Study of sedimentary organic carbon using δ13C, δ15N and TOC/TN as indicator in sediment core samples from Mumbai Harbor Bay

Elemental [Total Organic Carbon (TOC) and Total Nitrogen (TN)] compositions and stable isotope ratio of carbon (δ¹³C), and nitrogen (δ¹⁵N) compositions were measured in four sediment core samples from Mumbai Harbour Bay (MHB), Mumbai, India, to assess the impact of anthropogenic discharges on organic matter in the area and to identify the contribution of terrestrial and marine sources to sedimentary organic carbon. The average values for TOC (%), TN (%) and TOC/TN ratio at different sampling locations in the study area ranges from 1.86% to 2.29%, 0.16% to 0.22%, and 10.49 to 12.01, respectively. Similarly, the average values for δ¹³C and δ¹⁵N were found to vary from - 23.53‰ to - 21.12‰ and from 1.22‰ to 3.14‰, respectively. The sediment from regions impacted by anthropogenic activities had a higher terrestrial organic matter. Application of a two end-member mixing model indicated the contribution of marine sources to organic matter increased from 53.40 ± 11.24% at the northern end to 90.51 ± 6.91% at the southern end of the bay. The correlation between the measured parameters indicates that the organic matter in the region has undergone significant diagenesis and bacterial decomposition. Overall, this study highlights the importance of stable isotope ratios in understanding the complex dynamics of marine ecosystems and the source of organic matter.