Seasonal nutrient chemistry in mountainous river systems of tropical Western Peninsular India

Abstract

Nutrient chemistry was studied in three mountainous rivers (Mandovi, Zuari and Netravati), across western peninsular India (WPI) during south-west monsoon (SWM), post-monsoon and pre-monsoon seasons of year 2011–2012. Nutrients in rainwater were dominated by dissolved inorganic nitrogen (DIN) and urea, dependent upon industrial emissions and the rainfall location. Nutrients in river water were enriched with DIN and Si(OH)₄ as compared with during the SWM season. During pre-monsoon, the river water was enriched with dissolved organic nitrogen (DON), whereas enrichment of a particular nutrient species was not consistent during the post-monsoon season in all three studied river systems. Nutrients exports to the estuarine water were dependent upon the geomorphological feature of river catchment and on prevalent anthropogenic activities. The significant observed contribution of DON to total dissolved nitrogen in Mandovi (62%), Zuari (83%) and Netravati (69%) is important, in view of alterations in biogeochemical processes of adjacent Arabian Sea. Furthermore, the yield of nutrient such as was found to be a function of runoff per catchment area in studied river systems, is comparable with other tropical rivers of world, which highlights the importance of mountainous rivers along WPI in their contribution to the Global riverine nutrient flux.

Keywords:

• nutrients
• SW monsoon
• Mandovi
• Zuari and Netravati Rivers
• Arabian Sea

Acknowledgements

This study was made possible by sampling campaigns organised by PVS and group at National Institute of Oceanography (NIO). Authors sincerely thank to Director, NIO, for his support towards this study. The laboratory as well as field assistance provided by PVS and group members (P. Rahul and A. Shirodkar) is deeply appreciated. Suggestions from Prof. Su Mei Liu (Ocean University of China, Qingdao) greatly helped us in improving the earlier version of this manuscript. This study was partially supported by Natural Science Foundation of China (Nos. 41021064, 41076052), SKLEC (2010RCDW04, 2012RCDW05), 111 project (B08022). The first author sincerely thanks Ministry of Human Resources Development (India) and Chinese Scholarship Council (PR China) for providing him visiting fellowship. Finally, authors thank two anonymous reviewers for their critical reviews and concerns on the earlier version of this manuscript.