ORGANIC MATTER SOURCES TO THE SUPERFICIAL SEDIMENT OF THE ITAPICURU RIVER ESTUARY (BAHIA - BRAZIL)

ORGANIC MATTER SOURCES TO THE SUPERFICIAL SEDIMENT OF THE ITAPICURU RIVER ESTUARY (BAHIA - BRAZIL). The present study evaluated the sources of organic matter (O.M.) in the Itapicuru River estuary (IRE), which is in an environmentally protected area surrounded by the Atlantic Rainforest in the northeast of Brazil. Eleven sediment samples were collected along the study area. Total organic carbon (TOC) and the δ¹³C values were determined using an elemental analyzer coupled with an isotope ratio mass spectrometer. The n-alkanes composition was evaluated through gas chromatography coupled to a flame ionization detector. TOC and total n-alkanes concentrations ranged, respectively, from not detected to 0.72%, and from lower the limit of detection to 5024 ng g^-1. There was a significant concentration of n-C₂₂ and n-C₂₄ in some samples showing bacterial production and recycling of O.M. Values of δ¹³C ranged from -27.6 to -21.9‰. Carbon preference index, terrestrial-aquatic ratio, aquatic production index, average chain length, and the ratio between n-C₂₉ and n-C₃₁ values ranged, respectively, from 1.42 to 4.11; 2.82 to 9.40; 0.00 to 0.25; 27.7 to 29.9; and 0.27 to 0.43. These results show that concentrations of O.M. to IRE are low, and its main source is C₃ plants, such as those from mangroves. There is also the contribution of macrophytes.

Keywords:
estuary; n-alkanes; organic matter; rainforest