Frequency-dependent magnetic susceptibility as a proxy for monitoring ETM zones in a Volcanic River Estuary

• Published in: Journal of applied geophysics Vol. 242; p. 105896
• Main Authors: Hamdan, Abd Mujahid, Lubis, Syafrina Sari, Rifai, Hamdi
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.11.2025
• Subjects: Coastal; Estuary; ETM zone; Magnetic propertiy; Misroplastic; Volcanic; Coastal; Volcanic; ETM zone; Misroplastic; Estuary; Magnetic propertiy
• ISSN: 0926-9851
• DOI: 10.1016/j.jappgeo.2025.105896

Estuarine Turbidity Maximum (ETM) zones serve as critical convergence areas for suspended particles and pollutants, yet their detection in tropical volcanic estuaries remains poorly developed. This study introduces a novel application of frequency-dependent magnetic susceptibility (χFD) of surface sediments as a high-resolution geophysical proxy for tracking ETM dynamics and microplastic (MP) convergence. Unlike prior works focusing on suspended sediments or static sampling, this research implements a spatiotemporally resolved approach by incorporating both spatial (ΔχFD) and temporal (DχFD) gradients. Field measurements were conducted at 11 spatial stations over five consecutive days, capturing two tidal phases per day in the Krueng Aceh River estuary, Indonesia. χFD was analyzed alongside total suspended solids (TSS) and MP abundance, revealing a strong spatial correlation between ΔχFD and MP (r = 0.58), and a weaker correlation with ΔTSS (r = 0.27), emphasizing χFD's superior sensitivity in detecting microplastic retention. Magnetic characterization via hysteresis loops, supported by scanning electron microscopy coupled with energy-dispersive x-ray spectroscopy (SEM-EDS), transmission electron microscopy (TEM), and X-ray diffraction (XRD), confirmed the dominance of pseudo-single domain magnetic particles in surface sediments. These findings demonstrate the potential of χFD gradients as non-invasive, cost-effective indicators for identifying ETM zones and pollutant hotspots, laying the groundwork for advanced, real-time magnetic sensor technologies in estuarine and coastal monitoring. [Display omitted] •Frequency-dependent magnetic susceptibility (χFD) is applied to identify ETM zones in volcanic estuaries.•χFD correlates strongly with suspended solids and microplastic abundance.•Magnetic minerals from lithogenic sources dominate ETM sediment composition.•χFD serves as a geophysical proxy for spatial sediment dynamics.•Proposed approach supports non-invasive, rapid environmental monitoring.