A seismic monitoring approach to detect and quantify river sediment mobilization by steelhead redd‐building activity

Michael Dietze,James Losee,Daniel Palm,Lina Polvi

doi:10.1002/esp.4933

Abstract

AbstractThe role of spawning salmonids in altering river bed morphology and sediment transport is significant, yet poorly understood. This is due, in large part, to limitations in monitoring the redd‐building process in a continuous and spatially extended way. A complementary approach may be provided through the use of a small seismic sensor network analysing the ground motion signals generated by the agitation of sediment during the redd‐building process. We successfully tested the viability of this approach by detecting and locating artificially generated redd signals in a reach of the Mashel River, Washington State, USA. We then utilize records of 17 seismic stations, in which we automatically detected seismic events that were subsequently manually checked, yielding a catalogue of 45 potential redd‐building events. Such redd‐building events typically lasted between 1 and 20 min and consisted of a series of clusters of 50–100 short energetic pulses in the 20–60 Hz frequency range. The majority (>90%) of these redd‐building events occurred within 11 days, predominantly during the early morning and late afternoon. The seismically derived locations of the signals were in agreement with independently mapped redds. Improved network geometry and installation conditions are required for more efficient detection, robust location and improved energetic insights into redd‐building processes in larger reaches. The passive and continuous nature of the seismic approach in detecting redds and describing fish behaviour provides a novel tool for fish biologists and fisheries managers, but also for fluvial geomorphologists, interested in quantifying the amount of sediment mobilized by this ecosystem engineer. When complemented with classic approaches, it could allow for a more holistic picture of the kinetics and temporal patterns (at scales from seconds to multiple seasons) of a key phase of salmonid life cycles. © 2020 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd

Highlights

In the form of ecosystem engineers or bioturbators, biota can have significant effects on physical earth surface processes (Viles, 1988)
We demonstrate the potential of a seismic approach for identifying the spatial and temporal patterns of redd-building activity using two independent approaches: comparing seismic data collected during construction of man-made artificial redds and during construction of redds by native, wild salmonids
The artificially induced signals showed major spectral overlap with the frequency window of the river-induced seismic signature (Gimbert et al 2014; Dietze et al, 2019a, 2019b) and only type 1 and 2 agitation yielded a seismic signal sufficiently different from background noise (Figure 3a). This complements our work demonstrating the ability of our seismic approach to detect four redds created by steelhead in the natural setting

Summary

Introduction

In the form of ecosystem engineers or bioturbators, biota can have significant effects on physical earth surface processes (Viles, 1988). Ecosystem engineers and bioturbators serve both to trap sediment and reduce erosion, such as beaver and riparian plants stabilizing stream banks, and to increase erosion and sediment transport, such as grazing animals and crayfish (Polvi and Sarneel, 2018). While many of these examples are detectable and can be surveyed continuously, some biotically driven causes of sedimentation or erosion are much harder to constrain using traditional methods, and only their resulting effects can be surveyed. Gallagher and Gallagher (2005) documented redds for the anadromous form of Oncorhynchus mykiss known as steelhead, averaging 0.72 m in length

Results

Discussion

Conclusion