The Impact of Atmospheric Nitrogen Deposition on Vegetation Processes in Terrestrial, Non-Forest Ecosystems

Abstract

During the past few decades, the atmospheric deposition of nitrogen compounds has become a major threat to the species diversity of terrestrial ecosystems in north-west Europe. The two environmentally most damaging air-borne N compounds are nitrogen oxides (NO_x) and ammonia (NH₃). Nitrogen oxides originate mainly from stationary and non-stationary burning of fossil fuel. High levels of ammonia emissions especially occur in areas with high densities of animal husbandry (Buysman et al., 1987). This is most apparent in the Netherlands, where the amount of deposited NH_x is significantly related to the distribution of intensive farming systems (Asman and Maas, 1986). The deposition of reduced and of oxidised N compounds results in eutrophication and acidification of nutrient-poor ecosystems (Heij and Schneider, 1991; Bobbink et al., 1992a). Soil acidification as a result of the deposition of atmospheric pollutants, such as oxidised and reduced nitrogen compounds, is characterised by a wide variety of effects (Figure 4.1). First, there is a loss of buffer capacity (ANC) and a decrease in soil 2H. Furthermore, it leads to increased leaching of base cations, especially Ca²⁺ and Mg²⁺, and to increased availability of metals (A1³⁺ and Fe²⁺). Moreover, inhibition of nitrification occurs due to lower pH, and causes an increase of ammonium to nitrate ratios. Finally, acidification may lead to a decrease in the decomposition rate of organic matter.