Source: UNIVERSITY OF CALIFORNIA, BERKELEY submitted to NRP
REACTIVITY, AGGREGATION AND TRANSPORT OF NANOCRYSTALLINE SESQUIOXIDES IN THE SOIL SYSTEM
Sponsoring Institution
National Institute of Food and Agriculture
Project Status
COMPLETE
Funding Source
NRI COMPETITIVE GRANT
Reporting Frequency
Annual
Accession No.
0208715
Grant No.
2007-35107-17893
Cumulative Award Amt.
$123,471.00
Proposal No.
2006-02656
Multistate No.
(N/A)
Project Start Date
Feb 1, 2007
Project End Date
Jan 31, 2011
Grant Year
2007
Program Code
[25.0]- Soil Processes
Recipient Organization
UNIVERSITY OF CALIFORNIA, BERKELEY
(N/A)
BERKELEY,CA 94720
Performing Department
(N/A)
Non Technical Summary
Sesquioxides are common products of chemical weathering and important constituents of most soils. Soil organic matter and sesquioxides affect each other's dynamics, reactivity and transport. Currently we don't fully understand how the size and concentration of oxides and the composition of soil organic matter affect destabilization of carbon from the oxide surfaces and how the oxides are distributed in the soil system. This project will establish treshold oxide concentrations beyond which OM-oxide associations become irreversible; establish the influence of changing soil moisture conditions (due to global climate change scenarios) on carbon stabilization and tranport of nano-sized oxides; and develop a relationship between reactivity, aggregation and transport of nanoparticles in the soil system.
Animal Health Component
15%
Research Effort Categories
Basic
85%
Applied
15%
Developmental
(N/A)
Classification

Knowledge Area (KA)Subject of Investigation (SOI)Field of Science (FOS)Percent
1020199206140%
1040399204040%
1320499107020%
Knowledge Area
102 - Soil, Plant, Water, Nutrient Relationships; 104 - Protect Soil from Harmful Effects of Natural Elements; 132 - Weather and Climate;

Subject Of Investigation
0199 - Soil and land, general; 0399 - Watersheds and river basins, general; 0499 - Atmosphere, general/other;

Field Of Science
2040 - Mineralogy; 1070 - Ecology; 2061 - Pedology;
Goals / Objectives
Nano-sized sesquioxides are ubiquitous minerals in the environment. Reactivity, aggregation and transport of oxides strongly control sorption of anions, variable charge, soil physical characteristics, and mobility of nutrients and pollutants in the environment. These soil properties are critical for availability of nutrients, vitality of various organisms, and plant productivity in the soil system. But, we know very little about how concentration and size of different oxides affects desorption kinetics of organic matter (OM), and how different sizes and species of oxides aggregate and move through the soil system. This is particularly important and timely issue because anticipated future climatic changes in places like California could disrupt the current OM-sesquioxide association through their effect on quantity, quality and mobility of OM and weathering. The objective of this postdoctoral research is to make targeted contributions to address three critical questions concerning reactivity and distribution of sesquioxide in soils with different mineralogy. The study will specifically address the following questions: (1) how are size of oxide particles and their concentration related to quantity and quality of desorbed OM? (2) how does concentration an composition of dissolved OM (DOM) control aggregation of nanocrystalline sesquioxides? (3) how is transport of oxide particles through a soil column related to OM-oxide associations and aggregation? The project is a novel effort, combining methods and insights from the pedological, ecological, and geologic sciences. This proposed postdoctoral research project will characterize mechanisms and controlling variables of oxide reactivity, aggregation and transport in soils with different mineralogy in order to determine if there exist (1) thresholds oxide concentration beyond which OM-oxide associations become irreversible; (2) OM type and concentration that results in aggregation of fine oxide particles beyond the nano-range; (3) a relationship between reactivity, aggregation with transport of nanoparticles in the soil system; and (4) establish the influence of changing soil moisture conditions (due to anticipated global change scenarios) on C stabilization and transport of nano-sized oxides. The long-term goals of this project are to advance our understanding on the fate of oxides in the environment and their contribution to carbon sequestration.The proposed work will have broad impacts in several areas related to soil chemistry, physics and microbiology, and agricultural productivity and sustainability.
Project Methods
For the first part of the project (to address how the size of oxide particles and their concentration are related to quantity and quality of desorbed organic matter): (a) the amount of dissolved organic matter (DOM) that can be sorbed and desorbed from soils with different oxide concentrations will be determined by equilibrating soils with different DOM concentrations; (b) the chemical composition of the DOM before the sorption experiments will be compared with the composition after each batch of sorption and desorption experiment using liquid state 13C-NMR (nuclear magnetic resonance), in order to determine if type and concentration of the varying oxides affects the quality, as well as quantity of DOM in a soil system; and (c) the modified Langmuir adsorption isotherm will be tested to interpret the reactivity of the DOM with soils having different sesquioxides, at varying degrees of availability. For the second part of the project (to address how the concentration and composition of DOM control aggregation of nanocrystalline sesquioxides, and how transport of oxide particles through a soil column is related to OM-oxide associations and aggregation): (a) a series of column experiments with different DOM and oxide concentrations, at various fluid flow rates will be conducted to determine if the changes in DOM concentration and water flow rates observed in the climate change experiment at Angelo reserve will result in significant change particle size (aggregation) of the oxides; (b) the rates and concentration (of the total and different forms of iron and aluminum (Fe and Al)) that are transported through the soil column will be used to determine the types of Fe and Al oxides that are associated with formation of different sized aggregates and significant rates of oxide transport; and (c) I will determine if the chemical composition of the leaching solution changes after the column experiments using total organic carbon analysis and liquid state 13C-NMR.

Progress 02/01/07 to 01/31/08

Outputs
OUTPUTS: After additional research and careful considerations and consultations amongst our collaborators in the proposed field site, we slightly refocused the goals of this project towards answering two important questions: (1) how does association of organic matter and Fe and Aluminum oxyhydroxides change in the rainfall addition experiment (simulated climate change scenario in California)? And (2) Do changes in rainfall patterns result in significant effect on colloid (especially oxide) mobilization and reversibility of oxide-organic matter associations in Mediterranean soil systems. The objective of the work remains unchanged, to make targeted contributions that address three critical questions concerning reactivity and distribution of sesquioxides in soils. This study has already started to provide a systemic and integrated representation of the effect of changing amount and distribution of rainfall on reactivity, aggregation and transport of hydrous Fe and Al-oxides and their association with OM. The long-term goals of this project are to advance our understanding on the fate of oxides in the environment and their contribution to carbon sequestration. We have successfully completed all field work related to this project and are in the final stages of completing all lab work. We have determined concentration of C and N in bulk soil and free light fraction, biochemical composition of soil organic matter using 13C-NMR, concentrations of Fe and Al extractable with citrate dithionite, ammonium oxalate and sodium pyrophosphate, concentration of base cations in soil, cation exchange capacity, soil texture, bulk density, X-ray diffraction, Specific Surface Area, and sorption/desorption experiments with synthetic goethite and natural organic matter (from Peat) and synthetic humic acids. Results from this work were presented in 3 national conferences and we are currently analyzing data and preparing manuscripts for publication in peer reviewed journals. PARTICIPANTS: This work is being conducted as the postdoctoral project of A.A. Berhe (the PI). This project is being conducted under the guidance of my postdoctoral mentor Jill Banfield at UC Berkeley. The NMR work was conducted under a collaboration with Sarah D. Burton in the Pacific Northwest National Laboratory. I am currently starting to collaborate with Johan Six in UC Davis to look at dynamics of soil organic matter in deep soil layers that likely have significant accumulation of Fe and Al oxides. TARGET AUDIENCES: Scientists, educators and policy makers interested in understanding the role of soils in global climate change, especially carbon sequestration. PROJECT MODIFICATIONS: After additional research and careful considerations and consultations amongst our collaborators in the proposed field site, we slightly refocused the goals of this project towards answering two important questions: (1) how does association of organic matter and Fe and Aluminum oxyhydroxides change in the rainfall addition experiment (simulated climate change scenario in California)? And (2) Do changes in rainfall patterns result in significant effect on colloid (especially oxide) mobilization and reversibility of oxide-organic matter associations in Mediterranean soil systems. The objective of the work remains unchanged, to make targeted contributions that address three critical questions concerning reactivity and distribution of sesquioxides in soils.

Impacts
This study has showed that after 6 years, bulk soil organic matter near the soil surface shows little or no significant treatment effect. However at depth, extension of the rainy season into the spring and early summer months resulted in accumulation of more, less decomposed organic matter in soil. Our density fractionation work showed that up to 50% more C exists freely in the soil (the free light fraction, fLF, that is not physically or chemically associated with the soil mineral fraction) and appears to be less humified when the rainy season is extended into summer, compared to the control or plots receiving additional rainfall in the winter only. We found that rainfall addition had significant effect on concentration of poorly crystalline Fe oxides (oxalate extractable) and Fe oxides complexed with organic Fe (pyrophosphate extractable). Strength of association between %C and soil minerals decreases after extension of rainy season (spring) possibly pointing to changing mechanism of soil organic matter stabilization, away from dominance of oxide facilitated stabilization towards soil organic matter stabilization that is facilitated by cation bridging. Our laboratory experiments indicate that changing amount of oxides in soil and forms of association with organic matter are important since increasing oxide concentration (provision of more oxide surface area for sorption of OM) were found to have the ability to increase the amount of organic carbon sorbed/accumulated, but the efficiency of OM accumulation decreases with increasing amount of oxides. We found that more aromatic functional groups stabilized at low oxide concentrations while a significant fraction of the additional storage due to increased oxide concentrations was facilitated by aggregation (esp at low oxide concentrations) and not chemical binding of organic matter with the oxide surfaces.

Publications

  • No publications reported this period