GULLY EROSION, TEMPERATURE VARIABILITY, AND FREEZE-THAW PROCESSES IN CLAY-RICH SOILS, NORTHEAST TENNESSEE, USA

This study examines gully erosion in northeast Tennessee hillslopes within the context of temperature variability. Gully erosion is a form of mass sediment loss and transport resulting in deep channels and high, steep banks of sediment. Temperature controlled freeze thaw events dislodge soil particles and may serve as a catalyst for erosion. The study area is located in the Southern Appalachian Valley and Ridge province, where a thick sequence of red clay Ultisols overlies dolomite and limestone bedrock. Erosion in the Valley and Ridge province presents ecological problems for wildlife and agriculture. Weekly measurements of gully erosion were collected from 8/24/2013 to 9/10/2014 at the East Tennessee State University Valleybrook Research Facility in northeast Tennessee. Gully erosion was measured using 78 erosion pins placed in four adjacent gully systems in three different morphological settings: channels, interfluves, and sidewalls. Gully channels behaved dynamically, with repetitive pulses of erosion or deposition. The sidewalls and interfluves behaved differently from channels, showing continuous erosion throughout the study period. Temperature data were captured at an onsite weather station and a relationship between gully erosion and temperature was identified. When daily temperatures ranged from below freezing to above freezing, there was increased erosion and deposition in the channels. When daily temperature did not plunge below freezing, more stable gully conditions persisted. During the most active erosion/deposition period (11/23/2013 to 3/8/2014), 73% of days experienced freeze-thaw conditions, with an average channel pin length weekly change of 26.0 mm of erosion and 20.5 mm of deposition. In contrast, throughout the full study period, only 29% of days experienced freeze-thaw conditions and average weekly erosion and deposition at channel pins was approximately halved (14.0 mm and 10.7 mm respectively). This research shows that temperature variability and freeze-thaw processes are important factors contributing to gully erosion in northeast Tennessee soils.