Stable isotopes of bulk organic matter to trace carbon and nitrogen dynamics in an estuarine ecosystem in Babitonga Bay (Santa Catarina, Brazil)

Abstract

The biogeochemical processes affecting the transport and cycling of terrestrial organic carbon in coastal and transition areas are still not fully understood. One means of distinguishing between the sources of organic materials contributing to particulate organic matter (POM) in Babitonga Bay waters and sediments is by the direct measurement of δ 13C of dissolved inorganic carbon (DIC) and δ 13C and δ 15N in the organic constituents. An isotopic survey was taken from samples collected in the Bay in late spring of 2004. The results indicate that the δ 13C and δ 15N compositions of OM varied from − 21.7‰ to − 26.2‰ and from + 9.2‰ to − 0.1‰, respectively. δ 13C from DIC ranges from + 0.04‰ to − 12.7‰. The difference in the isotope compositions enables the determination of three distinct end-members: terrestrial, marine and urban. Moreover, the evaluation of source contribution to the particulate organic matter (POM) in the Bay, enables assessment of the anthropogenic impact. Comparing the depleted values of δ 13C DIC and δ 13C POC it is possible to further understand the carbon dynamic within Babitonga Bay.