Lallan P. Gupta

Distribution of C, N and P in the sediments of the Ganges–Brahmaputra–Meghna river system in the Bengal basin

The Bengal basin is one of the geologically youngest and tectonically active drainage regimes of the world which includes the total Lower Ganges–Brahmaputra–Meghna (GBM) river system, one of the highest sediment dispersal systems in the world. The sediment load in this system comprises exclusively fine sand, silt and clay. River bed sediments, and suspended matter from stations situated uniformly all over the basin, have been analyzed in order to understand the spatial distribution and biogeochemical processing of the C, N and P in the system. Among the Ganges, Brahmaputra and Meghna subbasins, variations in total phosphorus (TP) and nitrogen (TN) contents in the bulk and <63 μm fraction of the bed sediments are statistically insignificant, but total carbon (TC) content varies significantly among the three subbasins. There is a gradual increase in the concentration of TC from the Meglna towards the Ganges subbasin, attributable to the nature of the floodplain and bank materials which supply major sediment load to the river channels. The TP concentration is 2 to 5 times more in the suspended matter than that in any particle size fraction of the sediments. Although excellent correlation between Corg and TN suggests their coorigin, the influence of inorganic nitrogen is evident in very low C/N ratios. The C/N ratio varies from 2 to 11, suggesting complete degradation of the organic matter and/or enrichment of inorganic nitrogen in the sediments. The plant available phosphorus (PAP) varies from 1.78% to 6.98% of TP, and indicates a significant anthropogenic contribution. The Corg, TN and C/N ratio in the bed sediments of the Lower GBM system are in the range comparable with other river basins of the subcontinent.

Glacial–interglacial deep-water changes in the NW Pacific inferred from single foraminiferal δ18O and δ13C

Abstract Oxygen and carbon isotope values of single benthic foraminiferal tests in a core from the Shatsky Rise, NW Pacific Ocean, show greater intra-horizon variance during the Holocene than during the Last Glacial Maximum (LGM). This greater variance is caused by the introduction of glacial specimens some 20 cm upward from their original deposition layer due to bioturbation. In contrast, foraminiferal populations belonging to glacial layers do not include Holocene specimens. The difference in direction of bioturbation greatly modifies climate information in horizons formed during and after deglacial events. After omitting glacial specimens from Holocene sediments, the glacial–interglacial difference in δ18O suggests that Pacific deep-water temperature changed by 2.4–3.8°C at the most. The δ13C values suggest that nutrient concentration was higher during the LGM than the Holocene. The glacial deep North Pacific Ocean apparently was influenced by cold deep waters of southern origin.

Biogeochemical processes and labile composition of settling particulate organic matter in the south-west Pacific Ocean

Settling particles collected by sediment traps deployed for approximately 1 year in the Coral Sea and Tasman Sea were analysed to understand the biogeochemical processes controlling the cycling and flux of particulate organic matter (POM) in the south-west Pacific. Samples were analysed for 20 amino acids (AA) and two hexosamines (HA) and the data were interpreted together with already published data on opal (biogenic silica), organic carbon and total nitrogen contents. Mean fluxes of labile carbon and nitrogen at one site were significantly different (P < 0.04, t-test; n = 14–18) from those at other sites. The southernmost trap recorded the highest concentrations of AA, HA and organic carbon normalized AA. At a site in the south, POM was more degraded in the deep trap than in the shallow trap. Occasionally, higher fluxes were also recorded at the deep trap relative to the shallow trap. The C/Natomic ratio coupled with AA- and HA-based parameters clearly suggested contribution of POM through resuspension as well as lateral advection at the more southern site, whereas a strong influence of zooplankton on total mass flux was revealed at the northern site during the period August–September 1995. It is evident from the data that higher flux of particles having higher labile contents (AA and HA) is more prevalent in the Tasman Sea than in the Coral Sea.

Vertical and latitudinal variations in amino acid fluxes and compositions of settling particles along 175°E in the North Pacific Ocean

Settling particles collected by sediment traps deployed for about one year (1993–94) at four sites along 175°E longitude in the central North Pacific have been analyzed for amino acids (AA) and amino sugars (or hexosamines, HA). These compounds account for about 12.5–27.9% of particulate organic carbon flux to the deep ocean. Biogeochemical indicator parameters varied in the range comparable with similar studies conducted in other oceanic sites. Correlations between non-protein AA (β-alanine and γ-aminobutyric acid) and flux parameters indicate repackaging of settling particulate organic matter (POM) around intermediate water depth (below 1500 m) at all trap sites. Mean values of indicator parameters in the shallow trap differ significantly (Student’s t-test; p < 0.03) from those in deep traps at the same site. Latitudinal trends in POM flux and its labile composition suggest that relatively fresh POM is being deposited at a higher rate in the subarctic area of the Pacific. However, this trend is not so clear in deep traps, probably due to the influence of bioactive transport and deposition of laterally advected particles in these traps. Total and particulate organic carbon fluxes normalized to primary productivity estimates show a sharp rise in efficiency of the biological pump towards the subarctic area, which is responsible for enhanced fluxes of particles with a high labile content to the deep ocean in this part of the Pacific.

Chemistry of fly ash and cyclone ash leachate from waste materials and effects of ash leachates on bacterial growth, nitrogen-transformation activity, and metal accumulation.

The effects of waste ash leachates on soil microorganism were evaluated along with a chemical characterization of ash leachates. Thirty fly ash samples and cyclone ash samples obtained from the incineration of municipal solid waste, plastic waste, and construction waste were used. Twenty-one and 22 samples inhibited N transformation activity of soil microorganism and growth of Bacillus subtilis, respectively. On the other hand, 11 and 18 samples stimulated bacterial activity and growth, respectively, at low concentrations. Generally, cyclone ash contained a smaller amount of toxic metals than fly ash. Our results suggest that cyclone ash can be further studied for reuse, perhaps as a soil amendment. Pb was found to be highly accumulated in B. subtilis cells, and should be carefully monitored when waste ash is reused in the environment.

In Situ Ore Formation Experiment : Amino Acids and Amino Sugars Trapped in Artificial Chimneys on Deep-Sea Hydrothermal Systems at Suiyo Seamount, Izu-Bonin Arc, Pacific Ocean

The present study reports on the bio-organic composition of a deep-sea venting hydrothermal system originating from arc volcanism; the origin of the particulates in hydrothermal fluids from the Suiyo Seamount in the southern Izu-Bonin (Ogasawara) Arc is discussed with regard to amino compounds. Chimney samples on deep-sea hydrothermal systems and core samples at Suiyo Seamount were determined for amino acids, and occasionally amino sugars. Two types of chimney samples were obtained from active hydrothermal systems by submersible vehicles: one was natural chimney (NC) on a hydrothermal natural vent; the other was artificial chimneys (AC), mainly formed by the growth and deposition of sulfide-rich particulate components in a Kuwabara-type in situ incubator (KI incubator). Total hydrolyzed amino acids (THAA) and hydrolyzed hexosamines (HA) in AC ranged from 10.7 nmol/g to 64.0 nmol/g and from 0 nmol/g to 8.1 nmol/g, respectively, while THAA in hydrothermally altered core samples ranged from 26.0 nmol/g to 107.4 nmol/g-rock. The THAA was thus of the same order of magnitude in AC and core samples. The representative biochemical indicator ratios of {\beta}-alanine/aspartic acid and {\gamma}-aminobutyric acid/glutamic acid were low. This is consistent with a large microbial population and labile subterranean biogenic organic compounds. A micro energy dispersive X-ray spectrometer ({\mu}EDX) was used to show that the formation of massive pyrite- and chalcopyrite-ores, the major matrixes of the natural chimney structures, were processed during hydrothermal activity. These data suggest that labile particulate organic matter (POM) and/or dissolved organic matter (DOM) from hydrothermal fluid were continuously trapped to form concentrated organic matter in a sulfide-rich matrix.

Chapter 6 Understanding Biogeochemical Processes in the Pacific Ocean on the Basis of Labile Components of Settling Particles

Abstract Settling particles collected by sediment traps deployed intermittently for about 1 year at various locations in the Pacific Ocean showed spatial, sporadic and sometimes seasonal variations in flux and labile composition of the particles. The samples from the western Pacific warm pool (WPWP) provided clear evidence of El Nino–Southern Oscillation (ENSO)-related changes in the composition of particulate labile components (amino acids (AA) and hexosamines (HAs)) and in the flux of settling particles. The particle flux in the western WPWP was higher during El Nino, whereas in the eastern WPWP it was higher during La Nina. Settling particles in the WPWP were more labile during a La Nina event than during El Nino. On the other hand, settling particles collected from the Tasman Sea during La Nina showed the highest concentration of AAs, HAs and particulate organic carbon-normalised AAs, which is consistent with higher primary productivity in this part of the Pacific Ocean. Settling particles at deeper depths in the ocean are more deficient in labile components than those at shallow depths because of ongoing microbial decomposition of organic matter. Occasionally higher particle fluxes were also observed at deeper depths relative to those at shallow depths, probably as a result of lateral advection and re-suspension of highly degraded particulate organic matter in the deep ocean.