Change search
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Iron isotopes in aquatic systems
Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering. (Applied Geology)ORCID iD: 0000-0002-7313-5833
2019 (English)Doctoral thesis, comprehensive summary (Other academic)Alternative title
Järnisotoper i akvatiska system (Swedish)
Abstract [en]

The cycling of iron (Fe) is a key component for understanding water quality and biogeochemical processes. It serves as mediator during biotic and abiotic processes, as electron acceptor during the degradation of organic matter, as surface for trace element and organic matter adsorption, and is necessary for primary production processes. Since the beginning of Fe isotope studies, researchers focussed on the ratios in soils, rivers and oceans in various environments. The aim of this study was to characterize the Fe isotope ratios from the source (e.g. soils), along the river course, through the estuaries and into the adjacent sea within the boreal landscape. Therefore, seasonal sampling of water from Swedish headwater streams (2016/2017), rivers (2016), estuaries (2013/2014) and the Baltic Sea (2013/2014) were conducted, with the purpose to better understand the role and fate of riverine Fe export. Fe is transported in two main phases from the headwater streams into the oceans: organic Fe complexes and Fe(oxy)hydroxide. It has been proposed that these Fe phases varies in response to seasonal differences in hydrology.

                      This thesis includes the first Fe isotope dataset describing seasonal variations of headwater streams on a regional scale. In the headwater streams positive and negative Fe isotopes ratios can be used to distinguish between different Fe phases. Furthermore, Fe isotope ratios in headwater streams could verify regional drought periods and the subsequent rewetting of the subsurface soils.

Within the rivers and estuaries, we found positive Fe isotopes in the dissolved phase (< 0.22µm) and negative Fe isotopes (> 0.22µm) in the particulate phase during high discharge. The correlation between different chemical parameters, Fe and DOC showed that the Fe isotope composition during spring flood is evolving in the upper soil layers of headwater streams. Therefore, the lighter Fe isotope signal is correlated to the organic-rich soil layers of the riparian zones in forested catchments. During baseflow, particulate Fe has a positive Fe isotope signal. This shows that the Fe has different origin throughout the season within one catchment.

Salt-induced flocculation in the estuaries and under experimental conditions, is removing about 80 % of the dissolved and particulate Fe. Newly formed colloids and particles aggregate and sediment due to small changes in salinity. This major flocculation at low salinities might cause an underestimation of riverine Fe flux. Interestingly, salinity-induced aggregation experiments revealed that Fe(oxy)hydroxide, which dominated aggregates, displayed lower Fe isotope ratios than in the river samples Fe, while organic Fe complexes in the suspension had higher Fe isotope values. The seasonal variability in Fe isotope values could not be simply linked to Fe phases but was probably also influenced by variation in source areas of Fe and processes along the flow-path that alter both Fe phases and isotopic composition.

Within the estuarine mixing zone, no Fe isotope fractionation was observed. The Fe isotope signal is constant over time and space, which excludes fractionation processes for example by oxidation. The Fe isotope signal within the Bothnian Bay was positive showing that different surface properties of Fe-OC and Fe(oxy)hydroxide aggregates lead to the flocculation of negative Fe aggregates.

Place, publisher, year, edition, pages
Luleå: Luleå University of Technology, 2019.
Series
Doctoral thesis / Luleå University of Technology 1 jan 1997 → …, ISSN 1402-1544
National Category
Geochemistry
Research subject
Applied Geochemistry
Identifiers
URN: urn:nbn:se:ltu:diva-73763ISBN: 978-91-7790-376-5 (print)ISBN: 978-91-7790-377-2 (electronic)OAI: oai:DiVA.org:ltu-73763DiVA, id: diva2:1306856
Public defence
2019-06-20, F531, Luleå, 10:00 (English)
Opponent
Supervisors
Available from: 2019-04-25 Created: 2019-04-25 Last updated: 2019-06-05Bibliographically approved
List of papers
1. Distribution of Fe isotopes in particles and colloids in the salinity gradient along the Lena River plume, Laptev Sea
Open this publication in new window or tab >>Distribution of Fe isotopes in particles and colloids in the salinity gradient along the Lena River plume, Laptev Sea
Show others...
2019 (English)In: Biogeosciences, ISSN 1726-4170, E-ISSN 1726-4189, Vol. 16, no 6, p. 1305-1319Article in journal (Refereed) Published
Abstract [en]

 Riverine Fe input is the primary Fe source for the ocean. This study is focused on the distribution of Fe along the Lena River freshwater plume in the Laptev Sea using samples from a 600 km long transect in front of the Lena River mouth. Separation of the particulate ( >  0.22 μm), colloidal (0.22 μm–1 kDa), and truly dissolved (<  1 kDa) fractions of Fe was carried out. The total Fe concentrations ranged from 0.2 to 57μM with Fe dominantly as particulate Fe. The loss of >  99% of particulate Fe and about 90% of the colloidal Fe was observed across the shelf, while the truly dissolved phase was almost constant across the Laptev Sea. Thus, the truly dissolved Fe could be an important source of bioavailable Fe for plankton in the central Arctic Ocean, together with the colloidal Fe. Fe-isotope analysis showed that the particulate phase and the sediment below the Lena River freshwater plume had negative δ56Fe values (relative to IRMM-14). The colloidal Fe phase showed negative δ56Fe values close to the river mouth (about -0.20 ‰) and positive δ56Fe values in the outermost stations (about +0.10 ‰). We suggest that the shelf zone acts as a sink for Fe particles and colloids with negative δ56Fe values, representing chemically reactive ferrihydrites. The positive δ56Fe values of the colloidal phase within the outer Lena River freshwater plume might represent Fe oxyhydroxides, which remain in the water column, and will be the predominant δ56Fe composition in the Arctic Ocean.

Place, publisher, year, edition, pages
European Geosciences Union (EGU), 2019
Keywords
iron isotopes, estuarine mixing, iron particles, truly dissolved iron
National Category
Natural Sciences Geochemistry
Research subject
Applied Geochemistry
Identifiers
urn:nbn:se:ltu:diva-73352 (URN)10.5194/bg-16-1305-2019 (DOI)000462793900001 ()2-s2.0-85063632617 (Scopus ID)
Funder
Knut and Alice Wallenberg FoundationSwedish Research Council for Environment, Agricultural Sciences and Spatial Planning, 621-2004-4039Swedish Research Council for Environment, Agricultural Sciences and Spatial Planning, 211-621-2007Swedish Polar Research SecretariatSwedish Research Council for Environment, Agricultural Sciences and Spatial Planning, 2017-05687EU, European Research Council, ERC-AdG CCTOP project #695331
Note

Validerad;2019;Nivå 2;2019-04-03 (johcin)

Available from: 2019-03-29 Created: 2019-03-29 Last updated: 2019-04-25Bibliographically approved
2. The stability of Fe isotope signatures during low salinity mixing in subarctic estuaries
Open this publication in new window or tab >>The stability of Fe isotope signatures during low salinity mixing in subarctic estuaries
Show others...
2019 (English)In: Aquatic geochemistry, ISSN 1380-6165, E-ISSN 1573-1421Article in journal (Refereed) Epub ahead of print
Abstract [en]

We have studied iron (Fe)-isotope signals in particles (> 0.22 µm) and the dissolved phase (< 0.22 µm) in two subarctic, boreal rivers, their estuaries and the adjacent sea in northern Sweden. Both rivers, the Råne and the Kalix, are enriched in Fe and organic carbon (up to 29 µmol/L and up to 730 µmol/L, respectively). Observed changes in the particulate and dissolved phase during spring flood in May suggest different sources of Fe to the rivers during different seasons. While particles show a positive Fe-isotope signal during winter, during spring flood, the values are negative. Increased discharge due to snowmelt in the boreal region is most times accompanied by flushing of the organic-rich sub-surface layers. These upper podzol soil layers have been shown to be a source for Fe-organic carbon aggregates with a negative Fe-isotope signal. During winter, the rivers are mostly fed by deep groundwater, where Fe occurs as Fe(oxy)hydroxides, with a positive Fe-isotope signal. Flocculation during initial estuarine mixing does not change the Fe-isotope compositions of the two phases. Data indicate that the two groups of Fe aggregates flocculate diversely in the estuaries due to differences in their surface structure. Within the open sea, the particulate phase showed heavier δ56Fe values than in the estuaries. Our data indicate the flocculation of the negative Fe-isotope signal in a low salinity environment, due to changes in the ionic strength and further the increase of pH.

Place, publisher, year, edition, pages
Springer, 2019
Keywords
Fe-isotopes, Fe geochemistry, Dissolved and particulate Fe, Organically complexed Fe, Fe(oxy)hydroxides, Salinity gradient, Spring flood
National Category
Natural Sciences Geochemistry
Research subject
Applied Geochemistry
Identifiers
urn:nbn:se:ltu:diva-73760 (URN)10.1007/s10498-019-09360-z (DOI)000494758500001 ()
Available from: 2019-04-25 Created: 2019-04-25 Last updated: 2019-11-22
3. Spring flood induced shifts in Fe speciation and fate at increased salinity
Open this publication in new window or tab >>Spring flood induced shifts in Fe speciation and fate at increased salinity
Show others...
2019 (English)In: Applied Geochemistry, ISSN 0883-2927, E-ISSN 1872-9134, Vol. 109, article id 104385Article in journal (Refereed) Published
Abstract [en]

Rivers have traditionally been viewed as negligible sources of iron (Fe) to marine waters, as most Fe gets lost during estuarine mixing. However, recent findings demonstrate that Fe from boreal rivers display a higher resistance towards salinity-induced aggregation, presumably due to stabilizing interactions with organic matter. Previous studies have shown that Fe (oxy)hydroxides are selectively removed by aggregation processes, and that organic Fe complexes are less affected by increasing salinity. It has been further proposed that Fe speciation varies in response to seasonal differences in hydrology. In this study X-ray absorption spectroscopy (XAS) was used to determine the temporal variation in Fe speciation and the connection to Fe stability in response to increasing salinity in two boreal rivers (Kalix and Råne River), with the purpose to better understand the fate of riverine Fe export. Sampling was done from winter pre-flood, over the spring flood, to post-flood conditions (early April until mid June). In addition, parallel analyses for Fe speciation and isotope composition (δ56Fe relative to IRMM-14) were made on river samples, as well as salinity-induced aggregates and the fraction remaining in suspension, with the main objective to test if δ56Fe reflect the speciation of Fe.

The contribution of organically complexed Fe increased during spring flood compared to the pre- and post-flood, as did Fe transport capacity. However, since Fe (oxy)hydroxides were dominating throughout the sampling period, the seasonal variability was small. Interestingly, salinity-induced aggregation experiments revealed that Fe (oxy)hydroxides, which dominated aggregates, displayed lower δ56Fe than in the river samples Fe, while organic Fe complexes in suspension had higher δ56Fe values. The seasonal variability in Fe isotope signature could not be simply linked to Fe speciation, but was probably also influenced by variation in source areas of Fe and processes along the flow-path that alter both Fe speciation and isotopic composition.

Place, publisher, year, edition, pages
Elsevier, 2019
Keywords
Fe geochemistry, Fe speciation, Fe isotopes, Organically complexed Fe, Fe (oxy)hydroxides, Boreal, Sub-arctic, Transport capacity, Salinity gradient, XAS
National Category
Natural Sciences Geochemistry
Research subject
Applied Geochemistry
Identifiers
urn:nbn:se:ltu:diva-73761 (URN)10.1016/j.apgeochem.2019.104385 (DOI)2-s2.0-85070319579 (Scopus ID)
Note

Validerad;2019;Nivå 2;2019-08-20 (johcin);

Artikeln har tidigare förekommit som manuskript i avhandling.

Available from: 2019-04-25 Created: 2019-04-25 Last updated: 2019-08-27Bibliographically approved
4. Iron isotope pathways in the boreal landscape: Role of the riparian zone
Open this publication in new window or tab >>Iron isotope pathways in the boreal landscape: Role of the riparian zone
Show others...
2018 (English)In: Geochimica et Cosmochimica Acta, ISSN 0016-7037, E-ISSN 1872-9533, Vol. 239, p. 49-60Article in journal (Refereed) Published
Abstract [en]

Stable Fe isotope compositions have been measured in water samples of the subarctic Kalix River, a first-order stream, and soil water samples from a riparian soil profile adjacent to the first-order stream (Northern Sweden). In the first-order stream, dominated by forest, both the particulate (>0.22 µm) and dissolved (<0.22 µm) phase showed negative δ56Fe values (relative to IRMM-014) during base flow and meltwater discharge in May (−0.97 to −0.09‰). The Fe isotope composition in the water from the riparian soil profile varied between −0.20 and +0.91‰ with sharp gradients near the groundwater table. A linear correlation between the δ56Fe values and the TOC/Febulk ratio was measured during snowmelt in the unfiltered river waters (δ56Fe from −0.02 to +0.54‰), suggesting mixing of two Fe components. Two groups of Fe aggregates, with different Fe isotope compositions, are formed in the boreal landscape. We propose that carbon-rich aggregates, Fe(II)(III)-OC, have negative δ56Fe values and Fe-oxyhydroxides have positive δ56Fe values. A mixture of these two components can explain temporal variations of the Fe isotope composition in the Kalix River. This study suggests that stable Fe isotopes can be used as a tool to track and characterize suspended Fe-organic carbon aggregates during transport from the soil, via first-order streams and rivers, to coastal sediment. Furthermore, the differences in Fe isotope values in the Kalix River and the first-order stream during base flow conditions suggest that the primary Fe sources for river water change throughout the year. This model is combining the Fe isotope composition of first-order streams and rivers to weathering and transport processes in the riparian soil.

Place, publisher, year, edition, pages
Elsevier, 2018
National Category
Geochemistry
Research subject
Applied Geochemistry
Identifiers
urn:nbn:se:ltu:diva-70367 (URN)10.1016/j.gca.2018.07.030 (DOI)000445036400003 ()2-s2.0-85051391721 (Scopus ID)
Note

Validerad;2018;Nivå 2;2018-08-14 (andbra)

Available from: 2018-08-14 Created: 2018-08-14 Last updated: 2019-04-25Bibliographically approved
5. Iron isotopes in headwater streams
Open this publication in new window or tab >>Iron isotopes in headwater streams
(English)Manuscript (preprint) (Other academic)
National Category
Natural Sciences
Identifiers
urn:nbn:se:ltu:diva-73762 (URN)
Available from: 2019-04-25 Created: 2019-04-25 Last updated: 2019-04-25

Open Access in DiVA

fulltext(5750 kB)96 downloads
File information
File name FULLTEXT01.pdfFile size 5750 kBChecksum SHA-512
71d3e4d41da5c45f8c90b44e06cdc5c56716fad07a78ca0f97ecbcb4e902cbf03e70e8feb171bcbe32a4021659643f809c26fa916e12e2acfdeebadc36bbfb06
Type fulltextMimetype application/pdf

Search in DiVA

By author/editor
Conrad, Sarah
By organisation
Geosciences and Environmental Engineering
Geochemistry

Search outside of DiVA

GoogleGoogle Scholar
Total: 96 downloads
The number of downloads is the sum of all downloads of full texts. It may include eg previous versions that are now no longer available

isbn
urn-nbn

Altmetric score

isbn
urn-nbn
Total: 257 hits
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf