Geology topics

Zhaosheng Fan

Publications and source records attributed to Zhaosheng Fan.

6 recordsLinked to original sources

USGS2018

Approaches for improving field soil identification

Use of soil survey information by non-soil-scientists is often limited by their inability to select the correct soil map unit component (COMP). Here, we developed two approaches that can be deployed to smartphones for non-soil-scientists to identify COMP from the location alone or location together with easily observed field data (i.e., slope, depth to the restrictive layer, and soil texture by depth). In addition, we also compared the two newly developed approaches with a traditional approach identifying COMP based on the dominant COMP (DC-based approach). All three approaches were tested with the Rapid Assessment of US Soil Carbon database and the combined USDA- NRCS Soil Survey Geographic database and the USDA-NRCS State Soil Geographic Database. The results indicated that the observation-based approach performed significantly better than the other two approaches, suggesting that a small set of easy-to-measure site-specific observations could significantly improve COMP identification. The location- and DC-based approaches had similar low performance overall. However, the location-based approach slightly improved identifications over the DC-based approach for cases where (i) there were multiple possible components within the soil map unit and (ii) the components were located in close proximity to a boundary of a different soil map unit polygon. The benefit of using the location-based approach may be greater in specific soil survey areas where topography was the major factor leading to the creation of the map unit legend.

Soil Science Society of America Journal↗

USGS2012

The response of soil organic carbon of a rich fen peatland in interior Alaska to projected climate change

It is important to understand the fate of carbon in boreal peatland soils in response to climate change because a substantial change in release of this carbon as CO 2 and CH 4 could influence the climate system. The goal of this research was to synthesize the results of a field water table manipulation experiment conducted in a boreal rich fen into a process-based model to understand how soil organic carbon (SOC) of the rich fen might respond to projected climate change. This model, the peatland version of the dynamic organic soil Terrestrial Ecosystem Model (peatland DOS-TEM), was calibrated with data collected during 2005–2011 from the control treatment of a boreal rich fen in the Alaska Peatland Experiment (APEX). The performance of the model was validated with the experimental data measured from the raised and lowered water-table treatments of APEX during the same period. The model was then applied to simulate future SOC dynamics of the rich fen control site under various CO 2 emission scenarios. The results across these emissions scenarios suggest that the rate of SOC sequestration in the rich fen will increase between year 2012 and 2061 because the effects of warming increase heterotrophic respiration less than they increase carbon inputs via production. However, after 2061, the rate of SOC sequestration will be weakened and, as a result, the rich fen will likely become a carbon source to the atmosphere between 2062 and 2099. During this period, the effects of projected warming increase respiration so that it is greater than carbon inputs via production. Although changes in precipitation alone had relatively little effect on the dynamics of SOC, changes in precipitation did interact with warming to influence SOC dynamics for some climate scenarios.

Alaska↗

USGS2012

Spatiotemporal analysis of black spruce forest soils and implications for the fate of C

Post-fire storage of carbon (C) in organic-soil horizons was measured in one Canadian and three Alaskan chronosequences in black spruce forests, together spanning stand ages of nearly 200 yrs. We used a simple mass balance model to derive estimates of inputs, losses, and accumulation rates of C on timescales of years to centuries. The model performed well for the surface and total organic soil layers and presented questions for resolving the dynamics of deeper organic soils. C accumulation in all study areas is on the order of 20–40 gC/m 2 / yr for stand ages up to ∼200 yrs. Much larger fluxes, both positive and negative, are detected using incremental changes in soil C stocks and by other studies using eddy covariance methods for CO 2 . This difference suggests that over the course of stand replacement, about 80% of all net primary production (NPP) is returned to the atmosphere within a fire cycle, while about 20% of NPP enters the organic soil layers and becomes available for stabilization or loss via decomposition, leaching, or combustion. Shifts toward more frequent and more severe burning and degradation of deep organic horizons would likely result in an acceleration of the carbon cycle, with greater CO 2 emissions from these systems overall.

Journal of Geophysical Research↗

USGS2011

Water and heat transport in boreal soils: Implications for soil response to climate change

Soil water content strongly affects permafrost dynamics by changing the soil thermal properties. However, the movement of liquid water, which plays an important role in the heat transport of temperate soils, has been under-represented in boreal studies. Two different heat transport models with and without convective heat transport were compared to measurements of soil temperatures in four boreal sites with different stand ages and drainage classes. Overall, soil temperatures during the growing season tended to be over-estimated by 2–4 °C when movement of liquid water and water vapor was not represented in the model. The role of heat transport in water has broad implications for site responses to warming and suggests reduced vulnerability of permafrost to thaw at drier sites. This result is consistent with field observations of faster thaw in response to warming in wet sites compared to drier sites over the past 30 years in Canadian boreal forests. These results highlight that representation of water flow in heat transport models is important to simulate future soil thermal or permafrost dynamics under a changing climate.

Science of the Total Environment↗

USGS2010

Modeling the production, decomposition, and transport of dissolved organic carbon in boreal soils

The movement of dissolved organic carbon (DOC) through boreal ecosystems has drawn increased attention because of its potential impact on the feedback of OC stocks to global environmental change in this region. Few models of boreal DOC exist. Here we present a one-dimensional model with simultaneous production, decomposition, sorption/desorption, and transport of DOC to describe the behavior of DOC in the OC layers above the mineral soils. The field-observed concentration profiles of DOC in two moderately well-drained black spruce forest sites (one with permafrost and one without permafrost), coupled with hourly measured soil temperature and moisture, were used to inversely estimate the unknown parameters associated with the sorption/desorption kinetics using a global optimization strategy. The model, along with the estimated parameters, reasonably reproduces the concentration profiles of DOC and highlights some important potential controls over DOC production and cycling in boreal settings. The values of estimated parameters suggest that humic OC has a larger potential production capacity for DOC than fine OC, and most of the DOC produced from fine OC was associated with instantaneous sorption/desorption whereas most of the DOC produced from humic OC was associated with time-dependent sorption/desorption. The simulated DOC efflux at the bottom of soil OC layers was highly dependent on the component and structure of the OC layers. The DOC efflux was controlled by advection at the site with no humic OC and moist conditions and controlled by diffusion at the site with the presence of humic OC and dry conditions.

Soil Science↗

USGS2008

Boreal soil carbon dynamics under a changing climate: A model inversion approach

Several fundamental but important factors controlling the feedback of boreal organic carbon (OC) to climate change were examined using a mechanistic model of soil OC dynamics, including the combined effects of temperature and moisture on the decomposition of OC and the factors controlling carbon quality and decomposition with depth. To estimate decomposition rates and evaluate their variations with depth, the model was inverted using a global optimization algorithm. Three sites with different drainage conditions that represent a broad diversity of boreal black spruce ecosystems were modeled. The comparison among the models with different depth patterns of decomposition rates (i.e., constant, linear, and exponential decrease) revealed that the model with constant inherent decomposition rates through the soil profile was able to fit the observed data in the most efficient way. There were also lower turnover times in the wettest site compared to the drier site even after accounting for moisture and temperature differences. Taken together, these results indicate that decomposition (especially for the wetter site) was not accurately represented with standard moisture and temperature controls and that other important protection mechanisms (e.g., limitation of O 2 , redox conditions, and permafrost) rather than low inherent decomposition rates are responsible for the recalcitrance of deep OC. The simulation results also showed that most of the soil CO 2 efflux is generated from subsurface layers of OC because of the large OC stocks and optimal moisture conditions, suggesting that these deeper soil OC stocks are likely to be critically important to the future carbon dynamics.

Journal of Geophysical Research Biogeosciences↗