Abhra Chanda

Indentation strength method to determine the fracture toughness of La0.58Sr0.4Co0.2Fe0.8O3-δ and Ba0.5Sr0.5Co0.8Fe0.2O3-δ

The temperature-dependent fracture toughness of brittle ceramics can be conveniently assessed from bending tests of specimens with defined cracks introduced by indentation. However, the validity of this indentation strength in bending method (ISM) depends critically on the correct consideration of the residual stress induced by the indentation process. The ISM has been applied to La0.58Sr0.4Co0.2Fe0.8O3-δ (LSCF) and, for comparison, on Ba0.5Sr0.5Co0.2Fe0.8O3-δ (BSCF) perovskite. LSCF with rhombohedral phase exhibits ferro-elastic behavior at ambient temperature, whereas BSCF deforms linear-elastically. Pre-indented specimens of both perovskites were fractured at room temperature in biaxial bending, some of them after an additional annealing step. The fracture toughness values of BSCF match reasonably well when determined with equations which consider the presence or absence of residual indentation stress. Interestingly, annealing has little influence on the apparent toughness results obtained for rhombohedral LSCF, which appears to be related with stress relaxation by ferro-elastic deformation.

Estimating aboveground biomass in Avicennia marina plantation in Indian Sundarbans using high-resolution satellite data

Abstract Mangroves are active carbon sequesters playing a crucial role in coastal ecosystems. In the present study, aboveground biomass (AGB) was estimated in a 5-year-old Avicennia marina plantation (approximate area ≈ 190     ha ) of Indian Sundarbans using high-resolution satellite data in order to assess its carbon sequestration potential. The reflectance values of each band of LISS IV satellite data and the vegetation indices, viz., normalized difference vegetation index (NDVI), optimized soil adjusted vegetation index (OSAVI), and transformed difference vegetation index (TDVI), derived from the satellite data, were correlated with the AGB. OSAVI showed the strongest positive linear relationship with the AGB and hence carbon content of the stand. OSAVI was found to predict the AGB to a great extent ( r 2 = 0.72 ) as it is known to nullify the background soil reflectance effect added to vegetation reflectance. The total AGB of the entire plantation was estimated to be 236 metric tons having a carbon stock of 54.9 metric tons, sequestered within a time span of 5 years. Integration of this technique for monitoring and management of young mangrove plantations will give time and cost effective results.

A comparison of CO2 dynamics and air-water fluxes in a river-dominated estuary and a mangrove-dominated marine estuary

The fugacity of CO2 [fCO2 (water)] and air-water CO2 flux were compared between a river-dominated anthropogenically disturbed open estuary, the Hugli and a comparatively pristine mangrove dominated semi-closed marine estuary, the Matla on the east coast of India. Annual mean salinity of the Hugli Estuary (≈ 7.1) was much less compared to the Matla Estuary (≈ 20.0). All the stations of the Hugli Estuary were highly supersaturated with CO2 (annual mean ~ 2200 µatm) whereas, the Matla was marginally oversaturated (annual mean ~ 530 µatm). During the post-monsoon season, the outer station of the Matla Estuary was under saturated with respect to CO2 and acted as a sink. The annual mean CO2 emission from the Hugli Estuary (32.4 mol C m-2 yr-1) was 14 times higher than the Matla Estuary (2.3 mol C m-2 yr-1). CO2 efflux rate from the Hugli Estuary has increased drastically in the last decade, which is attributed to increased runoff from the river-dominated estuary.

Characterizing the multi-risk with respect to plausible natural hazards in the Balasore coast, Odisha, India: a multi-criteria analysis (MCA) appraisal

Coastal zones are often prone to several natural hazards, and where the coastal zone has high population density and infrastructural assets, these hazards can render severe loss to both life and properties. The present paper reports a comprehensive assessment of the multi-hazard and multi-risk (keeping in view the population and assets exposed to multi-hazards) in the Balasore coast, situated in the state of Odisha, India, facing the Bay of Bengal immediately to its east. In most of the multi-hazard and multi-risk assessments, the importance of any one hazard in relation to others is often determined arbitrarily. To overcome this limitation, this work presents a multi-criteria analysis implemented on six hazards, namely coastal erosion, storm surge, sea level rise, coastal flooding, tsunami, and earthquake. The respective hazards were ranked according to their relative weight computed by pair-wise comparison, and the overall multi-hazard map of the coast was prepared using weighted overlay technique in GIS environment. In order to assess the exposure, population density and urban assets of the study area were also mapped. Finally, the population and urban density data were overlain on the multi-hazard map in order to derive the final map portraying the multi-risk of the Balasore coast. Coastal erosion and storm surge inundation are the two most substantial natural hazards that regularly affect this coast. It is also observed that hazard from the perspective of coastal erosion is spatially concentrated along the central part of the coast, while in the southern part, the effect of storm surge is higher. The area in and around Chandipur, which is situated in the central portion of the Balasore coast, has been found to have the highest multi-risk, which also happens to be a popular tourist destination.

CO2 Fluxes in Mangrove Ecosystems

Mangroves have long been recognized as a potential sink of carbon owing to their high productivity and carbon sequestration potential. The short term CO2 dynamics of mangroves are often put under lenses to examine their potential to combat the human induced CO2 emission. Mainly three types of CO2 fluxes take place within a mangrove ecosystem namely (i) atmosphere-biosphere CO2 exchange, (ii) soil CO2 efflux and (iii) air-water CO2 flux. In this chapter, we have compiled all types of the CO2 flux data from mangrove ecosystems with special emphasis on the Sundarban, the world’s largest mangrove forest and analyzed the regulating factors of these fluxes. Summarizing all the studies, it can be inferred that the terrestrial compartments of mangroves acts as net sink for CO2, though the soil continually emit CO2 (apart from few exceptions). Almost all the mangrove surrounding waters act as source of CO2, however, the magnitude of air-water CO2 fluxes are much less than the inward fluxes of CO2 towards the canopy, hence the ecosystem as a whole acts as a net sink for CO2. Light conditions, air temperature, salinity, tidal cycle and so forth are mainly found to regulate the atmosphere-biosphere CO2 flux, whereas, soil temperature, moisture and waterlogging are the principal factors regulating the soil CO2fluxes. In case of air-water fluxes, the main governing factors are the variation in salinity, pore-water flushing during ebb tide and wind speed.

Threats to coastal communities of Mahanadi delta due to imminent consequences of erosion – Present and near future

Coastal erosion is a natural hazard which causes significant loss to properties as well as coastal habitats. Coastal districts of Mahanadi delta, one of the most populated deltas of the Indian subcontinent, are suffering from the ill effects of coastal erosion. An important amount of assets is being lost every year along with forced migration of huge portions of coastal communities due to erosion. An attempt has been made in this study to predict the future coastline of the Mahanadi Delta based on historical trends. Historical coastlines of the delta have been extracted using semi-automated Tasselled Cap technique from the LANDSAT satellite imageries of the year 1990, 1995, 2000, 2006 and 2010. Using Digital Shoreline Assessment System (DSAS) tool of USGS, the trend of the coastline has been assessed in the form of End Point Rate (EPR) and Linear Regression Rate (LRR). A hybrid methodology has been adopted using statistical (EPR) and trigonometric functions to predict the future positions of the coastlines of the years 2020, 2035 and 2050. The result showed that most of the coastline (≈65%) is facing erosion at present. The predicted outcome shows that by the end of year 2050 the erosion scenario will worsen which in turn would lead to very high erosion risk for 30% of the total coastal mouzas (small administrative blocks). This study revealed the coastal erosion trend of Mahanadi delta and based on the predicted coastlines it can be inferred that the coastal communities in near future would be facing substantial threat due to erosion particularly in areas surrounding Puri (a renowned tourist pilgrimage) and Paradwip (one of the busiest ports and harbours of the country).

Dynamics of the Sundarbans Mangroves in Bangladesh Under Climate Change

Mangroves provide a range of ecosystem services ranging from mitigation of global climate change by carbon capture to the sustenance of local communities whose livelihood depends upon mangrove forest products. A hybrid model is used to analyse and project the spatial distribution of mangrove species assemblages with results showing that the distribution will alter substantially within a hundred years associated with a significant decrease in the forest cover area. These changes are reflected in the amount of carbon sequestered in the mangroves in the form of biomass with a decrease anticipated over this century. Simulations of relative sea-level rise also indicate a loss in mangrove area mainly driven by erosion rather than inundation. Re-afforestation is one option of management strategy which could compensate for these changes.

Landslide Risk Assessment in Darjeeling Hills Using Multi-criteria Decision Support System: A Bayesian Network Approach

Landslide is one of the most recurrent and hazardous events of hilly slopes all over the world and particularly in the hilly regions of Himalayas. Darjeeling district of northern West Bengal, being the most important hill station in terms of tourism and trance-boundary strategic location, experiences landslide very often which causes intermittent loss of tourism revenues and is a problem for national security. In order to assess the landslide risk and accordingly prepare a landslide-risk zonation for the Darjeeling district, factors like slope, drainage density, rainfall soil depth, land use/land cover and geology have been considered. The factors responsible for landslide and their interdependency have been critically evaluated. In the present study, Bayesian network model has been implemented which is a probabilistic statistical graphical model that represents a set of variables and their conditional dependencies. Bayesian network was applied to assess the influences of the factors, and accordingly weightage and ranking of the contributing factors for landslide have been calculated. Finally, using multi-criteria decision support system (MCDSS) in GIS environment, landslide-risk zonation of the Darjeeling district has been prepared. Validation has been done taking into account 25 historical landslide locations, and more than 92% accuracy has been achieved. Rangli Rangliot is the most landslide-susceptible block of Darjeeling district. Kalimpong I, Kalimpong II, Mirik, Jorebunglow Sukhiapokhri and Bijanbari also come under the ambit of the highly susceptible areas.

An index for discrimination of mangroves from non-mangroves using LANDSAT 8 OLI imagery

Graphical abstract

Estimation of Air-Sea CO 2 Exchange and Decadal Change of Surface Water f CO 2 in a Shallow Continental Shelf Using in Situ and Remote Sensing Data During Winter

The air-sea CO2 exchange (fCO2) was estimated in the outer estuary to offshore transition zone of the northern Bay of Bengal using in situ measurements and remote sensing data obtained from moderate resolution imaging spectroradiometer (MODIS) and advanced very high resolution radiometer (AVHRR). The in situ measurements were done during winter months (December, January and February) of the year 2011–12. Sea surface CO2 fugacity (fCO2), sea surface temperature (SST) and chlorophyll-a were measured in situ to develop an empirical relationship with fCO2 but only the SST showed a significant correlation (r 2 = 0.55, n = 64, p < 0.05). This relationship was used to assess fCO2 (water) and its temporal change in decadal scale from the year 2002–2003 to 2011–2012 of the winter months using remotely sensed SST data. The study area acted as a mild sink for atmospheric CO2 at the mean rate of −28 µmol m−2 h−1 (MODIS derived) to −40 µmol m−2 h−1 (AVHRR derived). An overall winter-to-winter increasing trend of fCO2 was observed in the last decade which is accompanied by a similar decrease in the chlorophyll-a concentrations.