Acidification of solid and solution phases at greater depths ( 150 cm) at solling spruce site

摘要

The acidification of the soil and percolation water at soil depths from 150 to 500 cm was studied at the Solling spruce site from 1991 to 1996. NH4Cl exchangeable cations of the fine earth and bedrock fractions were obtained from different depths and the soil solution composition was monitored at 150, 200, 300, 400 and 500 cm depths using seven suction lysimeters at each depth. In the seepage water collected from 150 and 200 cm depth, pH values decreased in the period 1991 to 1996, but no significant changes were observed in solutions collected below 200 cm depth. Element budgets of Al and M-b (Na, K, Mg, Ca) cations indicated that buffering by exchange of Al with M-b cations occurred mainly in surface 200 cm soil depth. High variabilities in concentrations of SO4 (at 150 cm) and M-a (Al, Mn, H, Fe) cations (at 300 and 500 cm) were observed. High variabilities in M-a cations could be assigned to one of the lysimeters at each depth that extracted low pH solutions. The amount of exchangeable cations in the fine earth and the bedrock fractions indicated that the acidification front (exchangeable M-b cations < 80 equivalent percent) had occurred to soil depth of more than 360 cm, but the extent of acidification that might have occurred in the preindustrial period is not known. In both fine earth and bedrock fractions, depthwise changes of exchangeable M-a and M-b cations were quite similar, suggesting that rock fractions have contributed to proton buffering not only by silicate weathering but also by cation exchange. References: 44