Dynamic coupling of soil structure and gas fluxes measured with distributed sensor systems: implications for carbon modeling

The goal of the proposed research is to develop two in-situ sensor systems that measure in-ground gas concentrations and strain/moisture/temperature/suction at different scales in order to provide data on the dynamics of gas flux and soil structure. One is based on distributed fiber optic sensor (DFOS) system that can provide measurements at meters to kilometers-scale, whereas the other is based on low-power sensor coupled with in-ground mesh-network wireless sensor network (WSN) system that provides data at selected local points in distributed manner. Both technologies are currently being prototyped at UC Berkeley (UCB).

The developed sensor systems will be trialed first in the unique wind tunnel-soil experimental facility available at the Colorado School of Mines (CSM). We propose an experimental plan designed to manipulate soil moisture fluctuations by balancing subsurface water introduction through precipitation events and losses to evaporation and evapotranspiration as controlled by atmospheric perturbations (temperature, wind speed, and relative humidity) so as to make more informed biogeochemical predictions and soil structure changes under changing climate conditions. Under the controlled environment, we will quantify the precision errors of the developed sensor systems. The developed systems will also be implemented in the fields of Rothamsted Research (RR) to examine its feasibility in the actual field conditions. The ultimate goal is to improve the predictive understanding of how atmospheric carbon loading is affected by soil structure changes.

The proposed sensor development and experimental research will lead to a substantial improvement of soil carbon models such as the RothC model developed at RR]. Each compartment in the model decomposes by a first-order process with its own characteristic rate. The IOM compartment is resistant to decomposition. The model adjusts for soil texture and its changes by altering the partitioning between CO2 evolved and (BIO+HUM) formed during decomposition, rather than by using a rate modifying factor, such as that used for temperature. Moreover, total CO2 effluxes are largely controlled by root respiration, and microbial respiration of soil organic matter including rhizospheric organic carbon and all of these processes are highly sensitive to soil structure. In this proposed research, we therefore hypothesize that soil structure change is strongly linked to soil gas generation. We will develop and implement sensor systems that measure both, which in turn will allow us to quantify the link. These new models will in the future allow the effects of soil management on carbon dynamics to be predicted and hence give an understanding of the impact of different soil management strategies (e.g. tillage) on soil sustainability.

The research will complement ongoing field research at RR supported by the BBSRC in the National Capability scheme and in ISP funding streams; especially on the delivery of nutrients to plants. The processes to be studied in the project are expected to lead to improved formulations to include multi-scale, multi-physics under development at RR by: (1) more rationally representing the coupled surface-subsurface processes, (2) including vegetation hydrodynamics and carbon and nutrient allocation, and (3) incorporating soil and genome-enabled subsurface reactive transport models that have explicit and dynamic microbial representation.

The project will lead to the development of spatially-distributed sensing systems in the field that can (1) sense changes in soil stricture and (2) link these changes to fluxes of N2O, CH4, CO2 and O2 into and from soils.

The vision for this research and technology development is to improve the scientific understanding of how carbon loading from vegetated land occurs at field scale using innovative integrated distributed sensor technologies to monitor relevant subsurface soil parameters and variables. Our understanding of the effects of soil management on carbon cycling and the emission of major greenhouse gases is limited because we do not have the tools to make spatially distributed measurements at the field and landscape scale of gas concentration in soil. Furthermore, these gas concentration data need to be linked to soil structure and soil water content at various scales, since together these soil factors control the generation of greenhouse gases. Models of soil structure relating gas evolution to water content have been developed, but they cannot be applied to the field scale because of a lack of data. We will use changes in strain, measured by a distributed fiber optic system, to infer changes in soil structure, due to deformation caused by either traffic or the effects in soil drying and shrinkage. We expect that the measurements of the changes in soil strain enables us to infer changes in porosity and together with soil water content, provide inputs to models to allow greenhouse gas concentrations to be predicted and compared with measured data. This proposed sensing technology will lead to a step change in environmental monitoring, and substantially improve our understanding of how to manage land to reduce emissions of major greenhouse gases.

The focus is how the measurements of parameters that control the processes in coupled land and atmospheric systems lead to better insights to processes occurring at multiple scales varying from macroscopic to field scales, which in turn contributes to improving models of carbon loading to the atmosphere. This research converges to the development of innovative technologies for accurate measurements of critical soil-water parameters at low-cost at the field scale. As the fundamental issue that is addressed is related to carbon loading in the context of climate change, the impacts are very broad and significant. The developed technology will allow for the deployment of sensors in large geographical areas efficiently to gather data at unprecedented spatial scales and resolutions that are infeasible using point measurements alone. These types of data will be of use to other researchers involved in similar investigations of coupled porous media-free flow systems. The outreach strategy is focused on engaging with the wider community and the profession to raise awareness of the issues and provide tools to explore solutions. This project will educate and train graduate students and interns who will gain both experimental and modeling skills in coupled soil-plant-atmosphere systems, preparing them for a future in academia, research, or industry.

Dissemination efforts will be targeting different groups through a variety of approaches. The project website will provide a central location to access all the activities, tools, and news. A central section of the site will provide information on the project and outcomes, with updates on the ongoing activities. We will have an App that show the data from the sensor systems in the proposed experiments. The information gathered by the network of our sensor systems, once operational, will be accessible on the web in a similar manner. The users will be able to select specific stations and review the reading, historical records, and download the information. A simplified tool will be available on the website to explore future scenarios based on RothC. The app can be used as a valuable interface to access and manipulate data based on the needs of the planned learning activities. Allowing students to process and interpret actual data can be an enriching experience. Our diverse leadership team can also provide excellent role models for young people.