Paper No. 20-9
Presentation Time: 4:30 PM
HISTORIC LAND USE IMPACTS ON HILLSLOPE SOILS IN SOUTHERN NEW ENGLAND
Intensive land use fundamentally affects the physical structure and nutrient cycling of soils, and can lead to increased erosion. The northeast US provides the opportunity to study anthropogenic-induced changes to soils, with a rich and well documented ~300-year history of land modification. We use stone walls present in LiDAR to determine the extent of land used for 17th-20th agriculture activities, and aerial images from 1934 onwards to constrain land abandonment and reforestation to present day. At two sites in Mansfield, CT, we identify three primary land use classes characterized by different durations of historic agricultural impacts and use these classes to quantify changes to soil properties. The first class has clearly delineated fields outlined by stone walls and is abandoned in the mid-20th century, based on 1934-1950 aerial imagery (150-250 years of agricultural impacts). The second class is forested in 1934 imagery, but still has clearly delineated fields outlined by stone walls (75-150 years of agricultural impacts). The third class exhibits minimal evidence of historic activity with few or no primitive walls (0-25 years of agricultural impacts). Field work consisted of describing 5–10 soils pits for each of the classes at both sites. The two study sites have similar parent material and land use histories, but differ in terms of average hillslope gradients, with one site characterized by <7° hillslopes and the other by hillslopes up to 15-20°. Downslope transects were used in a catena style approach at the higher gradient site, and pits were dug at locations where stone walls may trap sediment by perpendicularly bisecting the hillslope. Two or more pits per class were sampled and analyzed for organic content and trace metals. Results show clear relationships between the thickness of the A horizon and mixing of trace metal profiles with the duration of land use. Sediment mobilization appears greater on the high slope, longest use class, and walls may play a role in sediment routing or storage. Detailed stone wall maps exist for large swaths of topography in the region, and future work aims to use these data to scale up the extent of the soil impacts. Furthermore, studies like this can lead to a better understanding of the generation and storage of legacy sediment in sites downslope of anthropogenically modified soils.