| NSF Org: |
EAR Division Of Earth Sciences |
| Recipient: |
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| Initial Amendment Date: | August 9, 2017 |
| Latest Amendment Date: | June 17, 2021 |
| Award Number: | 1660923 |
| Award Instrument: | Standard Grant |
| Program Manager: |
Jonathan G Wynn
jwynn@nsf.gov (703)292-4725 EAR Division Of Earth Sciences GEO Directorate for Geosciences |
| Start Date: | September 1, 2017 |
| End Date: | August 31, 2022 (Estimated) |
| Total Intended Award Amount: | $368,940.00 |
| Total Awarded Amount to Date: | $528,719.00 |
| Funds Obligated to Date: |
FY 2018 = $67,997.00 FY 2020 = $39,755.00 FY 2021 = $52,027.00 |
| History of Investigator: |
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| Recipient Sponsored Research Office: |
341 PINE TREE RD ITHACA NY US 14850-2820 (607)255-5014 |
| Sponsor Congressional District: |
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| Primary Place of Performance: |
112 Hollister Drive Ithaca NY US 14853-1504 |
| 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): |
Instrumentation & Facilities, Geobiology & Low-Temp Geochem |
| Primary Program Source: |
01001819DB NSF RESEARCH & RELATED ACTIVIT 01002021DB NSF RESEARCH & RELATED ACTIVIT 01002122DB NSF RESEARCH & RELATED ACTIVIT |
| Program Reference Code(s): | |
| Program Element Code(s): |
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| Award Agency Code: | 4900 |
| Fund Agency Code: | 4900 |
| Assistance Listing Number(s): | 47.050 |
ABSTRACT
Aluminum (Al) is a major component of common primary and secondary rock-forming minerals, and forms the "backbone" of major soil minerals and clays. Mineral transformations involving aluminum are fundamental to weathering and soil formation processes. Aluminum is not known to perform any beneficial role in organisms, and can be toxic to aquatic life at elevated concentrations. Aluminum can inhibit plant uptake of nutrients in soils, and high Al availability in soils has been shown to limit crop productivity. The chemical behavior of aluminum in the environment is complex, making it difficult to investigate. One of the tools that geochemists have used to study the behavior of many other elements is to use variations in naturally occurring isotopes as tracers, but aluminum only has one isotope. Instead, the investigator proposes to develop the ratio of gallium (Ga) to aluminum as a tracer for Al behavior. Ga has similar chemistry to Al, and shows overall coherent behavior. He can use Ga/Al ratios to identify key mineral sources and reaction pathways for Al in the environment. Further, gallium itself is a trace element with critical technological applications, used in key electronic components in common consumer products such as cellular telephones. As such, gallium is classified as a "strategic metal" by the US Department of Energy. The planned research should provide additional insight into processes that can enrich Ga to levels that are economically recoverable in bauxite ores, for example. Proposed research will work in conjunction with the Critical Zone Observatories National Office (CZO-NO) to create outreach and educational materials related to Critical Zone science. The applied aspects of Al toxicity and Ga as a critical resource provide an excellent opportunity to develop curricular resources linking basic research and societal impacts. The investigator will work with the CZO-NO to develop curricular resources for secondary school and undergraduate science programs in support of Next Generation Science Standards (NGSS, 2013). He will continue fostering outreach to HBCUs via engineering and biology departments to demonstrate intellectual excitement and societal impacts of Critical Zone science. Building connections at HBCUs is especially important for building geoscience diversity since most do not have geoscience departments and thus do not have a traditional pipeline to Earth science graduate programs.
The investigator proposes to develop gallium-aluminum ratios (Ga/Al) as an effective geochemical tracer for the behavior of Al in the Critical Zone. The overarching goal is to develop the necessary fundamental understanding to support the use of Ga/Al as an effective tool for mass balance and tracer studies of Al in the Critical Zone and beyond; a ?pseudo-isotope? for Al. He will focus on four of the processes that control the distribution of Al in the Critical Zone and may cause fractionation of Ga/Al in order to answer the following questions: 1) Is the neoformation of clay minerals and oxyhydroxides responsible for Ga/Al fractionation during weathering? 2) Is the fractionation of Ga and Al in the Critical Zone driven by solution chemistry (i.e. hydrolysis or ligand complex formation)? 3) Do differences in the incorporation of Ga and Al in colloids result in fractionation of Ga from Al during stream export? He will use a combination of field and laboratory-based studies on materials from granitoid catchments across four Critical Zone Observatories (Calhoun, Boulder Creek, Catalina-Jemez, and Luquillo). He will analyze rock, soil, plant, and water samples from each to characterize the behavior of Ga/Al ratio under different conditions of climate, weathering and biological activity. Mineral synthesis and soil column leaching experiments in the laboratory will provide understand partitioning of Ga in oxyhydroxides and the impact of organic ligands on Ga and Al in soils, supported by geochemical modeling. Development of an effective tracer for Al in the environment should be of broad interested to the environmental and geoscience community. Aluminum plays a central role in many geochemical processes and is associated with multiple issues in human health, water quality, and crop productivity. As a strategic metal, an improved understanding of gallium geochemistry is also of broad importance for society. The proposed work will provide insight into Ga geochemistry that will be of interest to the mineral exploration community, especially given that CZ processes are responsible for the formation of the main economic source of Ga, bauxites.
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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.
The environmental chemistry of aluminum is of interest for several reasons. Aluminum is the third most abundant element in the Earth?s crust, at 8.2 wt. % (Rudnick and Gao, 2003). Aluminum is a major component of primary and secondary aluminosilicate minerals. In the weathering environment of the Critical Zone the activity of dissolved Al species can be an important influence on the stability of both primary minerals and the rates of neoformation of clays and other secondary Al-bearing phases . It can be an important contributor to soil acidity (Essington, 2004; Sparks, 1995). Aluminum can impact the availability of phosphorous in soils and aquatic systems (Dakora and Phillips, 2002; Haynes and Mokolobate, 2001; Kopacek et al., 2005). Aluminum salts are in routine use in water quality treatment to flocculate suspended solids and remove pollutants, including P, organic pollutants and arsenic (Edzwald and Tobiason, 1999; Maier et al., 2004; Moore and Miller, 1994; Vanbenschoten and Edzwald, 1990). Aluminum has important direct impacts on biologic activity. There is an extensive literature on Al toxicity effects in animals and humans (e.g. Berthon, 2002; Lima et al., 2011), in aqueous systems (e.g. DeForest and Meyer, 2015; Lacoul et al., 2011) and plants (e.g. Poschenrieder et al., 2008; Kochian et al., 2015). Thus there is considerable interest in understanding sources, reactions and trasnport of aluminum in the environment.
Aluminum has only one stable isotope (27Al) and so isotopic variations are not available as a tool to study Al. However the element gallium (Ga) is chemically similar to Al and we can use the ratio of Ga to Al as a sort of ?pseudo-isotopic? tracer. Developing this tool requires that we have an improved understanding of the behavior of Ga in the environment. Ga also has some similarities to iron, as all three elements Al, Fe and Ga can exist in a similar +3 valence electron state. We carried out field, modeling and laboratory studies to learn more about Al-Fe-Ga behavior.
Field studies showed that basaltic soils suffered large losses of Al at moderate to high rainfall, and we used reactive chemistry models to show that the interaction of dissolved organic compounds played a major role in this loss. Organic compounds from soils and decaying plant materials can make strong complexes with dissolved Al, preventing it from reacting with silica and other elements to generate soil minerals. Interestingly this effect is much less pronounced for Ga at typical soil conditions, so Ga was retained in the soil profiles much more effectively than Al. At still higher rainfall, microbial processes caused iron to be leached out of the soils, but these process do not impact Ga, and so Ga was largely retained even under these conditions. The results tell us that Ga/Al ratios can indicate the extent to which organic chemistry is driving Al mobility because in that circumstance we should see quite different behavior from Ga. In contrast, in weathering profiles developed on shales Ga/Al showed much less variation, indicating that in this system the impacts of organic complexation or other mechanisms that would differentiate Al from Ga are much less important.
Establishing loss or gain of elements in soil can be difficult because they are complex environments. A useful approach to this problem is to measure the abundance of an element of interest relative to the abundance of an element we believe is immobile, i.e. neither lost nor gained. It can be tricky to establish which if any elements may be considered immobile in a given system. In the basaltic system we studied this is further complicated by varying chemistry of the lavas. We were able to show that some of what are known as high field strength elements (HFSE) including titanium (Ti), niobium (Nb) and tantalum (Ta) appear to be quite immobile which the allows us to do a good job defining losses and gains in soils of this type.
In the course of our work we also found that the loss of iron in soils under higher rainfall led to the loss of soil carbon that had been stored for more than 10,000 years. The carbon was protected from decomposition by iron oxide minerals, and when these minerals were dissolved the old carbon was made available to microbes for their metabolism. These results tell us that if climate change increases soil moisture in some environments this can result in release of old stored carbon to the environment as CO2, a potential newly identified indirect consequence of climate change.
Last Modified: 12/21/2022
Modified by: Louis A Derry
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