Seasonal dimethylsulfoniopropionate (DMSP) variability in Dona Paula bay     

Sree S. Kumar  Usha Chinchkar  Shanta Nair  P.A. Loka Bharathi  D. Chandramohan 《Estuarine, Coastal and Shelf Science》2009,81(3):301-310

Data on temporal variations of total dimethylsulfoniopropionate (DMSP_t) and the environmental factors that influence DMSP_t concentrations are important in understanding the biogeochemical cycling of organic sulfur compounds. Annual and diurnal variations of DMSP_t were investigated in relation to environmental variables at a fixed station in Dona Paula bay (west coast of India). DMSP concentrations were high in the day and low at night and ranged from 3.69 to 84 nM with a maximum at 17.00 h. The high concentrations of DMSP_t during daytime closely followed that of Chl a concentrations. The DMSP utilizers averaged 0.8 ± 0.3 × 10³ cells l^?1 during night and 0.4 ± 0.1 × 10³ cells l^?1 during the day. The diel variation of DMSP_t was influenced more by biological variables than hydrographic parameters. In the year-round study, the concentrations ranged from 0.69 to 15.8 nM. It was fourfold higher during the southwest monsoon season (13.4 ± 2 nM) and threefold higher during the post-monsoon season (9.96 ± 5 nM) compared to the pre-monsoon season (3.1 ± 1 nM). DMSP_t concentrations showed temporal variability, both during diurnal and annual studies. Diatoms were identified as producers of DMSP in Dona Paula bay. Dinoflagellates also contributed during the non-monsoon seasons. Another factor involved in the variability of DMSP_t was DMSP utilizing bacteria, which ranged from 1 to 10% of the total heterotrophic count.  相似文献   

Dynamics behind warming of the southeastern Arabian Sea and its interruption based on in situ measurements     

Simi Mathew  Usha Natesan  Ganesan Latha  Ramasamy Venkatesan 《Ocean Dynamics》2018,68(4-5):457-467

A study of the inter-annual variability of the warming of the southeastern Arabian Sea (SEAS) during the spring transition months was carried out from 2013 to 2015 based on in situ data from moored buoys. An attempt was made to identify the roles of the different variables in the warming of the SEAS (e.g., net heat flux, advection, entrainment, and thickness of the barrier layer during the previous northeast monsoon season). The intense freshening of the SEAS (approximately 2 PSU) occurring in each December, together with the presence of a downwelling Rossby wave, supports the formation of a thick barrier layer during the northeast monsoon season. It is known that the barrier layer thickness, varying each year, plays a major role in the spring warming of the SEAS. Interestingly, an anomalously thick barrier layer occurred during the northeast monsoon season of 2012–2013. However, the highest sea surface temperature (31 °C) was recorded during the last week of April 2015, while the lowest sea surface temperature (29.7 °C) was recorded during the last week of May 2013. The mixed layer heat budget analysis during the spring transition months proved that the intense warming has been mainly supported by the net heat flux, not by other factors like advection and entrainment. The inter-annual variability analysis of the net heat flux and its components, averaged over a box region of the SEAS, showed a substantial latent heat flux release and a reduction in net shortwave radiation in 2013. Both factors contributed to the negative net heat flux. Strong breaks in the warming were also observed in May due to the entrainment of cold sub-surface waters. These events are associated with the cyclonic eddy persisting over the SEAS during the same time. The entrainment term, favoring the cooling, was stronger in 2015 than that in 2013 and 2014. The surface temperatures measured in 2013 were lower than those in 2014 and 2015 despite the presence of a thick barrier layer. The substantial decrease in net heat flux along with entrainment cooling has been identified as causes for this behavior.  相似文献   

Site suitability evaluation for locating sanitary landfills using GIS     

Usha Natesan  E S M Suresh 《Journal of the Indian Society of Remote Sensing》2002,30(4):261-264

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Studies on the variations of heavy metals in the marine sediments off Kalpakkam,East Coast of India   总被引：1，自引：1，他引：0  

K. K. Satpathy  A. K. Mohanty  M. V. R. Prasad  Usha Natesan  S. K. Sarkar 《Environmental Earth Sciences》2012,65(1):89-101

During the last two decades, the coastal environment of southeast India has experienced intense developments in industry, urbanization and aquaculture. Moreover, the 2004 mega tsunami has devastated this coast, thus affecting the coastal sediment characteristics. These two phenomena prompted a study to characterize the sediment, to understand the mechanisms influencing the distribution of heavy metals and to create baseline data for future impact assessment. Results showed that the coastal sediment was carpeted with a mosaic of sand and silty sand with a minor amount of clay. Heavy metal values showed maximum variation for Fe and minimum for Cd. Their average values showed the following decreasing trend: Fe > Cu > Zn > Pb > Cr > Ni > Cd. This study shows that the major source of metals at Kalpakkam coast are land-based anthropogenic ones, such as, discharge from industrial waste, agricultural waste, urban, municipal and slum sewage into the Buckingham canal, which in turn discharges into the sea through backwaters, particularly during northeast monsoon period. A clear signature of the role of backwater discharge increasing the concentration of a few metals in the coastal sediments during monsoon period was observed. Assessments of the degree of pollution, concentration factor (CF), geoaccumulation index (I _geo) and pollution load index (PLI) have been calculated. CF values and I _geo indicated that the coastal sediment is moderately polluted by Cu and Cd. Increase in Cu, Pb and Zn concentration during the monsoon period (October–January) compared to the rest of the year was noticed. Factor analysis and correlation among the heavy metals concluded that Cr, Ni, Cd and Fe are of crustal origin, whereas, Cu, Pb and Zn are from anthropogenic sources. Organic carbon content in the sediment increased during monsoon period, pointing to the role of land runoff and backwater discharge in enhancing its content. The study also elucidates the impact of the recent tsunami in depleting metal content in the coastal sediment as compared to the pre-tsunami period.  相似文献   

Geochemical evidence of terrigenous influence in sediments of Buckingham canal,Ennore, Southeast coast of India   总被引：1，自引：1，他引：0  

B. R. R. Seshan  Usha Natesan  K. Deepthi 《Environmental Earth Sciences》2012,66(2):489-503

Five sediment cores were collected in July 2008 from Buckingham Canal, Ennore, India, a water body that is influenced by domestic and industrial effluents. Downcore variations in trace metal concentrations—Ni, Pb, Mn and Zn at every 2.5 cm increment was determined through acid extraction (hydro fluoric acid, nitric acid and sulphuric acid) and analysed by atomic emission spectrophotometer. The sandy clay environment is composed mostly of medium sized grains. Among the four trace metals studied in five cores, Mn and Ni are the highest and the least occurring metals respectively. Quantitative indices such as geoaccumalation index, anthropogenic factor, enrichment factor, contamination factor and degree and pollution load indices were computed. All these analyses classify Ennore as uncontaminated or moderately contaminated. Zn has the highest anthropogenic factor (2.29) indicating the increasing concentration of Zn in the recent times. Zn enrichment is observed only at surface sediments (top 7.5 cm) C4.  相似文献