Twenty years of nitrogen deposition to Norway spruce forests in Sweden

The yearly, total (dry+wet) deposition of inorganic nitrogen (inorg-N) to Norway spruce forests was estimated with afull spatial coverage over Sweden for a twenty-year period, 2001–2020, based on combined measurements with Teflonstring samplers, throughfall deposition and bulk deposition to the open field.

The results were based on a novel methodto apply estimates of the dry deposition based on measurements at a limited number of sites, to a larger number of siteswith only bulk deposition measurements, in turn based on the existence of a strong geographical gradient in the dry depositionof inorg-N from southwest to northeast Sweden. The method should be applicable for other geographical regionswhere gaseous NH3, NO2 and HNO3 are not main drivers of N dry deposition and where geographical gradientsin dry deposition could be defined.

It was shown that Norway spruce forests in south Sweden receive more N from depositionthan has been previously estimated, based onmodelling. Clear time trends were demonstrated for decreased depositionof inorg-N to Norway spruce forests in all parts of Sweden. The decreaseswere somewhat larger thanwhat couldbe expected from the decrease in the reported emissions of inorg-N from Europe. The results emphasize that estimates of the total deposition are necessary in order to map levels and follow the development of N deposition in forests.