Document Type


Journal/Book Title/Conference

Journal of Environmental Quality






American Society of Agronomy

Publication Date



impact, nitrification, soil acidification, cation leaching, red alder ecosystem

First Page


Last Page



The objectives of this study were to investigate the impacts of internal nitrification on soil and soil solution acidity and on the rate of nutrient export through NO3– mediated leaching. This was achieved by comparing soil chemical properties and soil solution composition within a naturally N-rich red alder (Alnus rubra Bong.) ecosystem to those of an adjacent Douglas-fir [Pseudotsuga menziesil (Mirbel) Franco] forest where soil N levels were significantly lower and no measurable HNO3 production could be observed. In the red alder system, where > 100 kg ha–1 yr–1 of N were added through symbiotic N2 fixation, the net annual NO3– leaching past the 40-cm soil depth amounted to 3460 mol charges ha–1, and NO3– concentrations in the solutions collected below 40 cm periodically exceeded drinking water standards of 10 mg L–1. The H+ and NO3– release was most pronounced in the forest floor and top 10 cm of the soil under alder occupancy and caused significant acidification of percolating solutions. Less than 1% of the total H+ input from internal (nitrification) and external (atmospheric) sources leached below the 40-cm depth, which was indicative for the strong buffering capacity of this particular soil. The cation displacement reactions involved in this pH buffering caused a 15% decline in base saturation and a significant acidification of the upper part of the soil profile. The presence of large amounts of mobile NO3– in solution triggered accelerated cation leaching, causing a selective redistribution of primarily exchangeable Ca2+ from the A to the B horizon. These field studies lead us to conclude that the rate and the selectivity of NO3– mediated leaching in a red alder system could significantly lower the exchangeable cation pool in the rooting zone or cause nutrient imbalance, if a site is managed for repeated rotations of red alder.