Magnetic Properties Of Iron Plaque On Roots Of Typical Plantsin Tadal Flat Of Eastern Chongming Island In The Yangtze Estuary

Iron plaque on the wetland plant roots plays an important role in elemental cycle including heavy metals. Therefore it receives wide attention regarding its iron oxide composition. However, characterization of iron plaque composition using the method of environmental magnetism, as far as we know, has not been reported. In the present study, analyses of magnetic properties, particle size and diffuse reflectance spectrophotometry were carried out on roots of Phragmites australis, Spartina alterniflora, and Scirpus X mariqueter, as well as the surrounding sediments from the tidal flat of Chongming Island, the Yangtze Estuary. The purpose was to investigate the magnetic mineralogy of iron plaque and the influencing factors. The main conclusions are as follows:1. Ferrimagnetic minerals dominate magnetic properties of sediments in the vegetation zone of Phragmites australis, Spartina alterniflora, and Scirpus X mariqueter. Magnetic minerals comprise two grain size, including finer ones in the clay and coarser ones in the sand fraction. The seasonal changes in magnetic properties are minor.2. Except for the Phragmites australis zone, Fe3+ content and properties in sediments are similar to redness (a*), suggesting that reactive iron and a* can indicate redox condition of the sediments. Sediments sampled in April show a higher a* and lower water content, suggesting stronger oxidizing condition in April. This is related to stronger root respiration in that season.3. Ferrimagnetic minerals dominate magnetic properties of roots of the vegetation. Both magnetite and goethite have been revealed by low-temperature cycle of room SIRM. In comparison to sediments, magnetite on the roots has a lower but finer grain size.4. Magnetic parameters (x, SIRM, HIRM,χARM, χARM/χ, and χARM/SIRM) of roots are higher in samples collected in April in comparison to those collected in October. Among the vegetations, magnetic parameters%, SIRM, HIRM, and χARM of Scirpus × mariqueter are higher in October in comparison to those of Phragmites australis and Spartina alterniflora.5. Among the vegetations, roots of Scirpus X mariqueter display lowest Mn/Fe values, which is consistent with relative reducing environment of this vegetation zone.χ, SIRM, HIRM, and χARM of roots display significant correlations with Fe content, suggesting that concentration-related magnetic parameters can be used reflected iron content on the roots.