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Environ Monit Assess
Environ Monit Assess
Environmental Monitoring and Assessment
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1573-2959
Springer International Publishing Cham

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12950
10.1007/s10661-024-12950-2
Research
Impact of sediment mobilization on trace elements release in Galician Rías (NW Iberian Peninsula): insights into aquaculture
Rubio Belén brubio@uvigo.gal

1
López-Pérez Ángel Enrique 1
León Iván 2
1 https://ror.org/05rdf8595 grid.6312.6 0000 0001 2097 6738 Centro de Investigación Mariña, Universidade de Vigo, GEOMA, 36310 Vigo, Spain
2 https://ror.org/05mm1w714 grid.441871.f 0000 0001 2180 2377 Facultad de Ciencias Básicas, Universidad del Atlántico, Grupo de Zona Costera, Barranquilla, Colombia
24 8 2024
24 8 2024
2024
196 9 8358 1 2024
1 8 2024
© The Author(s) 2024
2024
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In the latest years, the concentration levels of certain metals and metalloids in the sediments of the Galician Rías have shown an increasing trend (e.g., As, Zn, Cu, Pb, Hg). These areas are also characterized by their richness in nutrients and their great aquaculture or mariculture activity, with the presence of more than 3500 mussel rafts in the Rías Baixas. The inner areas of the Galician Rías are subjected to activities that resuspend the sediment such as high levels of maritime traffic and dredging or cleaning operations. It is likely that a transfer of these elements to the water column happens during the resuspension of sediments caused by natural events or anthropogenic activities. In this study, selected samples of surface sediments of the Ría de Pontevedra (NW Spain) were subjected to a procedure of aerobic oxidation to determine the concentration of some elements (Fe, Mn, Cu, Cr, Pb, Hg, and Zn) released from the sediment to the aqueous phase. The experiment was carried out within 5 days. Measurements of pH and total concentration were taken both in water and sediment samples. Furthermore, speciation of trace elements was carried out in the sediment samples. Trace element concentrations were lower in the sediments during aerobic oxidation, being released to the aqueous phase. From an environmental point of view, Cu was the only trace element released in quantities that may be toxic for the organisms in the area. This problem of sediment oxidation related to dredging activities or natural storm conditions should be considered in environmental impact studies and transferred to stakeholders.

Keywords

Aquaculture
Trace element speciation
Aerobic oxidation
Metal toxicity
Ría de Pontevedra
Autonomous Goverment Xunta de Galicia ReferenceED431B 2023/39 ED431B 2023/39 Rubio Belén López-Pérez Ángel Enrique Universidade de VigoOpen Access funding provided thanks to the CRUE-CSIC agreement with Springer Nature.

issue-copyright-statement© Springer Nature Switzerland AG 2024
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pmcIntroduction

Metal pollution has been reported in sediments and water column from the Galician Rias for the last decades (Beiras et al., 2003a, b; Prego and Cobelo-García, 2003; Cobelo-García and Prego, 2004; Prego et al., 2006; Álvarez-Iglesias et al., 2006, 2012; Bellas et al., 2008, 2011; Santos-Echeandía et al., 2008a, b; Álvarez-Iglesias & Rubio, 2009; Durán & Nieto, 2011; Rodríguez-Germade et al., 2014; Monaco et al., 2017; Guevara et al., 2021; Gardoki et al., 2023; Otero et al., 2024). Previous studies of metal speciation in the sediments of the Galician Rias have identified the geochemical fractions in which certain trace elements are found and have provided valuable information on the geochemical and environmental status of these sediments (Cela et al., 1992; Belzunce-Segarra et al., 1997, 2008; Prego and Cobelo-García, 2003; Álvarez-Iglesias et al., 2003; Villares et al., 2003; Rey et al., 2005; Ramírez-Pérez et al., 2017, 2020). In these sediments, a significant fraction of certain elements is concentrated mainly in the non-residual fraction, especially for the most harmful metals and metalloids such as Cu, Pb, As, and Hg (Álvarez-Iglesias & Rubio, 2008; León et al., 2004; Rubio et al., 2001). Although, in general, these elements are found in low proportions in the most labile fractions, in the inner areas of the rías, where the sediments are suboxic-anoxic, they are also concentrated in relatively high proportions in the oxidizable fractions of the sediment (sulfides and organic matter).

Aerobic oxidation of iron sulfides and organic matter, because of bioturbation or resuspension of the sediment, can lead to trace elements associated with these geochemical fractions being released into the water column (Huerta-Diaz et al., 1998; Otero et al., 2005). In general, anthropogenic activities have the greatest potential for such resuspension. There are usually many activities in the rias that contribute to resuspension. One of these is port activities, whose maritime traffic has increased considerably in recent decades (García et al., 2013; Navarro, 2000; Pérez-Cid et al., 2021). Others correspond to the cleaning and care activities of mussel cultivation in rafts, which also favor sediment resuspension, such as the mobilization of the large amount of bio-deposits, generally rich in trace elements, that they produce (Cabanas et al., 1979; Calvo de Anta et al., 1999; León et al., 2004; Otero et al., 2009; Rubio et al., 2011).

Furthermore, sediment dredging is a common practice in the ports of the Galician Rías. In the region of Galicia, dredging operations are regulated by the Law 6/2017, of December 12, on ports of Galicia. Studying the behavior and risk of trace elements during dredging activities is essential, as they have the potential to greatly influence the mobility of these elements within sediments, leading to their release into the water column (Ferrans et al., 2021; Torres et al., 2009). Galicia is a region where this type of dredging information is not stored in scientific publications or public archives. However, these dredging activities in the Ría of Pontevedra are frequently reported in the press. For instance, between 1990 and 2010, the port of Marín in the Ría of Pontevedra conducted eight dredging operations, displacing a total of 139,000 cubic meters of seabed material (https://www.farodevigo.es/pontevedra/2010/11/26/dragados-puerto-supusieron-15-anos-17798645.html). There are few scientific works that address the evaluation of the environmental impact of dredging in the Galician Rías. Rodríguez-Romero et al. (2016) evaluated the effect of dredging in Ría of Arousa, showing that the sediments in the study were not highly contaminated.

Understanding desorption/adsorption processes is also a fundamental requirement for understanding the geochemical characteristics of the environment, and the release mechanisms and the transport, mobility, and bioavailability patterns of these trace elements and metalloids.

For a proper environmental management decision-making, it is very important during the assessment process to know the mobility and possible adsorption of these elements, as these processes in the sediment are complex due to rapidly changing conditions. To understand these mechanisms, laboratory studies are conducted, subjecting both sediment and solution to various physicochemical conditions. Typically, the results are measured in the aqueous phase (Caille et al., 2003; Gambrell et al., 1991; Otero et al., 2005), but very little work has focused on the study of the variation in the distribution of the geochemical fractions of the sediment (e.g., Álvarez-Iglesias et al., 2003; Belzunce-Segarra et al., 2008; Madadi et al., 2023; Otero et al., 2005; Ramírez-Pérez et al., 2020), and particularly the studies focused in this distribution after oxidation are very scarce.

This research is focused on offering an integrated approach that links the transfer processes of trace elements between sediment and the water column. Additionally, it aims to identify geochemical oxidizable fractions through aerobic oxidation. The assessment of trace elements released shall be done by speciation of the elements in the sediment and by measuring the concentration of the elements in the aqueous phase. In addition, the potential hazard of the levels of trace elements released into the aqueous phase shall be assessed.

Study area

The ria de Pontevedra, located at the NW of the Iberian Peninsula, is about 30 km long and has a maximal width of 12 km at the mouth (Fig. 1). Geomorphologically, the ría can be divided into three sectors: the inner, the middle, and the outer, where it reaches a maximum depth of 60 m (Hernández-Otero et al., 2014). The ría is characterized by the presence of three islands: Tambo Island in the inner sector, and Ons and Onza Islands in the outer sector.Fig. 1 Map of location and granulometric distribution of the Ría de Pontevedra, showing the positions of samples P5 and P9 (middle sector) and P7 and PC (inner sector). The brown rectangles represent the areas with mussel rafts.

Modified from Vilas et al., (1996)

The region has a humid climate, with average summer temperatures around 19 °C and winter temperatures around 10 °C. Annual rainfall averages approximately 1000 mm (Rubio et al., 2001). The storm regime in the study area is controlled by the position of the Azores anticyclone. In summer, anticyclonic conditions prevail along the Galician coast, leading to northerly winds and little precipitation. During the winter months, the Azores anticyclone moves to lower latitudes, resulting in low-pressure conditions and the formation of Atlantic fronts with southwest winds, increasing storms and precipitation (Vilas et al., 1996).

The Ría de Pontevedra exhibits a mesotidal regime, featuring an average tidal range of 2.2 m and a semidiurnal tidal cycle (Rubio et al., 2001; Vilas et al., 2019). In the Galician Rias, tidal effects on the transport of sediments and post-sedimentary processes are recognizable in the inner most part; meanwhile in the external and central sectors, the tidal has a limited influence (Rey et al., 2005; Vilas et al., 2005, 2019). Furthermore, currents in the inner sector are influenced by factors such as river discharge, primarily from the Lérez River and wind (Prego et al., 2001). Additionally, the inner sector is more influenced by anthropogenic inputs and has a higher content of mud and organic matter compared to the other sectors of the estuary (Rubio et al., 2001).

The Ría de Pontevedra is also under the influence of an oceanic coastal circulation, such as upwelling and downwelling processes. The hydrography of the Ría is affected by upwelling conditions through the East North Atlantic Central Water (ENACW) during the summer when the dominant winds have a northerly component. In winter, the prevailing winds are from the southwest, influencing the Iberian Poleward Current (IPC) and the downwelling processes (Prego et al., 2001; Rubio et al., 2001; Vilas et al., 2019). Furthermore, there is an intense swell during winter conditions, reaching significant maximum wave heights (Hsmax) of around 8 m in the Galician Rías (Vilas et al., 2019). Numerical simulations conducted by Rey et al. (2005) indicate that sediment remobilization occurs with wave heights of 2.5 m and periods of 14 s, resulting in seabed sediment oxygenation.

In general, water circulation is marked by a prevalence of freshwater along the northern margin and marine water dominance along the southern margin (Rubio et al., 2001). Moreover, the sedimentation rates on the Ría de Pontevedra are about 1 mm year−1 (Rubio et al., 2001). Its sedimentary dynamics share similarities with wave-dominated estuaries, albeit with lower input of freshwater from the continent, and increased primary productivity attributable to the seasonal upwelling described (Rey et al., 2005). Waves play an important role in the distribution of sediments. In general, wave energy is lower in the axial region owing to the increased water depth, and in protected areas of the inner sector. These low-energy areas are characterized by the accumulation of fine-grained and organic-rich material. In contrast, in high-energy areas, such as the margins of the Ría and the outer sector, coarse-grained, carbonate-rich sediments are accumulated (Rey et al., 2005).

Material and methods

Surface sediment samples (0–5 cm) from gravity corers collected in the inner area (cores P7 and PC) and in the middle area (cores P5 and P9) from the Ría de Pontevedra (NW Spain) were selected based on their grain-size and physico-chemical characteristics (Figs. 1 and 2). The methodological strategy is shown in Fig. 3a, b.Fig. 2 Plot of the grain-size distribution for the cores P5, P9, P7, and PC along with the percentage of organic carbon, carbonates, and DOP

Fig. 3 a Flow chart with the methodology used in this work. b Photograph of the experimental setup where the samples were subjected to oxidation using an aquarium pump during 5 days

Sediment cores were obtained using a gravity corer, approximately 4.5 m in length and 12 cm in diameter, with an inner PVC tube that collects the sediment. They were collected from depths between 20 and 40 m, with lengths varying from 0.25 to 3.06 m. In the laboratory, the cores were stored in a refrigerated chamber at a temperature below 4 °C until analysis.

In terms of grain-size analyses, the samples were rinsed with water over a sieve with a 0.063 mm diameter to segregate the larger fractions from the finer ones. The particle size analysis of the larger fractions was conducted via dry sieving utilizing a set of sieves, each one phi. The total content of the fine fraction was determined using the Robinson pipette method. Finally, the analysis of fine grain size (< 0.063 mm) was performed using a Sedigraph 5100. The coarse fraction was considered to be anything larger than 2 mm, the sand fraction between 0.063 and 2 mm, and the fine fraction smaller than < 0.063 mm.

The contents of total carbon (TC) and total inorganic carbon (TIC) were determined using a Carlo-Erba™ elemental analyzer. The total organic carbon (TOC) was calculated by the difference between the TC and TIC contents.

The percentage of CaCO3 was estimated using the equation TIC × 100/12, where 100/12 is the molecular weight ratio of CaCO3 to carbon.

For the oxidation experiment, duplicates of the surface samples of the cores were placed in plastic bottles containing 100 ml of filtered ria seawater, which had previously undergone an ageing process for 1 week. The seawater was collected from the Ría de Pontevedra at a depth of 25 m. The sediments were kept in suspension by mounting the flasks in a Variomag Electronicrührer single-stage shaker. During the experiment, air with oxygen was pumped into the system with an aquarium pump (Fig. 3b).

The experiment was conducted over a time interval of 5 days. During this time, three measurements were made. The first determination was made at time zero (t0, day 0), the second at 24 h (t1, day 1), and the last at 120 h (t5, day 5).

In the seawater, pH and total trace element concentration were measured directly using a Metrohm 826 pH mobile electrode. The pH in the aqueous phase was measured using a glass electrode calibrated with analytical-grade buffer solutions. The remobilization experiment was conducted in the dark, at ambient temperature and atmospheric pressure. The bottles were sealed with paraffin wax, with small holes punctured to facilitate gas exchange while minimizing evaporation. T0 represents the measurement of trace elements in seawater prior to the experiment. On both day 1 and day 5, samples were withdrawn and centrifuged in a Tornax at 4000 rpm for a 30-min interval. The samples were filtered through 0.45 µm Millipore filters. The filtered samples were stored in plastic bottles, and the total concentrations of dissolved trace metals were immediately analyzed. The residue remaining from the filtration was washed twice with deionized water to remove present salts. Sequential extraction was performed on this residue to identify the geochemical fractions of trace metals (Huerta-Diaz & Morse, 1990). Sediment oxidation was calculated through the variation in metal concentrations in the geochemical fractions determined by the method used.

In the sediment, the sequential extraction of trace elements proposed by Huerta-Diaz & Morse, 1990) was carried out, in which four geochemical fractions were obtained: reactive (Freact), organic (Fmo), pyritic (Fpyr), and silicate-bound (Fsil). The oxidation of the sediments was calculated through the variation of the trace element concentrations in the geochemical fractions determined by the method used. The extractants used are shown in Table 1. Due to the high organic matter content in the analyzed sediments, concentrated H2SO4 was used as suggested by these authors. The analyses were conducted on 1 g of dry sediment sample in a fraction smaller than 0.063 mm. The procedure is as follows:Reactive fraction (Freact): Metals were extracted with 20 ml of 1N HCl after 16 h of continuous agitation at room temperature.

Fraction associated with aluminosilicates (Fsilic): To the previous residue, 30 ml of 30 M HF was added for 16 h of continuous agitation at room temperature.

Fraction associated with organic matter (Fmo): The residue from Fsilic was contacted with 10 ml of concentrated H2SO4 for 2 h of continuous agitation at room temperature.

Pyritic fraction or sulfide-associated fraction (Fpyr): Finally, metals associated with sulfides were extracted with 10 ml of concentrated HNO3 for 2 h of continuous agitation at room temperature.

Table 1 Extractants used for the sequential extraction of metals according to the method described by Huerta-Díaz and Morse (1990)

Fraction	Extractant	Sediment components	
Reactive Fe	20 ml HCl	Exchangeable ions, amorphous Fe oxides and hydroxides, carbonates, and acid-volatile sulfides (AVS)	
Silicate-bound Fe	30% v/v HF	Lithogenic minerals	
Organic matter-bound Fe	H2SO4-concentrated	Organic matter	
Pyritic Fe	HNO3	Pyrite	

At the end of each extraction, the samples were centrifuged at 4000 rpm (Tornax model) for 30 min. The supernatant was collected with a pipette and put into bottles for heavy trace metal analysis. The residue was washed with 8 ml of Milli-Q water and centrifuged again for 30 min at 4000 rpm. This second supernatant was discarded.

For each set of 7 samples, one sample was introduced in triplicate to verify the accuracy and reproducibility of the method. In all cases, the accuracy was within ± 2% at a confidence level of 95%. The results are expressed in milligrams per kilogram of dry sediment (mg kg−1), except for Fe (mg g−1) and Hg (µg kg−1). In seawater, they are expressed in µg l−1.The degree of pyritization(DOP)was determined using the formula DOP=FpyrFpyr+Freactive×100

Trace elements in sediment extracts and seawater were analyzed using inductively coupled plasma atomic emission spectroscopy (ICP-AES; model PerkinElmer Optima 4300 DV). Mercury concentration was analyzed by cold vapor atomic absorption spectrometry (CV-AAS) on a PerkinElmer FIMS 400. The detection limits of trace elements in sediment fractions and seawater are displayed in Table 2.Table 2 Detection limits (mg kg−1) of trace elements: (a) in fractions defined by the method of Huerta-Díaz and Morse (1990); (b) in seawater

(a)	
Trace elements	Detection limits (mg l−1)* in sediment fractions	
Reactive	Residual	Organic	Pyritic	
Fe	0.019	0.261	0.067	0.031	
Mn	0.001	0.001	0.013	0.001	
Cu	0.003	0.002	0.002	0.004	
Cr	0.007	0.012	0.008	0.005	
Ni	0.016	0.018	0.090	0.002	
Pb	0.010	0.012	0.001	0.001	
Zn	0.011	0.008	0.030	0.003	
As	0.040	0.290	1.050	0.050	
Hg	0.020	0.019	0.200	0.057	
* except Hg (µg l−1)					
b)	
Trace elements	Detection limits in seawater	
(µg l−1)	
Fe	0.1	
Mn	0.1	
Cu	0.4	
Cr	0.2	
Pb	0.1	
Zn	0.001–0.005 mg l−1	
Hg	 < 0.01–0.02	

Results

Grain size and chemical characterization

On average, inner area samples (cores P7 and PC) are muddy and richer in organic matter than the middle area ones (cores P5 and P9) with a high sand percentage and a lower organic matter content (Fig. 2). Cores P7 and PC display the highest percentages of the fine fraction (77.40% ± 9.70% and 75.24% ± 25.29%, respectively) and TOC (4.89% ± 0.98% and 4.45% ± 1.00%), and the lowest content of carbonates (5.84% ± 5.79% and 17.48% ± 12.04%, respectively) (Fig. 2).

In contrast, cores P5 and P9 show high percentages of sand (54.48 ± 8.49 and 56.58 ± 3.79, respectively) and CaCO3 (37.63 ± 9.98 and 26.32 ± 2.11, respectively) and the lowest content of TOC (2.03 ± 0.17 and 1.82 ± 0.45, respectively) (Fig. 2).

Considering the degree of pyritization (DOP) classification from León et al., (2004), the cores from the inner area of the Ría are anoxic, whereas the middle area ones are oxic-suboxic (Fig. 2). Cores P7 and PC exhibit the highest values of DOP (61.21% ± 5.61% and 61.49% ± 8.20%, respectively), in comparison to P5 and P9 (32.79% ± 11.36% and 44.33% ± 1.31%, respectively) (Fig. 2). This classification is derived from sedimentary DOP values obtained through HCl extraction. According to this classification, the sedimentary environment is considered oxic when DOP values are < 42%, dioxic or suboxic when they fall between 42 and 55%, anoxic between 55 and 75%, and euxinic when DOP exceeds 75% (León et al., 2004).

Aqueous phase: pH and trace elements variations

The temporal variation of pH in seawater shows a net decrease from the beginning to the end of the experiment (Fig. 4). During the initial stage of the experiment (from the beginning to day 1), there was a considerable decrease in pH in all samples, with the strongest decrease being reached in sample P7, the sample collected below the mussel rafts. On day 5, a slight increase in pH was observed in all samples. However, the values were still lower than the initial pH values of the experiment. In general, this decrease was more pronounced for samples from the inner sector (P7 and PC) than for those from the middle sector (P5 and P9) (Fig. 4).Fig. 4 Temporal variation of pH in the aqueous phase during the aerobic resuspension of sediments from the Ría de Pontevedra

The concentration of trace elements in the aqueous phase varied depending on the element considered (Table 3). Hg and Pb were always below the detection limit during the experiment. On average, the sediments of the inner sector showed a higher net trace element release than those of the middle sector (Fig. 5).Table 3 Trace metal concentrations in the aqueous phase during aerobic remobilization of sediments. Data reported in µg L−1

Sample	Time (days)	Fe	Mn	Cu	Cr	Zn	
P5	0	bdl*	4.00 ± 0.07	6.75 ± 0.64	0.57 ± 0.06	0.011 ± 0.003	
1	5.25 ± 0.20	8.50 ± 0.71	25.30 ± 0.14	0.68 ± 0.04	0.011 ± 0.001	
5	2.00 ± 0.30	1.00 ± 0.04	11.65 ± 0.05	0.74 ± 0.07	0.011 ± 0.001	
PC	0	bdl*	4.00 ± 0.07	6.75 ± 0.64	0.57 ± 0.06	0.011 ± 0.003	
1	101.50 ± 4.90	70.00 ± 2.83	11.50 ± 0.14	6.25 ± 0.21	0.030 ± 0.001	
5	bdl*	11.00 ± 0.71	12.74 ± 2.51	8.43 ± 0.15	0.045 ± 0.001	
P7	0	bdl*	4.00 ± 0.07	6.75 ± 0.64	0.57 ± 0.06	0.011 ± 0.003	
1	13.25 ± 0.40	93.50 ± 4.95	10.91 ± 0.37	bdl*	0.013 ± 0.001	
5	bdl*	63.00 ± 4.24	12.58 ± 1.75	bdl*	0.015 ± 0.001	
P9	0	bdl*	4.00 ± 0.07	6.75 ± 0.64	0.57 ± 0.06	0.011 ± 0.003	
1	7.90 ± 0.10	4.25 ± 0.35	10.13 ± 0.73	0.37 ± 0.02	0.011 ± 0.001	
5	bdl*	3.00 ± 0.09	11.65 ± 0.21	0.36 ± 0.09	0.011 ± 0.010	
*bdl = below the detection limit

Fig. 5 Concentration of trace elements released into the aqueous phase (mean values ± standard deviation) by sectors (P5 and P9, middle sector; P7 and PC, inner sector)

The release of Fe in sediments P5 and P9 (middle sector) was lower than in sediments P7 and PC (inner sector), with the highest amount of Fe released into the aqueous phase observed in the PC sample (Table 3). The dynamics of Fe release indicate that it was liberated very rapidly, reaching its maximum value at t1. Following this liberation of Fe, the concentrations decreased significantly until reaching undetectable levels in the aqueous phase (Table 3).

The Mn released into the aqueous phase followed a similar behavior to that observed for Fe. Sediments P7 and PC released the highest amounts of Mn into the aqueous phase (> 60 µg L−1), while samples P5 and P9 released a smaller amount of this trace element (< 8 µg L−1) (Table 3). The maximum values of Mn in the aqueous phase were determined on the first day of the experiment. Subsequent to this release, the concentrations of Mn in the aqueous phase decreased noticeably, though not as pronounced as in the case of Fe.

The release of Cu into the aqueous phase exhibited a different behavior compared to Fe and Mn. Cu release was continuous, with values increasing over time, except in the P5 sample, where the average value on day 1 (25.30 ± 0.14 µg L−1) was higher than on day 5 (11.65 ± 0.05 µg L−1) (Table 3).

The concentrations of Cr in the aqueous phase were very low. In samples P5 and PC, the dissolved Cr increased throughout the experiment. In the case of sample P5, it reached an average value of 0.74 ± 0.07 µg L−1 at t5, while in PC, it was 8.43 ± 0.15 µg L−1 (Table 3). On the other hand, Cr was not detected in the aqueous phase during the experiment in sample P7, while in sample P9, there was a decrease in concentration over time (Table 3).

Zinc exhibited very low concentrations in the original water sample, and the amount of this trace element transferred to the aqueous phase was also low. The values in the aqueous phase remained constant during the experiment in samples P5 and P9 (Table 3). In contrast, dissolved Zn was detected in samples P7 and PC with very low values (< 0.05 µg L−1) and a slight tendency to increase over time (Table 3).

Geochemical fractions of trace elements in the sediments

The behavior of the total trace element concentrations during the experiment is shown in Table 4. The most relevant aspect is the decrease of the total trace element concentrations in all samples, being more pronounced on day 1. On day 5, the trace elements Fe, Cu, Zn, and Pb slightly increased their concentrations in some sediment samples, although they were still lower than the initial values, except for Fe in P5 and PC (Table 4). The remaining trace elements (Mn, Cr, and Hg) showed a decreasing trend over time in all samples. The percentages of trace elements in the reactive (Freact), residual (Fsil), organic (Fom), and sulfide (Fpyr) fractions, in relation to the values of the total concentration of trace elements in the sediment samples, are shown in Tables 5, 6, 7 and 8.Table 4 Temporal variation of the total concentration of trace elements in the sediment during the experiment

Sample	Time (days)	Fe (mg g−1)	Mn (mg kg−1)	Cu (mg kg−1)	Cr (mg kg−1)	Zn (mg kg−1)	Hg (µg kg−1)	Pb (mg kg−1)	
P5	0	16.04	94.03	86.33	36.34	86.32	88.51	26.48	
1	15.59	87.75	50.40	31.50	66.64	73.69	18.84	
5	18.07	87.67	58.34	31.48	79.53	69.70	18.41	
PC	0	66.06	390.39	160.01	186.66	418.98	1755.08	239.88	
1	63.11	383.18	82.21	156.50	362.52	1285.74	175.34	
5	66.44	365.58	112.18	141.45	370.82	886.29	200.08	
P7	0	20.17	142.34	9.88	64.91	70.90	63.49	24.57	
1	18.78	138.70	7.85	59.74	67.14	45.48	18.99	
5	18.43	131.82	5.42	51.76	64.38	17.31	22.09	
P9	0	9.48	96.61	4.77	22.98	37.25	22.88	9.47	
1	9.05	90.52	3.59	21.29	33.94	15.47	7.53	
5	8.80	90.30	3.27	20.05	33.70	14.77	8.32	

Table 5 Percentages of trace elements, relative to the total concentration, in the silicate-bound fraction (Fsil)

Metal	Time	Core P5	Core PC	Core P9	Core P7	Mean	Standard deviation	
Fe	t0	46.26	60.88	68.59	54.99	57.68	9.43	
t1	47.00	62.61	70.30	58.94	59.71	9.71	
t5	40.91	59.22	72.66	60.15	58.23	13.07	
Mn	t0	67.97	61.52	69.09	67.32	66.48	3.38	
t1	72.71	62.48	72.99	68.60	69.20	4.90	
t5	72.50	65.35	73.59	72.42	70.97	3.78	
Cu	t0	4.15	10.04	0.00	0.00	3.55	4.75	
t1	6.99	18.92	0.00	0.00	6.48	8.93	
t5	6.04	13.71	0.00	0.00	4.94	6.51	
Cr	t0	22.01	26.87	71.19	30.66	37.68	22.62	
t1	25.31	31.71	74.59	32.91	41.13	22.56	
t5	25.32	34.73	79.14	38.43	44.41	23.80	
Zn	t0	21.87	35.87	74.81	64.95	49.37	24.68	
t1	28.13	41.41	81.41	67.07	54.51	24.14	
t5	23.67	40.25	82.54	69.95	54.10	26.94	
Hg	t0	0.00	0.00	0.00	0.00	0.00	0.00	
t1	0.00	0.00	0.00	0.00	0.00	0.00	
t5	0.00	0.00	0.00	0.00	0.00	0.00	
Pb	t0	6.44	3.09	16.61	5.81	7.99	5.93	
t1	8.75	4.23	20.78	7.47	10.30	7.24	
t5	9.00	3.70	18.65	6.38	9.43	6.52	

Table 6 Percentages of trace elements, relative to the total concentration, in the reactive fraction (Freact)

Metal	Time	Core P5	Core PC	Core P9	Core P7	Mean	Standard deviation	
Fe	t0	45.95	20.38	0.04	12.09	19.61	19.44	
t1	48.70	21.62	0.04	13.12	20.87	20.57	
t5	55.53	27.41	0.06	14.47	24.37	23.59	
Mn	t0	17.63	16.08	5.43	8.49	11.91	5.88	
t1	19.22	15.69	6.36	7.93	12.30	6.16	
t5	20.90	16.33	6.76	8.70	13.17	6.60	
Cu	t0	81.92	61.30	2.55	8.34	38.53	39.19	
t1	75.90	50.06	1.16	3.16	32.57	36.67	
t5	87.01	64.52	1.92	12.10	41.39	40.96	
Cr	t0	34.31	7.49	0.50	3.30	11.40	15.54	
t1	42.29	10.68	0.56	3.93	14.36	19.09	
t5	50.70	12.59	0.66	5.13	17.27	22.82	
Zn	t0	75.10	52.23	1.83	14.25	35.85	33.83	
t1	70.39	45.61	0.67	13.68	32.59	31.49	
t5	73.60	50.11	1.29	13.25	34.56	33.30	
Hg	t0	48.22	0.08	0.59	0.39	12.32	23.93	
t1	57.63	0.15	0.77	0.48	14.76	28.59	
t5	66.95	0.24	1.39	2.42	17.75	32.81	
Pb	t0	70.86	77.78	15.37	39.38	50.85	28.96	
t1	67.34	74.15	7.87	32.02	45.35	31.07	
t5	75.50	77.07	13.06	40.37	51.50	30.72	

Table 7 Percentages of trace elements, relative to the total concentration, in the reactive organic fraction (Fmo)

Metal	Time	Core P5	Core PC	Core P9	Core P7	Mean	Standard deviation	
Fe	t0	5.35	8.86	22.06	14.70	12.74	7.31	
t1	2.64	8.05	21.64	14.58	11.73	8.22	
t5	2.14	7.39	20.79	13.13	10.86	8.00	
Mn	t0	13.97	21.99	22.74	21.00	19.92	4.03	
t1	7.71	21.50	18.45	20.43	17.02	6.33	
t5	6.35	17.99	17.45	15.96	14.44	5.46	
Cu	t0	10.80	17.65	79.49	21.39	32.33	31.74	
t1	15.17	15.85	76.57	23.73	32.83	29.42	
t5	5.57	11.14	79.92	18.36	28.75	34.51	
Cr	t0	43.28	63.66	27.19	63.42	49.39	17.61	
t1	32.20	55.62	23.76	60.49	43.02	17.81	
t5	23.85	50.95	19.24	53.94	37.00	17.98	
Zn	t0	2.78	10.46	22.03	17.03	13.07	8.34	
t1	1.28	11.64	16.94	15.96	11.46	7.16	
t5	2.65	8.62	15.28	14.33	10.22	5.84	
Hg	t0	16.25	1.71	4.72	0.00	5.67	7.32	
t1	10.06	0.60	5.88	0.00	4.14	4.75	
t5	11.83	2.70	1.95	0.00	4.12	5.26	
Pb	t0	15.66	15.15	62.49	44.78	34.52	23.23	
t1	20.53	17.90	66.54	50.91	38.97	23.71	
t5	14.40	17.36	63.96	46.05	35.44	23.77	

Table 8 Percentages of trace elements, relative to the total concentration, in the pyritic fraction (Fpyr)

Metal	Time	Core P5	Core PC	Core P9	Core P7	Mean	Standard deviation	
Fe	t0	2.45	9.87	9.32	18.22	9.97	6.45	
t1	1.66	7.72	8.02	13.36	7.69	4.78	
t5	1.37	5.97	6.48	12.25	6.52	4.46	
Mn	t0	0.42	0.42	2.75	3.18	1.69	1.48	
t1	0.35	0.33	2.21	3.04	1.48	1.36	
t5	0.25	0.32	2.20	2.92	1.42	1.35	
Cu	t0	3.13	11.01	17.96	70.27	25.59	30.39	
t1	1.94	15.16	22.27	73.11	28.12	31.15	
t5	1.38	10.63	18.16	69.55	24.93	30.53	
Cr	t0	0.40	1.98	1.12	2.62	1.53	0.98	
t1	0.20	1.99	1.08	2.67	1.49	1.08	
t5	0.13	1.73	0.96	2.50	1.33	1.02	
Zn	t0	0.25	1.44	1.33	3.77	1.70	1.48	
t1	0.20	1.33	0.98	3.29	1.45	1.31	
t5	0.08	1.01	0.89	2.47	1.11	1.00	
Hg	t0	35.53	98.21	94.70	99.61	82.01	31.06	
t1	32.30	99.25	93.35	99.52	81.11	32.66	
t5	21.22	97.06	96.65	97.58	78.13	37.94	
Pb	t0	7.03	3.97	5.53	10.03	6.64	2.58	
t1	3.38	3.73	4.80	9.60	5.38	2.88	
t5	1.10	1.88	4.33	7.20	3.63	2.75	

When considering the different geochemical fractions of the sediment, it is observed that the concentrations of trace elements in the Fsil remained practically constant throughout the experiment: Fe, Mn, Cr, and Zn presented the highest average percentages of this fraction with respect to the total (> 36%), while Cu and Pb registered very low percentages (< 10%) and finally Hg was not detected in this fraction (Fig. 6; Table 5).Fig. 6 Results of the temporal variation in the concentration of trace elements in the silicate-bound fraction (Fsil) in the sediment

For Freact, Cu, Zn, and Pb presented the highest mean percentages (> 35%) in the sediment sample at t0, with the highest mean value for Pb (> 50%). The rest of the trace elements were below 20% in the samples (Fig. 7; Table 6). The time variation of trace elements in this fraction progressively increased for Fe, Mn, Cr, and Hg, while Cu, Zn, and Pb decreased at t1. At t5, the content of the latter trace elements increased in this fraction of the sediment, but with slightly lower values than those recorded prior to oxidation (t0).Fig. 7 Results of the temporal variation in the concentration of trace elements in the reactive fraction (Freact) in the sediment

For Fmo, the average proportion of Cu, Cr, and Pb at time zero was 30%, while for the rest of the trace elements it was less than 20% (Fig. 8; Table 7). At t1, the concentration of all trace elements in this fraction decreased, in some cases to more than 50% of their initial value. At t5, a slight increase was observed in this fraction in the concentrations of most trace elements, but their values were still lower than the initial values (Fig. 8; Table 7).Fig. 8 Results of the temporal variation in the concentration of trace elements in the organic fraction (Fmo) in the sediment

The concentration of trace elements in the Fpyr initially (t0) was very variable between elements. Mn, Cr, and Zn had the lowest average percentages (< 2%). While Cu and Hg had the highest concentrations in this fraction (> 25%) (Fig. 9; Table 8). With intermediate values, around 10%, Fe and Pb stand out. It should be noted that practically all the Hg was found in the form of sulfide (> 80% average value). Regarding the temporal evolution of the trace elements associated with this fraction, a continuous and progressive decrease in trace element concentration was observed over time for all samples, indicating that this fraction of the sediment is the most susceptible to aerobic oxidation.Fig. 9 Results of the temporal variation in the concentration of trace elements in the pyritic fraction (Fpyr) in the sediment

Discussion

pH variation in the aqueous phase

The decrease in pH in an oxygen-saturated aqueous environment is one of the consequences of the presence of oxidizable compounds in the sediment, which generate acidity, as suggested by Rimstidt and Vaughan (2003). These oxidizable substances in the sediment include sedimentary sulfides and organic matter.

The magnitude of pH variations in seawater in contact with sediment samples (Fig. 4), which is most pronounced in the inner sediments and less significant in the middle sector, is closely related to the amount of metallic sulfides, organic matter, and carbonates present in the sediments of the Ría de Pontevedra. Sediment samples from the inner sector exhibit more anoxic conditions with a predominance of pyrite and other mineral sulfides with pyritization levels exceeding 60% (León et al., 2004), in contrast to the middle sector, which is oxic-suboxic in nature, with values around 30%. Besides the lower pyrite concentration, the higher carbonate concentration in the middle sector of the estuary may contribute to this smaller pH decrease since carbonates act as efficient buffers at these pH levels. The slight pH increase on the fifth day might initially suggest a decrease in the oxidation process despite the continued vigorous airflow. However, sediment oxidation continued, as reflected in the decreasing values of trace elements associated with sulfides and organic matter in the sediments. Therefore, the slight pH increase on the fifth day is attributed to the strong buffering capacity of seawater and potential dissolution of carbonates.

Behavior of trace element oxidation

The decrease in the total trace element concentration in the sediment is another piece of evidence, along with the pH decrease, of the presence of oxidizable phases in the sediments of the Ría de Pontevedra. The lowest total concentrations of heavy trace elements were recorded in the middle sector sediments, specifically in sample P9. In contrast, the highest concentrations were found in the inner sector of the estuary, primarily in sample PC (Table 4). The inner sectors of the Rías Baixas are characterized by estuarine conditions, whereas the middle and outer sectors can be considered purely marine (Vilas et al., 2019). Furthermore, the inner sector is more influenced by anthropogenic inputs and has a higher content of silt and organic matter than other parts of the estuary, two factors that contribute to increasing the trace element concentration in the sediment (Rubio et al., 2001).

The rapid release of all trace elements from the sediment into the aqueous phase at the beginning of the experiment (t1) was facilitated by the decrease in pH. In contrast, at t5, the trace elements exhibited a withdrawal from the solution, which coincided with an increase in pH. The removal of trace elements from the aqueous phase, especially for Mn and Fe, is attributed to the rapid formation of Fe and Mn oxides and oxyhydroxides that precipitate or form coatings on the sediments.

Initially, the trace elements present in the Fmo and Fpyr were primarily oxidized and released into the aqueous phase. On the other hand, the trace elements in the Fsil did not exhibit significant changes in their concentrations throughout the experiment, suggesting that the oxidation of trace elements in this fraction can be considered negligible. Trace elements in the Freact of the sediment may have transferred to the aqueous phase during the early stages of the experiment, but it is highly likely that they precipitated by the end of the experiment, associated with the newly formed oxidized compounds of Fe and Mn.

Fe and Mn are the trace elements that control the temporal behavior of the other trace elements present in the aqueous phase. Fe and Mn, in their reduced forms, are Fe (II) and Mn (II), and these chemical forms are stable only under acidic conditions. The decrease in pH at t1 likely favored the release of Fe and Mn into the aqueous phase, along with the release of other trace elements. As the oxygen pumping system continued, the Fe2+ and Mn2+ ions oxidized to form Fe(III) and Mn(III, IV).

Therefore, the formation of Fe and Mn oxides and oxyhydroxides generally regulates the presence of certain trace elements like Hg and Pb, preventing their release into the aqueous phase. However, they did not act as sinks for other trace elements such as Zn, Cr, and especially Cu, whose concentrations during the experiment increased considerably. The maximum concentration of total dissolved Cu is higher than that indicated by other authors as a toxicity threshold (> 8.9 µg L−1) (Beiras & Albentosa, 2004) for organisms in the Galician estuaries. These results indicate that the aerobic oxidation of the analyzed sediments is an important process that elevates the concentrations of this trace element in the aqueous phase. The increase in the transfer of Cu to seawater in oxygenated sediments has also been observed in previous studies in the Ría of Vigo (Santos-Echeandia et al., 2009). This highlights the potential danger posed by sediment resuspension in the study area. It is important to consider that Galicia is the world’s leading producer and marketer of mussels and second in terms of production and extraction of this bivalve. For this reason, the regional administration approves triennial shellfish and fishing exploitation plans (General Shellfish Exploitation Plan for the 2024–2026 triennium). These plans regulate management strategies to ensure sustainable exploitation of shellfish resources. The significance and validity of our work lies in the fact that these management plans included in the General Plan encompass biological, ecological, economic, and social objectives, with reference levels and indicators, as well as action strategies. Among these strategies, the role of dredging, along with sediment remobilization and oxidation, is a key factor to be considered, as already suggested by other studies conducted in these estuarine environments (Norén et al., 2020; Rodríguez-Romero et al., 2016).

Conclusions

The aerobic oxidation of sediments in the Ría de Pontevedra led to the release of trace elements into the marine aqueous phase, as evidenced by the decrease in the total concentration of trace elements and the oxidizable sediment fractions (Fmo and Fpyr). Trace element release into the aqueous phase was the predominant mechanism on day 1, while their removal was the dominant process on day 5. The oxidized chemical species of Fe and Mn not only self-regulate their concentrations in the aqueous environment but also control the presence of other trace elements in it. Cu was the only trace element that was released in quantities sufficient to be toxic to marine organisms. It can be incorporated into filter-feeding and detritivore organisms, of commercial interest by reaching concentrations capable of producing biological effects and bioaccumulating in animal tissues.

Galicia leads globally in mussel production and ranks second in bivalve extraction. Triennial shellfish and fishing exploitation plans (General Shellfish Exploitation Plan for 2024–2026) are crucial for the management of the Galician Rías. These plans, covering biological, ecological, economic, and social aspects, ensure sustainable resource management through defined objectives, indicators, and action strategies. For this reason, the type of control carried out in this research should be considered in environmental impact studies and should be transferred to stakeholders when carrying out any anthropogenic activity that may affect the cultivation and wealth of shellfish in the ría environments.

Author Contribution

All authors contributed to the study conception and design. Material preparation, data collection and analysis were performed by B. Rubio, A. E. López-Pérez and I. León. The first draft of the manuscript was written by B. Rubio and A. E. López-Pérez, and all authors commented on previous versions of the manuscript. All authors read and approved the final manuscript.

Funding

Open Access funding provided thanks to the CRUE-CSIC agreement with Springer Nature. Autonomous Government Xunta de Galicia Reference (ED431B 2023/39). Funding for open access charge: Universidade de Vigo/CISUG.

Data availability

No datasets were generated or analysed during the current study.

Declarations

Competing interests

The authors declare no competing interests.

Publisher's Note

Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
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References

Álvarez-Iglesias P Rubio B The degree of trace metal pyritization in subtidal sediments of a mariculture area: Application to the assessment of toxic risk Marine Pollution Bulletin 2008 56 973 983 10.1016/j.marpolbul.2008.01.026 18308341
Álvarez-Iglesias, P., & Rubio, B. (2008). The degree of trace metal pyritization in subtidal sediments of a mariculture area: Application to the assessment of toxic risk. Marine Pollution Bulletin, 56, 973–983. 10.1016/j.marpolbul.2008.01.02618308341 10.1016/j.marpolbul.2008.01.026
Álvarez-Iglesias P Rubio B Redox status and heavy metal risk in intertidal sediments in NW Spain as inferred from the degrees of pyritization of iron and trace elements Marine Pollution Bulletin 2009 58 542 551 10.1016/j.marpolbul.2008.11.026 19114282
Álvarez-Iglesias, P., & Rubio, B. (2009). Redox status and heavy metal risk in intertidal sediments in NW Spain as inferred from the degrees of pyritization of iron and trace elements. Marine Pollution Bulletin, 58, 542–551. 10.1016/j.marpolbul.2008.11.02619114282 10.1016/j.marpolbul.2008.11.026
Álvarez-Iglesias P Rubio B Vilas F Pollution in intertidal sediments of San Simón Bay (Inner Ria de Vigo, NW of Spain): Total heavy metal concentrations and speciation Marine Pollution Bulletin 2003 46 491 503 10.1016/S0025-326X(03)00004-3 12705923
Álvarez-Iglesias, P., Rubio, B., & Vilas, F. (2003). Pollution in intertidal sediments of San Simón Bay (Inner Ria de Vigo, NW of Spain): Total heavy metal concentrations and speciation. Marine Pollution Bulletin, 46, 491–503. 10.1016/S0025-326X(03)00004-312705923 10.1016/S0025-326X(03)00004-3
Álvarez-Iglesias P Rubio B Pérez-Arlucea M Reliability of subtidal sediments as “geochemical recorders” of pollution input: San Simón Bay (Ría de Vigo, NW Spain) Estuarine, Coastal and Shelf Science 2006 70 507 521 10.1016/j.ecss.2006.07.001
Álvarez-Iglesias, P., Rubio, B., & Pérez-Arlucea, M. (2006). Reliability of subtidal sediments as “geochemical recorders” of pollution input: San Simón Bay (Ría de Vigo, NW Spain). Estuarine, Coastal and Shelf Science, 70, 507–521. 10.1016/j.ecss.2006.07.00110.1016/j.ecss.2006.07.001
Álvarez-Iglesias P Rubio B Millos J Isotopic identification of natural vs. anthropogenic lead sources in marine sediments from the inner Ría de Vigo (NW Spain) Science of the Total Environment 2012 437 22 35 10.1016/j.scitotenv.2012.07.063 22903001
Álvarez-Iglesias, P., Rubio, B., & Millos, J. (2012). Isotopic identification of natural vs. anthropogenic lead sources in marine sediments from the inner Ría de Vigo (NW Spain). Science of the Total Environment, 437, 22–35. 10.1016/j.scitotenv.2012.07.06322903001 10.1016/j.scitotenv.2012.07.063
Beiras R Albentosa M Inhibition of embryo development of the commercial bivalves Ruditapes decussatus and Mytilus galloprovincialis by trace metals; implications for the implementation of seawater quality criteria Aquaculture 2004 230 205 213 10.1016/S0044-8486(03)00432-0
Beiras, R., & Albentosa, M. (2004). Inhibition of embryo development of the commercial bivalves Ruditapes decussatus and Mytilus galloprovincialis by trace metals; implications for the implementation of seawater quality criteria. Aquaculture, 230, 205–213. 10.1016/S0044-8486(03)00432-010.1016/S0044-8486(03)00432-0
Beiras R Bellas J Fernández N Lorenzo JI Cobelo-García A Assessment of coastal marine pollution in Galicia (NW Iberian Peninsula); metal concentrations in seawater, sediments and mussels (Mytilus galloprovincialis) versus embryo–larval bioassays using Paracentrotus lividus and Ciona intestinalis Marine Environmental Research 2003 56 531 553 10.1016/S0141-1136(03)00042-4 12860437
Beiras, R., Bellas, J., Fernández, N., Lorenzo, J. I., & Cobelo-García, A. (2003). Assessment of coastal marine pollution in Galicia (NW Iberian Peninsula); metal concentrations in seawater, sediments and mussels (Mytilus galloprovincialis) versus embryo–larval bioassays using Paracentrotus lividus and Ciona intestinalis. Marine Environmental Research, 56, 531–553. 10.1016/S0141-1136(03)00042-412860437 10.1016/S0141-1136(03)00042-4
Beiras R Fernández N Bellas J Besada V González-Quijano A Nunes T Integrative assessment of marine pollution in Galician estuaries using sediment chemistry, mussel bioaccumulation, and embryo-larval toxicity bioassays Chemosphere 2003 52 1209 1224 10.1016/S0045-6535(03)00364-3 12821002
Beiras, R., Fernández, N., Bellas, J., Besada, V., González-Quijano, A., & Nunes, T. (2003). Integrative assessment of marine pollution in Galician estuaries using sediment chemistry, mussel bioaccumulation, and embryo-larval toxicity bioassays. Chemosphere, 52, 1209–1224. 10.1016/S0045-6535(03)00364-312821002 10.1016/S0045-6535(03)00364-3
Bellas J Fernández N Lorenzo I Beiras R Integrative assessment of coastal pollution in a Ría coastal system (Galicia, NW Spain): Correspondence between sediment chemistry and toxicity Chemosphere 2008 72 826 835 10.1016/j.chemosphere.2008.02.039 18377949
Bellas, J., Fernández, N., Lorenzo, I., & Beiras, R. (2008). Integrative assessment of coastal pollution in a Ría coastal system (Galicia, NW Spain): Correspondence between sediment chemistry and toxicity. Chemosphere, 72, 826–835. 10.1016/j.chemosphere.2008.02.03918377949 10.1016/j.chemosphere.2008.02.039
Bellas J Nieto Ó Beiras R Integrative assessment of coastal pollution: Development and evaluation of sediment quality criteria from chemical contamination and ecotoxicological data Continental Shelf Research 2011 31 448 456 10.1016/j.csr.2010.04.012
Bellas, J., Nieto, Ó., & Beiras, R. (2011). Integrative assessment of coastal pollution: Development and evaluation of sediment quality criteria from chemical contamination and ecotoxicological data. Continental Shelf Research, 31, 448–456. 10.1016/j.csr.2010.04.01210.1016/j.csr.2010.04.012
Belzunce-Segarra MJ Bacon JR Prego R Wilson MJ Chemical forms of heavy metals in surface sediments of the San Simón inlet, Ría de Vigo, Galicia. Journal of Environmental Science and Health Part a: Environmental Science and Engineering and Toxicology 1997 32 1271 1292 10.1080/10934529709376609
Belzunce-Segarra, M. J., Bacon, J. R., Prego, R., & Wilson, M. J. (1997). Chemical forms of heavy metals in surface sediments of the San Simón inlet, Ría de Vigo, Galicia. Journal of Environmental Science and Health. Part a: Environmental Science and Engineering and Toxicology, 32, 1271–1292. 10.1080/1093452970937660910.1080/10934529709376609
Belzunce-Segarra MJ Prego R Wilson MJ Bacon J Santos-Echeandía J Metal speciation in surface sediments of the Vigo Ria (NW Iberian Peninsula) Scientia Marina 2008 72 119 126
Belzunce-Segarra, M. J., Prego, R., Wilson, M. J., Bacon, J., & Santos-Echeandía, J. (2008). Metal speciation in surface sediments of the Vigo Ria (NW Iberian Peninsula). Scientia Marina, 72, 119–126.
Cabanas JM González JJ Mariño J Pérez A Román G Estudio del mejillón y de su epifauna en los cultivos flotantes de la Ría de Arosa. III. Observaciones previas sobre la retención de partículas y la biodeposición de una batea Boletín. Instituto Español De Oceanografía 1979 5 44 52
Cabanas, J. M., González, J. J., Mariño, J., Pérez, A., & Román, G. (1979). Estudio del mejillón y de su epifauna en los cultivos flotantes de la Ría de Arosa. III. Observaciones previas sobre la retención de partículas y la biodeposición de una batea. Boletín. Instituto Español De Oceanografía, 5, 44–52.
Caille N Tiffreau C Leyval C Morel JL Solubility of metals in an anoxic sediment during prolonged aeration Science of the Total Environment 2003 301 239 250 10.1016/S0048-9697(02)00289-9 12493200
Caille, N., Tiffreau, C., Leyval, C., & Morel, J. L. (2003). Solubility of metals in an anoxic sediment during prolonged aeration. Science of the Total Environment, 301, 239–250. 10.1016/S0048-9697(02)00289-912493200 10.1016/S0048-9697(02)00289-9
Calvo de Anta R Quintas Mosteiro Y Macías Vázquez F Caracterización de materiales para la recuperación de suelos degradados. I: Sedimentos biogénicos de las Rías de Galicia Edafología 1999 6 47 58
Calvo de Anta, R., Quintas Mosteiro, Y., & Macías Vázquez, F. (1999). Caracterización de materiales para la recuperación de suelos degradados. I: Sedimentos biogénicos de las Rías de Galicia. Edafología, 6, 47–58.
Cela R Lorenzo RA Rubi E Botana A Valiño M Casais C Garcia MS Mejuto MC Bollain MH Mercury speciation in raw sediments of the Pontevedra Estuary (Galicia-Spain) Environmental Technology 1992 13 11 22 10.1080/09593339209385124
Cela, R., Lorenzo, R. A., Rubi, E., Botana, A., Valiño, M., Casais, C., Garcia, M. S., Mejuto, M. C., & Bollain, M. H. (1992). Mercury speciation in raw sediments of the Pontevedra Estuary (Galicia-Spain). Environmental Technology, 13, 11–22. 10.1080/0959333920938512410.1080/09593339209385124
Cobelo-García A Prego R Chemical speciation of dissolved copper, lead and zinc in a ria coastal system: The role of resuspended sediments Analytica Chimica Acta 2004 524 109 114 10.1016/j.aca.2004.05.085
Cobelo-García, A., & Prego, R. (2004). Chemical speciation of dissolved copper, lead and zinc in a ria coastal system: The role of resuspended sediments. Analytica Chimica Acta, 524, 109–114. 10.1016/j.aca.2004.05.08510.1016/j.aca.2004.05.085
Durán I Nieto Ó Electrochemical speciation of dissolved Cu, Pb and Zn in an estuarine ecosystem (Ria de Vigo, NW Spain): Comparison between data treatment methods Talanta 2011 85 1888 1896 10.1016/j.talanta.2011.07.025 21872034
Durán, I., & Nieto, Ó. (2011). Electrochemical speciation of dissolved Cu, Pb and Zn in an estuarine ecosystem (Ria de Vigo, NW Spain): Comparison between data treatment methods. Talanta, 85, 1888–1896. 10.1016/j.talanta.2011.07.02521872034 10.1016/j.talanta.2011.07.025
Ferrans L Jani Y Burlakovs J Klavins M Hogland W Chemical speciation of metals from marine sediments: Assessment of potential pollution risk while dredging, a case study in southern Sweden Chemosphere 2021 263 128105 10.1016/j.chemosphere.2020.128105 33297100
Ferrans, L., Jani, Y., Burlakovs, J., Klavins, M., & Hogland, W. (2021). Chemical speciation of metals from marine sediments: Assessment of potential pollution risk while dredging, a case study in southern Sweden. Chemosphere, 263, 128105. 10.1016/j.chemosphere.2020.12810533297100 10.1016/j.chemosphere.2020.128105
Gambrell RP Wiesepape JB Patrick WH Duff MC The effects of pH, redox, and salinity on metal release from a contaminated sediment Water, Air, and Soil Pollution 1991 57–58 359 367 10.1007/BF00282899
Gambrell, R. P., Wiesepape, J. B., Patrick, W. H., & Duff, M. C. (1991). The effects of pH, redox, and salinity on metal release from a contaminated sediment. Water, Air, and Soil Pollution, 57–58, 359–367. 10.1007/BF0028289910.1007/BF00282899
García A Bernárdez P Prego R Copper in Galician ria sediments: Natural levels and harbour contamination Scientia Marina 2013 77 91 99 10.3989/scimar.03725.27H
García, A., Bernárdez, P., & Prego, R. (2013). Copper in Galician ria sediments: Natural levels and harbour contamination. Scientia Marina, 77, 91–99. 10.3989/scimar.03725.27H10.3989/scimar.03725.27H
Gardoki J Cearreta A Irabien MJ Gómez-Arozamena J Villasante-Marcos V García-Artola A Galaz-Samaniego CA Peñalba MC Bessa F Modern conditions and recent environmental evolution of the industrialized inner Ría of Ferrol (Galicia, NW Spain) Continental Shelf Research 2023 267 105098 10.1016/j.csr.2023.105098
Gardoki, J., Cearreta, A., Irabien, M. J., Gómez-Arozamena, J., Villasante-Marcos, V., García-Artola, A., Galaz-Samaniego, C. A., Peñalba, M. C., & Bessa, F. (2023). Modern conditions and recent environmental evolution of the industrialized inner Ría of Ferrol (Galicia, NW Spain). Continental Shelf Research, 267, 105098. 10.1016/j.csr.2023.10509810.1016/j.csr.2023.105098
Guevara P Pérez-Alberti A Carballo R Sánchez M López I Otero XL Impact of serpentinized peridotite mine waste on the composition and quality of sediments in the Ría de Ortigueira (Galicia, NW Spain) Marine Pollution Bulletin 2021 163 111963 10.1016/j.marpolbul.2020.111963 33486404
Guevara, P., Pérez-Alberti, A., Carballo, R., Sánchez, M., López, I., & Otero, X. L. (2021). Impact of serpentinized peridotite mine waste on the composition and quality of sediments in the Ría de Ortigueira (Galicia, NW Spain). Marine Pollution Bulletin, 163, 111963. 10.1016/j.marpolbul.2020.11196333486404 10.1016/j.marpolbul.2020.111963
Hernández-Otero A Martínez-Castro C Vázquez E Macho G Reproductive cycle of Ensis magnus in the Ría de Pontevedra (NW Spain): Spatial variability and fisheries management implications Journal of Sea Research 2014 91 45 57 10.1016/j.seares.2014.04.008
Hernández-Otero, A., Martínez-Castro, C., Vázquez, E., & Macho, G. (2014). Reproductive cycle of Ensis magnus in the Ría de Pontevedra (NW Spain): Spatial variability and fisheries management implications. Journal of Sea Research, 91, 45–57. 10.1016/j.seares.2014.04.00810.1016/j.seares.2014.04.008
Huerta-Diaz MA Morse JW A quantitative method for determination of trace metal concentrations in sedimentary pyrite Marine Chemistry 1990 29 119 144 10.1016/0304-4203(90)90009-2
Huerta-Diaz, M. A., & Morse, J. W. (1990). A quantitative method for determination of trace metal concentrations in sedimentary pyrite. Marine Chemistry, 29, 119–144.10.1016/0304-4203(90)90009-2
Huerta-Diaz MA Tessier A Carignan R Geochemistry of trace metals associated with reduced sulfur in freshwater sediments Applied Geochemistry 1998 13 213 233 10.1016/S0883-2927(97)00060-7
Huerta-Diaz, M. A., Tessier, A., & Carignan, R. (1998). Geochemistry of trace metals associated with reduced sulfur in freshwater sediments. Applied Geochemistry, 13, 213–233. 10.1016/S0883-2927(97)00060-710.1016/S0883-2927(97)00060-7
León I Méndez G Rubio B Geochemical phases of Fe and degree of pyritization in sediments from Ría de Pontevedra (NW Spain): Implications of mussel raft culture Ciencias Marinas 2004 30 585 602 10.7773/cm.v30i4.340
León, I., Méndez, G., & Rubio, B. (2004). Geochemical phases of Fe and degree of pyritization in sediments from Ría de Pontevedra (NW Spain): Implications of mussel raft culture. Ciencias Marinas, 30, 585–602. 10.7773/cm.v30i4.34010.7773/cm.v30i4.340
Madadi R Kachoueiyan F De-la-Torre GE Effect of redox potential on the heavy metals binding phases in estuarine sediment: Case study of the Musa Estuary Marine Pollution Bulletin 2023 195 115565 10.1016/j.marpolbul.2023.115565 37741167
Madadi, R., Kachoueiyan, F., & De-la-Torre, G. E. (2023). Effect of redox potential on the heavy metals binding phases in estuarine sediment: Case study of the Musa Estuary. Marine Pollution Bulletin, 195, 115565. 10.1016/j.marpolbul.2023.11556537741167 10.1016/j.marpolbul.2023.115565
Monaco D Chianese E Riccio A Delgado-Sanchez A Lacorte S Spatial distribution of heavy hydrocarbons, PAHs and metals in polluted areas. The case of “Galicia” Spain. Marine Pollution Bulletin 2017 121 230 237 10.1016/j.marpolbul.2017.06.003 28602310
Monaco, D., Chianese, E., Riccio, A., Delgado-Sanchez, A., & Lacorte, S. (2017). Spatial distribution of heavy hydrocarbons, PAHs and metals in polluted areas. The case of “Galicia.” Spain. Marine Pollution Bulletin, 121, 230–237. 10.1016/j.marpolbul.2017.06.00328602310 10.1016/j.marpolbul.2017.06.003
Navarro, M., (2000). Presente y futuro del Puerto Marín-Pontevedra. En: XVIII Semana de estudios del mar. Diputación Provincial de Pontevedra-ASESMAR, Pontevedra, 99–131
Norén A Karlfeldt Fedje K Strömvall A-M Rauch S Andersson-Sköld Y Integrated assessment of management strategies for metal-contaminated dredged sediments – What are the best approaches for ports, marinas and waterways? Science of the Total Environment 2020 716 135510 10.1016/j.scitotenv.2019.135510 31837871
Norén, A., Karlfeldt Fedje, K., Strömvall, A.-M., Rauch, S., & Andersson-Sköld, Y. (2020). Integrated assessment of management strategies for metal-contaminated dredged sediments – What are the best approaches for ports, marinas and waterways? Science of the Total Environment, 716, 135510. 10.1016/j.scitotenv.2019.13551031837871 10.1016/j.scitotenv.2019.135510
Otero XL Vidal-Torrado P Calvo De Anta RM Macías F Trace elements in biodeposits and sediments from mussel culture in the Ría de Arousa (Galicia, NW Spain) Environmental Pollution 2005 136 119 134 10.1016/j.envpol.2004.11.026 15809114
Otero, X. L., Vidal-Torrado, P., Calvo De Anta, R. M., & Macías, F. (2005). Trace elements in biodeposits and sediments from mussel culture in the Ría de Arousa (Galicia, NW Spain). Environmental Pollution, 136, 119–134. 10.1016/j.envpol.2004.11.02615809114 10.1016/j.envpol.2004.11.026
Otero XL Calvo De Anta RM Macías F Iron geochemistry under mussel rafts in the Galician ria system (Galicia-NW Spain) Estuarine, Coastal and Shelf Science 2009 81 83 93 10.1016/j.ecss.2008.10.006
Otero, X. L., Calvo De Anta, R. M., & Macías, F. (2009). Iron geochemistry under mussel rafts in the Galician ria system (Galicia-NW Spain). Estuarine, Coastal and Shelf Science, 81, 83–93. 10.1016/j.ecss.2008.10.00610.1016/j.ecss.2008.10.006
Otero XL Ramírez-Pérez AM Abernathy M Ying SC Queiroz HM Ferreira TO Huerta-Díaz MA De Blas E Manganese diagenesis in different geochemical environments of the Ria de Vigo (Galicia, NW Iberian Peninsula) Marine Geology 2024 470 107250 10.1016/j.margeo.2024.107250
Otero, X. L., Ramírez-Pérez, A. M., Abernathy, M., Ying, S. C., Queiroz, H. M., Ferreira, T. O., Huerta-Díaz, M. A., & De Blas, E. (2024). Manganese diagenesis in different geochemical environments of the Ria de Vigo (Galicia, NW Iberian Peninsula). Marine Geology, 470, 107250. 10.1016/j.margeo.2024.10725010.1016/j.margeo.2024.107250
Pérez-Cid B Falqué E Simal-Gandara J Coastline levels of dissolved heavy metals in the estuarine water–system of Vigo International Journal of Environmental Research and Public Health 2021 18 2136 10.3390/ijerph18042136 33671710
Pérez-Cid, B., Falqué, E., & Simal-Gandara, J. (2021). Coastline levels of dissolved heavy metals in the estuarine water–system of Vigo. International Journal of Environmental Research and Public Health, 18, 2136. 10.3390/ijerph1804213633671710 10.3390/ijerph18042136
Prego R Cobelo-García A Twentieth century overview of heavy metals in the Galician Rias (NW Iberian Peninsula) Environmental Pollution 2003 121 425 452 10.1016/S0269-7491(02)00231-2 12685770
Prego, R., & Cobelo-García, A. (2003). Twentieth century overview of heavy metals in the Galician Rias (NW Iberian Peninsula). Environmental Pollution, 121, 425–452. 10.1016/S0269-7491(02)00231-212685770 10.1016/S0269-7491(02)00231-2
Prego R Dale AW de Castro M Gómez-Gesteira M Taboada JJ Montero P Villareal MR Pérez-Villar V Hydrography of the Pontevedra Ria: Intra-annual spatial and temporal variability in a Galician coastal system (NW Spain) Journal of Geophysical Research: Oceans 2001 106 19845 19857 10.1029/2000JC000775
Prego, R., Dale, A. W., de Castro, M., Gómez-Gesteira, M., Taboada, J. J., Montero, P., Villareal, M. R., & Pérez-Villar, V. (2001). Hydrography of the Pontevedra Ria: Intra-annual spatial and temporal variability in a Galician coastal system (NW Spain). Journal of Geophysical Research: Oceans, 106, 19845–19857. 10.1029/2000JC00077510.1029/2000JC000775
Prego R Cotté M-H Cobelo-García A Martin J-M Trace metals in the water column of the Vigo Ria: Offshore exchange in mid-winter conditions Estuarine, Coastal and Shelf Science 2006 68 289 296 10.1016/j.ecss.2006.02.014
Prego, R., Cotté, M.-H., Cobelo-García, A., & Martin, J.-M. (2006). Trace metals in the water column of the Vigo Ria: Offshore exchange in mid-winter conditions. Estuarine, Coastal and Shelf Science, 68, 289–296. 10.1016/j.ecss.2006.02.01410.1016/j.ecss.2006.02.014
Ramírez-Pérez AM De Blas E García-Gil S Sulfur, iron, and manganese speciation in anoxic sediments with methane (Ría de Vigo, NW Spain) CLEAN - Soil, Air, Water 2017 45 1600700 10.1002/clen.201600700
Ramírez-Pérez, A. M., De Blas, E., & García-Gil, S. (2017). Sulfur, iron, and manganese speciation in anoxic sediments with methane (Ría de Vigo, NW Spain). CLEAN - Soil, Air, Water, 45, 1600700. 10.1002/clen.20160070010.1002/clen.201600700
Ramírez-Pérez A MaríaA M Álvarez-Vázquez MA De Uña-Álvarez E De Blas E Environmental assessment of trace metals in San Simon Bay sediments (NW Iberian Peninsula) Minerals 2020 10 826 10.3390/min10090826
Ramírez-Pérez, A., MaríaA, M., Álvarez-Vázquez, M. A., De Uña-Álvarez, E., & De Blas, E. (2020). Environmental assessment of trace metals in San Simon Bay sediments (NW Iberian Peninsula). Minerals, 10, 826. 10.3390/min1009082610.3390/min10090826
Rey D Mohamed KJ Bernabeu A Rubio B Vilas F Early diagenesis of magnetic minerals in marine transitional environments: Geochemical signatures of hydrodynamic forcing Marine Geology 2005 215 215 236 10.1016/j.margeo.2004.12.001
Rey, D., Mohamed, K. J., Bernabeu, A., Rubio, B., & Vilas, F. (2005). Early diagenesis of magnetic minerals in marine transitional environments: Geochemical signatures of hydrodynamic forcing. Marine Geology, 215, 215–236. 10.1016/j.margeo.2004.12.00110.1016/j.margeo.2004.12.001
Rimstidt JD Vaughan DJ Pyrite oxidation: A state-of-the-art assessment of the reaction mechanism Geochimica Et Cosmochimica Acta 2003 67 873 880 10.1016/S0016-7037(02)01165-1
Rimstidt, J. D., & Vaughan, D. J. (2003). Pyrite oxidation: A state-of-the-art assessment of the reaction mechanism. Geochimica Et Cosmochimica Acta, 67, 873–880. 10.1016/S0016-7037(02)01165-110.1016/S0016-7037(02)01165-1
Rodríguez-Germade I Rubio B Rey D XRF scanners as a quick screening tool for detecting toxic pollutant elements in sediments from Marín harbour in the Ría de Pontevedra (NW Spain) Marine Pollution Bulletin 2014 86 458 467 10.1016/j.marpolbul.2014.06.029 25044038
Rodríguez-Germade, I., Rubio, B., & Rey, D. (2014). XRF scanners as a quick screening tool for detecting toxic pollutant elements in sediments from Marín harbour in the Ría de Pontevedra (NW Spain). Marine Pollution Bulletin, 86, 458–467. 10.1016/j.marpolbul.2014.06.02925044038 10.1016/j.marpolbul.2014.06.029
Rodríguez-Romero A Khosrovyan A DelValls TA Riba I Dredged material characterization and management frameworks: A case study at the port Vilagarcia (NW, Spain) Journal of Hazardous Materials 2016 302 129 136 10.1016/j.jhazmat.2015.09.034 26453824
Rodríguez-Romero, A., Khosrovyan, A., DelValls, T. A., & Riba, I. (2016). Dredged material characterization and management frameworks: A case study at the port Vilagarcia (NW, Spain). Journal of Hazardous Materials, 302, 129–136. 10.1016/j.jhazmat.2015.09.03426453824 10.1016/j.jhazmat.2015.09.034
Rubio B Pye K Rae JE Rey D Sedimentological characteristics, heavy metal distribution and magnetic properties in subtidal sediments, Ria de Pontevedra, NW Spain Sedimentology 2001 48 1277 1296 10.1046/j.1365-3091.2001.00422.x
Rubio, B., Pye, K., Rae, J. E., & Rey, D. (2001). Sedimentological characteristics, heavy metal distribution and magnetic properties in subtidal sediments, Ria de Pontevedra, NW Spain. Sedimentology, 48, 1277–1296. 10.1046/j.1365-3091.2001.00422.x10.1046/j.1365-3091.2001.00422.x
Rubio, B., Alvarez-Iglesias, P., Ana, M., Leon, I., Kais, J., Rey, D., Vilas, F. (2011). Factors controlling the incorporation of trace metals to coastal marine sediments: Cases of study in the Galician Rías Baixas (NW Spain). In: Agboola, J. (Ed.), Relevant perspectives in global environmental change. InTech. 10.5772/27772
Santos-Echeandía J Laglera LM Prego R Van Den Berg CMG Copper speciation in estuarine waters by forward and reverse titrations Marine Chemistry 2008 108 148 158 10.1016/j.marchem.2007.11.004
Santos-Echeandía, J., Laglera, L. M., Prego, R., & Van Den Berg, C. M. G. (2008). Copper speciation in estuarine waters by forward and reverse titrations. Marine Chemistry, 108, 148–158. 10.1016/j.marchem.2007.11.00410.1016/j.marchem.2007.11.004
Santos-Echeandía J Laglera LM Prego R Van Den Berg CMG Dissolved copper speciation behaviour during estuarine mixing in the San Simon Inlet (wet season, Galicia). Influence of particulate matter Estuarine, Coastal and Shelf Science 2008 76 447 453 10.1016/j.ecss.2007.07.007
Santos-Echeandía, J., Laglera, L. M., Prego, R., & Van Den Berg, C. M. G. (2008). Dissolved copper speciation behaviour during estuarine mixing in the San Simon Inlet (wet season, Galicia). Influence of particulate matter. Estuarine, Coastal and Shelf Science, 76, 447–453. 10.1016/j.ecss.2007.07.00710.1016/j.ecss.2007.07.007
Santos-Echeandia J Prego R Cobelo-García A Millward GE Porewater geochemistry in a Galician Ria (NW Iberian Peninsula): Implications for benthic fluxes of dissolved trace elements (Co, Cu, Ni, Pb, V, Zn) Marine Chemistry 2009 117 77 87 10.1016/j.marchem.2009.05.001
Santos-Echeandia, J., Prego, R., Cobelo-García, A., & Millward, G. E. (2009). Porewater geochemistry in a Galician Ria (NW Iberian Peninsula): Implications for benthic fluxes of dissolved trace elements (Co, Cu, Ni, Pb, V, Zn). Marine Chemistry, 117, 77–87. 10.1016/j.marchem.2009.05.00110.1016/j.marchem.2009.05.001
Torres RJ Abessa DMS Santos FC Maranho LA Davanso MB Do Nascimento MRL Mozeto AA Effects of dredging operations on sediment quality: Contaminant mobilization in dredged sediments from the Port of Santos, SP, Brazil Journal of Soils and Sediments 2009 9 420 432 10.1007/s11368-009-0121-x
Torres, R. J., Abessa, D. M. S., Santos, F. C., Maranho, L. A., Davanso, M. B., Do Nascimento, M. R. L., & Mozeto, A. A. (2009). Effects of dredging operations on sediment quality: Contaminant mobilization in dredged sediments from the Port of Santos, SP, Brazil. Journal of Soils and Sediments, 9, 420–432. 10.1007/s11368-009-0121-x10.1007/s11368-009-0121-x
Vilas F Bernabeu AM Méndez G Sediment distribution pattern in the Rias Baixas (NW Spain): Main facies and hydrodynamic dependence Journal of Marine Systems 2005 54 261 276 10.1016/j.jmarsys.2004.07.016
Vilas, F., Bernabeu, A. M., & Méndez, G. (2005). Sediment distribution pattern in the Rias Baixas (NW Spain): Main facies and hydrodynamic dependence. Journal of Marine Systems, 54, 261–276. 10.1016/j.jmarsys.2004.07.01610.1016/j.jmarsys.2004.07.016
Vilas, F., García-Gil, E., García-Gil, S., Nombela, M.A., Alejo, I., Rubio, B., Pazos, O., 1996. Cartografía de sedimentos submarinos, Ría de Pontevedra. E: 1:50000. Xunta de Galicia. Consellería de Pesca, Marisqueo e Acuicultura.
Vilas, F., Bernabéu, A., Rubio, B., Rey, D., 2019. The Galician Rías. NW Coast of Spain. In: Morales, J.A. (Ed.), The Spanish coastal systems: dynamic processes, sediments and management. Springer International Publishing, Cham, pp. 387–414. 10.1007/978-3-319-93169-2_17
Villares R Puente X Carballeira A Heavy metals in sandy sediments of the Rías Baixas (NW Spain) Environmental Monitoring and Assessment 2003 83 129 144 10.1023/A:1022542416249 12691527
Villares, R., Puente, X., & Carballeira, A. (2003). Heavy metals in sandy sediments of the Rías Baixas (NW Spain). Environmental Monitoring and Assessment, 83, 129–144.12691527 10.1023/A:1022542416249
