Quantifying the temporal dynamics of wood in large rivers: field trials of wood surveying, dating, tracking, and monitoring techniques

Abstract

Wood plays an important role in stream ecology and geomorphology. Previous studies of wood in rivers have quantifi ed spatial distributions but temporal dynamics remain poorly documented. The lack of such data is related to limitations of existing methods, especially when applied to large rivers. Five techniques are fi eld-tested to assess their utility for quantifying the temporal dynamics in rivers: repeated high-resolution aerial surveys, the measurement of wood physical characteristics as proxies for 14 C dating, passive and active radio frequency identifi cation (RFID) tags, radio transmitters, and video. The spatial distribution of wood is surveyed using aerial imagery with a resolution fi ner than 0·10 m. The estimation of temporal trends by repeated aerial-based surveys needs to consider vegetation growth and hiding. Wood residence times can be calculated using 14 C analysis, but the assessment of wood physical characteristics including decay status and wood density offers a cheaper, if less accurate, alternative. Wood resistance to penetration is tested but results are not signifi cant. Radio transmitters are reliable for multi-year (~5 year) surveys and can be detected at 800 m. Passive RFID tags are limited by a read range of 0·30 m but are reliable for longer term (>5 year) studies. Active RFID tags combine a moderate read range (10-300 m) and low cost with in-fl ood detection but require more testing. Video monitoring of wood passing on the surface of a river is successfully implemented. For a single fl ood on the Ain River (France), wood transport rates are an order of magnitude higher on the rising limb of the hydrograph than on the falling limb. Overall, the techniques improve the ability to gather the data needed to understand wood transfer processes and calibrate budgets of wood in rivers.

The mass distribution of coarse particulate organic matter exported from an Alpine headwater stream

“…However, if the scaling exponent of the mass distribution is known, and if for a given event a certain size fraction has been sampled representatively, the complete CPOM export can be calculated. Our study results suggest that CPOM export for all size fractions can be estimated from the volumes of LWD exported in a large event, for example by measuring piece sizes trapped in a reservoir or by video monitoring the passage of wood pieces (e.g., MacVicar and Piégay, 2012;MacVicar et al, 2009;Moulin and Pié-gay, 2004;Seo et al, 2008;West et al, 2011). In addition to scaling down from LWD deposits with the aim to estimate total CPOM export, the scaling relations also permit scaling up from measurements of small CPOM to estimate LWD transport.…”

Tracking log displacement during floods in the Tagliamento River using RFID and GPS tracker devices

“…Displacement length and velocity data have been analysed using active radio frequency identification (RFID) tags and GPS devices fixed to logs lying on low, active bars. Both devices operated reasonably well, allowing a recovery rate comparable with the study of MacVicar et al (2009). Fixed antennas, especially if multiple, could provide even better insights on log dynamics, as GPS equipped with a GSM transmitting system could as well, being able to send to a receiver the GPS position of a transported log overtime.…”

“…3). The RFID tag is powered by a small battery and emits a signal at 443 MHz every two seconds (MacVicar et al, 2009). The signal can be read by a mobile receiver connected to an antenna, whose detection range is about 200 m. The RFID tags were implanted in holes scoured on the trunks of 113 logs and fixed using silicone caulk.…”

“…The signal can be read by a mobile receiver connected to an antenna, whose detection range is about 200 m. The RFID tags were implanted in holes scoured on the trunks of 113 logs and fixed using silicone caulk. Similar devices have been previously used in other environments for tracking logs in river systems (MacVicar et al, 2009;Schenk et al, 2013). During several field surveys (July, August, and December 2010, and then in March, April, May, July, August, and October 2011), the whole study site and ~18 km of the downstream area were explored with the RFID mobile antenna searching for tagged logs.…”

The role of log jams and exceptional flood events in mobilizing coarse particulate organic matter in a steep headwater stream

“…2) were tagged with radio frequency identification (RFID) transponders, a technique that has successfully been employed to monitor bedload (Lamarre et al, 2005;Schneider et al, 2010Schneider et al, , 2014 and woody debris (MacVicar et al, 2009;Schenk et al, 2013;Ravazzolo et al, 2015). The RFID glass transponders we used were 3.12 cm long, 0.38 cm in diameter, emitting at 134.2 kHz frequency, and were glued into holes drilled into the tracer logs.…”