Experimental constraints on the origin of potassic adakites in eastern China

Abstract

A sequential dissolution technique and a prolonged extraction method were used to investigate aluminium (Al) release from 4 Haplic Acrisols in southeastern China. The results show that the order of acidification of the 4 soils is: Tunxi soil>Yongchun soil>Shengxian soil>Ninghai soil. The amount of exchangeable Al is directly proportional to the extent of soil acidification. Al was released from both organically bound and inorganic Al pools after acid input. During several initial cycles of extraction the release of Al was mainly from the weakly organically bound Al pool. After prolonged extraction, Al release from the inorganic Al pool became more important to the total dissolved Al due to a rapid depletion of the weakly organically bound Al pool. The sizes of readily reactive Al pools in the Ninghai soil and Shengxian soil are larger than in the Yongchun soil and Tunxi soil. Al released from the inorganic Al pool in the Ninghai soil, Shengxian soil and Yongchun soil after 20 cycles of extraction was higher than from the organically bound Al pool, whereas the opposite was the case for the Tunxi soil. A low saturation of Al binding on soil organic matter (SOM) does not necessarily lead to a low Al release as in the case of the Shengxian soil. Also a relatively high saturation does not necessarily ensure a large Al release from the Al pool as in the case of the Tunxi soil and Yongchun soil. Once both organically bound and inorganic Al pools are depleted of readily reactive Al phases due to high soil acidification, Al dissolution would be small even under strong acid input. The high concentration of aqueous Al after rapid Al release from the weakly organically bound Al pool and subsequent depletion of the pool may have significant ecological and environmental effects.