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• • • • SECTION 6.0 EVALUATION OF REMEDY PERFORMANCE • • plants.As pH values decrease below 5.5,levels of free aluminum increase.Elevated • aluminum can be detrimental to plant growth in several ways: • • High levels of aluminum in the soil pore water inhibit root growth and root branching, • especially into the subsoil,which can increase susceptibility to drought(Adams,1984). • • Elevated aluminum can inhibit uptake of calcium and magnesium,which are essential • plant nutrients(Marshner,1995). • • Aluminum-induced deficiencies of other nutrient elements,such as phosphorus and • iron have also been reported (Adams,1984). • • Negative impacts to microbial communities may occur. • These effects resulting from soil acidity,alone or in combination,could have contributed to • susceptibility of poplar trees in the former bagging plant area to the clearwing moth infestation.Because one of the main symptoms of aluminum toxicity is stunted root • development,it is unlikely that strong root proliferation through highly acidic subsoil • occurred.Preferential flow through decaying root channels associated with poplar tree mortality does not completely explain the nitrate and ammonium movement that has been • observed since 2002.However,the pH measured in 2000 (5.6 to 7.2) at the 0 to 4-foot depth • interval was not as low as that measured in 2006(4.25 to 5.08).Therefore,some deeper penetration by roots could have been possible before extreme acidification occurred. • Therefore,an examination of the extent and depth of tree roots and old root channels in the • 3K sampling area is recommended (see Section 7.0). • • • • • • • • • • • • • • • • • • RDDI112370001(CAH5003.DOCX) 6-7 emersiwzraersoo • • •