{"id":{"repo_id":"penn","oai_identifier":"oai:repository.upenn.edu:20.500.14332/29138"},"canonical_url":"https://search.dev.ndltd.org/etd/penn/oai:repository.upenn.edu:20.500.14332/29138","repository":{"repo_id":"penn","name":"University of Pennsylvania","base_url":"https://repository.upenn.edu/server/oai/request"},"display":{"title":"Iron-Carbon Associations In Tropical Soils Of The Luquillo Critical Zone","abstract":"Much of the uncertainty in the biogeochemical behavior of soil carbon (C) in humid tropical ecosystems derives from an incomplete understanding of soil C stabilization processes. Long-term soil C stability is traditionally attributed to organomineral interactions, however, the 2:1 phyllosilicate clays often associated with temperate organomineral complexation are largely absent in humid tropical soils due to extensive weathering. In contrast, these soils contain a spectrum of iron- and aluminum-bearing minerals, exhibiting a broad range of crystallinity, surface area and surface charge, and susceptible to frequent reduction-oxidation (redox) oscillations. This dissertation investigates the composition, distribution, and function of iron-mediated organomineral associations across a range of spatial scales within the Luquillo Critical Zone Observatory (LCZO). Underlain by contrasting lithologies, the LCZO is characterized by highly-weathered, volcaniclastic Oxisols or quartz diorite-derived Inceptisols, producing an experimental gradient of iron content and speciation. To characterize the interactions between inherently heterogeneous soil C and often amorphous mineralogy, this dissertation paired high-resolution analytical techniques and inorganic selective dissolution experiments. We found low-crystallinity, short-range-order (SRO) iron and crystalline iron phases exert control on distinct reservoirs of soil C across both soil types. Notably, organomineral associations were responsible for accumulation of a subset of soil C, rather than driving trends in total soil C. Examination of solid-phase speciation across soil types revealed evidence for unique mineral matrix architecture in each soil. SRO FeIII-oxhydroxide phases in Oxisol soils were also found to be resistant to laboratory reduction events, suggesting that these phases are immune to redox-induced dissolution and may provide a long-term C stabilization mechanism. Investigation of iron-associated C at the molecular scale revealed preferential complexation of distinct C compounds has occurred at mineral interfaces of varying crystallinity and reactivity, suggesting that the array of association mechanisms described may be fractionating soil C. This work demonstrates that iron-mediated organomineral association serves as a reactive filter for soil C across spatial and temporal scales, which may impact both the quantity and identity of C cycling through the critical zone.","abstract_html":"Much of the uncertainty in the biogeochemical behavior of soil carbon (C) in humid tropical ecosystems derives from an incomplete understanding of soil C stabilization processes. Long-term soil C stability is traditionally attributed to organomineral interactions, however, the 2:1 phyllosilicate clays often associated with temperate organomineral complexation are largely absent in humid tropical soils due to extensive weathering. In contrast, these soils contain a spectrum of iron- and aluminum-bearing minerals, exhibiting a broad range of crystallinity, surface area and surface charge, and susceptible to frequent reduction-oxidation (redox) oscillations. This dissertation investigates the composition, distribution, and function of iron-mediated organomineral associations across a range of spatial scales within the Luquillo Critical Zone Observatory (LCZO). Underlain by contrasting lithologies, the LCZO is characterized by highly-weathered, volcaniclastic Oxisols or quartz diorite-derived Inceptisols, producing an experimental gradient of iron content and speciation. To characterize the interactions between inherently heterogeneous soil C and often amorphous mineralogy, this dissertation paired high-resolution analytical techniques and inorganic selective dissolution experiments. We found low-crystallinity, short-range-order (SRO) iron and crystalline iron phases exert control on distinct reservoirs of soil C across both soil types. Notably, organomineral associations were responsible for accumulation of a subset of soil C, rather than driving trends in total soil C. Examination of solid-phase speciation across soil types revealed evidence for unique mineral matrix architecture in each soil. SRO FeIII-oxhydroxide phases in Oxisol soils were also found to be resistant to laboratory reduction events, suggesting that these phases are immune to redox-induced dissolution and may provide a long-term C stabilization mechanism. Investigation of iron-associated C at the molecular scale revealed preferential complexation of distinct C compounds has occurred at mineral interfaces of varying crystallinity and reactivity, suggesting that the array of association mechanisms described may be fractionating soil C. This work demonstrates that iron-mediated organomineral association serves as a reactive filter for soil C across spatial and temporal scales, which may impact both the quantity and identity of C cycling through the critical zone.","abstract_has_math":false,"creators":["Coward, Elizabeth Katherine"],"institution":null,"degree_name":null,"degree_level":null,"degree_discipline":null,"degree_department":null,"school":null,"contributors":[],"advisors":["Alain F. Plante"],"committee_chairs":[],"committee_members":[],"year":2017,"date_issued":"2017","date_published":"2017","updated_at":"2026-07-24T03:45:49Z","subjects":[],"languages":["en"],"rights":["Elizabeth Katherine Coward"],"rights_urls":[],"identifier_entries":[]},"links":{"outbound_url":"https://repository.upenn.edu/handle/20.500.14332/29138","outbound_label":"Repository record","outbound_source":"dc:identifier.uri"},"metadata_groups":[{"id":"people","label":"People","entries":[{"key":"dc:contributor.advisor","label":"Advisor","values":["Alain F. Plante"]},{"key":"dc:creator","label":"Author","values":["Coward, Elizabeth Katherine"]}]},{"id":"academic_context","label":"Academic Context","entries":[{"key":"dc:date","label":"Dc Date","values":["2023-05-17T19:25:11.000"]},{"key":"dc:date.accessioned","label":"Dc Date Accessioned","values":["2023-05-22T17:01:07Z"]},{"key":"dc:date.available","label":"Dc Date Available","values":["2020-08-15T00:00:00Z"]},{"key":"dc:date.issued","label":"Date","values":["2017"]},{"key":"dc:type","label":"Dc Type","values":["Dissertation/Thesis"]}]},{"id":"language_rights","label":"Language and Rights","entries":[{"key":"dc:language","label":"Dc Language","values":["en"]},{"key":"dc:rights","label":"Dc Rights","values":["Elizabeth Katherine Coward"]}]},{"id":"identifiers","label":"Identifiers","entries":[{"key":"dc:identifier.uri","label":"Identifier URI","values":["https://repository.upenn.edu/handle/20.500.14332/29138"]}]},{"id":"additional","label":"Additional Metadata","entries":[{"key":"dc:description.abstract","label":"Abstract","values":["Much of the uncertainty in the biogeochemical behavior of soil carbon (C) in humid tropical ecosystems derives from an incomplete understanding of soil C stabilization processes. Long-term soil C stability is traditionally attributed to organomineral interactions, however, the 2:1 phyllosilicate clays often associated with temperate organomineral complexation are largely absent in humid tropical soils due to extensive weathering. In contrast, these soils contain a spectrum of iron- and aluminum-bearing minerals, exhibiting a broad range of crystallinity, surface area and surface charge, and susceptible to frequent reduction-oxidation (redox) oscillations. This dissertation investigates the composition, distribution, and function of iron-mediated organomineral associations across a range of spatial scales within the Luquillo Critical Zone Observatory (LCZO). Underlain by contrasting lithologies, the LCZO is characterized by highly-weathered, volcaniclastic Oxisols or quartz diorite-derived Inceptisols, producing an experimental gradient of iron content and speciation. To characterize the interactions between inherently heterogeneous soil C and often amorphous mineralogy, this dissertation paired high-resolution analytical techniques and inorganic selective dissolution experiments. We found low-crystallinity, short-range-order (SRO) iron and crystalline iron phases exert control on distinct reservoirs of soil C across both soil types. Notably, organomineral associations were responsible for accumulation of a subset of soil C, rather than driving trends in total soil C. Examination of solid-phase speciation across soil types revealed evidence for unique mineral matrix architecture in each soil. SRO FeIII-oxhydroxide phases in Oxisol soils were also found to be resistant to laboratory reduction events, suggesting that these phases are immune to redox-induced dissolution and may provide a long-term C stabilization mechanism. Investigation of iron-associated C at the molecular scale revealed preferential complexation of distinct C compounds has occurred at mineral interfaces of varying crystallinity and reactivity, suggesting that the array of association mechanisms described may be fractionating soil C. This work demonstrates that iron-mediated organomineral association serves as a reactive filter for soil C across spatial and temporal scales, which may impact both the quantity and identity of C cycling through the critical zone."]},{"key":"dc:description.degree","label":"Dc Description Degree","values":["Doctor of Philosophy (PhD)"]},{"key":"dc:format.mimetype","label":"Dc Format Mimetype","values":["application/pdf"]},{"key":"dc:title","label":"Title","values":["Iron-Carbon Associations In Tropical Soils Of The Luquillo Critical Zone"]}]}],"canonical_facts":{"dc:contributor.advisor":["Alain F. Plante"],"dc:creator":["Coward, Elizabeth Katherine"],"dc:date":["2023-05-17T19:25:11.000"],"dc:date.accessioned":["2023-05-22T17:01:07Z"],"dc:date.available":["2020-08-15T00:00:00Z"],"dc:date.issued":["2017"],"dc:description.abstract":["Much of the uncertainty in the biogeochemical behavior of soil carbon (C) in humid tropical ecosystems derives from an incomplete understanding of soil C stabilization processes. Long-term soil C stability is traditionally attributed to organomineral interactions, however, the 2:1 phyllosilicate clays often associated with temperate organomineral complexation are largely absent in humid tropical soils due to extensive weathering. In contrast, these soils contain a spectrum of iron- and aluminum-bearing minerals, exhibiting a broad range of crystallinity, surface area and surface charge, and susceptible to frequent reduction-oxidation (redox) oscillations. This dissertation investigates the composition, distribution, and function of iron-mediated organomineral associations across a range of spatial scales within the Luquillo Critical Zone Observatory (LCZO). Underlain by contrasting lithologies, the LCZO is characterized by highly-weathered, volcaniclastic Oxisols or quartz diorite-derived Inceptisols, producing an experimental gradient of iron content and speciation. To characterize the interactions between inherently heterogeneous soil C and often amorphous mineralogy, this dissertation paired high-resolution analytical techniques and inorganic selective dissolution experiments. We found low-crystallinity, short-range-order (SRO) iron and crystalline iron phases exert control on distinct reservoirs of soil C across both soil types. Notably, organomineral associations were responsible for accumulation of a subset of soil C, rather than driving trends in total soil C. Examination of solid-phase speciation across soil types revealed evidence for unique mineral matrix architecture in each soil. SRO FeIII-oxhydroxide phases in Oxisol soils were also found to be resistant to laboratory reduction events, suggesting that these phases are immune to redox-induced dissolution and may provide a long-term C stabilization mechanism. Investigation of iron-associated C at the molecular scale revealed preferential complexation of distinct C compounds has occurred at mineral interfaces of varying crystallinity and reactivity, suggesting that the array of association mechanisms described may be fractionating soil C. This work demonstrates that iron-mediated organomineral association serves as a reactive filter for soil C across spatial and temporal scales, which may impact both the quantity and identity of C cycling through the critical zone."],"dc:description.degree":["Doctor of Philosophy (PhD)"],"dc:format.mimetype":["application/pdf"],"dc:identifier.uri":["https://repository.upenn.edu/handle/20.500.14332/29138"],"dc:language":["en"],"dc:rights":["Elizabeth Katherine Coward"],"dc:title":["Iron-Carbon Associations In Tropical Soils Of The Luquillo Critical Zone"],"dc:type":["Dissertation/Thesis"]},"updated_at":"2026-07-24T03:45:49Z"}