| NSF Org: |
OCE Division Of Ocean Sciences |
| Recipient: |
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| Initial Amendment Date: | December 28, 2011 |
| Latest Amendment Date: | December 28, 2011 |
| Award Number: | 1155385 |
| Award Instrument: | Standard Grant |
| Program Manager: |
Henrietta Edmonds
hedmonds@nsf.gov (703)292-7427 OCE Division Of Ocean Sciences GEO Directorate For Geosciences |
| Start Date: | February 1, 2012 |
| End Date: | January 31, 2016 (Estimated) |
| Total Intended Award Amount: | $410,915.00 |
| Total Awarded Amount to Date: | $410,915.00 |
| Funds Obligated to Date: |
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| History of Investigator: |
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| Recipient Sponsored Research Office: |
220 HULLIHEN HALL NEWARK DE US 19716-0099 (302)831-2136 |
| Sponsor Congressional District: |
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| Primary Place of Performance: |
700 Pilottown Rd Lewes DE US 19958-1298 |
| Primary Place of Performance Congressional District: |
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| Unique Entity Identifier (UEI): |
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| Parent UEI: |
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| NSF Program(s): | Chemical Oceanography |
| Primary Program Source: |
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| Program Reference Code(s): |
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| Program Element Code(s): |
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| Award Agency Code: | 4900 |
| Fund Agency Code: | 4900 |
| Assistance Listing Number(s): | 47.050 |
ABSTRACT
The research conducted by investigators in the School of Marine Science and Policy at the University of Delaware and within the Department of Environmental and Biomolecular Systems of Oregon Health and Science University will examine the importance of soluble Mn(III) in the biogeochemical cycling of Mn. To date, most studies of Mn in marine environments have not considered Mn(III), the intermediate oxidation state between the soluble reduced state (Mn(II)) and the more insoluble oxidized state (Mn(IV)). The presence and stability of Mn(III) in marine systems, especially those where oxygen levels are reduced, changes the dynamics and stability, solubility and fate and transport of Mn in these locations, and at interfaces between oxic and low oxygen environments. This is not understood at present and the proposed research is poised to provide new information concerning the Mn cycle and is potentially transformative research. The PIs have developed new methods to examine Mn(III) levels in the environment and this capability will bolster the successful accomplishment of the project?s goals. The studies will not only focus on understanding the cycling of Mn between its various oxidation states but will determine the concentration and distribution of Mn(II) in stratified coastal ocean waters and in sediment porewaters. The study will also examine the potentially important role of Mn(III) in mediating and influencing the biogeochemical cycling of Mn with that of Fe and S, which are both important components of the major ocean chemical cycles. A better understanding of the biogeochemistry of Mn will inform not only scientists interested in metal cycling in the ocean but also those focused on studies across redox transition zones. The proposed research has an international component and the investigators have developed plans to broadly disseminate their results to students at all levels and to the community. The Principal Investigators have a strong history in education and graduate student and post-doctoral support and mentoring and this will continue under the current grant.
PUBLICATIONS PRODUCED AS A RESULT OF THIS RESEARCH
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PROJECT OUTCOMES REPORT
Disclaimer
This Project Outcomes Report for the General Public is displayed verbatim as submitted by the Principal Investigator (PI) for this award. Any opinions, findings, and conclusions or recommendations expressed in this Report are those of the PI and do not necessarily reflect the views of the National Science Foundation; NSF has not approved or endorsed its content.
Scientists have discovered that a particular form of soluble manganese (Mn) found in marine sediments is significantly more abundant than previously thought. This research, carried out by researchers at the University of Delaware, the Oregon Health and Science University and McGill University in Canada, transforms our understanding of the role of Mn in ocean biogeochemistry.
An essential element for life, Mn plays a critical role in photosynthesis and the biogeochemical cycles of nutrients, carbon, nitrogen and iron. Improved understanding of soluble Mn could shed light on the complex connections between biology, geology and chemistry in ocean environments. It may also advance our understanding of deep-sea Mn nodule formation and organic matter bacterial decomposition in the ocean's low oxygen (O2) environments.
Like other trace metals, Mn exists in multiple oxidation states: Mn(II), Mn(III) and Mn(IV). However, manganese was thought to exist primarily in two forms in marine waters and sediments; soluble Mn(II) and solid Mn(IV). Previous analytical methods did not discriminate other soluble forms, especially Mn(III). With updated techniques to improve the detection limit for dissolved or soluble Mn(III), we have shown that soluble Mn(III) accounts for up to 100 % of the total dissolved Mn found in marine sediments and waters.
Soluble Mn(III) is important because it can oxidize other reduced chemicals by accepting an electron becoming soluble Mn(II), or reduce other oxidized chemicals by donating an electron and becoming solid manganese dioxide [Mn(IV)]. This chemical behavior indicates that it can be a reactive intermediate or catalyst in the Mn cycle which is coupled to other elemental cycles in the environment (see Figure 1 and text below).
In accomplishing our objectives, we were able to measure soluble Mn(III) in all of the diverse systems studied, which included the sedimentary porewaters of the Lower Saint Lawrence Estuary (LSLE) and the water column of the Chesapeake Bay that have low or nondetectable oxygen concentrations. Data from both field and laboratory incubation studies demonstrated that soluble Mn(III) could form from the oxidation of soluble Mn(II) by bacteria in the presence of downward diffusing oxygen and the reduction of solid Mn(IV) oxides. In the Chesapeake Bay, soluble Mn(III) reacted with hydrogen sulfide (H2S) to form harmless elemental sulfur and Mn(II), which was re-oxidized by bacteria to form both soluble Mn(III) and solid Mn(IV) oxides. The coupling of all these reactions is a catalytic cycle between manganese, sulfur and oxygen that prevents toxic H2S from reaching surface waters.
Preliminary data in fully oxygenated waters of the Lower Saint Lawrence Estuary and the Broadkill River Estuary of southern Delaware indicate that soluble Mn(III) can account for up to 66% and 100% of the total dissolved Mn(III), respectively.
As part of this work, we were able to provide information on the nature of the organic ligands binding to soluble Mn(III), and its effect on the reactivity and stability of soluble Mn(III) in the environment. We found that both weak and/or strong Mn(III)L complexes exist in a variety of environments ranging from in the presence of low concentrations of hydrogen sulfide to nondetectable concentrations of hydrogen sulfide, and from nondetectable oxygen to fully oxygenated waters. Also, we were able to develop a method to measure the strength of Mn(III) binding which allows us to quantify weak versus strong organic ligands binding Mn(III). The porewaters of the Lower Saint Lawrence Estuary provide predominantly weaker ligands derived from organic matter decomposition whereas the oxic water column of the LSLE and the surface oxygenated waters of the Broadkill River estuary provide stronger ligands, which are of h...
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