Variation of Stable Carbon and Nitrogen Isotopic Composition of PM10 at Urban Sites of Indo Gangetic Plain (IGP) of India.

This paper presents the variation of elemental concentrations of total carbon (TC), total nitrogen (TN) and isotopic ratios of δ13C and δ15N along with δ13OC and OC of PM10 mass over Delhi, Varanasi and Kolkata of the Indo Gangetic Plain (IGP), India. For Delhi, the average concentrations of TC and TN of PM10 were 53.0±33.6 and 14.9±10.8 µg m(-3), whereas δ13C and δ15N of PM10 were -25.5±0.5 and 9.6±2.8‰, respectively. For Varanasi, the average values of δ13C and δ15N of PM10 were -25.4±0.8 and 6.8±2.4‰, respectively. For Kolkata, TC and TN values for PM10 ranged from 9.1-98.2 to 1.4-25.9 µg m(-3), respectively with average values of 32.6±24.9 and 9.3±8.2 µg m(-3), respectively. The average concentrations of δ13C and δ15N were -26.0±0.4 and 7.4±2.7‰, respectively over Kolkata with ranges of -26.6 to -24.9‰ and 2.8±11.5‰, respectively. The isotopic analysis revealed that biomass burning, vehicular emission and secondary inorganic aerosols were likely sources of PM10 mass over IGP, India.

Dissolved methane in Indian freshwater reservoirs.

Emission of methane (CH4), a potent greenhouse gas, from tropical reservoirs is of interest because such reservoirs experience conducive conditions for CH4 production through anaerobic microbial activities. It has been suggested that Indian reservoirs have the potential to emit as much as 33.5 MT of CH4 per annum to the atmosphere. However, this estimate is based on assumptions rather than actual measurements. We present here the first data on dissolved CH4 concentrations from eight freshwater reservoirs in India, most of which experience seasonal anaerobic conditions and CH4 buildup in the hypolimnia. However, strong stratification prevents the CH4-rich subsurface layers to ventilate CH4 directly to the atmosphere, and surface water CH4 concentrations in these reservoirs are generally quite low (0.0028-0.305 µM). Moreover, only in two small reservoirs substantial CH4 accumulation occurred at depths shallower than the level where water is used for power generation and irrigation, and in the only case where measurements were made in the outflowing water, CH4 concentrations were quite low. In conjunction with short periods of CH4 accumulation and generally lower concentrations than previously assumed, our study implies that CH4 emission from Indian reservoirs has been greatly overestimated.

Spatial variations of DMS, DMSP and phytoplankton in the Bay of Bengal during the summer monsoon 2001.

Data on the distribution of dimethylsulphide (DMS) and dimethylsulphoniopropionate (DMSP) in relation to phytoplankton abundance in different oceanic environments is important to understand the biogeochemistry of DMS, which plays an important role in the radiation balance of the earth. During the summer monsoon of 2001 measurements were made for DMS and DMSPt (total DMSP) together with related biological parameters in the Bay of Bengal. Both DMS and DMSPt were restricted to the upper 40 m of the water column. Diatoms accounted for more than 95% of the phytoplankton and were the major contributors to the DMS and DMSPt pool. The mean concentration of DMS in the upper 40 m was observed to be around 1.8+/-1.9 nM in the study area, while DMSPt concentrations varied between 0.7 nM and 40.2 nM with a mean of 10.4+/-8.2 nM. The observed lower DMSPt in the northern Bay in spite of higher mean primary productivity, chlorophyll a and phytoplankton cell counts seemed to result from grazing. Though salinity divides the Bay into different biogeochemical provinces there is no relation between salinity and DMS or DMSPt. On the other hand DMS was linearly related to chlorophyll a:phaeopigments ratio. The results suggest the need for deeper insight into the role of diatoms in the biogeochemical cycling of DMS.

Temporal variations in dimethylsulphoniopropionate and dimethyl sulphide in the Zuari estuary, Goa (India).

Despite tropical estuarine systems representing important sites for active biogeochemical processes, studies on dimethyl sulphide (DMS) in these systems are sparse. Here we report on DMS and dimethylsulphoniopropionate (DMSP) variability in relation to physicochemical and biological parameters for a period of 14 months in a tropical estuarine environment. DMS and DMSP showed high temporal variations with maximal concentrations during the southwest monsoon coinciding with a dinoflagellate bloom. Dinoflagellates appear to be the major contributors to the DMSP pool. Average DMS and DMSP concentrations (surface and bottom) suggested that much of the DMSP produced is converted to forms other than DMS. Surface DMS varied between 0.3 and 15.4 nmol dm(-3) while DMSP ranged from 0.8 to 419.5 nmol dm(-3). The DMS flux was 0.03-1.9 microM m(-2) d(-1) (average=0.6 microM m(-2) d(-1)) during the study period, that concurs well with the values reported for temperate estuaries.