TRACKING THE RECRUITMENT, STORAGE, AND TRANSPORT OF LARGE WOOD IN A SMALL UPLAND WATERSHED, OHIO, USA

Large accumulations of wood in rivers—commonly referred to as Large Woody Debris—are a healthy and natural source of geomorphic and biogeochemical complexity, despite the seemingly negative connotation of “debris.” Indeed, our previous work on Raccoon Creek, a 264 km², low-gradient, agricultural, upland watershed, demonstrates a link between logjams and enhanced respiration in streambed ecosystems. A challenge remains: how best to generalize high-resolution, reach-scale biogeochemical observations to the entire watershed. To this end, here we quantify the dynamics of wood recruitment, storage, and transport from the headwaters of Raccoon Creek to its outlet, focusing on the 46 km main stem of the system. We use point cloud data from a 1 m-resolution airborne lidar survey to identify all trees in the riparian buffer that are both tall enough and close enough to the river to potentially become fluvial wood; this population has previously been defined as Potential Large Woody Debris or PLWD. We used 8 cm-resolution aerial photographs from 2022 and 2023 to map all in-channel large wood (LW) along the 46 kilometers of Raccoon Creek. We mapped the wetted width of the river at 100 m stations using the 2023 aerial imagery and quantified sinuosity and average channel gradient within 1 km-reach bins using a 1 m-resolution, lidar-derived digital elevation model. Our results indicate ~7,000 trees available for recruitment into Raccoon Creek with a maximum rate of 272 PLWD/km and a minimum rate of 14 PLWD/km. We mapped 1,133 instances of LW for 2023 and 1,153 instances of LW in 2022. If considered over 1 km reaches, 46% of Raccoon Creek showed a decrease in LW between 2022 and 2023, 41% gained LW, and 13% showed no change in LW accumulations. This suggests that from year to year LW is mobile in Raccoon Creek and/or new wood is recruited into the river. LW is either exported downstream to the Licking River system or removed by stakeholders within the Raccoon Creek watershed. There are no correlations between LW/km and PLWD/km, stream gradient, drainage area, or wetted width. There is a weak correlation between sinuosity and LW/km. This lack of any significant relationship between LW occurrences and potential external controls is somewhat surprising, and none of these metrics can be used to anticipate the presence or movement of LW in this system.