“…Organic matter was removed for laser-diffraction particle size study. Pretreatments for grain-size analysis frequently use oxidative treatments (Buurman, Pape, & Muggler, 1996;Fullen, Zheng, & Brandsma, 1996;Scott-Jackson & Walkington, 2005;Wang, Jin, Bu, Zhou, & Wu, 2006). All of the samples were mixed with a dispersing agent (.3% sodium hexametaphosphate) in order to disperse the clay particles.…”