Caravelas Estuary Research Articles

Shoreline Retraction and the Opening of a New Inlet: Implications on Estuarine Processes

The dynamics of estuarine systems is sensitive to changes in its forcing conditions, including the morphology of its inlets. Coastline retraction, which may be induced by climate change, can result in modifications of estuarine inlet morphology. Through the use of a validated numerical model, we evaluate the effects of the opening of a new inlet on a tide-dominated estuary (Caravelas estuary, Brazil). During the last decades, shoreline retraction and the breach of an internal drainage channel led to the formation of a new inlet that became the main estuarine channel. The morphological changes of the estuary resulted in changes to its estuarine processes, including the general increase in the influence of the tide on the system and changes to its asymmetry. Internal channels that interconnect adjacent estuaries present great changes caused by the morphological alterations, not only in the magnitude of the processes but also in the resulting net transport direction. The increase in the water flow caused by the opening of the channel leads to an increase in the amount of water and materials carried toward the estuary. The changes presented here for the Caravelas estuarine system and the possible implications for the functioning of such systems demonstrate the importance of evaluating morphological aspects in relation to their use and management.

Environmental changes reflected by sedimentary geochemistry for the last one hundred years of a tropical estuary

Abstract Based on multiple proxies, such as major and trace elements, mineralogy, Corg/Ntotal ratio and δ13C, we assessed the natural and anthropogenic depositional record in a tropical estuary (Caravelas, Brazil). The Caravelas estuary was once a pristine area of highly important ecological role, due to its mangroves and proximity to the largest reef system in the South Atlantic (Abrolhos Archipelago). However, during the past decades, the estuary has been subjected to both natural and anthropogenic impacts, such as a natural opening of an inlet and changes in land use. This study is based on three dated cores, taken from the inlet to the main channel. A shift in the organic and inorganic proxies, in the early 1960s, shows the impact of this natural opening on the hydrodynamics and sediment distribution. Furthermore, there is a clear spatial pattern in the contribution of the main sources to the organic matter content in the cores: the core collected further away from the inlet shows a strong C3 plant contribution while the ones recovered closer show a higher marine influence. Only a slight increase in enrichment factors of the selected trace metals has been observed and they have been attributed to land use changes rather than direct inputs from industrial and urban sources. Such information is vital for the effective management of coastal systems, mainly when considering natural and ongoing anthropogenic changes in its forcing conditions that are exacerbated by climate change.

Variability and Transport of Inorganic Carbon Dioxide in a Tropical Estuary

Marine ecosystems are a known net source of greenhouse gases emissions. On the other hand, the geochemical fluxes, particularly from the developing countries estuarine areas, are poorly evaluated. In the present study, temporal and longitudinal water samplings were taken hourly and seasonally during full semidiurnal tidal-cycles, along the Caravelas estuary, located in northeast region of Brazil. It was analyzed the pH, total alkalinity, aragonite saturation state, calcite saturation state, dissolved inorganic carbon, aqueous CO2 and partial pressure of CO2 found in estuarine waters. Results showed that the total alkalinity values decreased from the estuary mouth up-river during the dry season, which reflects the low buffering capacity of river water. The estuarine total alkalinity and dissolved inorganic carbon fluxes were significantly higher in the dry season during the spring tide. The spring and neap tides were typically oversaturated with CO2 in both the dry and rainy seasons. The highest average values were found in the dry season for both the neap and spring tides, while the CO2 air-water flux values throughout the dry and rainy seasons, retained a positive variation range. Finally, the annual surface water flux of dissolved inorganic carbon revealed to be positive suggesting dissolved inorganic carbon exportation to coastal water.

Spatial sediment variability in a tropical tide dominated estuary: Sources and drivers

Surficial sediment composition and spatial variability reflect the dynamics and level of natural and anthropogenic impact in estuarine systems. The aim of this study is to evaluate some key environmental and sedimentary variables, as well as to evaluate the current environmental quality in the tide-dominated Caravelas estuarine system (Brazil). Sixty-five surficial sediment samples were studied for grain size as well as calcium carbonate, total organic carbon, total nitrogen, metals, semi-metals and rare earth elements and for organic matter δ13C. Based on the spatial distribution of these data and summarizing our findings, three sectors can be individualized in the Caravelas estuarine system: i. Barra Velha inlet; ii. the main channel of the Caravelas estuary, and iii. the channel interconnecting Caravelas and Nova Viçosa estuaries. In the inlet the sedimentary organic matter is provided essentially by marine sources, which corroborates the small continental input. Freshwater dissolved organic carbon and particulate organic carbon occur in the interconnecting channel, proving the occurrence of the residual transport towards the Caravelas estuary, with continental contribution towards Caravelas River. The geochemical fingerprint indicates that the Barreiras Group, composed by Neogene terrigenous deposits, located west of the study area, as an important source of terrigenous material to the entire Caravelas estuary system. The higher values of heavy rare earth elements (between 20 and 30 mg kg−1) in the northern sector of the study area may be related to the high degree of chemical weathering in magmatic or metamorphic rocks, which occur to the north of the study area.

Observation of an Estuarine Turbidity Maximum in the Highly Impacted Capibaribe Estuary, Brazil

Estuarine turbidity maxima (ETM) are features present in some estuaries where the concentration of suspended particulate matter (SPM) is higher than elsewhere along the fresh-marine water transition in the estuarine domain (POSTMA, 1967; SCHUBEL, 1968; GEYER, 1993; DYER, 1995). The presence of ETM has important ecological implications: since they occur at places where there is an accumulation of organic matter: bacterioplancton and zooplankton dynamics in estuaries is affected by ETM behavior (CRUMP; BAROSS, 1996; MORGAN et al., 1997). ETM are also important in the pollutants dynamics of an estuary, mainly for those that occur adsorbed to fine clayey sediments (BRUNK et al., 1996). ETM are formed and maintained as the result of complex interactions between river discharge, tidal dynamics and gravitational circulation (DYER, 1988). The concentration of SPM in the ETM varies over time on tidal, sinodical and seasonal time scales (GRABEMANN et al., 1997). ETM have been studied in many estuaries abroad (ALLEN et al., 1980; GELFENBAUM, 1983; UNCLES et al., 1994; WOLANSKI et al., 1995). In some estuaries they are of an ephemeral nature (KISTNER; PETTIGREW, 2001), while in other cases they do not occur at all (SCHETTINI; TOLDO JUNIOR, 2006; SCHETTINI et al., 2006). The physics underlying the formation of the ETM has been studied using both analytical and numerical models (GEYER, 1993; JAY; MUSIAK, 1994; BURCHARD; BAUMERT, 1998; YU et al., 2014) in which the effect of gravitational circulation and tidal pumping is of primary importance, with a high degree of interaction between the flow and the bed. Most ETM have been reported in meso or macro-tidal estuaries. As regards the Brazilian coast, it is not expected to find ETM in the Southeastern and Southern Regions basically because the tidal regime is microtidal. Some papers have reported ETM processes in Paranagua Bay (PR) (e.g., RIBEIRO et al., 2011), although the higher turbidity zone in that estuary is linked rather to re-suspension due to tidal currents (MANTOVANELLI et al., 2004) than to the occurrence of a true ETM. Other studies on SPM in southern Brazilian estuaries have not reported the presence of ETM (SCHETTINI; TOLDO JUNIOR, 2006; D´AQUINO et al., 2010). On the other hand, meso and macro tides occur on the shores of the Northeastern and Northern Regions, where there would be a greater likelihood of observing ETM. Nevertheless, there are not many studies of the fine sediment dynamics of this area, and the few that are available do not report the presence of ETM. The fine sediment dynamics of the Caravelas estuary, Bahia has been assessed (SCHETTINI; MIRANDA, 2010; SCHETTINI et al., 2013), despite the fact that this estuary presents a very small freshwater inflow, and the major source of sediments is the inner shelf. Such conditions are unfavorable to the formation of ETM. The eastern shores of Para seem to present favorable conditions for the formation of ETM, and a single survey carried out in the Caete estuary has shown a feature in the longitudinal distribution of SPM which fits in with what is expected of an ETM (ASP et al., 2012), even though it has not yet been assessed.A series of surveys has been carried out in the Capibaribe estuary since 2012 to investigate its circulation, fine sediment transport, deposition patterns and recent environmental evolution. The main appeal of and reason for these assessments was the fact that the Capibaribe estuary is a relatively small system (~ 10 km

An assessment of transport timescales and return coefficient in adjacent tropical estuaries

Transport timescales (TTS), namely residence time and exposure time, were computed for adjacent shallow meso-tidal tropical estuarines system using the Lagrangian model D-Waq Part coupled with the hydrodynamic model Delft3D-Flow, and the Constituent-oriented Age and Residence time Theory, CART. The main results are threefold: (a) The TTS differs more between releases at high or low tide than between those at spring and neap tides. The exposure time was also calculated and found to be larger than the residence time by a few days. (b) The exposure and residence times were used to evaluate the return coefficient (r) for different scenarios. As with residence and exposure times, the return coefficient was found to differ more between releases at high or low tide than between those at spring and neap tides. (c) For the Caravelas Estuary, where the river inflow was low (~4m3s−1), the residence time was found to be much larger than for the Peruípe Estuary, where the river discharge was greater and nearly constant during the sampling period (~20m3s−1). These results shows the importance of advection in decreasing TTS in the Peruípe Estuary compared to the Caravelas Estuary. The influence of the advection and dispersion agrees with previous simple estimates obtained using the newly modified Land Ocean Interaction Coastal Zone (LOICZ) model by Andutta et al. (2014).

Recent sedimentation rates in the Caravelas estuary (Bahia, Brazil) using unsupported 210Pb and 137Cs modeling

Abstract The Caravelas estuary is located in a zone of the Brazilian coast (Southern Bahia State) which has been submitted to different kinds of land uses during the last 50 years. This zone has an important ecological role, due to its mangroves and its location next to Abrolhos coral reef, the most important in the Southern Atlantic Ocean. 210Pb and 137Cs dating methods, accompanied by a sedimentological study, were applied to sediment cores in order to establish sedimentation rates and identify historical trends of land use and erosive processes. Sedimentation rates were established according to the “Constant Rate of Supply” (CRS) 210Pb dating model, which was preferred rather than the “Constant Initial Concentration” (CIC) model. Corrected sedimentation rates obtained from 210Pb dating were corroborated through a second independent radionuclide tracer such as 137Cs. The sedimentation rates obtained according to the CRS model for the cores were 1.07 ± 0.13 cm yr –1 for T#2 (inner sector), 0.65 ± 0.06 cm yr –1 for T#5 and 0.85 ± 0.09 cm yr –1 for T#8 (outer sector). The difference in sedimentation rates among the sampling sites could be due to hydrodynamic processes and could be related to the tendency of increase of erosive processes, conditioned by the changes in the landscape and land use to, which this region has been submitted.

Application of organic carbon and nitrogen stable isotope and C/N ratios as source indicators of organic matter of Nova Viçosa-Caravelas estuarine complex, southern Bahia, Brazil

This study characterized the elementary ratio and isotopes (δ13C, δ15N and C/N) of surface sediments and suspended solids in surface water of 20 sample points in the estuarine complex of Nova Vicosa-Caravelas, southern Bahia, Brazil . The d13C DIC of the dissolved inorganic carbon (DIC), the δ18O and δD and physico-chemical parameters of water was analyzed to estimate the contribution of continental sources, marine and anthropogenic interference in the study area. The area is characterized by the influence of adjacent coastal area through the main channel of Caravelas Estuary entrance and the Peruipe River in Nova Vicosa Estuary, as the main freshwater intake. The highest values of δ13C in sediment and DIC in water were found in the Caravelas bar and higher values of total organic carbon and C/N ratio found within the two channels that interconnect the estuaries of Caravelas and Nova Vicosa. The isotope ratios of carbon and nitrogen indicate that the analyzed organic matter has terrestrial origin with strong signature of mangroves, characteristic of estuarine regions. Although the values of C/N indicate an anthropogenic contribution at some sampling points, the δ15N found, compared with the literature, suggests that processes of N series cycling in the estuary are sufficient to keep the impact of human activity in the region at low levels. The results may serve as a baseline for future monitoring and environmental studies in estuarine complex of Nova Vicosa-Caravelas.

Residual fluxes of suspended sediment in a tidally dominated tropical estuary

This paper assesses the fine sediment fluxes in the Caravelas estuarine system (Bahia, Brazil, 17o45'S and 039o12'W). The estuary reaches the ocean at the shore across from the Abrolhos Bank, the largest tropical reef habitat in the South Atlantic. The Caravelas estuarine system is composed of several meandering channels, which are connected to the ocean by a double inlet system. These two openings – the Caravelas and Nova Viçosa estuaries – are connected by a narrow, 30km long channel. The Caravelas estuary does not receive significant continental input, while the Nova Viçosa estuary receives the contribution of the Peruíbe River, which drains an area of approximately 5000km2. To understand the fine sediment dynamics and net transport, observations of tides, currents, salinity and suspended sediment concentration (SSC) were recorded in 13-h tidal surveys (spring and neap tide) and with 20-day long CTDs/ADCP moorings at the Caravelas estuary and in the interconnection channel. The SSC dynamic in the Caravelas estuary is primarily driven by advection, with SSC originating in the inlet and inner shelf area. Residual water and sediment transport are up-estuary in the Caravelas estuary and toward the Caravelas estuary in the interconnection channel. The residual transport showed pronounced synodical modulation and was stronger during spring tide. The Caravelas estuary function as a trap for inner shelf materials and fine sediments delivered by the Peruípe River at Nova Viçosa.

Environmental Evolution of the Caravelas Estuary (Northeastern Brazilian Coast, 17° S, 39° W) Based on Multiple Proxies in a Sedimentary Record of the Last Century

ABSTRACT Sousa, S.H.M.; Amaral, P.G.C.; Martins, V.; Figueira, R.C.L.; Siegle, E.; Ferreira, P.A.L.; Silva, I.S.; Shinagawa, E.; Salaroli, A.; Schettini, C.A.F.; Santa-Cruz, J., and Mahiques, M.M., 2014. Environmental evolution of the Caravelas Estuary (northeastern Brazilian coast, 17° S, 39° W) based on multiple proxies in a sedimentary record of the last century, A sediment core (∼100 cm long) taken from the upper Caravelas estuary was interpreted based on sedimentological, microfaunal, geochemical, and historical data for the last 70 years. Outcomes are a significant contribution to the understanding of the relationship between anthropogenic impact and natural ecosystem change. The results obtained for the period between the 1930s and the beginning of the 1970s do not reveal any evidence of natural and/or anthropogenic impacts in the estuary. This period is characterized by a higher percentage of sandy sediments, lower pollution load index (PLI) values, and a mixed source of organic matter (C3 land pl...

Hidrodinâmica e transporte de material particulado em suspensão sazonal em um estuário dominado por maré: Estuário de Caravelas (BA)

The objective of the present paper is to characterize the hydrodynamics and the suspended particulate matter (SPM) in the Caravelas Estuary under different tidal and river regimes. Four hydrographic campaigns were carried out comprising a complete semi-diurnal tidal cycle, comprising neap and spring tidal phases, and during dry and wet seasons. Water level, current speed and direction, salinity, temperature and turbidity were recorded in an anchored station near to the estuarine mouth. The residual SPM flux and the mechanisms of transport were calculated. The higher SPM concentrations were recorded during the spring tidal phase. During neap tides, the net SPM flux was up-estuary, although with low scale. During spring tides the tidal currents are strongly ebb dominant, and the net flux can be either up- or down-estuary. The estuary was classified as well mixed or weakly stratified. The hydrography and the sediment balance are firstly modulated by the tidal range, and the fresh water inflow is negligible.

Circulation and suspended particulate matter transport in a tidally dominated estuary: caravelas estuary, Bahia, Brazil

The circulation and transport of suspended particulate matter in the Caravelas Estuary are assessed. Nearly-synoptic hourly hydrographic, current (ADCP velocity and volume transport) and suspended particulate matter data were collected during a full semidiurnal spring tide, on the two transects Boca do Tomba and Barra Velha and on longitudinal sections at low and high tide. On the first transect the peak ebb currents (-1.5 ms-1) were almost twice as strong as those of the wider and shallow Barra Velha inlet (-0.80 ms-1) and the peak flood currents were 0.75 and 0.60 ms-1, respectively. Due to the strong tidal currents both inlets had weak vertical salinity stratification and were classified with the Stratification-circulation Diagram as Type 2a (partially mixed-weakly stratified) and Type 1a (well mixed). Volume transports were very close, ranging from -3,500 to 3,100 m³s-1 at the ebb and flood, respectively, with a residual -630 m³s-1. The concentration of the suspended particulate matter was closely related to the tidal variation and decreased landwards from 50 mg.L-1 at the estuary mouth, to 10 mg.L-1 at distances of 9 and 16 km for the low and high tide experiments, respectively. The total residual SPM transport was out of the estuary at rates of -18 tons per tidal cycle.

Seasonal and spatial variability of appendicularian density and taxonomic composition in the Caravelas Estuary (Northeastern Brazil) and adjacent coastal area

This study aimed to identify and assess the seasonal and spatial variations of the appendicularians in the Caravelas River estuary and the adjacent coastal area. Samples were taken during 12 campaigns over five years (2001 and 2003-2006). Ten species were identified; the most abundant were Oikopleura dioica, Oikopleura rufescens, and Oikopleura longicauda. These species represented more than 95% of the total numbers of appendicularians. The remaining species were less frequent and occurred in low densities. The mean density of appendicularians found at the coastal stations (804 ind.m-3.) was higher than in the estuary (66 ind.m-3). However, the differences observed between the estuary and coastal stations were not significant (p=0.54). The samples taken during the dry season showed a higher mean density (587 ind.m-3) than in the rainy season (376 ind.m-3), and the differences between the seasons were statistically significant (p=0.004).