Aluminum Output Fluxes from Forest Ecosystems in Europe: A Regional Assessment

Abstract

Data from 89 forested catchments and plots across Europe were used to define empirical relationships between aluminum leaching and input fluxes of major ions, output fluxes of major ions, ecosystem parameters such as soil pH, and combinations of these. Forests that release dissolved Al to seepage or surface waters are located primarily in areas receiving the highest loading of acid rain, and the output flux of Al shows the highest correlations to the throughfall flux of inorganic nitrogen, the output fluxes of NO3-, H+, and SO4(2-), and the mineral soil pH. If the speciation of Al is taken to be Al3+ (an overestimate), Al is released in a nearly 1:1 molar charge ratio with the sum of NO3- and SO4(2-) in runoff or seepage water over a wide range of basepoor bedrock types and acid deposition across Europe. The empirical data point to a threshold range of N deposition of 80 to 150 mmolc N m(-2) yr(-1) and a (less clearly defined) range of S deposition of 100 to 200 mmolc SO4(-2) m(-2) yr(-1) above which Al released from forests exceeds 100 mmolc Al m(-2) yr(-1). Within this threshold range, the sites that release little or no dissolved Al are those that continue to assimilate input N and/or have high soil pH (>4.5).

Nitrogen deposition contributes to soil acidification in tropical ecosystems

“…Accordingly, acid deposition generally causes persistent declines in soil base cation pool (or base saturation, BS), leaching of sulfate and nitrate ions and Al, and acidification of soils and surface waters; meanwhile, elevated Al mobilization with its toxicity to soil biota is a common characteristic in acidified soil (Dise et al, 2001;Edwards et al, 2002;Driscoll et al, 2003;Högberg et al, 2006;Warby et al, 2009).…”

N fluxes in two nitrogen saturated forested catchments in Germany: dynamics and modelling with INCA

“…However, even a small increase in NO 3 losses from forests may have large implications for drinking water management, since these waters are often used to dilute polluted water from other areas. Furthermore, NO 3 losses cause changes in the biogeochemistry of the catchments by increasing cation losses and inducing a higher risk of water acidification due to Al leaching (Dise et al, 2001).…”

Modelling and mapping critical loads and exceedances for the Georgia Basin, British Columbia, using a zero base-cation depletion criterion

“…This exchange follows the laws of mass action and charge conservation. Cation exchange processes in acidic soils, typically dominated by Ca 2+ (or Ca 2+ + Mg 2+ ), Al 3+ and H + ions, are generally represented by Gapon and Gaines-Thomas formulations (Matschonat & Vogt 1998), but cation leachate from soils tends to be linearly equivalent to incoming atmospheric S and N deposition loads (Dise et al 2001). Translating this into a simple expression for cation exchange between the soil solution and exchange sites under steady-state leads to: Setting current levels of base saturation in % (denoted as BS CL ) as the reference criterion for zero base-cation depletion, it follows from Eqn 1 and Eqn 4 with Δx = 0 that: The annual base-cation losses or gains from current to final BS levels can be derived from Eqn 4 by solving for Δx:…”