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<p>This study investigates the seasonal dynamics and fluxes of dissolved organic carbon (DOC), dissolved silica (DSi) and dissolved nitrate in the Sharavati River catchment, Western Ghats, and their transfer to the estuary. DOC exhibited moderate seasonal and spatial variability, with maximum concentrations in pre- and post-monsoon (up to 5.66&#xa0;mg/L) linked to leaching of forest litter and soil organic matter mobilization, while monsoon values were lowest due to dilution. DSi showed spatial control over its concentrations across different seasons. DSi concentrations were highest upstream (27&#xa0;mg/L in pre-monsoon 2019) due to intense silicate weathering, but declined downstream under the influence of damming, biological uptake, and dilution. Nitrate concentrations exhibited strong seasonal as well as spatial control. Nitrate peaked during the enhanced monsoon by cyclonic events (up to 1.56&#xa0;mg/L), reflecting runoff and agricultural inputs, whereas pre-monsoon levels were minimal due to reduced discharge and enhanced denitrification. The estimated annual fluxes to the estuary were 1,966 t yr⁻¹ for nitrate, 6,610 t yr⁻¹ for DOC, and 36,000 t yr⁻¹ for DSi. Relative to other west-flowing rivers of India, the Sharavati displayed lower nitrate and DOC fluxes (65 and 104&#xa0;kg km⁻² yr⁻¹, respectively), consistent with its largely forested catchment, while its DSi flux (753&#xa0;kg km⁻² yr⁻¹) was moderate, shaped by lithology and reservoir regulation. These findings underscore the role of monsoonal effects enhanced by cyclones and damming in controlling nutrient and carbon export. This study contributes to biogeochemical datasets assessing Arabian Sea ecosystem responses.</p>

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Dissolved nutrient (DOC, DSi and nitrate) dynamics of a regulated tropical river from Western Ghats, Sharavati: emphasis on cyclone-enhanced monsoons

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2026年7月10日

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  • Vadakkeveedu Narayan Amrish,
  • V. Sakthivel,
  • Keshava Balakrishna,
  • Kumar Arun,
  • D’Souza Nishitha,
  • Harikripa Narayana Udayashankar

摘要

This study investigates the seasonal dynamics and fluxes of dissolved organic carbon (DOC), dissolved silica (DSi) and dissolved nitrate in the Sharavati River catchment, Western Ghats, and their transfer to the estuary. DOC exhibited moderate seasonal and spatial variability, with maximum concentrations in pre- and post-monsoon (up to 5.66 mg/L) linked to leaching of forest litter and soil organic matter mobilization, while monsoon values were lowest due to dilution. DSi showed spatial control over its concentrations across different seasons. DSi concentrations were highest upstream (27 mg/L in pre-monsoon 2019) due to intense silicate weathering, but declined downstream under the influence of damming, biological uptake, and dilution. Nitrate concentrations exhibited strong seasonal as well as spatial control. Nitrate peaked during the enhanced monsoon by cyclonic events (up to 1.56 mg/L), reflecting runoff and agricultural inputs, whereas pre-monsoon levels were minimal due to reduced discharge and enhanced denitrification. The estimated annual fluxes to the estuary were 1,966 t yr⁻¹ for nitrate, 6,610 t yr⁻¹ for DOC, and 36,000 t yr⁻¹ for DSi. Relative to other west-flowing rivers of India, the Sharavati displayed lower nitrate and DOC fluxes (65 and 104 kg km⁻² yr⁻¹, respectively), consistent with its largely forested catchment, while its DSi flux (753 kg km⁻² yr⁻¹) was moderate, shaped by lithology and reservoir regulation. These findings underscore the role of monsoonal effects enhanced by cyclones and damming in controlling nutrient and carbon export. This study contributes to biogeochemical datasets assessing Arabian Sea ecosystem responses.