Occurrence of red clay horizon in soil profiles of the Yellow River Delta: Implications for accumulation of heavy metals

Abstract

a b s t r a c t a r t i c l e i n f oThe source-area weathering and pedogenesis processes in the alluvial soil profiles might affect depth distribution of heavy metals. Red clay horizon (RCH) with a thickness of 5-50 cm in a 1 m soil profile has been found ubiquitously in the Yellow River Delta (YRD). The occurrence of this RCH was supposed to be related with the frequent shifting of the Yellow River tail channel in the Yellow River Delta (YRD). The geochemical features of the RCH were distinct from its upper or lower yellow silt horizon (YSH). The average median grain size of the RCH (10.5 μm) was almost three times lower than that of the YSH (29.9 μm). Meanwhile, the RCH was characterized of higher chemical index of alteration (CIA), magnetic susceptibility (χ lf ) and frequency-dependent magnetic susceptibility (χ fd ) values than the YSH, which implied a stronger source-area weathering and pedogenesis intensity of the RCH. Besides the distinctive characteristics of the RCH, it also accumulated significantly (p b 0.05) higher mean contents of Cu, Zn, Pb, Cr, Ni and Co, and maximum content of Cd in the RCH than that in the YSH. The principal component analysis (PCA) suggested that distribution of the heavy metals in the YRD soil profiles was significantly related to the content of aluminosilicates, oxides, clay fraction, χ lf and χ fd , however, such a correlation was not found except for Pb in the YSH. In addition, result of BCR sequential extraction indicated that a higher percentage of Fe-Mn oxides associated fraction was in the RCH than in the YSH for the heavy metals of Pb and Co. Cadmium was observed at higher percentage of exchangeable fraction in the RCH than in the YSH, implying a higher environmental risk of the Cd in the RCH.

Factors of soil diversity in the Batumi delta (Georgia)

“…Soil particle size distribution, soil OM content, and bulk density are generally recognized as the most important factors affecting soil water retention (Liao et al, 2011;Botula et al, 2012;Yang et al, 2014). In this context, researchers reported that an increase in the clay and OM content also leads to an increase in water retention because of adsorptive effects of clay content, and affinity to water and influence on soil structure of OM (Hillel, 1971;Kirkham, 2004;.…”

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“…Ratio of volume magnetic susceptibility of the soil reference material versus susceptibility measured in field (Boyko et al 2004). Boletín de la Sociedad Geológica Mexicana / 72 (1) / 2020 / 23 http://dx.doi.org/10.18268/BSGM2018v72n1a111219 Artícle A111219 MAGNETIC MONITORING OF ANTHROPOGENIC POLLUTION consistent with higher weathering and pedogenic processes compared to the silt layers (Li et al, 2017). The clay layer also showed values of χ fd% > 6%, that were higher than those in the silt layer, indicating larger amounts of SP grains.…”

“…Health risk of heavy metals via dermal contact arises through skin absorption in the shower, by washing hands with contaminated water, or while swimming (e.g., Li et al, 2018). Few studies report on the risks of absorption via dermal contact, with many of them claiming no or a low health risk through the skin pathway.…”

“…Furthermore, depth variations of the magnetic parameters along the soil profiles suggest that with time after recultivation, magnetic particles from pedogenic processes and/or from fly ash spread progressively deeper, reaching about 15 cm in the 25-year-old silver-birch forest. Li et al (2017) combined magnetic methods with XRF and other non-magnetic methods to investigate the fate of heavy metals in different types of soil horizons. The heavy-metal contents may differ in particular soil horizons because soils are governed by their proper physicochemical properties such as pH, soil moisture, and amount of organic matter and clay minerals.…”

A potential contribution of a Fe(III)-rich red clay horizon to methane release: Biogenetic magnetite-mediated methanogenesis

“…In the past ten years, a great number of studies have confirmed that methanogenic processes also proceed in the presence of electron acceptors such as Fe(III) and nitrate (Mitterer, 2010;Yoshioka et al, 2010). Recently, a special red clay horizon (RCH) has been found to exist ubiquitously in the Yellow River Delta, eastern China (Li et al, 2017;Y. Li et al, 2018b).…”