield and carbon uptake by all plant parts, and their preferential partitioning to root. Increases in fresh root weight, volume and length have also been observed. Relative contribution of medium-sized root to total root length increased at the expense of very fine roots at elevated CO2 level. All active carbon-fractions gained due to elevated atmospheric CO2 concentration, and the order followed their relative labilities. All the C-pools have recorded a significant increase over initial status, and are expected to impart short-to-medium-term effect on soil carbon sequestration.     

Escape from competition: neighbors reduce Centaurea stoebe performance at home but not away

The greater abundance of some exotic plants in their nonnative ranges might be explained in part by biogeographic differences in the strength of competition, but these competitive effects have not been experimentally examined in the field. We compared the effects of neighbors on the growth and reproduction of spotted knapweed (Centaurea stoebe) in Europe, where it is native, and in Montana, where it is invasive. There were strong negative competitive effects of neighboring vegetation on C. stoebe growth and reproduction in Europe. In contrast, identical experiments in Montana resulted in insignificant impacts on C. stoebe. Although the mechanisms that produce this dramatic biogeographic difference in competitive outcome remain unknown, our results indicate that differences in net competitive interactions between ranges may contribute to the striking dominance of C. stoebe in parts of North America.     

Variations in seasonal phytoplankton assemblages as a response to environmental changes in the surface waters of a hypo saline coastal station along the Bhagirathi�CHooghly estuary

Due to the close proximity of the Bay of Bengal and the freshwater inflow of Bhagirathi-Hooghly, Diamond Harbour appeared as an important coastal station of the Bhagirathi-Hooghly estuary. The spatial and temporal composition and abundance of microphytoplankton species was examined in relation to physical and chemical surface water variables (i.e., salinity, nutrient, and temperature).The primary objective of the study was to observe the variations in phytoplankton species assemblages as a response to environmental variables. Hierarchical cluster analysis and non-metric multidimensional scaling were used to find out distinct seasonal groups based on the composition of phytoplankton. The results indicate that several key environmental factors like temperature, DIN content, and molar ratio of nutrients like DIN-DIP and DIN-DSi influenced seasonal phytoplankton assemblages within the estuary. The distribution of phytoplankton population showed two main groups where the blue-green and green algal populations favored the warmer conditions of summer and monsoon months, whereas the diatom population primarily flourished in the cooler months of autumn and winter.     

Hydrodynamics and turbulence in emergent and sparsely vegetated open channel flow

This present study reports the results of an experimental study characterizing thorough variation of turbulent hydrodynamics and flow distribution in emergent and sparsely vegetated open channel flow. An emergent and rigid sparse vegetation patch with regular spacing between stems along the flow and transverse directions was fixed in the central region of the cross-section of open channel. Experiments were conducted in subcritical flow conditions and velocity measurements were obtained with an acoustic Doppler Velocimetry system. Large variations of the turbulence intensities, Reynolds shear stress, turbulent kinetic energy and vortical motions are found in and around the vegetation patch. At any cross-section through the interior of the vegetation patch, streamwise velocity decreases with increase in streamwise length and the velocity profiles converge from the log-law to a linear profile with increasing slope. Time-averaged lateral and vertical velocities inside the vegetation patch increase with increasing streamwise distance and converge from negative values to positive values. Turbulence intensities interior of the sparse vegetation patch are more than those of without the vegetation patch. Similar to the trend of streamwise velocity profiles inside the vegetation, turbulence intensities and longitudinal-normal Reynolds shear stress profile decreases with streamwise direction. In the interior of the vegetation patch and downstream of the trailing edge, turbulent kinetic energy profiles are exhibiting irregular fluctuations and the maximum values are occurring in the outer layer. Analysis of flow distribution confirms sparse vegetation patch is inducing a serpentine flow pattern in its vicinity. At the leading edge, flow is rushing towards the right hand sidewall, and at the trailing edge, flow is turning to the left hand sidewall. In between the leading and trailing edges, the streamlines are following a zig-zag fashion at varied degree along the streamwise and lateral directions. Immediate upstream of the leading edge and in the interior of the vegetation patch, vortex motion is clearly visible and the vortices are stretched along the width of the channel with streamwise direction.     

Commensal in conflict: Livestock depredation patterns by free-ranging domestic dogs in the Upper Spiti Landscape,Himachal Pradesh,India

In human-populated landscapes worldwide, domestic dogs (Canis lupus familiaris) are the most abundant terrestrial carnivore. Although dogs have been used for the protection of livestock from wild carnivores, they have also been implicated as predators of livestock. We used a combination of methods (field surveys, interview surveys, and data from secondary sources) to examine the patterns and factors driving livestock depredation by free-ranging dogs, as well as economic losses to local communities in a Trans-Himalayan agro-pastoralist landscape in India. Our results show that livestock abundance was a better predictor of depredation in the villages than local dog abundance. Dogs mainly killed small-bodied livestock and sheep were the most selected prey. Dogs were responsible for the majority of livestock losses, with losses being comparable to that by snow leopards. This high level of conflict may disrupt community benefits from conservation programs and potentially undermine the conservation efforts in the region through a range of cascading effects.     

Photocatalytic degradation of N-heterocyclic aromatics—effects of number and position of nitrogen atoms in the ring

This study demonstrates the influences of position, number of nitrogen (N) atoms and –C–N– or –N=N– linkage present in the six membered heterocyclic compounds such as pyridine, pyrazine, and pyridazine on their photocatalytic degradation by Au, Ag, and Fe⁺² deposited TiO₂ photocatalyst. The photodegradation rate of these heterocyclic compounds follow the order pyridine > pyrazine > pyridazine due to the different extent of hydroxylation and difference in position and number of N atoms in the aromatic moiety. The Au photodeposition significantly improved the TiO₂ photoactivity as compared to Ag and Fe⁺² loading. The presence of two N atoms in pyrazine and pyridazine as compared to one N atom in pyridine hamper the nucleophilc attack of OH radicals in comparison to easy hydroxylation of pyridine ring. There is 1 N atom, 4C–C, 1C–N and 1C=N bond in pyridine, 2 N atoms in the 1 and 4 positions, 2C–C, 2C–N bonds and 2C=N bonds in pyrazine, and pyridazine ring contains 2 N atoms in the 1 and 2 positions, 3C–C, 1N–N bond and 2C=N bonds. The bond strength/energy decreases gradually as: C=N– (615 KJ/mol)?>?–N=N– (418 KJ/mol)?>?–C–C– (347 KJ/mol)?>?–C–N– (305 KJ/mol)?>?–N–N– (163 KJ/mol). As pyridine has 1C–N, 1C=N, and no N–N bond, it photodegrades easily as compared to 1 N–N and 2C=N bonds of pyridazine of lowest photodecomposition rate. The improved photoactivity of Au–TiO₂ is explained on the basis of its favorable redox potential, work function, and electron-capturing capacity, etc.