Impacts of local vegetation changes in the organic matters input for a preserved tropical estuary (Itapicuru - BA River Estuary)

Estuaries are major areas of organic matter (OM) deposition, playing an important role in the global carbon cycle. The Itapicuru's river estuary (IRE) is in the North Coast of Bahia (Brazil), in na Environmental Protected Area. Although it presents preserved conditions, some environmental changes caused by human activities can be observed. This study evaluated the anthropogenic impacts importance in concentrations/sources of OM deposited in IRE. n-Alkanes and stable isotopes (δ13C and δ15N) were analyzed in a sediment core collected in the studied region. Total n-alkanes (n-C15 to n-C35), TOC and TN concentrations varied from 1,333 to 7,384 ng g-1, 0.65% to 2.51% and 0.07% to 0.13%, respectively. Values of δ13C and δ15N ranged from -28.8‰ to -24.3‰, -6.23‰ to 1.87‰, respectively. By the means of the isotopic composition and the selected n-alkanes diagnostic ratios values (Productivity aquatic index; Carbon Preference Index; Average Chain Length and Alkane index), the main OM sources for IRE were determined as C3 terrestrial plants. This area is covered by mangrove/riparian vegetation, which mainly species have this photosynthetic pathway. Temporal changes in deposited OM occurred due natural and anthropogenic processes, such urban growth in the IRE upstream region.