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Other Titles: Composition of disslved and particulate organic matter in salt gradient of Paraiba do Sul river and Sepetiba Bay estuaries, RJ.
Keywords: Ciclo de maré;  Esteróis;  Isótopos;  N-alcanos;  Marcadores;  Tidal cycle;  Sterols;  Isotopes;  N-alkanes;  Markers
Issue Date: 28-Mar-2012
Abstract: The characterization of organic material that reaches the estuaries is essential for elucidation transport and decomposition processes that occur in these environments. The study aimed to characterize the different fractions of organic matter in the estuarine salinity gradient under different hydrodynamic conditions and relate with sources and processes in the continent-ocean interface. Paraiba do Sul River Estuary (PSR) and Sepetiba Bay (SB) were sampled in wet and dry periods considering tidal cycle and salt gradient, respectively. The physico-chemical parameters, suspended particulate matter (SPM) and chlorophyll a showed the absence of saline wedge influence in tidal cycle during rainyseason at PSR. Less variation in those parameters were observed due to high turbidity and water mass mixing, opposite to that found in dry period. In SB there was a spatial gradient with salinity increasefrom São Francisco Channel to the central of the Bay, salinity 32. The C/N ratio showed low values in the SPM fraction (>0.7&#956;m), ranging between 1.1 and 6.1 in both estuaries. In the suspended material>20 and>64&#956;m C/N range from 4.4 to 18.6. This parameter showed negative correlation with the &#948;13C (-0.80 in SPM fraction and-0.82 in >20 and >64&#956;m; p<0.05). The &#948;13C showed similar behavior between those fractions in estuaries, with lighter values in lower salinities, marking terrestrial C3 plants (minimum -25.5 ) and tending to heavier values towardsin more saline water, marking phytoplankton (maximum -17.1 ). Unlike, the &#948;15N did not showed trend with salt gradient, presenting isotopic fractionation between>0.7&#956;m (0.7 to 6.2 ) and>20 and>64&#956;m (5.2 to 18.8 ). The sterolspointedfor multiple sources. The fraction>0.7&#956;m showed the sum of sterols (mean 14.85 and 30.51&#956;g.L-1 in PSR and SB, respectively) two magnitude orders higher than found for the dissolved fraction (mean 135.2 and 174,0ng.L-1 in PSR and SB, respectively). In PSR, the particulate fractions showed similar mean values (>20&#956;m: 34.4&#956;g.L-1 and>64&#956;m: 35.9&#956;g.L-1), differing from SB that presented 47.3&#956;g.L-1(>20&#956;m) and 134.6&#956;g.L-1(>64&#956;m). The relative proportion between sterols showed the predominance of terrigenous sources and sewage, withmajor importance of &#946;- sitosterol and coprostanol in lower salinities. The estuarine trophic processes were highlighted by cholesterol and campesterol in higher salinities. Cholestanol and cholestanone, especially during dry period in BS (particulate and dissolved), suggest intense bacterial activity acting on organic matter decomposition. A bimodal distribution of n-alkanes was found in the two estuaries, indicating mixture sources. Short chain n-alkanes (n-C10 n-C20) predominated in pairs, with emphasis on the n-C10 and n-C16 to n-C20. In the long chain (n-C21 n-C40), there was no predominance of odd/even, most notably from n-C27 to n-C33In exporter estuary PSR, there is a predominance of terrigenous sources with high precipitation, neutralizing tide influence, but with greater estuarine processes in dry period. In retainer estuary SB, is a salt gradient with continental influence restricted to river area and predominance of authoctonous compounds and processes in other bay areas.
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