HOW DOES BURNING AFFECT SOIL STRUCTURE AND VADOSE HYDROLOGY OF TALLGRASS PRAIRIE?

The vadose zone provides the interface between the atmospheric and lithospheric components of the critical zone and so exerts a critical influence on the overall hydrology of an ecosystem. Vegetation burning, either as a natural or an anthropomorphic process, alters soil carbon quantity and fractions, which has implications for soil structural characteristics. Burning may therefore have short- (<1 year) or long-term (multi-year) effects on vadose hydrology by altering soil moisture dynamics both at the surface (e.g. via altered evapotranspiration) and within the soil profile (e.g. via altered hydraulic parameters). The Long Term Ecological Research program at the Konza Prairie Biological Station (north-eastern Kansas) operates watershed-scale burn frequency treatments, ranging from annual to twenty-year burn intervals. The present study will examine changes in soil moisture, temperature and pore gas/water chemistry during and subsequent to the burning of tallgrass prairie vegetation in Fall 2016 and Spring 2017 using vadose zone monitoring arrays. In addition, soil pits will be excavated to c. 1 m depth in an unburned watershed (control) and watersheds subject to annual, biennial, four or twenty year burn intervals. In each pit the soil water characteristic curve, bulk and particle density, aggregate stability, hydraulic conductivity, total/labile/microbially-available and mineralizable carbon of each horizon will be determined. Statistical analysis will be conducted to determine whether there are correlations between burn frequency and changes in these soil parameters. Numerical modelling (using Hydrus software) will be conducted to ascertain resulting changes in water movement and availability within the vadose zone, and to work towards a comprehensive understanding of prairie hydrology under various burn frequencies. This project is contributing to a conceptual framework for the Konza Prairie Biological Station as a possible new critical zone observatory.