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The ITRAX core scanner, a useful tool to distinguish Anthropic vs. Climatic influences in lagoon of Aveiro (N Portugal)
Abstract
The main goal of this work is to distinguish anthropic and climatic influences in sediments from the lagoon of Aveiro (Portugal). This study is based on a core (240-cm long) collected in Murtosa Channel. Optical and X-radiographic images and high-resolution elemental profiles were acquired with ITRAX micro-X-ray fluorescence (XRF) core scanner. Samples collected at each ≈3 cm along the core were analysed for grain size and total organic carbon. Furthermore, the fine fraction of selected layers was subjected to geochemical analysis by ICP-MS, after total acid digestion of the sediments, and mineralogical analysis, by XRD techniques. A radiocarbon age was determined by AMS, using molluscs shells collected at a depth of 90 cm.
Sediments along the core are composed by fine and medium sand, with several mud layers. Sediments composing the first 100-cm may have been deposited after 1950, as it is indicated by the radiocarbon data, the increasing trend of Zn/Al, Pb/Al and Cu/Al and total concentrations of Zn, Pb, Cu, V, Cr, As and Ni in this interval that therefore might be linked with industrial activities of Chemical Complex of Estarreja. The progressive increase of Si/Al, Cl/Al, Rb/Al, K/Al and Br/Al and reduced Al concentrations, from the base to the top of this core, are interpreted as being related to higher marine influence and greater differences in tidal currents with longer exposition to air of the sediments with the consequent formation of brines favouring minerals precipitation in the area (e.g. anhydrite). These results seem to be a consequence of several works developed over time like: i) dredging to improve the navigation access to the harbour, located in the external sector of the lagoon; ii) the control of the course of some rivers influencing the supply of sediments. The tendency of sea level rise may have also emphasized the gradual increase of marine influence in this area. Fine-grained sections, related to an increase in Al, phyllosilicates, organic matter, pyrite and siderite contents would be attributed to phases of greater supply of fine-sediments during heavy rainfall events by the nearby Antuã river and other streams during negative phases of North Atlantic Oscillation. Higher deposition of organic matter enhanced diagenetic changes with pyrite and siderite formation. In the bottom of the core another record of pollution was unveiled to mining activities at the beginning of 20th century.
... Additionally, the higher elemental ratios S/Al, Pb/Al and Fe/Al, which are related with terrigenous inputs (e.g. Richter et al., 2006;Martins et al., 2013), were rather observed along core MS_V9 than in core MS_V4. This pattern also points to a greater continental influence in the former core (Figs. 5 and 6). ...
... Specifically, Fe may be used to trace fluctuations in terrigenous materials (Richter et al., 2006) and Pb can be regarded as an anthropogenic indicator related with pollution inputs which are accumulated in clay sediments or levels rich in organic matter (e.g. Croudace et al., 2006;Martins et al., 2013). Ca/Al ratio should highlight the influx of marine carbonate. ...
... In general, it might be assumed that the variation of the geochemical proxies may be linked to grain size variations, i.e. sand or clay content, which again mirror the influence of climatic variability (e.g. Martins et al., 2013). However, taking into account that the variations of the different elements do not exhibit a coherent pattern with the major rainfall events, we infer that they are indicative of different provenances of the shelf sediments. ...
... At the upper slope of Buenos Aires Province, Ca in contouritic deposits would explain biogenic supports while Fe the terrigenous inputs (Voigt et al., 2013). Dealing with modern estuaries (Aveiro coastal lagoon, Portugal), the lithogenic origin was related to the content of Al, Fe, Ti, Si, Rb, Ba, K, Cl, Br, S, Mn and Zr (Martins et al., 2013). As this coast of Portugal had mining activities, the contents of Pb, Cr, V, Ni, As, Cu and W was explained by human influence before 1920. ...
... As this coast of Portugal had mining activities, the contents of Pb, Cr, V, Ni, As, Cu and W was explained by human influence before 1920. The increase in the ratio between Si/Al was interpreted as a higher input in quartz (Martins et al., 2013). ...
The Chubut River flows from the Andes to the Atlantic Ocean, and is interrupted by a single dam built at the middle valley. The lower valley is dominated by the aggradation of an alluvial plain induced by a complex of spits that enclosed the inlet in the last 5000 years. The river has reduced its flow because the blocking of the upper basin by terminal moraines during the Upper Pleistocene. At least the last two marine transgressions have flooded this estuary, and contributed to the aggradation during regressions. The area is of particular interest in regard to irrigation channels practiced since the XIX century. Today, the mean monthly flow is less than 10 m3/s although peaks of 95 m3/s have been recorded in Gaiman in July 2001. The dynamics of the estuary is dominated by waves (wave-dominated estuary) as tidal effects attenuate in less than 5 km. Three vibracores were collected within this floodplain: (a) at Gaiman, an area without any effect of the sea (35 km from the coast); (b) at Trelew, at the former avulsion plain of the river (18 km from the coast); and (c) at Playa Magagna, a saltmarsh located 0.4 km from the beach.
... Elements' contents are expressed as peak areas (the area integrals of the elements' characteristic peaks presented in each spectrum) that are proportional to element concentrations in the sediment. Despite the semi-quantitative nature of the Itrax data, several authors have demonstrated the ability of this kind of scanners to detect metal pollution in sediments, even at low concentrations [16,[24][25][26][27]. However, we showthe utility of the Itrax for monitoring pollutionover time and as a complementary tool to support radionuclide analyses. ...
... Actually, the definition of the base of this new epoch is, somehow, still a matter of debate, since the geological/ geochemical evidence of the end of the Holocene can be interpreted in different ways (Steffen et al., 2007;Leorri et al., 2014;Irabien et al., 2015;Zalasiewicz et al., 2015;Waters et al., 2016). It is worth observing that in different coastal and marine areas the evidence goes back to pre-Industrial ages (Crutzen and Steffen, 2003;Martins et al., 2013;Leorri et al., 2014;Irabien et al., 2015). ...
In this work, we present a brief revision of the geological evidence of human activities in the coast of São Paulo (Southeast Brazil), from pre-historical times to the present. We analyze case studies in different sectors of the coast, identifying the main historical causes that resulted in environmental changes with their consequent imprint in the sedimentary column. There was a south-to-north trend in the occupation at the colonization period (1500 onwards), essentially determined by differences in the geomorphology of the area. Finally, the accumulation of artificial radionuclides and plastic debris in the sediments is discussed. © 2018 Associacao Brasileira de Estudos do Quaternario. All Rights Reserved.
... Actually, the definition of the base of this new epoch is, somehow, still a matter of debate, since the geological/ geochemical evidence of the end of the Holocene can be interpreted in different ways (Steffen et al., 2007;Leorri et al., 2014;Irabien et al., 2015;Zalasiewicz et al., 2015;Waters et al., 2016). It is worth observing that in different coastal and marine areas the evidence goes back to pre-Industrial ages (Crutzen and Steffen, 2003;Martins et al., 2013;Leorri et al., 2014;Irabien et al., 2015). ...
In this work, we present a brief revision of the geological evidence of human activities in the coast of São Paulo (Southeast Brazil), from pre-historical times to the present. We analyze case studies in different sectors of the coast, identifying the main historical causes that resulted in environmental changes with their consequent imprint in the sedimentary column. There was a south-to-north trend in the occupation at the colonization period (1500 onwards), essentially determined by differences in the geomorphology of the area. Finally, the accumulation of artificial radionuclides and plastic debris in the sediments is discussed.
... Actually, the definition of the base of this new epoch is, somehow, still a matter of debate, since the geological/ geochemical evidence of the end of the Holocene can be interpreted in different ways (Steffen et al., 2007;Leorri et al., 2014;Irabien et al., 2015;Zalasiewicz et al., 2015;Waters et al., 2016). It is worth observing that in different coastal and marine areas the evidence goes back to pre-Industrial ages (Crutzen and Steffen, 2003;Martins et al., 2013;Leorri et al., 2014;Irabien et al., 2015). ...
From sambaquis (shell mounds) to plastic debris: a summary of the geological imprint of human occupation in the coast of São Paulo (Southeast Brazil) Dos sambaquis (montes de conchas) aos destroços plásticos: um resumo da marca geológica da ocupação humana no litoral de São Paulo (Sudeste do Brasil) Abstract In this work, we present a brief revision of the geological evidence of human activities in the coast of São Paulo (Southeast Brazil), from pre-historical times to the present. We analyze case studies in different sectors of the coast, identifying the main historical causes that resulted in environmental changes with their consequent imprint in the sedimentary column. There was a south-to-north trend in the occupation at the colonization period (1500 onwards), essentially determined by differences in the geomorphology of the area. Finally, the accumulation of artificial radionuclides and plastic debris in the sediments is discussed. Resumo Neste trabalho, apresentamos uma breve revisão das evidências geológicas das atividades humanas no litoral de São Paulo (Sudeste do Brasil), desde os tempos pré-históricos até o presente. Analisamos estudos de caso em diferentes setores da costa, identificando as principais causas históricas que resultaram em mudanças ambientais com sua consequente impressão na coluna sedimentar. Havia uma tendência sul-norte na ocupação no período de colonização (1500 em diante), essencialmente determinada por diferenças na geomorfologia da área. Finalmente, o acúmulo de radionuclídeos artificiais e detritos plásticos nos sedimentos é discutido. Palavras-chave: Ocupação humana; litoral; SE do Brasil
... Likewise, variations of magnetic parameters measured in U-channels from several cores of the Portuguese Margin were interpreted in terms of environmental and climatic variations (Thouveny et al., 2000;Moreno et al., 2002;Thouveny et al., 2004). Martins et al. (2013a) studied the sediments of the lagoon of Aveiro (Portugal) in order to distinguish between anthropogenic vs climatic influences through the analysis of the XRF core scanner. They observed increases in the Zn, Pb and Cu records at the top of the sequence that clearly reflect human contributions and show the usefulness of the XRF Figure 8. Continuous and non-destructive geophysical and geochemical data of core MD03-2704 compared with other destructive data used for the identification and characterization of turbidite layers (T) in the Horeshoe Abyssal Plain. ...
Sediment sequences are the most valuable record of long-term environmental conditions at local, regional and/or global scales. Consequently, they are amongst the best archives of the climatic and oceanographic history of the Earth. In the last few decades a strong effort has been made, both in terms of quantity and quality, to improve our knowledge regarding the evolution of our planet from marine and lake sediment records, and also from other records such as ice cores. Such an effort requires reinforcing the geographical coverage and achieving the highest possible robustness in the reconstruction of past environments. Such a target requires the optimization of the time resolution of the records and reconstructions so that fast, high frequency shifts, such as those occurring nowadays due to the on-going global warming, can be disentangled. Beyond paleoenvironmental research, other disciplines have also contributed significantly to the fast growing number of sediment cores already available worldwide. Knowing the physical state and the chemical composition of sedimentary deposits is essential for land management purposes and for many industrial applications. A number of key technological developments are now allowing the acquisition for the first time of massive amounts of multiple parameters from sediment cores in a non-destructive, fast, continuous, repetitive and high-resolution form. In this paper we provide an overview of the state-of-the-art continuous and non-destructive analytical techniques used by the geoscientific community for the study of sediment cores and we present some examples of the application of these methods in several studies carried out around the Iberian Margin. © 2015, Instituto Geologico y Minero de Espana. All rights reserved.
... The uppermost part (∼2 cm) of the sediment was collected for geochemical, mineralogical and grain size analyses in each station and was cool preserved once on board. The thickness of 2 cm of sediment should correspond to about 1 year of sedimentation (as can be estimated by the chronology presented in Martins et al. (2013c) and other not published data). Thus, the studied assemblages of foraminifera which are also compared with sedimentological data may correspond to a memory of up to 1 year. ...
... The uppermost part (∼2 cm) of the sediment was collected for geochemical, mineralogical and grain size analyses in each station and was cool preserved once on board. The thickness of 2 cm of sediment should correspond to about 1 year of sedimentation (as can be estimated by the chronology presented in Martins et al. (2013c) and other not published data). Thus, the studied assemblages of foraminifera which are also compared with sedimentological data may correspond to a memory of up to 1 year. ...
Ria de Aveiro, which is located in the centre of Portugal (40° 38' N, 8° 45' W), is a well-mixed and complex coastal lagoon that is separated from the sea by a sandy barrier and connects with the Atlantic through an artificial inlet. Tidal currents are the main factor controlling the lagoon's hydrodynamics and, to a great extent, the sedimentary dynamic. The inner lagoonal zones receive input from several rivers and experience the pressure caused by the accumulation of organic matter and pollutants (namely, trace metals) from diverse anthropic activities. This paper is the first piece of work aiming to recognize, characterize and explain the main benthic foraminiferal biotopes in Ria de Aveiro. To provide a broad overview of this kind of setting, our results are compared to those of previous published studies conducted in similar transitional environments. The research is based on an investigation of 225 sites spread throughout this ecosystem. Utilizing a statistical approach, this study analyses the details of dead benthic foraminiferal assemblages composed of 260 taxa, the texture and composition (mineralogical and geochemical) of the sediment and physicochemical data. On the basis of the results of R-mode and Q-mode cluster analyses, several different biotopes can be defined as marsh biotope/near-marsh biotope; marginal urban/marginal urban mixing biotope; inner-outer lagoon biotope or enclosed lagoon; outer lagoon biotope, mixed sub-biotope; and outer lagoon, marine sub-biotope. These biotopes are related to foraminifera assemblages and substrate type and are influenced by local currents, water depth, chemical and physicochemical conditions, river or oceanic proximity, and anthropogenic impact, as evidenced by the mapping of the six factor loadings of the principal component analysis conducted herein. Based on a similar methodology of analysis as that applied in previous studies in the Lagoon of Venice, comparable biotypes were identified in Lagoon of Aveiro.
The littoral between Espinho and Mira (Portugal), generally known as the coast of Aveiro, where the coastal lagoon of the same name is located, is a paradigmatic example of interactive evolution between Man and Environment.
When the average sea level reached the current quota, about 3000 years ago, this coast corresponded to a large bay open to the very energetic Atlantic sea waves. Up till the end of the 1st millennium the situation remained more or less the same, with the environment in an almost pristine condition.
At the end of the 1" millennium, mainly due to the movement of the "Christian Reconquista" observed in the Iberian Peninsula and that progressed from north to south, there was a concentration of Christians in the north of the Douro River. This led to a great expansion of agriculture in the region between Douro and Minho (facilitated by the Little Climate Optimum), which led to a major expansion of sediment supply and the subsequent rapid growth of a sandy area near Espinho (south of the Douro estuary). Due to the incidence direction of the dominant sea waves that sandy area grew towards SSW, converting the large bay, little by little, into a coastal lagoon.
The formation of this lagoon zone led to the creation of new environments. Therefore, new opportunities emerged allowing to meet basic and secondary needs (fishing, salt mining, ports, agriculture and maritime trade growth).
With the migration towards south of the lagoon bar, it began losing hydraulic efficiency. Around 1757, the bar was in its most southerly position ever. To use the port of Aveiro, ships had to follow a long, difficult and dangerous route, leading to the virtual abandonment of this harbor. The region became insalubrious and the exploration of salt was quite scarce. After some unsuccessful attempts, in 1802 began the artificial opening of a new bar at the place where it is currently located, in front of Aveiro, which allowed the economic and social recovery of the region.
Over the past centuries, the level of human disturbance of the lagoon environment has been gradually increasing (fishing, dredging, agriculture, livestock, industry, urban expansion, tourism development, etc..). In Estarreja, at the inner edge of the lagoon, it was settled, in the 1930s, but especially after the end of World War II, one of the most important centers of the Portuguese chemical industry, with its inherent impacts.
The lagoon of Aveiro is now heavily impacted, with interventions of diverse types and intensities. On its banks, the landscape is dominated by the geometry of buildings and by the contrast of road structures (bridges, etc.), and the chimneys of the chemical industry and ceramics. At the lagoon, harbor structures and dredging radically changed the hydrodynamic standards. Besides, the sedimentary substrate is preserving the records of different human activities (among many others, agrochemical and chemical contamination).
In the area of the sandy barrier, the jetties of the port of Aveiro led, as usual, to a large accumulation of sediments and simultaneously to very strong erosion. To remedy the situation great coastal protection works were undertaken in the area south of the bar, having the whole area evolved into a strong anthropic coast where the coastline is often materialized through coastal engineering structures.
The Ria de Aveiro estuary-coastal lagoon system of northern Portugal is estimated to currently receive mean annual influxes of total nitrogen (N) and total phosphorus (P) of c. 6118 t y–1 and 779 t y–1, respectively, from its influent rivers. In low summer flows the mean N and P fluxes decrease to c. 10% of the annual average. The sewage contribution to the inland-derived N load on an annual basis is c. 5% but, during the summer low flow conditions, the sewage component increases to c. 65% of the total river loading. The sewage contribution to the inland-derived P load on an annual basis is c. 11% but, during the dry season, it is 1.2 times larger than the river-derived flux. The construction of a regional sewer system linked to a submarine outfall, due for completion in 2005, is expected to lead to a reduction in nutrient fluxes from inland to the lagoon of c. 15% for N and c. 26% for P relative to the present values. While this system will reduce the nutrient loading in the upper reaches of the lagoon, an increase in nutrients derived from the ocean is anticipated, due to the proximity of the outfall to the inlet.
An effort has been made to assemble a data set on the evolution of coastal morphology of the West Iberian Continental Margin in Portugal, which has occurred since the Last Glacial Maximum. In this integrated review a particular attention was given to the analyses of coastline shaping phenomena on different time scales. Several overlapping processes such as shore erosion, local sediment supply rate, climatic changes, anthropic impacts and mean sea level rise (MSLR) were identified and their combined effects assessed. The eustatic see level rise appears as a principal factor in shaping the shore line contour until mid Holocene. Since then, the non eustatic factors namely the terrigenous sediment supply rate and the dynamics of barriers and spits systems became dominant in the evolution of the near shore morphology. Since the 15th century AD, the anthropogenic activities, namely deforestation and land cultivation contributed decisively to the positive sedimentary balance in the Portuguese coastal zone. Finally, the multiple damming of the major rivers in 20th century and exploitation of sand and gravel from the river beds led to the sediment starving of the coastal zone and generalized shore line retreat.
Flood events in many river basins with highly variable discharge values remove accumulated sediments from the riverbed and estuaries. These sediments are exported to the shelf and the adjacent coastlines. Data for rainfall and river discharge for the Guadiana River basin in southwestern Iberia show a strong link with North Atlantic Oscillation (NAO) index patterns. A negative NAO index usually results in more rainfall, and subsequent flooding in the river basin during winter months. During the second half of the 20 th century, the flow regime of the Guadiana River and its tributaries have been increasingly constrained by the construction of dams. The consequences were a reduction of coarse-grained sediment export from the upper river basin to the estuary, and a reduction in the number and type of floods.
Greenland ice-core data have revealed large decadal climate variations over the North Atlantic that can be related to a major
source of low-frequency variability, the North Atlantic Oscillation. Over the past decade, the Oscillation has remained in
one extreme phase during the winters, contributing significantly to the recent wintertime warmth across Europe and to cold
conditions in the northwest Atlantic. An evaluation of the atmospheric moisture budget reveals coherent large-scale changes
since 1980 that are linked to recent dry conditions over southern Europe and the Mediterranean, whereas northern Europe and
parts of Scandinavia have generally experienced wetter than normal conditions.
Greenland ice-core data have revealed large decadal climate variations over the North Atlantic that can be related to a major source of low-frequency variability, the North Atlantic Oscillation. Over the past decade, the Oscillation has remained in one extreme phase during the winters, contributing significantly to the recent wintertime warmth across Europe and to cold conditions in the northwest Atlantic. An evaluation of the atmospheric moisture budget reveals coherent large-scale changes since 1980 that are linked to recent dry conditions over southern Europe and the Mediterranean, whereas northern Europe and parts of Scandinavia have generally experienced wetter than normal conditions.
Ria de Aveiro is a shallow vertically homogeneous lagoon, located in the Northwest of Portugal, connected to the Atlantic through a very narrow artificial channel, and supplied with freshwater by two major rivers, Antuã and Vouga. The present study describes the application of a twodimensional depth integrated mathematical model, to predict tide-induced water level and depth mean current for the entire lagoon. The model computes time series of those variables as well as their instantaneous distribution at different times of the tidal cycle. Properties of tides and tidal currents in Ria de Aveiro are characterized and discussed. Special emphasis is given to the study of the hydrodynamic behaviour of the lagoon in extreme conditions of astronomical tide forcing, considering spring and neap tide conditions. Tides propagate from the mouth of Ria de Aveiro and are present in the entire lagoon. The tidal amplitude decreases with the distance from the mouth while the phase lag in the high and low water (which is different) increases. The tidal range increases for the spring tide at the far end of the channels correspond to a local increase of the high tide level, which result in a fortnightly variation of the mean levels at those places.
This paper describes a sediment survey undertaken to unravel patterns of distribution and dispersion of trace metals in an Iberian Peninsula northwestern coastal lagoon (Ria de Aveiro). Cadmium, lead, chromium, copper and zinc were analyzed in bottom sediments. Geochemical normalization is performed and two different regression models for each metal versus aluminum are tested and compared using the respective enrichment factors (EF), an estimation of the relative importance of anthropogenic contributions to the studied sediments. Mean sediment quality guideline quotients (mSQGQ) are used to evaluate sediment quality and associated potential risk to biota with effects range low as empirical sediment quality guideline (SQG) in the basis for mSQGQ calculation. Additionally, the geoaccumulation index is calculated to compare studied sediment levels to global baseline levels. The application of SQGs revealed insufficient characterization capability, especially when contrasted to EF calculated from the regression methods. These pointed a mildly enriched system with localized “hot spot” areas. Therefore, it can be considered that bottom sediments in the Ria de Aveiro system are in their majority unpolluted, zinc being the only metal of concern, presenting enrichment in all four main channels. The major rivers outlets (Caster, Antuã, and Vouga) constitute point sources, thus presenting potential risk for biota. Yet, the strong tidal influence creates a damping effect by efficiently redistributing sediment bound metals.
Harbours are important man made economic structures that are usually constructed in hydrodynamic complex settings. Their life/service cycle, integrity and maintenance are highly dependent on the knowledge of these settings and the capability to predict future changes and thus their economic impact. In this paper, data regarding bottom and suspended sediments of the Aveiro Harbour inlet were gathered and analysed. Measurements of suspended sediment concentrations (SSC) in the Aveiro inlet were taken during eight tidal cycles in 2007, including spring and neap tides throughout winter and summer oceanographic regimes. Results suggest significant temporal variability. Sediments were imported from the ocean sink, mostly near the south jetty and the western side of the Mira Channel, as textural, mineralogical, compositional, geochemical and microfaunal data of bottom sediments suggest. Higher stabilization of the Aveiro Harbour structures is achieved on these accretional areas. The high tidal-current velocities contribute to the erosive character which dominates the central area of the entrance channel, which is located between both breakwaters and close to the north jetty; thus some segments of the north jetty could become damaged through erosion. This is evidenced as much bottom sediments characteristics as patterns of SSC. SSC are in general higher during the winter, due to climatic conditions, current velocities, wind stress and greater availability of sediments provided by the local-river flooding. Our data also suggest that SSC are predominantly higher during ebb and low tide throughout the year, as compared to periods of flood, when a higher flux of sediments is transported seaward than landward. The lagoon exports to the continental shelf mostly muddy sediments, composed essentially of quartz and phyllosilicates.
The hydrological features of Ria de Aveiro, a coastal lagoon on the northwest Atlantic coast of Portugal, were investigated in two sampling surveys carried out between 3/6 and 24/6/97 and between 29/6 and 7/7/97, respectively. There was a significant freshwater inflow into the lagoon during the first survey, especially in the first days, due to the recent rainfalls. Records concerning water level, salinity, temperature and current velocity were performed at several stations located along the four main channels of the lagoon. The type of tide at the mouth was determined and was observed that astronomical tide is the main forcing agent driving water circulation in Ria de Aveiro. The tide at the mouth is semidiurnal and the tidal wave propagation in the lagoon has the characteristics of a damped progressive wave. Typical estuarine longitudinal salinity and temperature gradients connected with the distance to the mouth were identified, whereas vertical and transverse gradients were found unimportant, except in the frontal zone between oceanic and fresh water masses. According to the results, even though Ria de Aveiro should be considered as vertically homogeneous, some channels may reveal characteristics of a partially mixed estuary, depending on the freshwater input.
Ria de Aveiro is a very important area of the Portuguese coast, which has been under an increasing anthropogenic pressure, for several decades, contributing to the degradation of the lagoon's water quality.A water quality model was applied to predict concentrations of inorganic nutrients, chlorophyll-a, and dissolved oxygen (DO) in the Ria de Aveiro lagoon, Portugal. Both data and modelling results point out that the DO distribution in the lagoon is controlled by tidal transport processes. The DO distribution in the Ria de Aveiro seems to be mainly controlled by tidal processes, as its concentration remains relatively high and close to sea values. The far end of the lagoon, where the intertidal salt marshes are important, the DO concentration is dominantly affected by re-aeration and the flooding/drying processes over the intertidal salt marshes, the phytoplankton activity, the nitrification processes and oxidation of the organic matter. These processes play an important role in the creation of the summer hypoxic/anoxic situations, when primary production and advective transport are low. Data and modelling results show strong relationship between nutrients and the CHL-a concentrations during spring–summer, but weak during winter–spring, evidencing the light and nutrients limiting effect during, respectively the last and the former period. High NO3 and NH4 concentrations or important spikes in the concentration precede or coincide, in general, with the CHL-a increase. The main results concerning the DO evolution and distribution demonstrate that a generalized eutrophication state is unlikely to occur within the lagoon, except near its very far end, during summer and in a situation of high BOD concentrations. The good connection between Ria de Aveiro lagoon and the sea and the circulation pattern inside the lagoon are, therefore, responsible for relatively high level of oxygen water content in the water column, throughout its main channels.
This work investigates the recent morphological changes at the inlet of a complex coastal system (Ria de Aveiro lagoon, Portugal). This study was carried out using bathymetric data analysis and numerical simulations obtained with the
2DH morphodynamic modelling system MORSYS2D. The present simulations considered only tidal forcing, and a sensitivity analysis
was performed by tuning the formula used to compute the sediment transports. A non-uniform sediment grain size distribution
for the Ria de Aveiro inlet is considered in the numerical simulations, based on surveys performed in this area. The model results are analysed
to assess if they resemble the observed trends of erosion and deposition, as calculated from bathymetric data. A quantitative
analysis of the differences between the bathymetric changes obtained through surveys and the numerical results over a period
of 3years considering different sediment transport formulations shows that the formulations of Ackers and White (1973) and Engelund and Hansen (1967) are the ones that best describe the morphodynamic changes driven by tides in the Ria de Aveiro inlet.
KeywordsMorphodynamics-Sensitivity analysis-Tidal inlet-Aveiro lagoon
Textural, mineralogical, geochemical and microfaunal data (benthic foraminifera) were studied along the OMEX core KSGX 40 recovered in the Galicia Mud Deposit, of the NW Iberian outer continental shelf, off the Ría de Vigo (North of Spain). This core included the records of the last ca. 4.8 ka cal BP and consists, from the base to the top, of a sedimentary sequence exhibiting gradual upward decrease in grain size. Sediments of this core are mainly siliciclastic, largely composed of quartz, K-feldspars, plagioclases, and phyllosilicates (mica/illite, kaolinite and chlorite) showing a great continental influence in this zone. Two periods of deposition of finer sediments are registered between ∼ 2.2–1.2 ka cal BP and ∼ 0.5–0 ka cal BP.Since the last ∼ 2.2 ka BP, but mainly during both muddy intervals, the Galicia Mud Deposit was nourished with a lower and finer supply of detrital minerals compensated by higher amounts of organic matter, as it is suggested by a Benthic Foraminifera High Productivity (BFHP) proxy. Processes involved in organic matter degradation by aerobic organisms led to depressed levels of oxygen in the sediments, as shown by a Benthic Foraminiferal Oxygen Index (BFOI). Peaks of redox-sensitive elements, like Mn, Fe, Cu, Ni, Cr, Co, Zn, Ni and Pb as well as the presence of diagenetic minerals, such as pyrite, suggest the development of anoxic conditions beneath the sedimentary surface and early diagenetic changes due to high organic matter flux, in both muddy intervals.Two different hydrodynamic regimes were inferred through the analysis of the different proxies (textural, mineralogical, geochemical and benthic foraminifera): (1) A strong hydrodynamic regime between ∼ 4.8 and 2.2 ka cal BP characterized by the prevalence of winter storms, which gave rise to a deep mixed layer on the shelf. (2) Weak hydrodynamic regime between ∼ 2.2–1.2 ka cal BP and ∼ 0.5–0 ka cal BP with a high predominance of upwelling and an increase in oceanic stratification.
Ria de Aveiro is a very important area of the Portuguese coast, which has been under an increasing anthropogenic pressure for several decades and, contributes to the degradation of the lagoon's water quality. This work presents both a characterisation of the water quality of the Ria de Aveiro lagoon, using physical, chemical and biological experimental data, and an implementation of a numerical model for the water quality of the lagoon. The ultimate goal is to obtain an accurate numerical model able to simulate major water quality features of the lagoon under the influence of different forcing conditions. Data analysis reveals good correlations between the salinity and almost all the water quality variables as well as between the different variables. The maximum biochemical oxygen demand concentration (BOD) depends on the light intensity, the temperature and the river inputs. The main vulnerable areas of the lagoon, from the water quality point of view, seem to be the far end of the main channels, where low dissolved oxygen concentration (DO) and high BOD concentrations are observed. The numerical model of the Ria de Aveiro has reproduced both winter-spring and spring-summer events related to the lagoon water quality as well as its main pattern. Both data and modelling results show that the BOD5 concentrations (where the subscript '5' means that the BOD measurements were conducted for five days, without inhibitor of nitrification) are driven by the river influence, during the winter-spring period, and by the biological activity during the spring-summer period. The DO concentrations show high values in the spring-summer period and smaller concentrations in the winter-spring period at the far end of the lagoon. The application of the model to the study of scenarios has demonstrated the role of nutrients and light in the phytoplankton growth, the relationship between DO and phytoplankton concentrations, as well as the effect of the BOD degradation in the ammonia (NH4) regeneration.
Estudo dos mecanismos de dispersão de elementos vestigiais em sedimentos de correntes e águas superficiais da bacia hidrográfica do rio Antuã
- F S B A Moreno
Moreno, F.S.B.A., 2000. Estudo dos mecanismos de dispersão de
elementos vestigiais em sedimentos de correntes e águas superficiais da
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