Leaching of nitrate and ammonium in heathland and forest ecosystems in Northwest Germany under the influence of enhanced nitrogen deposition

To study the impact of high atmospheric nitrogen deposition on the leaching of $\mathrm{N}{\mathrm{O}}_{3}^{-}$ and $\mathrm{N}{\mathrm{H}}_{4}^{+}$ beneath forest and heathland vegetation, investigations were carried out in adjacent forest and heathland ecosystems in Northwest Germany. The study area is subjected to high deposition of nitrogen ranging from 15.9 kg ha-1 yr-1 in bulk precipitation to 65.3 kg ha-1 yr-1 beneath a stand of Pinus sylvestris L. with NH4–N accounting for 70–80% of the nitrogen deposited. Considerable leaching of nitrogen compounds from the upper horizons of the soil, mostly as nitrate, occurred at most of the forest sites and below a mixed stand of Calluna vulgaris (L.) Hull, and Erica tetralix, but was low in a Betula pubescens Ehrh. swamp forest as well as beneath Erica tetralix L. wet heath and heath dominated by Molinia caerulea (L.) Moench. Ground water concentrations of both NO3–N and NH4–N did not exceed 1 mg L-1 at most of the sites investigated.