The pulse of driftwood export from a very large forested river basin over multiple time scales, Slave River, Canada

Abstract

This study presents a case study of large wood transport on the great Slave River in northern Canada with the objective to better understand the processes of and variability in pulsed wood fluxes from large forested catchments. We use a varied approach, integrating field characterization of wood, historical anecdotes, repeat aerial imagery of stored wood, and time‐lapse imagery of moving wood, for a robust analysis and synthesis of processes behind pulsed wood flux, from yearly uncongested export to rare congested wood floods. Repeat monitoring of known sites of temporary storage with new or historic imagery proved to be a very useful tool for constraining wood flux histories. Pulsed wood export on the Slave River is not an artifact of episodic recruitment from major up‐basin disturbances, but rather reflects decadal‐ to half‐century‐scale discharge patterns that redistribute wood recruited from channel migration and bank slumping. We suggest that the multiyear flow history is of paramount importance for estimating wood flux magnitude, followed in declining importance by the yearly sequence of peaks and the magnitude and characteristics of the rising limb of individual floods.

River logjams cause frequent large-scale forest die-off events in southwestern Amazonia

“…However, dynamics similar to the ones described here for the Bolivian Amazon have also been reported for rivers in temperate latitudes (Kramer et al, 2017;Triska, 1984;Wohl, 2014), suggesting that what we currently see in Bolivia could have been more common in temperate regions prior to the anthropic modification of river catchments (Wohl, 2014). The almost pristine environmental conditions of the Bolivian Amazon and the recent change in land use here offer an excellent natural laboratory to study the dynamics of wood in lowland tropical rivers, the process of forest disturbance and community successions, and how changes in LW recruitment affect both river dynamics and tree communities.…”

Reply to Wohl

“…Most of the studies on logjams have been carried out for rivers in temperate regions, where fluvial dynamics have been impacted by human activity throughout history and logjam dynamics differ from tropical regions (Wohl, 2013). However, dynamics similar to the ones described here for the Bolivian Amazon have also been reported for rivers in temperate latitudes (Kramer et al, 2017;Triska, 1984;Wohl, 2014), suggesting that what we currently see in Bolivia could have been more common in temperate regions prior to the anthropic modification of river catchments (Wohl, 2014). The almost pristine environmental conditions of the Bolivian Amazon and the recent change in land use here offer an excellent natural laboratory to study the dynamics of wood in lowland tropical rivers, the process of forest disturbance and community successions, and how changes in LW recruitment affect both river dynamics and tree communities.…”

Porosity problems: Comparing and reviewing methods for estimating porosity and volume of wood jams in the field

“…Wood dynamics on the Slave River reflect the aggregate of up‐basin recruitment of wood by bank failures, riparian ice gouging, and lateral migration into riparian forests along meander bends in the boreal plains. The jam was deposited at the head of a mid‐river, bedrock island during a driftwood flood in 2011 (see Kramer et al, 2017; Figure 3C).…”

“…Methods to efficiently estimate total wood volume within jams are therefore needed to generate accurate and consistent measurements of wood volume across multiple jams. As high resolution imagery is increasingly used for wood research (Atha, 2013; Kramer et al, 2017; Steeb et al, 2017; Wohl et al, 2018), validating remotely‐estimated wood volumes with accurate field measurements will allow for leveraging remote datasets and extrapolating across larger areas. These datasets can also be used to validate numerical models of wood transport and deposition (e.g.…”