Atmospheric deposition of ammonia to semi-natural vegetation in the Netherlands-methods for mapping and evaluation

In this paper an overview is presented of most of the experimental and modelling work conducted in recent years in the Netherlands leading to estimates of deposition of reduced nitrogen to seminatural vegetation on a 5 km x 5 km scale. The average deposition in the Netherlands was 2000 mol ha(-1)yr(-1) in 1993, about 200 molha(-1)yr(-1) lower than in 1980. Deposition to deciduous forests was on the average 2080 molha(-1)yr(-1), 2430 molha(-1)yr(-1) to coniferous forest, 2210 molha(-1)yr(-1) to heathland and 1460 molha(-1)yr(-1) to other nature areas. The main uncertainty in the deposition estimates is determined by the emission estimates and the surface exchange parametrisation. The dry deposition process description needs to be extended with the dynamics in the bi-directional surface exchange of NH3. Furthermore, there is lack of independent dry deposition measurements which can be used for model evaluation. (C) 1998 Elsevier Science Ltd. All rights reserved.