Anirban Akhand

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.

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.

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.