Coastal vegetation dynamics in response to climatic and relative sea level changes in Mahanadi River delta, NE coast of India

Abstract

This research assesses the impacts of climate change and relative sea level (RSL) fluctuations on coastal vegetation during the past 2000 years along the Mahanadi River delta, northeast coast of India. Sediment samples of a 2.6 m trench from Barhatubi area located in the lower flood plain of Mahanadi River delta were studied for sedimentological and pollen analysis. Mangrove succession can be divided into three zones: (1) Freshwater marsh (∼1980–1420 cal yr BP); (2) Tidal flat (∼1420–770 cal yr BP) and (3) Landward mangrove margin (∼770 cal yr BP-Present). A transgressive shift from floodplain freshwater marsh to a tidal flat is recorded between ∼1980–1420 cal yr BP which is evidenced by upland tree taxa, Poaceae, pteridophyte and fungal spores along with low percentage of mangroves such as Avicennia, Sonneratia and Rhizophora representing the landward edge of the tidal region. Dominance of Sonneratia and a decline in terrestrial taxa reflects a rise in the relative sea level around ∼1420 cal yr BP with less freshwater input from land suggesting a weakened monsoon condition. After ∼770 cal yr BP, an overall regressive phase with small cycles of relative sea level rise/fall has been observed due to the dominance of salt tolerant Avicennia along with Rhizophora, Excoecaria agallocha and Aegialitis rotundifolia alternating with Sonneratia and other marine palynomorphs.

Keywords:

• Palynology
• mangroves
• relative sea level
• climate
• India

Acknowledgements

The authors thank the Director, Birbal Sahni Institute of Palaeosciences for providing necessary facilities to accomplish this work. PS is grateful to Ms. Priyanka Singh for her valuable help regarding Age-depth model. PS is thankful to DST INSPIRE (DST/INSPIRE FELLOWSHIP/2017/IF170769) for providing financial support as a JRF.

Authors’ contribution

Pujarini Samal has contributed in the palynological analysis, interpretation and writing the MS. Singarasubramanian SR has contributed to the interpretation and writing the MS. Jyoti Srivastava has contributed to the palynological analysis, interpretation and in writing of MS. Partha Sarathi Jena, Ajay Shivam and Ravi Bhushan have contributed in the Radiocarbon dating analysis of the samples.

Disclosure statement

The authors of this manuscript have no conflict of interest.

Additional information

Funding

The present work is supported by Department of Science and Technology (DST), Ministry of Science and Technology, Government of India, New Delhi under award no: DST/INSIPRE/Fellowship/2017/IF170769.