The work with the establishment of reference conditions in Danish coastal waters has so far been based on the distribution of eelgrass around 1900, and current measurements of nitrogen concentration in watercourses with virtually no agricultural activity, as well as estimated historical national nitrogen balances. In a new publication in the international journal Ambio, researchers from Aarhus University review the problems surrounding the assumptions about low nitrogen emissions from agriculture around 1900. In addition, they propose an alternative method, which is based on land use at parish level, collected around 1900, combined with measurements from contemporary field trials with the year 1900-relevant cultivation, as a starting point for calculating nitrogen emissions.