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In Situ, High-Resolution Profiles of Labile Metals in Sediments of Lake Taihu

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ABSTRACT

Characterizing labile metal distribution and biogeochemical behavior in sediments is crucial for understanding their contamination characteristics in lakes, for which in situ, high-resolution data is scare. The diffusive gradient in thin films (DGT) technique was used in-situ at five sites across Lake Taihu in the Yangtze River delta in China to characterize the distribution and mobility of eight labile metals (Fe, Mn, Zn, Ni, Cu, Pb, Co and Cd) in sediments at a 3 mm spatial resolution. The results showed a great spatial heterogeneity in the distributions of redox-sensitive labile Fe, Mn and Co in sediments, while other metals had much less marked structure, except for downward decreases of labile Pb, Ni, Zn and Cu in the surface sediment layers. Similar distributions were found between labile Mn and Co and among labile Ni, Cu and Zn, reflecting a close link between their geochemical behaviors. The relative mobility, defined as the ratio of metals accumulated by DGT to the total contents in a volume of sediments with a thickness of 10 mm close to the surface of DGT probe, was the greatest for Mn and Cd, followed by Zn, Ni, Cu and Co, while Pb and Fe had the lowest mobility; this order generally agreed with that defined by the modified BCR approach. Further analyses showed that the downward increases of pH values in surface sediment layer may decrease the lability of Pb, Ni, Zn and Cu as detected by DGT, while the remobilization of redox-insensitive metals in deep sediment layer may relate to Mn cycling through sulphide coprecipitation, reflected by several corresponding minima between these metals and Mn. These in situ data provided the possibility for a deep insight into the mechanisms involved in the remobilization of metals in freshwater sediments.

No MeSH data available.


The distribution profiles of pH and TOC in sediments of five sites in Lake Taihu.
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ijerph-13-00884-f002: The distribution profiles of pH and TOC in sediments of five sites in Lake Taihu.

Mentions: Sediment pH and TOC can influence metal lability, by changing the partition of labile forms [24,45,46]. Figure 2 presents the distribution profiles of pH and TOC in sediments of five sites. The pH value increased downward in surface sediments from the SWI to depths of 40, 50, 80, 20 and 30 mm at Sites 1 to 5, respectively, followed by a steady stage or a slight decrease until to the bottom of the profiles. The pH values at Site 4, ranging from 7.12 to 7.64, were evidently higher than those of other sites; the pH values at Site 3, ranging from 6.53 to 7.26, were followed after Site 4. Algal- and macrophyte-dominated regions showed similar pH variations across the profiles, with the pH values ranging from 6.22 to 6.99.


In Situ, High-Resolution Profiles of Labile Metals in Sediments of Lake Taihu
The distribution profiles of pH and TOC in sediments of five sites in Lake Taihu.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5036717&req=5

ijerph-13-00884-f002: The distribution profiles of pH and TOC in sediments of five sites in Lake Taihu.
Mentions: Sediment pH and TOC can influence metal lability, by changing the partition of labile forms [24,45,46]. Figure 2 presents the distribution profiles of pH and TOC in sediments of five sites. The pH value increased downward in surface sediments from the SWI to depths of 40, 50, 80, 20 and 30 mm at Sites 1 to 5, respectively, followed by a steady stage or a slight decrease until to the bottom of the profiles. The pH values at Site 4, ranging from 7.12 to 7.64, were evidently higher than those of other sites; the pH values at Site 3, ranging from 6.53 to 7.26, were followed after Site 4. Algal- and macrophyte-dominated regions showed similar pH variations across the profiles, with the pH values ranging from 6.22 to 6.99.

View Article: PubMed Central - PubMed

ABSTRACT

Characterizing labile metal distribution and biogeochemical behavior in sediments is crucial for understanding their contamination characteristics in lakes, for which in situ, high-resolution data is scare. The diffusive gradient in thin films (DGT) technique was used in-situ at five sites across Lake Taihu in the Yangtze River delta in China to characterize the distribution and mobility of eight labile metals (Fe, Mn, Zn, Ni, Cu, Pb, Co and Cd) in sediments at a 3 mm spatial resolution. The results showed a great spatial heterogeneity in the distributions of redox-sensitive labile Fe, Mn and Co in sediments, while other metals had much less marked structure, except for downward decreases of labile Pb, Ni, Zn and Cu in the surface sediment layers. Similar distributions were found between labile Mn and Co and among labile Ni, Cu and Zn, reflecting a close link between their geochemical behaviors. The relative mobility, defined as the ratio of metals accumulated by DGT to the total contents in a volume of sediments with a thickness of 10 mm close to the surface of DGT probe, was the greatest for Mn and Cd, followed by Zn, Ni, Cu and Co, while Pb and Fe had the lowest mobility; this order generally agreed with that defined by the modified BCR approach. Further analyses showed that the downward increases of pH values in surface sediment layer may decrease the lability of Pb, Ni, Zn and Cu as detected by DGT, while the remobilization of redox-insensitive metals in deep sediment layer may relate to Mn cycling through sulphide coprecipitation, reflected by several corresponding minima between these metals and Mn. These in situ data provided the possibility for a deep insight into the mechanisms involved in the remobilization of metals in freshwater sediments.

No MeSH data available.