J. C. Pett-Ridge

J. C. Pett-Ridge
Oregon State University | OSU · Department of Crop and Soil Science

PhD

About

51
Publications
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1,093
Citations

Publications

Publications (51)
Poster
On geologic timescales, global climate is controlled by the supply of fresh minerals to Earth’s surface. Carbonic acid driven weathering of silicate minerals removes carbon dioxide (CO2) from the atmosphere, but weathering of accessory carbonates and sulfides within silicate rocks can at the same time be a source of CO2 to the atmosphere. Similarly...
Article
Data sharing benefits the researcher, the scientific community, and the public by allowing the impact of data to be generalized beyond one project and by making science more transparent. However, many scientific communities have not developed protocols or standards for publishing, citing, and versioning datasets. One community that lags in data man...
Presentation
This study investigates the effect of erosion rate on the chemical weathering and characterizes the dissolved geochemistry of two contrasting watersheds. The Eel and Umpqua Rivers share many key characteristics in terms of size, discharge, climate, and vegetation, but they have a 10-fold difference in sediment yield due to their tectonic setting an...
Article
Full-text available
Symbiotic nitrogen- (N) fixing trees can influence multiple biogeochemical cycles by fixing atmospheric N, which drives net primary productivity and soil carbon (C) and N accumulation, as well as by mobilizing soil phosphorus (P) and other nutrients to support growth and metabolism. The soil micronutrient molybdenum (Mo) is essential to N-fixation,...
Presentation
Georespiration, which refers to the mineralization of organic carbon in rocks, is a major source of CO2 to the atmosphere and an important control on Earth’s climate over geologic timescales. The goal of our research project is to investigate the relationship between erosion and geologic respiration. In this study, we examine how geologic respirati...
Article
Full-text available
Symbiotic nitrogen (N)-fixing trees supply significant N inputs to forest ecosystems, leading to increased soil fertility, forest growth, and carbon storage. Rapid growth and stoichiometric constraints of N fixers also create high demands for rock-derived nutrients such as phosphorus (P), while excess fixed N can generate acidity and accelerate lea...
Article
Redox state fluctuations are a primary mechanism controlling the mobilization of trace metals in soils. However, underlying lithology may modulate the effect that redox fluctuations have on trace metal mobility by influencing soil particle size and mineral composition. To investigate the relationships among trace metal behavior, lithology, and redo...
Article
The abundance and isotopic composition of molybdenum (Mo) in marine sediments has been used to reconstruct the evolution of the ocean's oxidation-reduction (redox) potential. However, the utility of Mo as a redox tracer relies on quantifying the flux and isotopic composition of Mo delivered to the ocean, and understanding how these parameters may c...
Article
The thick regolith developed in the humid tropics represents an endmember of critical zone evolution, where shallow and deep biogeochemical cycles can be decoupled in terms of the predominant source of trace elements (atmospheric input at the surface, weathering at depth) and of the processes that control their cycling. To investigate the influence...
Article
Microbe-mediated Fe reduction modulates the role of Fe-bearing minerals, and can occur without saturation, in upland soils. Quantifying this Fe reduction is difficult, but critical for identifying climates in which Fe reduction plays a role in soil biogeochemistry. We measured potential for Fe reduction in upland soils along a rainfall gradient in...
Article
Organic matter is of emerging interest as a control on molybdenum (Mo) biogeochemistry, and information on isotope fractionation during adsorption to organic matter can improve interpretations of Mo isotope variations in natural settings. Molybdenum isotope fractionation was investigated during adsorption onto insolubilized humic acid (IHA), a surr...
Article
Full-text available
Multiple nutrient cycles regulate biological nitrogen (N) fixation in forests, yet long-term feedbacks between N-fixation and coupled element cycles remain largely unexplored. We examined soil nutrients and heterotrophic N-fixation across a gradient of 24 temperate conifer forests shaped by legacies of symbiotic N-fixing trees. We observed positive...
Article
Full-text available
Nitrogen (N) is a key nutrient that shapes cycles of other essential elements in forests, including calcium (Ca). When N availability exceeds ecosystem demands, excess N can stimulate Ca leaching and deplete Ca from soils. Over the long term, these processes may alter the proportion of available Ca that is derived from atmospheric deposition vs. be...
Article
Full-text available
Nitrogen-fixing lichens (cyanolichens) are an important source of nitrogen (N) in Pacific Northwest forests, but limitation of lichen growth by elements essential for N fixation is poorly understood. To investigate how nutrient limitation may affect cyanolichen growth rates, we fertilized a tripartite cyanobacterial lichen (Lobaria pulmonaria) and...
Article
Full-text available
The trace element molybdenum (Mo) is essential to a suite of nitrogen (N) cycling processes in ecosystems, but there is limited information on its distribution within soils and relationship to plant and bedrock pools. We examined soil, bedrock, and plant Mo variation across 24 forests spanning wide soil pH gradients on both basaltic and sedimentary...
Article
Full-text available
Dust deposition provides rock-derived nutrients such as phosphorus (P) to terrestrial ecosystems. Over pedogenic timescales, as bedrock sources of P are depleted, dust sources of P may support productivity in certain ecosystems, but controls on the spatial variability of dust in montane forested systems are largely unknown. Here, we use neodymium (...
Article
Molybdenum isotope fractionation accompanying soil development is studied across three pedogenic gradients encompassing a range of controlling factors. These factors include variable redox conditions, organic matter content, Fe and Mn oxy(hydr)oxide content, mineral composition, degree of weathering, pH, type and amount of atmospheric inputs, age,...
Article
Full-text available
Weexplored the links between geomorphology,weathering and cation availability across themost common forest types and geologic provinces in the El Yunque National Forest, Puerto Rico. Our goal was to connect the controls on primary mineral supply to soil with stocks of plant-available cations. We established a network of 216 soil profiles comprising...
Article
Full-text available
Molybdenum (Mo) is a redox-sensitive element that has been used to constrain paleo-oxygen conditions in marine sediments and could potentially be used similarly in soils. Sedimentary Mo ultimately comes from the terrestrial weathering of rocks during soil development (pedogenesis), but the mechanisms controlling Mo loss and mobility in soils are no...
Conference Paper
Background/Question/Methods Ecosystem nitrogen supply strongly influences the biogeochemical cycling and availability of other essential nutrients in temperate forests, especially calcium. Short-term additions of nitrogen often increase dissolved nitrate fluxes and decrease soil pH, which can stimulate soil calcium loss. However, the long-term eff...
Data
a b s t r a c t Four soil profiles of known age (40, 250, 600 and 3000 ka) from the Merced soil chronosequence in California were analysed for U and Th isotopes, and for major-and trace-element compositions, to test the assumption that leaching of U-series isotopes is a first order process with an invariant rate constant, as frequently assumed when...
Article
The steep volcanic terrain on the wet western side of the Cascade Range is likely to support relatively fast chemical weathering rates. In this study we present preliminary data from an investigation of weathering in the H. J. Andrews Experimental Forest, located in the central western Oregon Cascades. The H. J. Andrews Experimental Forest has long...
Article
The oxygenation state of Earth's oceans is a driver of evolution and extinction events as well as climate change. In recent years stable isotope fractionation of redox sensitive elements such as molybdenum (Mo) have been used as quantitative tracers of past redox-conditions in a number of marine environments. However, little is known about the proc...
Article
Critical Zone (CZ) research investigates the chemical, physical, and biological processes that modulate the Earth's surface. Here, we advance 12 hypotheses that must be tested to improve our understanding of the CZ: (1) Solar-to-chemical conversion of energy by plants regulates flows of carbon, water, and nutrients through plant-microbe soil networ...
Article
Understanding of ecosystem nutrient dynamics and ecosystem response to environmental change is limited by the lack of estimates of nutrient fluxes and their spatial and temporal variability. In particular, the importance of mineral aerosol (dust) inputs to phosphorus (P) cycling in tropical forest ecosystems is not well known. A new dust deposition...
Article
The oceans play a major role in regulating global climate because they both react and drive changes in other geochemical reservoirs. Non-traditional stable isotope systems have become important proxies for changes in ocean chemistry making the quantification of these changes possible. Molybdenum isotopes have great potential as tracers of changes i...
Article
We investigated Ca and Sr cycling in a humid tropical forest by analyzing Ca/Sr ratios and 87Sr/86Sr ratios in soil minerals, soil exchangeable cations, soil porewater, and plant roots, wood and leaves, and calculating the relative contributions of Sr from atmospheric inputs and weathering of local bedrock. An unexpectedly large contribution of bed...
Article
The input of phosphorus (P) through mineral aerosol dust deposition may be an important component of nutrient dynamics in tropical forest ecosystems. A new dust deposition calculation is used to construct a broad analysis of the importance of dust-derived P to the P budget of a montane wet tropical forest in the Luquillo Mountains of Puerto Rico. T...
Article
Sr isotope data from soils, water, and atmospheric inputs in a small tropical granitoid watershed in the Luquillo Mountains of Puerto Rico constrain soil mineral development, weathering fluxes, and atmospheric deposition. This study provides new information on pedogenic processes and geochemical fluxes that is not apparent in watershed mass balance...
Article
Molybdenum isotopes have become an important tracer for paleo-redox conditions in the oceans and paleo- oceans. Mo is also an essential enzyme co-factor in organisms and therefore important in studies of nitrogen fixation and reduction. With an increasing amount of data on the biogeochemical behavior of Mo in the oceans, it is now possible to bette...
Article
Four soil profiles of known age (40, 250, 600 and 3000 ka) from the Merced soil chronosequence in California were analysed for U and Th isotopes, and for major-and trace-element compositions, to test the assumption that leaching of U-series isotopes is a first order process with an invariant rate constant, as frequently assumed when applying this i...
Article
The long-range transport of mineral aerosols (dust) in the atmosphere influences radiative transfer in the atmosphere and affects ocean productivity via Fe fertilization. Dust transport also affects terrestrial systems by contributing to geochemical fluxes of both sediments and solutes, adding nutrients and nutrient-holding capacity to ecosystems,...
Article
A long-term budget of uranium calculated for a chronosequence of Hawaiian soils demonstrates the importance of mineral aerosol deposition as a geochemical pathway. A series of sequential extractions on the same soils shows a strong association between Fe-oxides and uranium, especially the amorphous and poorly-crystalline Fe-oxides present in interm...
Article
Recent studies have employed U-series disequilibria as a tracer of both weathering profile development and of timescale of erosion for whole watersheds. We have undertaken a detailed analysis of the behavior of the U- series isotopes in a previously well-characterized watershed in order to test this approach. In the Rio Icacos watershed in the Luqu...
Article
Ge/Si and 87Sr/86Sr data from primary and secondary minerals, soil waters, and stream waters in a tropical granitoid catchment quantitatively reflect mineral alteration reactions that occur at different levels within the bedrock–saprolite–soil zone. Near the bedrock–saprolite interface, plagioclase to kaolinite reaction yields low Ge/Si and 87Sr/86...
Article
We studied strontium isotope systematics in the Rio Icacos watershed in Puerto Rico in order to trace the relative contributions of individual minerals to weathering fluxes. This study compliments work done with 234U/238U disequilibria and Ge/Si ratios in the same system, providing critical information about the mechanisms of biotite weathering in...
Article
Variations in 234U/238U activity ratios may be used to constrain weathering sources, weathering fluxes, soil development timescales, and water flow-paths in a watershed. The use of uranium-series disequilibria as a tracer and chronometer, however, hinges on a full understanding of the processes governing the behavior of uranium in the whole system,...
Article
The fate of U in a chronosequence of Hawaiian soils was studied as a result of soil development processes including leaching, parent material weathering, dust deposition and subsequent weathering, adsorption and/or precipitation, and secondary mineral formation. The long-term mass balance of U in these systems was quantified by two different approa...

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