Effects Of Chemical Remediation And Simulated Nitrogen Deposition On Acidified Forest Soil

Acid deposition turns into an important globle scale environmental problem, as theemissions of sulfur oxides （SO_x） and nitrogent oxides （NO_x） are increasing with rapiddevelopment of economy. In recent years，the growth of SO2emission has been cubedas the Chinese government took strict measurs to reduce national SO₂emissionsefficiently. However, the NO_xand NH₃emissions are increasing continuously alongwith rapid increases of social industry and agriculture, may counteract the positiveeffects of SO₂abatement and lead a deeper depravation to the forest by nitrogensaturation and soil acidification. So it is of great theoretical and practical significanceto research on the acidified soil remediation technology and the change of soilchemistry under enhancing nitrogen.We set field experiments at a site in a typical acidified mason pine forest catchment inThieshanping, Chonging, China. We limed the soil with limestone and magnesite at2004, and stimulated the nitrogen deposition by spraying ammonium nitrate andsodium nitrate each month since2005respectively. We hope to get the responses offorest ecosystem to these treatments by soil chemistry changes. After seven yearsobservations, it was indicated that the remediation agents leaded to the recovery ofacidified soil by significant increase of pH value both in soil and soil water and basesaturation in soil，and notable decrease of inorganic monomeric aluminum in soilwater. However, the accelerated leaching of NO₃^-and SO₄^2-might somewhatcounteract the positive effects. Since the limestone powder applied was much finerand thus more soluble than the magenesite powder, Ca in limestone plots was moremobile than Mg in magnesite ones in the first two years. However, the overallamounts of leaching out of the five years were nearly the same, with less than20%ofthe initial limestone Ca and the initial magnesite Mg retained in the soil as exchangecations. The decrease trend of pH value and Ca²⁺and Mg²⁺concentration in the upperlayer soil water in the liming plots are symbols that more agents should be applied tomaintain the remediation effect.In2005, the fact that yearly leaching amount of dissolved organic nitrogen （DIN） were more than the DIN yearly flow amout of throughfall indicated that the siteachieved nitrogen saturation before the experiment setup. The added DIN wasleached totally mainly as NO₃^-with the chronic nitrogen amendment. Compared withthe controlled plotes, the net nitrifying amount rised after the NH₄NO₃abatement andfell after NaNO3abatemen. It shows that NH₄⁺may accelerate nitrification as well asNO₃^-may decrease nitrification. Though Nitrogen depositipon had no effects on pHvalue, it increased Al³⁺and Al/BC remarkably, especially in sites with NH4NO3input.In short, it is important to control the emission of NO_xand NH₃in order to preventsoil nitrogen saturation, and ammonia （NH₃） emission control need more attentionconsidering the soil acidification effect.