Climatic controls on deep soil organic matter stock and stability

IMG_6715.jpgAs part of the Southern Sierra Critical Zone observatory, we are studying how climate controls the amount, nature, stability and stabilization mechanisms of soil organic matter along the Western Sierra Climosequence. Through this work we are also collaborating with Craig Rasmussen’s group at University of Arizona to develop a cross-CZO collaborative project to investigate climatic controls and deep SOM dynamics.

Student: Kimber Moreland
Funding: Partial support from NSF – Souther Sierra Critical Zone Observatory; CZO National office SAVI grant

Phosphorous dynamics along the Sierra Nevada and White Mountain Climosequences

IMG_6729.jpgIn this project we are studying how climate controls the stock speciation of phosphorus in soil along two climatically distinct climosequences: Western Slopes of the Sierra Nevada and the White Mountains in the western US.

Student: Morgan Barnes
Collaborators: Stephen C. Hart (UC Merced), Robert Graham (UC Riverside)
Funding: Partial support from NSF – Souther Sierra Critical Zone Observatory; ISEECI

Source of eroded organic matter in low-order catchments in the southern part of the Sierra Nevada Mountains

shapeimage_2As part of the Southern Sierra Critical Zone observatory, we have been investigating the effect of soil erosion on dynamics of organic matter. In this larger project we seek to get a better mechanistic understanding of the mechanisms that control fate and stability of soil organic matter in eroding, fire affected systems of the Sierra Nevada.

Student: Emma McCorkle; Collaborators: Steve Hart (UC Merced), Dale Johnson (University of Nevada, Reno), Carolyn Hunsaker (US Forest Service, PSW), Caroline Masiello (Rice University); Funding: NSF, Hellman Research Grant, and Additional partial support from NSF – Souther Sierra Critical Zone Observatory


Role of erosion on terrestrial carbon sequestration and mechanisms of soil organic matter stabilization

Soil erosion can lead to terrestrial carbon sequestration as long as: i) eroded  soil carbon is, at least partially, replaced in the eroding slopes and/or ii) deposited soil carbon is protected from decomposition in depositional settings. In response to the need to provide more field data, a study is being conducted in La Rogativa watershed, south-eastern Spain, by the research group of Carolina Boix-Fayos. Part of the study we are collaborating in seeks to quantify rate of eroded soil organic carbon replacement by production of new photosynthate and mean residence time of soil organic matter in eroding vs. depositional settings to determine if eroded SOM is stabilized upon deposition. Findings of this study will be helpful in furthering our understanding of SOC dynamics in eroding watersheds.

Visting Student: Elisabet Nadeu; Collaborators: Carolina Boix Fayos (Centro de Edafología y Biología Aplicada del Segura (CEBAS), Spain)

The effect of fire on soil aggregation and physical stability of soil organic matter

droppedImage_1 Fire has significant impact on dynamics of organic matter in soil and soil health. Over the last couple of decades, our understanding of how fires affect chemical composition of organic matter, and lead to accumulation of fire-altered (pyrogenic) matter in soil has improved. However, there is still very little published data on how combustion temperature affects chemical and physical properties of topsoil and its implication on mineral-OM association in soil that have important implications for formation and stability of aggregates, and physical protection of OM from decomposition. In this project we are determining how combustion temperature affects chemical reactivity of soil, stability of soil aggregates, and physical protection of organic matter from decomposition.

Student: Samuel Negusse Araya
Funding: UC Merced Graduate Research Council

Interactive effect of Fire and Erosion on persistence of soil organic matter


Fire changes soil organic matter amount, composition, and several soil physical and chemical properties. Fire and erosion routinely overlap in time and space. But our understanding of how soil erosion affects the lateral transport of pyrogenic carbon and its implications for determining residence times of bulk SOM as well as pyrogenic C is incomplete. In this study we are investigating the interactive effects of fire and erosion on SOM dynamics in forested upland ecosystem in Southern Lake Tahoe.

Student: Rebecca Lever; Collaborators: Dale Johnson (UNR) and Jonathan Sanderman (CSIRO Adelaide); Funding: Faculty Startup funds.

Role of metal oxides in Stabilization and distribution of soil organic matter

Nano-sized sesquioxides have tremendous potential to react, aggregate and get transported in the presence of soil organic carbon. Metal oxide availability, concentration and phases exert strong control on behavior of organic matter in soil, as well as that of phosphorus and contaminants such as arsenic. We are studying the sorption and desorption kinetics of crystalline and poorly crystalline metal oxides with  organic matter to get important insights into the general fate of natural and synthetic nanocrystals in the environment and ways nano-sized sesquioxides can affect destabilization of soil organic carbon.

Student: Lixia Jin, Funding: Pending

Methods in Soil Organic Matter Biogeochemistry

3231BerheZhukovaUltrasonication: Application of ultrasonic energy is an effective method of dispersing soil aggregates that range in size over multiple orders of magnitude (µm to mm). This technique is used to analyze relationships between amount of applied energy, aggregate size class distribution, and organic matter turnover in soils. Application of increasing amounts of ultrasonic energy, to breakup progressively small and more tightly bound aggregates, likely leads to creation of artifacts that affect the interpretation of experimental findings. However, the type and magnitude of the created artifacts has not been thoroughly investigated. In this study we are quantifying how application of varying amounts of ultrasonic energy affect different soil minerals and organic matter in different types of soils.

shapeimage_3Experimental artifacts from common soil techniques: Soil sample pretreament and soil organic matter (SOM) fractionation procedures have become common in terrestrial biogeochemistry research. Experimental conditions during sample pretreatment and fractionation of SOM affect the characteristics of separated organic matter (OM). However, the effect of these treatments on the nature of the soil and SOM, and their implications for explanatory power of the measured data are rarely considered. In this project we are compiling information on method-related modifications of soil and SOM characteristics during air drying, rewetting, application of ultra sound energy, and sodium pryrophosphate (Na4P₂O₇) extraction. Here we aim to develop recommendations for adaptation of the sample-specific experimental designs to reduce method-related artifacts and aid in interpretation of experimental data.

Postdoc: Michael Kaiser; Collaborators: Markus Kleber (Oregon State University); Funding: Faculty Startup funds

Deep soil CO2 fluxes 

In this study we are monitoring the spatial and temporal variability of the soil gaseous and soluble organic matter (OM) fluxes, in near surface vs. deep soil layers. In this project, we are using continuous long-term measurements of soil gaseous and soluble element fluxes (being conducted in the student farm at UC Davis) to determine how new vs. old photosynthate is incorporated into soil organic matter at different depths and fluxes associated with it.  This study is expected to yield important insights regarding (1) the distribution, chemical composition, reactivity, and stabilization of new vs. old organic matter along a soil profile, and (2) the relationship between the temporal dynamics of dissolved organic matter concentration and chemical composition in deep soil layers and soil CO₂ production at depth vs. near the soil surface.

Collaborators: Johan Six (UC Davis); Funding: Kearney Foundation of Soil Science

Coupled biogeochemistry and hydrology in high elevation meadows

3223BerheZhukovaHigh elevation meadow stability has traditionally been viewed as a product of two parameters, geological stability and biological stability. Hydrologic conditions in meadows exert strong control on rate of organic matter decomposition/storage where amount and composition of SOM can have important implications for the amount of water stored in the meadow. However, there is currently a lack of significant understanding of the mechanisms by which the SOM in meadows retains water and contributes to the biogeochemical stability of high elevation meadows. It is important to

Yosemite waterfall

close this knowledge gap because meadows play fundamental role in the filtering, storage and slow release of water in snowmelt dominated watersheds in the Sierra Nevada and beyond, and their stability expected to be sensitive to changes in climate. This research examines the interconnected role that SOM quality/quantity and hydrology play on meadow stability.

Student: Chelsea Arnold; Collaborators: Teamrat A. Ghezzehei (UC Merced); Funding: UC Merced Academic Senate, UC Graduate Research Council, National Reserve System (Mathias Grant)



  1. Decomposition of organic substrates in deep vs. near surface soil layers along topographic gradients (Berhe, 2012)
  2. Effect of litterbags on rate of organic substrate decomposition in deep vs. near surface soils along a topographic gradient (Berhe, 2013)
  3. Mechanisms of soil organic matter stabilization in eroding vs. depositional landform positions (Berhe et al 2008, Berhe et al, 2012)
  4. Effect of changing amount and timing of rainfall on soil organic matter dynamics (Berhe et al, 2012)
  5. Using biochar to recover nutrients from dairy waste (Sarkhot et al, 2012, 2013 JEQ)
  6. Role of soil erosion in terrestrial carbon sequestration in naturally eroding watershed (Berhe et al, 2007, 2008)
  7. Effect of landmines on land degradation (Berhe 2007)
  8. Soil organic matter biogeochemistry in permafrost under anticipated climate change (Waldrop, et al 2010)

For information about our work or to inquire about joining our group please contact Prof. Asmeret Asefaw Berhe at aaberhe(at)ucmerced(dot)edu.