LINKING SOIL STRUCTURE AND GAS FLUXES TO CHANGING LAND COVER CONDITIONS

Historically, assessments of soil structure have been done through qualitative descriptions, yet emerging evidence indicates quantitative metrics are needed as soil structure responds to climate and land cover changes over time. This project aims to quantify soil structure and relate the quantifiable metrics to soil mass and energy transport and their response to land cover changes. This produces objective data regarding the movement of gases such as carbon dioxide, oxygen, and nitrogen between the soil and the atmosphere. This research compares structural information from Multistripe Laser Triangulation - a scanner that provides metrics to soil pore morphology - to pore information from water retention measurements (from soil cores) to determine if changes in land use create systematic changes in soil structure.

Fieldwork was conducted at the Konza Prairie Biological Research Station, Manhattan, KS, a semi-arid grassland experiencing woody encroachment due to fire suppression. Six soil pits were dug along three hillslope positions (summit, backslope, and toeslope) under woody and grassy vegetation covers. Bulk soil samples were taken from the pits at each horizon for soil aggregate and chemical analyses. We analyzed for pH, electrical conductivity, total nitrogen and carbon, and organic matter. Undisturbed soil samples were also taken at each horizon to conduct water retention analysis. Sensors were installed into pit faces to measure soil moisture, temperature, matric potential, and gas fluxes of carbon dioxide and oxygen. It is expected for grasslands to have greater gas fluxes and aggregate size distributions.

Preliminary results show an increased abundance of smaller soil aggregates in woody areas compared to grasslands. The mean size of soil aggregates generally decreased with soil depth and was higher in grasslands. Chemical analysis of bulk soil samples shows total carbon, active (readily permanganate-oxidizable) carbon, and nitrogen decrease with depth at the toe slopes of both areas, with higher total carbon in grassland areas. Sensor data show higher levels of dissolved carbon dioxide under grassy toeslope positions compared to woody encroached toe slopes. Elevated carbon dioxide was found in the backslope and summit of the woodland site.

Current data supports that gas fluxes and soil pore structure are different in the two land covers due to differences in root architecture and distribution between the two regions.