The Effect of Heterogeneities in Soil Physical and Chemical Properties on Redox Biogeochemistry in Subsurface Soils

Redox biogeochemistry is considered as a key factor to understand the structure and function of ecosystems. Although these factors are highly variable, there are limited studies which try to link redox distribution with soil physical and chemical properties at the watershed scale. Moreover, investigation of redox dynamics has been typically done in surface soils (top 0-30 cm) since this layer considered as the most biologically active portion of the soil. However, studying deeper soils should also be taken into account because (1) they encompass considerable pools of carbon, nitrogen, and other important elements, (2) they can be hot spots of biogeochemical processes as they might be a place where subsurface hydrologic flowpaths converge, and (3) deeper soils are unsaturated in organic carbon and have a great potential to sequestrate additional carbon. To our knowledge, however, no study has explicitly assessed the spatial pattern of carbon, nitrogen and redox pools in deeper portions of the soil profile at the watershed scale. Therefore, our objectives are (1) to evaluate the effect of different land use and land covers of Brazos River Basin on the concentrations of electron acceptors (O₂, NO₃, and SO₄) and reduced products (Mn(II), Fe(II)) in the surface and deep soil as well as carbon and nitrogen pools, (2) to investigate the effects of soil physical and hydraulic properties on the redox biogeochemistry, and (3) to assess the importance of deeper soil horizons to landscape-scale estimates of carbon and nitrogen pools and see if any of soil horizons represented biogeochemical hot spots in the landscape. Our preliminary data shows that biogeochemical processes would be more profound in the areas with higher temperature and precipitation as these factors stimulate microbial activity and thus influence redox biogeochemistry. Also concentrations of C and N are greater in woodlands relative to remnant grasslands as a consequence of the greater above- and below-ground productivity of woodlands relative to remnant grasslands. Additionally, results showed that, redox biogeochemistry has been profound in soil layers with different soil physical and chemical characteristics. Spatio-temporal data with initial evaluation of biogeochemical factors/processes for different land covers will be presented.