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Latin american journal of aquatic research

versión On-line ISSN 0718-560X

Lat. Am. J. Aquat. Res. vol.43 no.3 Valparaíso jul. 2015

http://dx.doi.org/10.3856/vol43-issue3-fulltext-20 

Short Communication

 

Characterization of Baker Fjord region through its heavy metal content on sediments (Central Chilean Patagonia)

Caracterización de la región del fiordo Baker en relación al contenido de metales pesados en los sedimentos (Patagonia Central de Chile)

 

Ramón Ahumada1, Elizabeth González1, Christian Díaz2 & Nelson Silva3

1 Facultad de Ciencias, Universidad Católica de la Santísima Concepción Alonso de Ribera 2850, Concepción, Chile
2
Facultad de Ingeniería, Universidad Católica de la Santísima Concepción Alonso de Ribera 2850, Concepción, Chile
3
Escuela de Ciencias del Mar, Pontificia Universidad Católica de Valparaíso Av. Altamirano 1480, Valparaíso, Chile
Corresponding author: Ramón Ahumada (rahuma@ucsc.cl)
Corresponding editor: Ricardo Prego


ABSTRACT. The spatial distribution of heavy metals content (Ba, Cd, Cu, Pb, Sr and Zn) in sediments of the Baker Fjord and surrounding channels in the central region of the Chilean fjords (47°45'S, 48°15'S) is analyzed. The aim of the study was characterized the patterns of abundance and distribution of these metals in surface sediments. The area corresponds to a poorly studied zone with low human activity. Distribution patterns would be influenced by rainfall conditions (local erosion), fluvial (continental sediments carried by rivers), glacier (glacier flour) and estuarine circulation. Cluster analysis allows differentiation among the sampled sites and group with similar characteristics. Finally, the concentrations found were contrasted with average values of metamorphic rocks and show with some certainty that the values found for calendar for this area and the greatest concentrations are the result of natural enrichment.

Keywords: heavy metals, unpolluted sediments, fjords, Patagonia, Chile.


RESUMEN. Se analiza la distribución espacial del contenido de metales pesados (Ba, Cd, Cu, Pb, Sr y Zn) en sedimentos del Fiordo Baker y canales aledaños, en la región central de los fiordos patagónicos chilenos (47°45'S, 48°15'S). El objetivo del estudio fue caracterizar los patrones de abundancia y distribución de estos metales en los sedimentos superficiales. La zona corresponde a un área escasamente estudiada con baja actividad antrópica. Los patrones de distribución estarían influenciados por condiciones pluviales (erosión local), fluvial (sedimentos continentales arrastrados por los ríos), glaciar (harina de glaciar) y circulación estuarina. El análisis de conglomerados permite establecer diferencias entre los sitios muestreados y agruparlos con características semejantes. Finalmente, las concentraciones encontradas fueron contrastadas con valores promedios de rocas metamórficas y muestran con cierta certidumbre, que los valores encontrados corresponden a los naturales para esta zona y las concentraciones mayores son producto de enriquecimiento natural.

Palabras clave: metales pesados, sedimentos no contaminados, fiordos, Patagonia, Chile.


 

The Baker Fjord is located in the extreme north-eastern zone of the Central Chilean Patagonian Fjords (~48°00'S), in between the Northern and Southern Patagonian Ice Field Glaciers. The basin of the Baker Fjord disrupts the continuity of these two glacier systems, and it receives inflow from the Baker (870 m3 s-1) and Pascua (574 m3 s-1) rivers. This fjord is also influenced by marine waters coming from the Gulf of Penas generating a two layer estuarine circulation system (Pickard, 1971; Sievers & Silva, 2006).

The scarce population of this region (0.1 inhabitants km-2; INE, 2012) minimizes the possible influence of human activity in the area. Therefore the fjord sediment's metal content should be representative of concentrations due to erosion and the natural lixiviation of the rocks that form the geological landscape (Ospina-Alvarez et al., 2014). The first study concerning sediment metal composition of Baker Fjord area was performed in 1997 during the research cruise CIMAR 2 Fiordos (Ahumada & Contreras, 1999; Ahumada, 2006). In this study the metal content was analyzed only at three oceanographic stations, generating a limited amount of information. In 2009 during the CIMAR 14 Fiordos cruise, new sediment samples were taken at seven oceanographic stations, with the objective of characterizing its surface sediment through the analysis of its metal content. Specific aims were to identify areas of enrichment and the patterns of distribution of six metals (Zn, Ba, Cu, Sr, Pb and Cd) and its association with adjacent continental basins. The sampling was performed on board the research vessel R/V "AGOR Vidal Gormaz" between October 27th and November 26th 2009, where seven oceano-graphic stations were sampled with a box corer (box size 30x30x40 cm) (Fig. 1). From each box corer, 4 to 6 subsamples were taken with a 30 cm long PVC tube of 10 cm in diameter.

 

Figure 1. Position of sampling sites used within the area of study.

 

The samples were sealed with PCV lids to keep them humid and stored in a freezer until their physical and chemical analyses, at the Laboratorio de Oceanografía Química of Universidad Católica de la Santísima Concepción (UCSC). From each subsample, the upper 3 cm of the sediment were extracted and divided in four portions or quarters. One was used to analyze sediment texture and the second quarter was used to analyze total organic material (TOM). Texture was determined by means of the wet method and sieved according the Udden Wentworth grain-size scale (Fütterer, 2000). The TOM content was gravimetrically determined using the weight loss-on-ignition method (Mook & Hoskin, 1982) burning the dry sediment subsample in a furnace at a temperature of 450°C.

The third subsample quarter was used for the metal analysis and the last one was kept as a reference sample. These subsamples were dried and crushed in an agate mortar until very fine dust. 0.5 g were extracted and subjected to acid digestion (HNO3, HF, and HQO4), which was carried out in covered Teflon cups at 70°C until the samples were dry. The residue was dissolved in 10 mL of HCl Suprapur® (Merck) and gauged to 25 mL using Milli-Q (EMD Millipore). Following this, 50 μL of the acid fraction were analyzed using thermospray flame furnace atomic absorption spectrometry (TS-FF-AAS) in a GBC 902 atomic absorption spectrophotometer (González et al., 2004). For metal determinations, MESS-3 Certified Reference Materials were used.

Once the analytic data was obtained, the geoaccumulation index (Igeo) was computed according to Müller (1979):

Igeo = log2 (Cm/1.5 Bn)

where: Cm = experimentally measured mean concentration; Bn = background superficial sediments, using the baseline value previously established by Ahumada (2006) for this central fjord region, i.e., Ba = 649.7 μg g-1; Cu = 18.0 μg g-1; Pb = 27.6 μg g-1; Sr =155.8 μg g-1; and Zn = 102.5 μg g-1.

The enrichment factor was calculated according to Chester (2003):

FE = (CExp m /CExp n) / (CBn m/CBn n)

where: CExp*m= experimentally measured concentration; CExp*n= experimentally measured concentration of the standardization element; CBn*m = base line (background) concentration of the metal; and CBn*n = background concentration of the standardization element.

The geoaccumulation index (Table 1) and enrichment factor (Table 2) were conceptually defined for the sake of interpretation.

 

Table 1. Scale and concepts used for interpreting the values
obtained by the geoaccumulation index (Igeo). Source:
Modified from Ahumada (2006).

 

Table 2. Scale and concepts used for interpreting total values of metal concentration
obtain through the application of the enrichment factor (EF). (Modified from Lawson &
Winchester, 1979).

 

The relation between metals and sample sites was analyzed through bilateral Pearson correlations (P < 0.0001). A dendrogram was used for the exploratory analysis of characteristic patterns of distribution, and a multivariate analysis was applied to group the sampling sites considering their metal concentrations and spatial dispersion.

Table 3 lists the characteristics of the collected sediments, and it is possible to observe that five of the sampling site had a depth of more than 300 m.

 

Table 3. Grain-size of sediments (i.e., texture) determined by the Udden Wentworth (U-W)
scale, including soil moisture (SM) and total organic material (TOM).

 

The collected sediment was predominated by grey silt-clayed sediment (>95%). Two sites (4 and 10) were an exception to this tendency, with presence of coarse, fine and very fine sand (> 25%). TOM content fluctuated between 2.6 and 5.6, with higher values towards the oceanic zone. The color of the sediment varied from clear grey to a clear grey/brown and until a dark grey (Table 3).

The metals analytical results were averaged and shown in Table 4. Relative abundance metals values, were the same for all sampled fjords and sites, with the following order: Ba > Sr > Zn > Pb > Cu > Cd. The exception to this was found for Steffen Fjord, where Sr was found in greater concentration than Ba.

 

Table 4. Averaged concentrations of metals in fjord's
sediments (Unit ug g-1, dw).

 

Table 5 shows the co-variation of the metal concentrations, which was calculated through the Pearson correlation coefficient (r). Zn presented a significant positive correlation with Ba, Cu, and Pb, and a significant negative correlation with Sr (P < 0.0001). Moreover, a positive correlation was observed between Cu and Pb (P < 0.0001). Concentrations of Sr and Cd were dominant at inland sites, suggesting a more continental origin, whereas Ba and Zn were dominant at sampling sites with coastal influence.

 

Table 5. Bivariate correlations (r) of metal content from the Baker Fjord. ***P < 0.0001,
**P < 0.001, *P < 0.01.

 

Patterns of distribution and abundance of metal contents in sediments were examined through cluster analysis, with the aim of establishing the sources of origin and the compositions associated with the areas of influence conditions. The results estimated considering three Euclidean distances (Fig. 2) allowed us to distinguish three basins. The head of the Steffen Fjord basin which is influenced by the Steffen Glacier (site 15), which originates from the Northern Patagonian Ice Field; the mouth of the Baker Fjord which correspond to a confluence zone of estuarine and marine waters (sites 4, 5, and 17); and the head of the Baker Fjord influenced by the Pascua River fresh water drainage (sites 6, 9, 10).

 

Figure 2. Dendrogram of sampling sites from the Baker area,
establishing relations of similarity where A) head of Steffen
Fjord, B) mouth of Baker Fjord, and C) head of the Baker Fjord.

 

In order to confirm the patterns inferred through the cluster analysis, a new classification analysis was performed (Fig. 3).

 

Figure 3. Spatial grouping pattern for the metal contents of
the Baker area.

 

This analysis confirmed the previous observations and defined the same spatial groups. (i.e., sites 15 (Steffen), 4 (Baker), and 10 (Baker), located towards the extreme boundary of the studied area, while sites 9 (Baker) and 7 (Baker) were close to the influence of site 10, and sites 5 (Baker) and 17 (Messier) were under the influence of site 4 (Baker). These results reflect the coastal influence that extends towards the Messier Fjord (site 17). Site 15 showed the greatest distance and was influenced by the Steffen Glacier, which is part of the Northern Patagonian Ice Fields, is active, and is in retreat. Site 10 and those associated with it were influenced by the Pascua River.

The segregation established by the distribution patterns of the metals, as corroborated by the performed statistical tests and the geographic grouping of sampling sites (Fig. 4), would allow for making associations between distribution and local processes.

 

Figure 4. Grouping pattern of sampling sites according to
sediment analysis of metal content and correlations.

 

The computation of the Igeo index of the studied metals using the Ahumada's (2006) base line values, give results less than 0, which corresponds to natural concentrations found in unaltered areas (Table 6). The calculated value for Sr (Igeo = 1.71) was obtained from the Steffen Fjord and is an exception to the pattern observed for other sites. This would indicate that the accumulation of fine sediments is due to the Steffen Glacier (Table 4).

 

Table 6. Geoaccumulation index (Igeo) values calculated from averaged data
of each sampling site.

 

The calculated EF values (Table 7) showed values less than 1.5. Those EF vales would confirm that metal concentrations in the sediments are originated from metals released from the parent rock.

 

Table 7. Calculated values for the enrichment factor (EF).

 

When comparing the obtained average concentration values (Table 4) with averages from existing literature (Table 8), it appears that values for Zn could be associated with averages for basalts and shale (Libes, 1992). In turn, Cu and Pb content appear close to contents from granite, basalt, and shale, while, the content of Cd would be closest to shale due to its low concentration and high variance.

 

Table 8. Concentration values (dw μg g-1), for comparative purposes, of metals reported
in the existing literature for different marine localities. (1) Chester, 2003; (2, 3) Libes,
1992; (4*) Ahumada, et al. (2008); (4**) Silva, et al. (2009); (5) Ahumada et al. (2008);
(6) This study; (7) Loring & Asmund (1996); (8 y 9) Prego & Cobelo-García, 2003.

 

The observed enrichment (i.e., site 15, Steffen Fjord) would be due to the dynamic conditions and influences of specific zones (Glacial silt, see Table 3). Müller (1979) suggested increases up to 50% over the baseline for unaltered values (i.e., the calculation algorithm for Igeo). Using this, it is possible to postulate that the present study area presented concentration values corresponding to the accumulation of glacier erosion and natural lixiviation of the rocks that form the geological landscape. The relative abundance of metals according to geological zone was found to be Ba > Sr > Zn > Cu > Pb > Cd, with concentrations of Ba = 552 μg g-1; Sr = 300 μg g-1; Zn = 100 μg g-1; Cu = 22 μg g-1; Pb = 25 μg g-1; and Cd = 0.3 μg g-1 (Table 4). These values concur with the abundance and distributions patterns reported by Ahumada & Contreras (1999) and Silva et al. (2009) for the northern Patagonian fjords an compared with references values (Table 8).

The Baker study area was characterized by relatively homogeneous concentrations and with a variability derived from local specific processes, as determined through geological composition, and from processes related to glacier erosion, natural lixiviation, fluvial influences, and from advection derived from estuarial circulation.

ACKNOWLEDGEMENTS

We thank the National Oceanographic Committee (CONA) for financing this study through CONA-C14F 08-01, granted to Ramón Ahumada B. We also thank the commander and crew of the R/V "AGOR Vidal Gormaz" for the assistance on board during CIMAR 14 Fiordos cruise, and Miss Emma Cascales for her help in sediment sampling. Finally, we thank to Professor A. Rudolph for her patient during the reviewing of the manuscript and to the Dirección de Investigación of the Universidad Católica de la Santísima Concepción for their additional support.

 

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Received: 1 September 2014;
Accepted: 19 December 2014

 

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