Paq proxy was applied on mid and long-chain n-alkanes in order to develop an index to assist in the long-term assessment of changes and exchanges between aquatic communities in estuarine environments as a result of increased saline incursion. New boundaries are proposed according to n-alkanes abundance in the leaves of local mangrove tree species for better definition of emergent aquatic plant end-member. Molecular distribution and δ13C isotopic signatures of n-alkanes were also used to support the parameter. A predominance of odd carbon-numbered long chain (> C27 n-alkanes) indicated a main terrestrial input, although mid-chain n-alkanes (23 and 25 carbons) were also identified. Short-chain n-alkanes (< 19) were absent or found in a very small concentration. Carbon Preference Index and C/N ratio reinforced a terrestrial origin for the sedimentary organic matter. δ13C signatures of n-alkanes for C23, C25, C29 and C31 were characteristic of mangrove input, ranging from -27.57 ‰ (C23) to -34.40 ‰ (C29) for Piraquê-Mirim River (PM) and from -27.36 ‰ (C23) to -32.84 ‰ (C31) for Piraquê-Açu River (PA) without any particular trend. Paq proxy was successfully used to identify rises in marine macrophytes (mid-chain n-alkanes) input mainly in the confluence and PM probably as consequence of drought periods. The confluence presented a mixing sources of OM. PA was identified as a stable mangrove environment while PM was characterized by pulses of marine macrophytes input and should be managed with care in respect to its catchment for water use and dam constructions as a shortage of fresh water can alter the estuarine ecology.

The Piraquê-Açú and Piraquê-Mirim estuarine system (PAPMES) is considered to be a hydrologically unaltered estuary; however, several human activities including introduction of pollutants may have contributed to changes in this system. We have studied hydrocarbons, major elements (Al, Mg, Fe and Mn), trace elements (As, Ba, Cd, Co, Cr, Cu, Li, Ni, Pb, V and Zn), Corg./Ntotal ratio, and δ13C and δ15N stable isotopic composition of organic matter to assess the natural and anthropogenic depositional record in three sediment cores dated by 210Pb geochronology. The sediments showed a strong terrestrial C3 plant contribution to organic matter input in the rivers (−29.2 ≤ δ13C ≤ −25.1h; 2.1 ≤ δ15N ≤ 5.3h; 23.3 ≤ Corg./Ntotal ≤ 53.9), with a higher phytoplankton influence downstream (−29.3 ≤ δ13C ≤ −20.7h; 0.4 ≤ δ15N ≤ 6.6h, and 15.4 ≤ Corg./Ntotal ≤ 34.4). Greater n-alkane concentrations typical of higher plants (nC27, nC29, nC31) confirmed the terrestrial inputs. There was no indication of contamination by petrogenic sources, but relatively high amounts of 17β(H), 21β(H) and 17β(H), 21α(H) terpanes, indicate a possible association with biogenic activities (bacteria). The distributions of major and trace elements were associated with a high lithogenic input and iron and manganese oxides/hydroxides. Although there is little evidence of enrichment by direct human activity, the downstream sediments may be influenced by deforestation for charcoal production which occurred between the 1950s and 70s, exposing soils to weathering and erosion.

Although the Passagem Channel estuary, Espírito Santo State, Brazil, is located in an urbanized and industrialized region, it has a large mangrove system. Here we examined natural and anthropogenic inputs that may influence trace metal (Cd, Cr, Cu, Ni, Sc, Pb and Zn) and hydrocarbon (n-alkane and terpane) deposition in three sediment cores collected in the tidal flat zone of the estuary. The cores were also analyzed for carbonate, grain size and stable isotopic composition (δ13Corg. and δ15Ntotal). Metal enrichment and its association to petroleum hydrocarbons in the surficial sediments of one of the cores, indicate crude oil and derivative inputs, possibly from small vessels and road run-off from local heavy automobile traffic. At the landward sites, the major contributions for metals and hydrocarbons are from natural sources, but in one case, Cu may have been enriched by domestic effluent inputs.

Estuaries are coastal environments that normally accumulate many contaminants in their sediments, where the estuary of the Canal da Passagem (Vitória-ES) falls in this type of coastal environment, because it is a region that has been suffering with urbanization and industrialization around. In order to evaluate the quality of the sediment of the estuary, were analyzed trace metals cadmium (Cd), Chromium (Cr), Copper (Cu), Nickel (Ni), Lead (Pb), Scandium (Sc) and Zinc (Zn), hydrocarbons (n-alkanes and hopanes), organic carbon and total nitrogen ratio (Corg/Ntotal) and stable isotopes (δ13C) in 3 sediment cores (P1, P2 and P3). The metal concentrations ranged from 0.06 to 0.93 μg/g (Cd) 4.03 to 63.45 μg/g (Cr) 1.27 to 32.72 μg/g (Cu), 1.12 - 10, 05 μg / g (Ni), 1.69 to 22.85 μg/g (Pb), 0.62 to 4.29 μg/g (Sc) and 19.62 to 166.17 μg/g (Zn).The concentrations hydrocarbon were 0.29 to 32.50 μg/g for the n-alkanes and from 0.06 to 14.44 μg/g for the hopanes. While the values of Corg/Ntotal and δ13C varied from 12.96 to 60.96, -36.20 to -25.01‰, respectively. The results show that the estuary of the Canal da Passagem has suffered an accumulation of pollutants over time, especially in the region of core P1, which showed characteristics of anthropogenic contribution to the contamination with oil and derivatives being the main source of metals and hopanes.

The present work evaluate the molecular and isotopic composition of n-alkanes from mangrove species Rizophora mangle (RZ), Laguncularia racemosa (LA) and Avicennia schaueriana (AV) at Mangrove Biological Reserve of Piraquê-Açu and Piraquê-Mirim rivers (Aracruz-ES/Brazil). The n-alkanes total concentrations ranged from 0.89 (R. mangle green leaf) to 398.67 ug.g-1 dry weight (A. schaueriana, senescent leaf), been the senescent leaves having the most abundance independent from specie. The CPI (Carbon Preference Index) values were in the proposed limit for terrestrial plants waxes, where the average between senescent and green leaves from each species were RZ = 6,70; LA = 20,73; and AV = 8,30. The δ13C from C25 to C31 n-alkanes average values indicated a pattern distribution based on saline and hydric stress (L. racemosa = -36.94; R. mangle = -35.98; A. schaueriana = -35.03‰).