5 results on '"Gonsalves, Maria Judith"'
Search Results
2. Role of sulfur-oxidizing bacteria on the ecology in tropical mangrove sediments
- Author
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A., SamKamaleson and Gonsalves, Maria-Judith
- Published
- 2019
- Full Text
- View/download PDF
3. Microbial iron reduction and methane oxidation in subsurface sediments of the Arabian Sea.
- Author
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Fernandes, Christabelle E.G., Gonsalves, Maria Judith B.D., Nazareth, Delcy R., Nagarchi, Lubbnaz, and Kamaleso, Sam A.
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IRON ores , *OXIDATION , *METHANE , *SEDIMENTS , *GEOLOGY - Abstract
Arabian Sea is one of the most productive regions of the world's ocean with seasonal upwelling and a characteristic oxygen minimum zone. It receives a continuous input of windborne iron-rich dust which possibly stimulates phytoplankton productivity. A sediment core from this area, which is on the western continental margin of India in the Kerala-Konkan basin was studied from the surface to 63 m below seafloor, to establish the co-occurrence of microbial iron reducing activity and methane oxidation. Total bacterial abundance (TC), viable aerobic counts accounting for aerobic and facultative anaerobes (TVCa), viable anaerobic counts (TVCan), methane, sulfate, ferrous [Fe(II], hydroxylamine extractable iron and HCl extractable iron concentrations were measured. Average TC was 52.6 ± 29.8 × 10 5 cells g −1 sediment while TVCa and TVCan were an order less. Methane and sulfate concentrations were 1.3 ppm and 23.2 mM, respectively. Average Fe(II) concentration, hydroxylamine and HCl extractable Fe was 0.32 ± 0.26, 0.86 ± 1.44 and 1.90 ± 2.47 mmol g −1 sediment, respectively. Interestingly, Fe(II) significantly correlated with TVCan (r = 0.66, p ≤ 0.001). In the experimental tubes, the build-up of Fe(II) was accompanied by the disappearance of methane. Average methane concentration and Fe(II) concentration in the experimental sediment slurries was 0.56 ± 0.76 ppb and 0.50 ± 0.27 mmol g −1 sediment respectively. The microcosm experiment showed that Fe(II) determined was significantly higher (ANOVA, F = 6.74, p ≤ 0.014) after 5 days of incubation, thus implying microbial iron reducing activity. A strong negative linear correlation (p ≤ 0.001) of methane concentration with Fe(II) suggests that increasing activity of microbial iron reduction caused suppression in methane production. This is also indicative of the co-occurrence of iron reduction and methane oxidation in these sediments. [ABSTRACT FROM AUTHOR]
- Published
- 2015
- Full Text
- View/download PDF
4. Manganese cycling and its implication on methane related processes in the Andaman continental slope sediments.
- Author
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Sujith, P.P., Gonsalves, Maria Judith B.D., Rajkumar, V., and Miriam Sheba, V.
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METHANE , *MANGANESE , *HYDROLOGIC cycle , *CONTINENTAL slopes , *SEDIMENTS , *MICROBIAL communities - Abstract
In the deep subsurface sediments of the Andaman continental slope, in situ methane generation/oxidation could be coupled to the cycling of Mn, as the fluid flow characterized by high methane and Mn could occur in accretionary wedge sediments by diagenetic and tectonic processes. Laboratory studies on Mn cycling by subsurface sediment microbial communities were therefore undertaken 1) to study, further, possible in situ mechanisms of Mn cycling and 2) to examine how Mn redox reactions might be coupled to methane generation/oxidation. Biotic experiments were conducted with uniformly mixed subsamples amended with 100 μM Mn 2+ in the presence (G + ) and absence (G − ) of added glucose (55.5 μM). The corresponding abiotic controls included set-ups poisoned with 15 mM sodium azide. Further, to relate the results of in vitro experiments on Mn cycling, to the methane related processes occurring in the subsurface sediments, pore water concentration of Mn, total cell numbers and the abundance of methanogens, methanotrophs and fermenters were determined. Results of the experiment on Mn cycling showed the immobilization of Mn occurred under oxic conditions and mobilization under suboxic conditions in the absence of added glucose at P ≤ 0.001 with abiotic > biotic. Whereas, in the presence of added glucose, immobilization occurred under both oxic and suboxic conditions at P ≤ 0.001 with biotic > abiotic, oxic > suboxic. The biotic cycling of Mn at 360 mbsf coincided with the total cell numbers (1.53 × 10 8 cells g −1 ), increased methane levels (89,100 ppm-v) and the abundance of methanogens (1.0 × 10 3 MPN g −1 ). Besides, the distribution of aerobic methanotrophs decreased in abundance with depth. Also, the abundance of fermenters (3.5 × 10 3 cells g −1 ) at 626.7 mbsf coincided with the relatively high concentration of Mn (319.1 μM) in sediment pore water. The results indicate that subsurface sediments harbor microorganisms that partake significantly in the cycling of Mn wherein, the availability of organic carbon dictates the direction in which the reactions occur. Besides, aerobic oxidation of methane and Mn has been reported to occur under reducing conditions. Thus, the present findings suggest that Mn redox changes affect the methane oxidation/production rates by serving either as an electron donor and/or an electron acceptor. [ABSTRACT FROM AUTHOR]
- Published
- 2014
- Full Text
- View/download PDF
5. Denitrification activity in mangrove sediments varies with associated vegetation.
- Author
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Fernandes, Sheryl Oliveira, Dutta, Pinky, Gonsalves, Maria-Judith, Bonin, Patricia C., and LokaBharathi, P.A.
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DENITRIFICATION , *STATISTICAL hypothesis testing , *MANGROVE ecology , *RHIZOPHORA mucronata , *SALINITY - Abstract
To test the hypothesis that mangrove vegetation associated sediment characteristics could influence an ecologically important function such as denitrification, a study was carried out at the Divar mangrove ecosystem in Goa, India. The composition of intertidal mangroves was assessed based on which the down-core (0–10 cm) variation in environmental variables and denitrification activity (DNT) associated with dominant vegetation types was examined. Our observations revealed a distinct zonation pattern of mangroves with the dominance of Rhizophora mucronata (RM) in the lower intertidal zone followed by Avicennia marina (AM) in the mid region. Acanthus ilicifolius (AI) was restricted to the upper intertidal zone (UIZ) which was characterized by relatively lower sediment temperatures, higher porewater salinity and intense reducing conditions. A zonation pattern in occurrence of DNT was also observed. Denitrification activity generally decreased with depth and increased in intensity from the seaward to the landward side. Maximum DNT of 4.06 ± 0.44 nmol N 2 O g −1 h −1 was recorded in the surficial AI sediments followed by AM and RM sediments. Surface plant litter content also increased from the lower to UIZ. A negative relationship of NH 4 + and total organic carbon content (n = 15, r = −0.388, p < 0.05) in AI sediments was observed. This suggested that re-mineralization of accumulated organic matter (up to 3.07 ± 0.58% at 0–2 cm) enhanced NH 4 + availability in the porewater which in turn could support nitrification-denitrification. Thus, degradation of vegetation-derived organic matter was important in sustaining nutrients mainly towards the landward side proving our hypothesis that vegetation could have an influence on DNT, albeit indirectly. [ABSTRACT FROM AUTHOR]
- Published
- 2016
- Full Text
- View/download PDF
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