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      https://www.ias.ac.in/article/fulltext/jess/130/0150

    • Keywords

       

      Estuaries; Sundarbans; salinity; stand of the tide; Hoogly; mangroves.

    • Abstract

       

      The Sundarbans Estuarine System (SES), comprising the southernmost part of the Indian portion of the Ganga-Brahmaputra delta bordering the Bay of Bengal, is India’s largest monsoonal, macro-tidal, delta-front estuarine system. The Sundarbans Estuarine Programme (SEP), covering six semi-diurnal tidal cycles during 18–21 March 2011 (the Equinoctial Spring Phase), was the first comprehensive observational programme in the SES. The 30 observation stations, spread over more than 3600 km2km2, covered the seven inner estuaries of the SES: the Saptamukhi, Thakuran, Matla, Bidya, Gomdi, Harinbhanga, and Raimangal. At all stations or time-series locations (TSLs), the water level was measured every 15 min and water samples were collected every hour for estimating salinity. We report the observed spatio-temporal variations of salinity in this paper. The mean salinity over the six tidal cycles decreased upstream and the mean range of salinity over a tidal cycle increased upstream. In addition to this along-channel variation, the mean salinity also varied zonally across the SES. Salinity was lowest in the eastern SES, with the lowest value occurring at the TSLs on the Raimangal. Though higher than at the Raimangal TSLs, the mean salinity was also low at Mahendranagar, the westernmost TSL located on the West Gulley of the Saptamukhi. Salinity tended to be higher in the central part of the SES. CTD (conductivity–temperature–depth) measurements at three stations on the Matla show a well-mixed profile. Only the Raimangal has a freshwater source at its head. Therefore, the upstream decrease of salinity in the SES is likely to be the effect of the preceding summer monsoon, which would have freshened the estuary, and the ingress of salt from the seaward end due to the tide following the cessation of of the monsoon rains. The freshwater inflow from the Raimangal leads to the lowest salinities occurring in the eastern SES. The lower salinity in the western SES also suggests inflow from the Hoogly estuary, whose freshwater source is regulated via the Farakka Barrage. At 20 of the 30 TSLs, the salinity varied semi-diurnally, like the water level, and the maximum (minimum) salinity tended to occur at or around high (low) water. The temporal variation was more complex at the other 10 TSLs. Even at the TSLs at which a tidal stand exceeding 75 min was seen in the water level, the salinity oscillated with a semi-diurnal period. Thus, the salinity variation was unaffected by the stand of the tide that has been reported from the SES.

      $\bf{Highlights}$

      $\bullet$ Comprehensive description of salinity variability in the Sundarbans Estuarine System (SES)

      $\bullet$ Semi-diurnal variation seen at a majority of the stations and the estuaries are well-mixed

      $\bullet$ Mean salinity decreases upstream and is lower in the eastern and western SES

      $\bullet$ The upstream decrease is due to the preceding monsoon and the tidal ingress of salt

      $\bullet$ Direct (indirect) inflow from the Ganga (Hoogly) lowers salinity in the eastern (western) SES

    • Author Affiliations

       

      MEENAKSHI CHATTERJEE1 2 D SHANKAR3 V VIJITH3 4 G K SEN2 5 D SUNDAR3 G S MICHAEL3 P AMOL3 6 ABHISEK CHATTERJEE3 7 P SANYAL2 SIDDHARTHA CHATTERJEE2 8 ANWESHA BASU2 9 SARANYA CHAKRABORTI2 10 SURJA KANTA MISHRA2 11 K SUPRIT3 7 DEBABRATA MUKHERJEE2 12 A MUKHERJEE3 13 SOUMYA MUKHOPADHYAY14 15 GOPAL MONDAL2 16 ARAVIND KALLA3 17 MADHUMITA DAS2

      1. Basanti Devi College, Kolkata 700 029, India.
      2. School of Oceanographic Studies, Jadavpur University, Kolkata 700 032, India.
      3. CSIR-National Institute of Oceanography, Dona Paula, Goa 403 004, India.
      4. Present address: School of Marine Sciences, Cochin University of Science and Technology, Kochi, India.
      5. Present address: National Council of Education Bengal, Jadavpur University, Kolkata, India.
      6. Present address: CSIR-National Institute of Oceanography Regional Centre, Visakhapatnam, India.
      7. Present address: ESSO-Indian National Centre for Ocean Information Services, Hyderabad, India.
      8. Present address: Department of Disaster Management, Government of West Bengal, Howrah, India.
      9. Present address: Lyons Calcutta (Greater) Vidya Mandir, Kolkata, India.
      10. Present address: School of Environmental Studies, Jadavpur University, Kolkata, India.
      11. Present address: Kharki High School, Kharki, Kheyadaha, Sonarpur, West Bengal, India.
      12. Present address: Chakbad High School (HS) Purulia, Santaldih, West Bengal, India.
      13. Present address: ESSO-National Centre for Polar and Oceanic Research, Vasco da Gama, Goa, India.
      14. Department of Mathematics, Jadavpur University, Kolkata, India.
      15. Present address: ESSO-Indian Institute of Tropical Meteorology, Pune, India.
      16. Present address: Vivekananda Mission Mahavidyalaya, Haldia, West Bengal, India.
      17. Present address: CGI Inc., Bengaluru, India.
    • Dates

       
  • Journal of Earth System Science | News

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