The last few decades have seen an exponential increase in the atmospheric concentration of reactive nitrogen. This has led to concerns from scientists, ecologists, and land managers regarding a cascade of ecosystem impacts, and the potential for elevated atmospheric inputs to significantly alter nutrient-poor systems. At particular risk are fragile mountain ecosystems, normally low in nutrients. Control of enhanced nitrogen deposition is required to prevent damage to terrestrial biodiversity and soil water quality, and decrease the release of excess nitrogen into headwaters to the detriment of aquatic ecology. To meet this challenge, control measures operate through legislation aimed at reducing emissions or by ecosystem management at a local level. Current legislation to reduce emissions is under review, whilst techniques aimed at managing nitrogen in lowland ecosystems are impractical in most remote mountain environments. Here we present research which shows the extent of ecosystem damage from enhanced nitrogen deposition and aims to inform future policy in support of national and international action to reduce nitrogen emissions.