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Natural and Anthropogenic Influences on Nutrient Export from Tropical Mountainous Rivers into the Arabian Sea
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  • Kiran Kumar Reddy Shiligireddy,
  • Harish Gupta,
  • Dontireddy Venkat,
  • Rama Mohan Kurakalva,
  • Devender Kumar
Kiran Kumar Reddy Shiligireddy
National Geophysical Research Institute

Corresponding Author:[email protected]

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Harish Gupta
Osmania University
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Dontireddy Venkat
National Geophysical Research Institute
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Rama Mohan Kurakalva
National Geophysical Research Institute
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Devender Kumar
National Geophysical Research Institute
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Abstract

The land-sea connection of nutrients via rivers is an essential component in the global nutrient biogeochemistry. Rivers alone transport approximately 80% of the dissolved nutrients from land to ocean and play a vital role in nourishing riverine, coastal and oceanic ecosystems. During the past decades, global scale investigations have estimated the riverine nutrient flux to the oceans along with the significant drivers. However, most of the previous estimations are based on nutrient discharge by a few major rivers. Despite being large in number and high yields, the tropical coastal/mountainous rivers have received less attention. To fill the gap, we have investigated 70 west-flowing coastal rivers, draining the Western Ghats (WG), for their Dissolved Inorganic Nutrient (DIN) transport characteristics and influencing factors. Previous studies in the selected estuaries along the WG coast are combined to update the land-sea fluxes estimation to understand the spatial pattern of DIN over the WG rivers-the Arabian sea coast continuum. Altogether, the DIN fluxes from entire WG (including non-sampled rivers) region to the estuaries are 664, 241 and 6277 Tg yr-1 for Nitrate (N), Phosphate (P) and Silicate (DSi) respectively. The natural factors, such as discharge, cropland, and forest cover each explain 30–85% of the spatial variation in DIN levels at the basin scales. DIN concentrations of rivers reduces to ~ 90% after reaching the respective estuaries. Based on Redfield ratio of C:N:P (106:16:1), annual export of 66.4 Tg of dissolved inorganic N from the WG rivers would support 439.9 Tg of new carbon production in the Arabian Sea coast. The humid tropical climate and high population density (> 300 people per km2 among the bio-diversity hotspots) of the WG region favour the high DIN export, thus, making the Arabian sea coast highly productive among the global coastal regions. Keywords: Dissolved Inorganic Nutrients; Rivers-Coast Continuum; Influencing Factors; Small Mountainous Rivers; Western Ghats.