Application Of Environmental Magnetism To Cedar Beach, Western Lake Erie, Canada

The use of magnetic methods to examine sediment transport and motion processes on beaches has been studied on Cedar Beach (Western Lake Erie), in order to evaluate their applicability in understanding natural and anthropogenic coastal erosion and accretion. Magnetic studies of the heavy mineral-enriched, dark-reddish sands present on Cedar Beach (41.68°N, 82.40°W) showed that (low-Ti) magnetite (dominant PSD-MD and some SD-SP) is the dominant magnetic mineral and the hard magnetic mineral (HM) (i.e. maghemite, hematite or goethite) is the secondary in these sands. This study reveals spatial variations in the concentration, sand grain size (SGS), magnetic grain size (MGS) and heavy mineral assemblages, on the beach, and indicates a correlation between them. It also examines the influence of seasonal changes on the beach, and hightlights chemical (biochemical) effects on the beach sand, especially on the larger size ones in the areas close to water.Surficial magnetic susceptibility values defined three zones: a lakeward region close to the water's line (Zone 1), the upper swash zone (Zone 2) and the landward region beyond the upper swash zone (Zone 3). The slightly higher upland areas or sand dunes (UD) neighbour to Zone 3 and back the beach face. Three groups of cross-shore transects (West, Middle and East) were chosen to investigate the profile changes in the western, central and eastern sections of the beach.Across the shore, Zone 2 showed the highest bulk susceptibility (κ), mass percentage of smaller grain-size (<250μm) fractions (i.e. heavy mineral assemblage) in the bulk sand sample, mass-normalized susceptibility (χ), mass-normalized saturation isothermal remanent magnetization (SIRM_mass) and mass-normalized anhysteretic remanent magnetization (ARM_mass). All magnetic concentration values decrease both towards the lake (Zone 1) and towards the land (Zone 3) on the West and Middle, while these values are slowly increasing from Zone 1 to Zone 3 on the East. The variations of magnetic concentration parameters (i.e.κ,χ, SIRM_mass and ARM_mass) correlate with the distribution of the heavy mineral assemblage and the small SGS of the beach sand. From Zone 1 to Zone 2, the percentage of heavy minerals increased and SGS fined on three (West, Middle and East) sections. From Zone 2 to Zone 3, the percentage of heavy minerals decreased and SGS coarsened on the West and Middle, while the percentage of heavy minerals increased and SGS fined on the East. Contrary to the variability of SGS, MGS slightly increased from Zone 1 (PSD-small MD and more SD-SP) to Zone 3 (large PSD-MD and less SD-SP). Zone 1 had slightly more HM than Zone 2 and Zone 3 on the West and Middle, while Zone 1 and Zone 2 had more HM than Zone 3 on the East. UD showed similar features to their neighbouring Zone 3.Along the shore, the West showed the highest magnetic concentration (i.e. percentage of heavy minerals). From the West to East, magnetic concentration values decreased, and thus the percentage of heavy minerals decreased and SGS increased. MGS somewhat decreased from the West (large PSD-MD and less SD) to the East (PSD-small MD and more SD). The West showed less HM than the Middle and East transects.This spatial variation results from the preferential separation of large, less dense particles by waves and currents both along and across the beach. The prevailing strong west-southwest winds generated dominant east-northeastward directed waves. The eroded western section of Cedar Beach showed much higher concentrations of heavy minerals including magnetite, and finer sand grain sizes than the accreting eastern section, as the waves and longshore currents transported the eroded sand alongshore and deposited it in the east section. Lake-level changes induced by climate factors such as strong winds and storm waves, have probably influenced both the distribution of the beach sands and the orientation of the shoreline due to erosion and accretion. Effects of secondary beach processes (Chemical actions including biochemical actions) during sediment transport and deposit might be helpful for the enrichment of MGS ranges and creation of HMs, and grain-sorting processes by waves and currents can further promote the more regular distribution of MGSs and hard minerals on the beach. This study has led to a better understanding of the beach's dynamics, thereby enabling more useful information for a lake-beach ecological system and better environmental management of this recreational region.