Rishikesh Singh

Nitrogen-mineralization in dry tropical savanna : effects of burning and grazing

The effects or burning and grazing on plant available nitrogen (NO3-N + NH4-N) and N-mineralization in a dry tropical savanna were examined. The plant available N ranged from 2.8 to 10.6 μg g−1 with maximum values in the dry period (summer season) and minimum values in the wet period (rainy season). The trend for N-mineralization was opposite to that of the size of the available N pool. N-mineralization rates ranged from 1.8 to 30.6 μg g−1 mo−1 within an annual cycle. On average the pool of available N was 54% higher in the burned treatment and 48% higher in the grazed treatment compared to the protected treatment, similarly the mean annual N-mineralization was 20% higher in the burned and 16% higher in the grazed savanna.

Characterization of different road dusts in opencast coal mining areas of India

Dust from haul and transport roads are the major source of air pollution in opencast coal mining areas. Dust generated during mining operations pollutes air which causes different health problems. Various available techniques are implemented in the field to minimize and control dust in mining areas. However, they are not very effective because dust deposited on road surfaces are not removed by these techniques. For effective control of dust in opencast mining areas, it has to be regularly collected from road surfaces and may be converted into solid form, and subsequently can be used as a domestic fuel considering its physicochemical properties. The present paper describes a comparative study of qualitative and quantitative aspects of road dust samples of four coalfields of India. The pH of the dust was found to be in the range of 5.1–7.7. Moisture, ash, volatile matter, fixed carbon, water-holding capacity, bulk density, and specific gravity of dust samples were found to be in the range of 0.5–3.0%, 45–76%, 12.6–20.0%, 10.2–45.3%, 21.17–31.71%, 1.15–1.70, and 1.73–2.30xa0gu2009cm−3, respectively. Observing the overall generation and characteristics of coal dust, it is suggested that coal dust from haul and transport roads of mining areas can be effectively collected and used as domestic fuel.

Emerging trends in photodegradation of petrochemical wastes: a review

Various human activities like mining and extraction of mineral oils have been used for the modernization of society and well-beings. However, the by-products such as petrochemical wastes generated from such industries are carcinogenic and toxic, which had increased environmental pollution and risks to human health several folds. Various methods such as physical, chemical and biological methods have been used to degrade these pollutants from wastewater. Advance oxidation processes (AOPs) are evolving techniques for efficient sequestration of chemically stable and less biodegradable organic pollutants. In the present review, photocatalytic degradation of petrochemical wastes containing monoaromatic and poly-aromatic hydrocarbons has been studied using various heterogeneous photocatalysts (such as TiO2, ZnO and CdS. The present article seeks to offer a scientific and technical overview of the current trend in the use of the photocatalyst for remediation and degradation of petrochemical waste depending upon the recent advances in photodegradation of petrochemical research using bibliometric analysis. We further outlined the effect of various heterogeneous catalysts and their ecotoxicity, various degradation pathways of petrochemical wastes, the key regulatory parameters and the reactors used. A critical analysis of the available literature revealed that TiO2 is widely reported in the degradation processes along with other semiconductors/nanomaterials in visible and UV light irradiation. Further, various degradation studies have been carried out at laboratory scale in the presence of UV light. However, further elaborative research is needed for successful application of the laboratory scale techniques to pilot-scale operation and to develop environmental friendly catalysts which support the sustainable treatment technology with the “zero concept” of industrial wastewater. Nevertheless, there is a need to develop more effective methods which consume less energy and are more efficient in pilot scale for the demineralization of pollutant.

Impact of post-mining subsidence on nitrogen transformation in southern tropical dry deciduous forest, India

The goal of our research was to assess the impact of post-mining land subsidence, caused due to underground coal mining operations, on fine root biomass and root tips count; plant available nutrient status, microbial biomass N (MBN) and N-mineralization rates of a Southern tropical dry deciduous forest of Singareni Coalfields of India. The changes were quantified in all the three (rainy, winter and summer) seasons, in slope and depression microsites of the subsided land and an adjacent undamaged forest microsite. Physico-chemical characteristics were found to be altered after subsidence, showing a positive impact of subsidence on soil moisture, bulk density, water holding capacity, organic carbon content, total N and total P. The increase in all the parameters was found in depression microsites, while in slope microsites, the values were lower. Fine root biomass and root tips count increased in the subsided depression microsites, as demonstrated by increases of 62% and 45%, respectively. Soil nitrate-N and phosphate-P concentrations were also found to be higher in depression microsite, showing an increase of 35.68% and 24.74%, respectively. Depression microsite has also shown the higher MBN value with an increase over control. Net nitrification, net N-mineralization and MBN were increased in depression microsite by 29.77%, 25.72% and 34%, respectively. There was a positive relation of microbial N with organic C, fine root biomass and root tips.

Comparative study of dye degradation using TiO2-activated carbon nanocomposites as catalysts in photocatalytic, sonocatalytic, and photosonocatalytic reactor

AbstractIn the present study, activated carbon-based TiO2 nanocomposites with carbon loading were synthesized by sol–gel method for photocatalytic, sonocatalytic, and sonophotocatalytic degradation of colored compound in wastewater. The prepared catalysts were characterized by Brunauer–Emmet–Teller surface area analysis, X-ray diffraction (XRD), scanning electron microscopy (SEM), and Fourier transform infrared analysis (FT-IR). The degradation efficiencies of the synthesized composites were determined by the degradation of Direct Blue-199 dye under three different reactors viz., photocatalytic, sonocatalytic, and sonophotocatalytic. Reaction kinetic modeling was done for these processes and the degradation rate was found maximum for sonophotocatalytic process as compared to individual ones. However, on considering the energy efficiency and degradation efficiency, photochemical reactor was found to be most economical. Therefore, for the treatment of wastewater-containing dye from industries, a photocataly...

Current and emerging trends in bioremediation of petrochemical waste: A review

ABSTRACT Various industries release harmful petrochemical contaminants into the environment. To treat these petrochemical contaminants at source, different physical, chemical, and biological methods have been proposed and applied worldwide. However, physical and chemical methods have their own advantages and limitations; in this review, we majorly focused on the biodegradation of petrochemical wastes. First, a background study on the literature available in this field is presented. Second is a review of the toxic effects of petrochemical waste and various physical and chemical processes, followed by elaborate biological processes available for petrochemical waste degradation. Further, different aspects of bioremediation, such as modes, factors, limitations, and future perspectives are critically reviewed and presented. It was found that most of the studies performed on bioremediation of petrochemical waste employed bacteria for the degradation purpose. Some studies also made use of algae, fungi, yeast, genetically modified organisms, biosurfactants, or a consortium of these microbes. Moreover, use of bioremediation is still limited at field scale due to certain limitations, which have been elaborated in this article. Overall, we strongly believe that with bioremediation capturing the attention of environmentalists worldwide, there is still a prevailing need to scale up from lab to land level applications and adaptations.

Soil Carbon Dynamics Under Changing Climate—A Research Transition from Absolute to Relative Roles of Inorganic Nitrogen Pools and Associated Microbial Processes: A Review

Abstract It is globally accepted that soil carbon (C) dynamics are at the core of interlinked environmental problems, deteriorating soil quality and changing climate. Its management remains a complex enigma for the scientific community due to its intricate relationship with soil nitrogen (N) availability and moisture-temperature interactions. This article reviews the management aspects of soil C dynamics in light of recent advances, particularly in relation to the availability of inorganic N pools and associated microbial processes under changing climate. Globally, drastic alterations in soil C dynamics under changing land use and management practices have been primarily attributed to the variation in soil N availability, resulting in a higher decomposition rate and a considerable decline in soil organic C (SOC) levels due to increased soil CO2 emissions, degraded soil quality, and increased atmospheric CO2 concentrations, leading to climate warming. Predicted climate warming is proposed to enhance SOC decomposition, which may further increase soil N availability, leading to higher soil CO2 efflux. However, a literature survey revealed that soil may also act as a potential C sink, if we could manage soil inorganic N pools and link microbial processes properly. Studies also indicated that the relative, rather than the absolute, availability of inorganic N pools might be of key importance under changing climate, as these N pools are variably affected by moisture-temperature interactions, and they have variable impacts on SOC turnover. Therefore, multi-factorial studies are required to understand how the relative availability of inorganic N pools and associated microbial processes may determine SOC dynamics for improved soil C management.

Assessment of ground and surface water quality along the river Varuna, Varanasi, India

Multivariate statistical techniques were employed for monitoring of ground-surface water interactions in rivers. The river Varuna is situated in the Indo-Gangetic plain and is a small tributary of river Ganga. The study area was monitored at seven sampling sites for 3xa0years (2010–12), and eight physio-chemical parameters were taken into account for this study. The data obtained were analysed by multivariate statistical techniques so as to reveal the underlying implicit information regarding proposed interactions for the relevant area. The principal component analysis (PCA) and cluster analysis (CA), and the results of correlations were also studied for all parameters monitored at every site. Methods used in this study are essentially multivariate statistical in nature and facilitate the interpretation of data so as to extract meaningful information from the datasets. The PCA technique was able to compress the data from eight to three parameters and captured about 78.5xa0% of the total variance by performing varimax rotation over the principal components. The varifactors, as yielded from PCA, were treated by CA which grouped them convincingly into three groups having similar characteristics and source of contamination. Moreover, the loading of variables on significant PCs showed correlations between various ground water and surface water (GW-SW) parameters. The correlation coefficients calculated for various physiochemical parameters for ground and surface water established the correlations between them. Thus, this study presents the utility of multivariate statistical techniques for evaluation of the proposed interactions and effective future monitoring of potential sites.

A new insight into the warming potential of organically amended agro-ecosystems

Organic fertilization enhances the global warming potential of the soil, which is primarily attributed to higher CO2 emission from the soil. However, long-term studies under organic fertilization to observe its impact on soil’s warming potential with respect to CO2 efflux are limited in the dry tropical ecosystem. Therefore, we observed the changes in soil organic matter (C, N), soil CO2 efflux (SCE), soil moisture, microbial biomass C, and dehydrogenase activity in the plots under 1, 3, 5, and 10xa0years of organic fertilization, designated as OM1, OM3, OM5, and OM10, respectively. Also, a nearby native forest was taken as a standard reference system (NF) in the present study for comparative purpose. We observed that organic fertilization significantly (Pxa0≤xa00.05) increased soil organic carbon (SOC), soil organic nitrogen (SON), SCE, moisture, microbial biomass C, and dehydrogenase activity, whereas decreased the SOC/SON ratio after 10xa0years, which also approached closer to NF. However, only the plots under 10xa0years of organic fertilization showed SCE significantly (Pxa0≤xa00.05) similar to NF. It indicates that long-term organic fertilization is required for the improvement in soil properties. SCE showed a significantly (Pxa0≤xa00.05) higher value (on average, by 61%) in OM10 site as compared to OM1. However, SCE on unit C basis (SCER) showed no change (Pxa0>xa00.05). This increase in SCE after 10xa0years of organic fertilization might be attributed to the significant (Pxa0≤xa00.05) increase in SOC, soil moisture, microbial biomass C, and dehydrogenase activity. However, no change in SCER after 10xa0years shows that organic fertilization has possibly been misinterpreted with respect to their impact on soil’s global warming potential. It might be attributed to the C protective nature of the organic fertilization. Overall, our results contradict with the often publicized higher warming potential of the organically amended systems. This indicates that organic fertilization does not increase the soil’s global warming potential, which is often misrepresented because SCE is not observed with respect to the existing SOC content.

Tree seedling establishment in dry tropics: an urgent need of interaction studies

The current anthropogenic activities and climate change are increasingly becoming a growing global concern for dry tropical forests. Worldwide, these ecologically important forests have degraded considerably since the past few decades due to such factors. These factors have harmful consequences on the vegetation structure and diversity especially tree seedlings, which may further aggravate climate change. Generally, the vegetation recovery is very slow and unpredictable in the dry tropics due to complex interaction among tree seedling, site (particularly, soil) and climatic conditions. We inculcated that a better understanding of the behavior of individuals of different tree species at seedling stage in dry forests is of immense importance. It is increasingly being recognized for explaining and managing the future composition of plant communities under changing environmental conditions. In this regard, the multi-factorial interaction studies under various resource–disturbance combinations are needed in dry tropical ecosystems to understand the: (1) impact of relative variability in resources and disturbances on the responses of tree seedlings of native species and (2) how the later relates to distinct functional and life history traits of the individual tree species. Most importantly, such studies would improve our limited understanding of how variation (natural and man-made) in nutrient availability, under the influence of other local environmental factors (such as water, light, grass competition, herbivory, fire, allelopathy and enhanced CO2 conditions), would affect the dynamics of dry tropical forest community. It may help in the proper management of these forests. Moreover, it may prove helpful in the current climate change scenario, as change in forest community dynamics may have consequences on soil C sequestration and CO2 efflux at global scale.