Magnetic Fingerprinting of Fluvial Suspended Particles in the Context of Soil Erosion: Example of the Canche River Watershed (Northern France)

Abstract

In Northern France, land use is dominated by agriculture. Erosion by runoff results in heavy loss of fertile soil into surface waters. There is a need for cost-effective tools to trace the sediment flux in catchments. This study highlights the potential of environmental magnetism to provide rapid non-destructive parameters to characterize the spatiotemporal runoff versus bedload signal in a watershed. Between 2015 and 2017, within the Canche River watershed, several spatiotemporal sampling campaigns of suspended particulate matter (SPM) were undertaken and two distinct "snapshot campaigns" of flood events were conducted at key locations acquiring, in addition, hydrodynamical observations (discharge, turbidity, sediment load, etc.). Agricultural soils and SPM within the watershed have similar values for bulk magnetic concentration (isothermal remanent magnetization, IRM). The magnetic mineral assemblage of the SPM is dominated by soft ferromagnetic (sensu lato) minerals during low water conditions and is enriched in high-coercivity phases during high water stages associated with rainfall events. Low-temperature remanence experiments identified goethite and hematite as the high-coercivity phases. IRM acquisition component analysis of the room temperature results quantify the relative input of high-versus low-coercivity components focused on a given confluence site. Results from snapshot campaigns highlight the link between the enhanced runoff input of high-coercivity particles during flood events and show that the S ratio parameter is an effective tool to trace erosion of topsoils.

Control of Source‐To‐Sink Processes on the Dispersal, Fractionation, and Deposition of Magnetic Minerals in a Tropical Mesotidal Estuarine System

“…(2017) and Franke et al. (2020), the dependence of grain size between bulk sediment and magnetic fraction and concentration of magnetic particles are the crucial factors which need to be considered while deconvolving magnetic variability caused by sediments originating from catchment (different lithology, topography), eroded soils from riverbanks, and the prevailing hydrodynamics regime.…”

“…Magnetic methods have been successfully utilized for tracing the soil erosion in the fluvial systems. For example, Franke et al (2020) established a linkage between the enhanced runoff input of high-coercivity particles in suspended sediment load and flood events in the Canche River watershed (Northern France). A mineral magnetic study on catchment soils successfully identified the highly eroding sites in the Shibanqiao Catchment, Guizhou Plateau, southwest China (Wang et al, 2011).…”

“…The present study also highlights that S-ratio values of a sample from a particular site are sensitive to the concentration of high coercivity magnetic fraction derived from various sources (catchment, riverbank erosion) and local hydrodynamic regime. As previously highlighted by Kayvantash et al (2017) and Franke et al (2020), the dependence of grain size between bulk sediment and magnetic fraction and concentration of magnetic particles are the crucial factors which need to be considered while deconvolving magnetic variability caused by sediments originating from catchment (different lithology, topography), eroded soils from riverbanks, and the prevailing hydrodynamics regime.…”

“…Easy detection of geological and hydrodynamic processes by magnetic methods makes magnetic minerals, an exemplary proxy to gain vital insights into the dynamics of magnetic particles in sedimentary systems (Hatfield, 2014; Kulgemeyer et al., 2017). Magnetic methods have been increasingly used to study the estuarine and coastal systems for example, to decipher the origin, and dynamics of heavy (magnetic) minerals (Gallaway et al., 2012; Hatfield et al., 2010; Kulgemeyer et al., 2017), identify the sediment accretion and erosion sites (Franke et al., 2020; Hatfield et al., 2010; Kayvantash et al., 2017; Wang et al., 2011), track changes in sediment provenance, transport pathways, and depositional system (Booth et al., 2005; Hatfield, 2014; Maher et al., 2009; Prizomwala et al., 2013), map the heavy (magnetic) mineral deposits (Badesab et al., 2012; Troch et al., 2021), reconstruct the pollution history (Blaha et al., 2011), characterize the sedimentary environment and littoral drift system (Chaparro et al., 2017; Hatfield & Maher, 2008, 2009; Kulgemeyer et al., 2016), and investigate the magnetic mineral diagenesis (Ahn et al., 2021; Zhang et al., 2001).…”