<p dir="ltr">Per- and polyfluoroalkyl substances (PFAS) are a group of synthetic chemicals known for their persistence in the environment and potential health risks. PFAS are linked to several adverse effects in human and wildlife health. The detection of PFAS in biosolids has raised concerns about their use in agricultural and land application practices. This is because some PFAS are known to enter the food system through plant uptake and some leach into groundwater. The purpose of this study was to examine the PFAS profile in soils and porewater with depth at an agricultural site with historical biosolids applications. The site selected has received biosolids at agronomic rates for corn for approximately four decades. This study utilized a total of six lysimeters, three “shallow” at 60 cm and three “deep” at 120 cm, to monitor PFAS leaching in soil. Porewater samples were collected within 1-3 days after rain events based on rainfall amount and response of the moisture sensor installed at the site. For each of five porewater sampling events, PFAS and supplemental water parameters like total organic carbon (TOC) and pH were measured. Soil cores, taken in one-foot increments before and after the 3-month study, were analyzed for PFAS, soil OC, moisture, and grain size. All samples were analyzed using high resolution mass spectrometry for 54 PFAS and in line with EPA 1633 method. Soil characteristics such as texture, moisture, and soil OC significantly influence PFAS transport and sorption capacity within the soil profile, impacting PFAS distribution across soil depths. PFAS in the soil profile decreased with increasing depth and directly correlated with soil OC. Long chain PFAS were strongly retained in the top 60 cm and minimally distributed to the porewater. Short-chain PFAS proportionally dominated porewater samples, with elevated concentrations observed in shallow porewater driven by increased saturation (perched water) from a low permeability clay layer. Unsaturated conditions enhance PFAS retardation through air-water interface partitioning in addition to soil particle sorption mechanisms. In this study, less than 0.1% of PFAS leach from the vadose zone of a biosolid impacted plot annually, underscoring the longevity of PFAS in the soil profile and importance of understanding PFAS transport dynamics for effective environmental management.</p>

<p dir="ltr">Globally, soils hold more carbon than both the atmosphere and aboveground terrestrial biosphere combined. Changes in land use and land cover have the potential to alter soil carbon cycling throughout the soil profile, from the surface to meters deep, yet most studies focus only on the near surface impact (< 25 cm deep). This research bias toward shallow soil carbon cycling has ramifications for understanding the full impacts of agricultural and restoration management practices on soil organic and inorganic carbon dynamics. The primary objective of my thesis research is to evaluate the factors controlling the impact of deep-rooting perennial grass on soil carbon cycling during prairie restoration of soil following long term, row crop agriculture. Paired soil pits were established to compare the effects of restoration on soil C dynamics in a corn-soy cropping system (minimal tillage) and restored prairie sites in Nebraska and Illinois. At each site, soil organic carbon (SOC) and inorganic carbon (SIC) content, stock, and stable carbon isotope analysis were preformed to ~2 m depth to assess long term integrated C dynamics. Estimating the contribution of prairie carbon inputs to the SOC in the soil profile was examined using stable carbon isotopic signatures in the SOC in relation to the above ground vegetation changes in C₃ and C₄ photosynthetic pathway plant community composition. Comparative analysis of edaphic properties and soil carbon suggests that deep loess deposits in Nebraska permit enhanced water infiltration and SOC deposition to depths of ~100 cm in 60 years of prairie restoration. In Illinois, poorly drained, clay/lime rich soils on glacial till and a younger restored prairie age (15 years) restricted the influence of prairie restoration to the upper 30 cm. Comparing the δ¹³C values of SOC and SIC in each system demonstrated that SIC at each site is likely of lithogenic origin. This work indicates that the magnitude of influence of restoration management is dependent on edaphic properties inherited from geological and geomorphological controls. Future work should quantify root structures and redox properties to better understand the influence of rooting depth on soil carbon concentrations. Fast-cycling C dynamics can be assessed using continuous, in-situ CO₂ and O₂ soil gas concentration changes. The secondary objective of my thesis was to determine if manual, low temporal resolution gas sampling and analysis are a low cost and effective means of measuring soil O₂ and CO₂, by comparing it with data from in-situ continuous (hourly) sensors. Manual analysis of soil CO₂ and O₂ from field replicates of buried gas collection cups resulted in measurement differences from the continuous sensors. Measuring CO2 concentration with manual methods often resulted in higher concentrations than hourly, continuous measurements across all sites. Additionally, O₂ concentrations measured by manual methods were higher than hourly values in the restored prairie and less in agricultural sites. A variety of spatial variability, pressure perturbations, calibration offsets, and system leakage influences on both analysis methods could cause the discrepancy.</p>