Footpaths: Pedogenic and geomorphological long-term effects of human trampling

Abstract

Footpaths are of the oldest and most widely distributed forms of human imprint on the landscape. These elongated features are the result of continuous usage of a certain route for walking, at time scales ranging from days to centuries or millennia. In this qualitative investigation, we take a holistic approach combining micromorphology (including voids analysis), chemical soil parameters (such as selective iron oxide dissolution), and remote sensing (spatial distribution and orientation of footpaths in the landscape) to evaluate the long-term residues and environmental effects resulting from the formation of footpaths. Our diverse case studies incorporate footpaths used for recreational and transport purposes in temperate and sub-humid climates from both recent and historical perspectives. A reduction of the large pores was observed down to 3 cm below current and historical surfaces compared to control areas without footpaths. The lower porosity subsequently hinders of the supply of oxygen and/or water into the sub-surface and encourages water stagnation on the compacted footpath surface. These processes result in higher amounts of pedogenic Fe oxides and, at times, macro-organic residues under footpaths and hindering of soil formation. As an additional result of compaction, surface runoff is promoted. The latter may either trigger the initiation of gullies directly downslope from footpaths or lead to incision of the footpaths themselves. Incised footpaths are more likely to occur when the footpath is oriented parallel to the stream network. Once an incised footpath is formed, it may reduce gully erosion susceptibility downslope as the incised footpath acts as a channel that decreases a footpath’s ‘overbank’ flow. With a better understanding of footpaths as landscape units we can (1) pose archaeological questions related to human environmental interaction, (2) assess carbon storage potential under footpaths and (3) use incised footpaths as possible measures against gully erosion.