Soil property changes after four decades of wastewater irrigation: A landscape perspective
For over 40 years, The Pennsylvania State University (PSU) has irrigated its wastewater onto both cropped and forested lands. Despite local weather conditions, approximately 50 mm/week of wastewater have been spray-irrigated onto the land since 1962. This irrigation, combined with the natural precipitation, amounts to approximately 3550 mm of water per year. The objective of this study was to investigate the morphological and functional changes in soils of this area as a result of this significantly-increased water load. The research area has a karst geology and is dominated by rolling hills with many small depressions that act as sinks for water and sediments. Together with six soil trenches, 47 soil cores were taken across a 6.5-ha field. Previous studies conducted at this site provided a reference for interpreting the changes in soil properties over time. Soil morphological properties, including structure, horizonation, and redoximorphic features, were evaluated from the soil cores and in situ soil pits. In addition, soil functional parameters, including saturated hydraulic conductivity (Ksat), bulk density, organic matter content, and soil pH, were evaluated to determine the soil functional changes. Results indicate that the soils have experienced periods of local saturation and soil transport, which are reflected by the distribution of redoximorphic features and A-horizon thickness across the study area. Sample locations were grouped into three landscape positions (summit, midslope, and depression) that exhibited similar soil properties. The depth of the A-horizon was significantly greater in the depressions, while the midslope position had the highest manganese oxide coating percentage, and the summit position had the highest bulk density. This reflects the likely hydrologic path from the summit to the depression. The depression areas had the highest mean surface Ksat (10.2 cm/h), while the summit areas had the lowest mean surface Ksat (1.2 cm/h). Both organic matter content and soil pH have increased considerably since 1971. Overall, although soil properties have changed through the decades of irrigation, the wastewater spray irrigation system remains functional in this area and the soils are still performing reasonably well; however, some concerns about reduced soil functionality need to be addressed from a landscape perspective in order to sustain this system.