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Carbon isotopic and biochemical fingerprints of sedimentary organic matter in lower Narmada and Tapi rivers, north-west coast of India

Pradhan, U. K., Wu, Y., Shirodkar, P. V.
Chemistry in ecology 2019 v.35 no.6 pp. 537-552
algae, biomarkers, carbon nitrogen ratio, coasts, estuaries, lignin, organic carbon, phenol, plant tissues, rivers, sediments, soil, stable isotopes, India
Sources of organic matter (OM) in lower Narmada and Tapi river-estuaries were examined using organic carbon to nitrogen ratio (Cₒᵣg/N), stable carbon isotope ratio (δ¹³Cₒᵣg) and lignin phenol biomarkers. The signature of lower Cₒᵣg (av. 0.50%) and higher δ¹³Cₒᵣg (av. –20.3‰) in Narmada and, higher Cₒᵣg (av. 0.85%) and lower δ¹³Cₒᵣg (av. –22.8‰) in Tapi highlight the difference in OM characteristics of both systems, nevertheless they flow adjacent to each other. The OM in Tapi was predominated by fresh plant tissues, as indicated by higher Λ8 = 1.2–3.2 mg/100 mg Cₒᵣg, lower Ad/Alᵥ = 0.22–0.46 and lower LPVI = 17–23. The plant OM present in the sediments of Narmada was previously degraded and mixed with soil. The OM contribution from algae was restricted to estuarine stations in both the rivers, which was ∼50% in Narmada and ∼35% in Tapi. The contribution of OM from fresh vascular plant was higher (20% to 63%) in Tapi than Narmada (2% to 35%). This study illustrated the benefits of using lignin phenols along with Cₒᵣg/N and δ¹³Cₒᵣg to identify the potential OM sources in two large river–estuary systems of India, which highlighted the complex interaction of natural and anthropogenic processes acted on the terrestrial OM compositions.