Search

Small estuaries often remain neglected while characterizing air-water CO2 flux dynamics. This study reports the seasonal, spatial, and multi-annual variability of carbon biogeochemistry, emphasizing air-water CO2 flux from a small tropical mangrove-dominated estuary (Dhamra Estuary) of the Bay of Bengal, based on the 9-year-long sampling survey (2013 to 2021). The sampling covered twelve pre-fixed locations of this estuary. A suite of biogeochemical parameters was kept within the purview of this study to deliniate the interrelationship between CO2 fluxes and potential factors that can regulate/govern pCO2(aq) dynamics. Air water CO2 exchange rates were calculated using five globally accepted empirical gas transfer velocity equations and varied in a range of − 832.5 to 7904 μmol m–2 h–1. The estuary was a sink for CO2 in monsoon season, having the highest average flux rates of − 380.9 ± 125.5 μmol m–2 h–1, whereas a source in pre-monsoon (38.29 ± 913.1 μmol m–2 h–1) and post-monsoon (91.81 ± 1009.8 μmol m–2 h–1). The significant factors governing pCO2 were pH, salinity, total alkalinity and dissolved inorganic carbon (DIC). This long-term seasonal study emphasizes the need to include small regional estuaries for more accurate estimates of global CO2 flux to upscale the global carbon budget and its controlling mechanism. [ABSTRACT FROM AUTHOR]

The seasonal and interannual variation in the partial pressure of carbon dioxide in water [pCO2(water)] and air-water CO2 exchange in the Mahanadi estuary situated on the east coast of India was studied between March 2013 and March 2021. The principal aim of the study was to analyze the spatiotemporal variability and future trend of pCO2 and air-water CO2 fluxes along with the related carbonate chemistry parameters like water temperature, pH, salinity, nutrients, and total alkalinity, over 9 years. The seasonal CO2 flux over nine years was also calculated using five worldwide accepted equations. The seasonal map of pCO2(water) followed a general trend of being high in monsoon (2628 ± 3484 μatm) associated with high river inflow and low during pre-monsoon (445.6 ± 270.0 μatm). High pCO2 in water compared to the atmosphere (average 407.6–409.4 μatm) was observed in the estuary throughout the sampling period. The CO2 efflux computed using different gas transfer velocity formulas was also consistent with pCO2 water acquiring the peak during monsoon in the Mahanadi estuary (6033 ± 9478 μmol m−2 h−1) and trough during pre-monsoon (21.66± 187.2 μmol m−2 h−1). The estuary acted as a net source of CO2 throughout the study period, with significant seasonality in the flux magnitudes. However, CO2 sequestration via photosynthesis by phytoplankton resulted in lower emission rates toward the atmosphere in summer. This study uses the autoregressive integrated moving average (ARIMA) model to forecast pCO2(water) for the future. Using measured and predicted values, our work demonstrated that pCO2(water) has an upward trend in the Mahanadi estuary. Our results demonstrate that long-term observations from estuaries should be prioritized to upscale the global carbon budget. [ABSTRACT FROM AUTHOR]

Preparation of good quality magnesium oxide from seawater is the most challenging job because the vast majority of undesired impurities come from seawater during the precipitation stage. Hence, the double salt route has been developed as a very unique technique to prepare refractory grade magnesium oxide from seawater. Controlled addition of carrier reagent at the precipitating stage precipitates magnesium as double salt. The double salt is transformed to magnesium carbonate (MgCO3), which after calcination forms magnesium oxide (MgO). The product quality has been established by elemental analysis, PXRD, FTIR, TG/DTG, and FESEM. Commercially available MgCO3 and MgO of HiMedia have also been characterized simultaneously for comparison. The prepared magnesium oxide shows very high purity of 99.75%, which is shown from EDS measurement and PXRD and can be suitable as basic refractory material for industrial purposes. [ABSTRACT FROM AUTHOR]

The exchange of CO2 between the air–water interfaces of estuaries is crucial from the perspective of the global carbon cycle and climate change feedback. In this regard, we evaluated the air–water CO2 exchanges in two major estuaries—the Mahanadi estuary (ME) and the Dhamra estuary (DE) in the northern part of the Bay of Bengal, India. Biogeochemical properties of these estuarine waters were quantified in three distinct seasons, namely, pre-monsoon (March to May), monsoon (June to October), and post-monsoon (November to February). The significant properties of water, such as the water temperature, pH, salinity, nutrients, dissolved oxygen, chlorophyll-a (chl a), and photosynthetic pigment fluorescence of phytoplankton, were estimated and correlated with CO2 fluxes. We found that the ME acted as a source of CO2 fluxes in the monsoon and post-monsoon, while DE acted as a sink during the monsoon. The stepwise regression model showed that the fluxes were primarily driven by water temperature, pH, and salinity, and they correlated well with the phytoplankton characteristics. The chl a content, fluorescence yield, and phycobilisomes-to-photosystem II fluorescence ratios were major drivers of the fluxes. Therefore, for predicting air–water CO2 exchanges precisely in a large area over a seasonal and annual scale in the estuaries of the Bay of Bengal, India, critical key parameters such as water temperature, pH, salinity, chl a, and fluorescence yield of phytoplankton should be taken into consideration. However, the responses of phytoplankton, both in terms of production and CO2 capture, are critical research areas for a better understanding of air–water CO2 exchanges in coastal ecology under climate change scenarios. [ABSTRACT FROM AUTHOR]

Short-term variability in physico-chemical properties of Dhamra estuarine system located in north-eastern India was investigated to understand the inter-seasonal variability. The oxygen data show 89–92% saturation in winter months compared to 60–70% during summer. Overall, the nitrate ranged between < 1.0 and 22.0 µmol l−1; however, phosphate concentrations never exceeded 1 µmol l−1 during the whole study period. In general, the lowest nutrient values were recorded during March and December irrespective of the year sampled. Pearson correlation matrix shows poor relationships between inorganic nitrate and phosphate suggesting decoupling in the Dhamra estuary. However, relationship between surface chlorophyll and nitrate was significant highlighting modest control on phytoplankton population. Interestingly, pCO2(air) exhibited considerable monthly variability during the sampling period, thereby accentuating the sea–air CO2 gradient. The pCO2(air) varied between 370 and 421 µatm, whereas pCO2(water) ranged between 146 and 751 µatm. The ΔpCO2 therefore showed monthly fluctuation and acted as a weak to moderate source to the immediate atmosphere. Our observation from Dhamra estuary suggests large inter-annual variability which therefore necessitates the need for near real-time measurements which is now a possibility with emerging coastal biogeochemical buoys. [ABSTRACT FROM AUTHOR]

A halotolerant chromate [Cr(VI)]-resistant bacterium, CrRPSD40, isolated from marine sediments of Paradip port, Odisha, India, was identified and used in Cr(VI) reduction study. Based on biochemical characterization and 16S rRNA gene sequencing, the bacterium CrRPSD40 was identified as Brevibacillus laterosporus, with 97.7% homology to B. laterosporus. The bacterium has a high Cr(VI) resistance (up to 2,100 mg/L) and a high salt tolerance (up to 11% w/v NaCl) capacity. Bacterial growth in the presence of Cr(VI) (100 and 500 mg/L) showed a relatively longer lag phase (0-12 h) and a shorter exponential phase (12-72 h) compared with growth without Cr(VI). Cr(VI) reduction by B. laterosporus was studied at various ranges of pH (4.0-10.0) and NaCl (1-11% w/v) concentration, at 35°C temperature, and at 130 rpm agitation speed. The optimum saline and pH condition for better growth and Cr(VI) reduction by CrRPSD40 were found to be 3% w/v NaCl and 8.0, respectively. Under the optimum condition, CrRPSD40 exhibited efficient Cr(VI) reduction as much as 92% and >50% of 100 mg/L Cr(VI) in just 120 and 60 h of treatment, respectively. Comparative changes in bacterial cell surface morphology due to interaction with Cr(VI) were evident from the field emission scanning electron microscope-energy dispersive X-ray spectroscopy (FESEM-EDX) and Fourier transform infrared (FTIR) analyses. The present investigation described the significant reduction potential of the native marine B. laterosporus (CrRPSD40) under the wide range of saline and pH conditions for its successful implementation in Cr(VI) detoxification of a saline metal-polluted environment. [ABSTRACT FROM AUTHOR]

Hexavalent chromium-tolerant (1500 mg/L) bacterium MW1 was isolated from harbour water of Paradip Port and evaluated for Cr(VI) reduction potential. The isolate was identified asExiguobacterium indicumby biochemical and 16S rRNA gene sequence methods. Salt tolerance of the bacterium was evaluated in a wide range of NaCl concentrations (0.5–13%, w/v). The Cr(VI) reduction of the strain was evaluated and optimised with varied Cr(VI) concentrations (100–1000 mg/L), pH (5.0–9.0), temperature (30–40°C) and shaking velocity (100–150 rpm) in two different minimal media (M9 and Acetate). Under optimised conditions, after 192 h of incubation nearly 92%, 50% and 46% reduction in the M9 minimal medium and 91%, 47% and 40% reduction in the acetate minimal medium were observed for 100, 500 and 1000 mg/L of Cr(VI), respectively. The exponential rate equation for Cr(VI) reduction yielded higher rate constant value, that is, 1.27 × 10−2 h−1(M9) and 1.17 × 10−2 h−1(Acetate) in case of 100 mg/L and became lower for 500 and 1000 mg/L Cr(VI) concentrations. Further, the association of bacterial cells with reduced product was ascertained by Fourier transform infrared spectrometer, UV–Vis–DRS and field-emission scanning electron microscope–energy-dispersive X-ray analyses. The above study suggests that the higher reducing ability of the marine bacteriumE. indicumMW1 will be suitable for Cr(VI) reduction from saline effluents. [ABSTRACT FROM AUTHOR]

The increasing human population and rapid development along the east coast of India pose potential threats to coastal water quality. To assess the water quality of two tropical estuaries of Odisha, India, diurnal and seasonal variations along with the influence of differential anthropogenic impacts have been studied. From the results, it was evident, the seasonal variations in the water quality were largely influenced by anthropogenic sources at both the estuaries. Relatively lower seasonal variations in salinity were recorded in Mahanadi compared to Dhamara. Dissolved inorganic nitrogen (DIN) concentrations were found to be higher in the Dhamara estuary when compared to the Mahanadi estuary that can be attributed to decay of organic materials followed by the nitrification process. A reverse trend was recorded for dissolved inorganic phosphate (DIP), with significantly higher values recorded in Mahanadi. The partial pressure of carbon dioxide (pCO 2) showed strong temporal variations in both the estuaries dominated by moderate CO 2 supersaturation with respect to the atmosphere. The mean annual pCO 2 was higher in the Mahanadi estuary and was largely attributed to its significant increase during the post-monsoon season. This study indicated the stronger influence of freshwater input and tidal activities compared to that of in situ biological processes in regulating the temporal variations in water quality of both the estuaries. The present study is helpful in understanding the natural state of the estuarine water and protection of ecosystems resources to fulfil the sustainable development at the regional level. • Mahanadi and Dhamara are two meso-tidal estuaries along the Odisha coast of India. • Surface water quality was monitored diurnally for three seasons. • The influence of freshwater mixing was more in Mahanadi compared to the Dhamara. • Higher DIP in Mahanadi due to the discharge of effluents from fertilizer plants. • Freshwater mixing regulated surface pCO 2 higher than biological activities. [ABSTRACT FROM AUTHOR]