The Impact of Nitrification on Soil Acidification and Cation Leaching in a Red Alder Ecosystem

Abstract

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.

Nitrogen Excess in North American Ecosystems: Predisposing Factors, Ecosystem Responses, and Management Strategies

“…In many re-gional studies the degree of N saturation and the level of N deposition inputs are closely related (Johnson and Lindberg 1992, Stoddard 1994, Jeffries 1995, Bytnerowicz and Fenn 1996, Williams et al 1996a. Much of the variability in ecosystem N loss seems to be explained by differences in stand age and successional status Reiners 1975, Peet 1992), species composition (Van Miegroet and Cole 1984, climate, soil N pool size (Cole et al 1992, Van Miegroet et al 1992a, Stoddard 1994, past management, and land use (Feger 1992, Magill et al 1996. Forests prone to developing symptoms of N saturation typically have low net primary productivity (NPP), high N deposition, and high soil N reserves; they are limited by other factors (e.g., P, short growing season); and they are in the late successional stages.…”

“…Alder growing on gravelly granitic soil at Cedar Creek, Washington, had large losses of be-Ϫ NO 3 cause of high N 2 fixation rates (Van Miegroet and Cole 1984). However, alder stands growing on weatherable sandstone soils at Cascade Head, Oregon, accumulated 20 Mg N/ha with little loss (Franklin et al 1968, Ϫ NO 3 Bormann et al 1993b).…”

“…Podzolization or reduced biotic regulation due to a short growing season may explain high N losses observed in coastal Alaska (Stednick 1981). Nitrogen fixation inputs can sometimes far exceed atmospheric inputs Cole 1984, Bormann et al 1993b) and contribute to leaching of and cations in gravelly Ϫ NO 3 soils (Binkley et al 1982, Van Miegroet andCole 1984). Coastal alder stands with fine soils lose little , even after burning (Brown et al 1973), and can Ϫ NO 3 accumulate Ͼ20 Mg N/ha (Franklin et al 1968).…”

Ecological issues related to N deposition to natural ecosystems: research needs

“…Nitrogen fixation can contribute significantly to the available N pools in some natural ecosystems. Red alder (Alnus rubra) was found to contribute 50-150 kg N h a ' year-' (Binkley et al, 1994), a sufficient amount to create conditions of N saturation (van Miegroet and Cole, 1984;. Black locust (Robinia pseudoacacia) contributed fiom 35 to 300 kg N h a ' year-' (Boring and Swank, 1984).…”

Speciation of Al in soil solution from forest soils in northern Kyoto with special reference to their pedogenetic process

“…It was considered that a high level of nitrification may occur (NO3 content was often higher than 0.1 mmol(--) L-I), which was reported to be an important internal proton load in some forested ecosystems (Van Miegroet and Cole 1984). The measured anion deficit (0.1 to 0.3 mmol(--) L -1) may be attributed to the dissociation of dissolved organic acids, or of H2COa especially in the B horizons (Ugolini and Sletten 1991).…”