Agricultural management practices are among the major drivers of agricultural nitrogen (N) loss, with agriculture accounting for 70-90 % of diffuse total nitrogen loads.
Legislation and management incentives for measures to mitigate nitrogen loss should eventually be carried out at the individual farm level. Consequently, an appropriate scale to simulate nitrogen loss from a scientific perspective should be at the farm scale.
As part of the BONUS RECOCA-project researchers from BNI have, together with Nordic colleagues, identified hot spots of agricultural nitrogen loss within the entire Baltic Sea drainage basin with the help of modelling.
The analysis is done at a relevant level of spatial detail and has taken into account differences in farm types and farm structure between regions.
Daisy-simulations to identify drivers of N loss
A data set of more than 4000 agricultural fields with combinations of climate, soils and agricultural management which overall describes the variations found in the Baltic Sea drainage basin was constructed.
With the state-of-the-art soil-vegetation-atmosphere model Daisy (Hansen et al. 2012), the team simulated nitrogen loss from the root zone of all agricultural fields in the data set.
By using multiple regression statistics and by developing a statistical nitrogen loss model from the set of simulations, the researchers could identify the most important drivers for nitrogen loss.
Calculating root-zone losses from Baltic Sea drainage basin
The researchers then applied this model to a basin-wide data set on climate, soils and agricultural management at a 10 × 10 km scale.
This made it possible to calculate root-zone nitrogen losses from the entire Baltic Sea drainage basin. The identification of nitrogen loss hot spots were done in a consistent way and at a level of detail hitherto not seen for this geographical area.
Further, the root-zone N loss model was coupled to estimates of nitrogen retention in catchments separated into retention in groundwater and retention in surface waters allowing calculation of the coastal N loading.
Calculating coastal nitrogen loading
With this data and simulations, the coastal nitrogen loading can be calculated. The research team demonstrated the capability of this tool to calculate scenarios on agriculture and land use.
The ongoing intensification of agriculture in the countries in the south-eastern part of the Baltic Sea drainage basin is of special concern.
One scenario demonstrated a possible future increase in N loading to the Baltic Sea of 30 %, contrary to the aims of the HELCOM Baltic Sea Action Plan.
This study is of particular interest for scientist and managers working with agriculture, wanting to reduce emissions of nitrogen to the Baltic Sea for others who wish to learn new methods of how to calculate scenarios on agriculture and land use.
Download this publication here and more about the RECOCA project here.