On 19 September PBL researcher Arthur Beusen obtained his PhD at the Utrecht University. His thesis is titled ‘Transport of nutrients from land to sea: Global modeling approaches and uncertainty analyses’, for which he developed four mathematical models describing various components of the global biogeochemical cycles of plant nutrients.
Nitrogen, phosphorus and silicon are important nutrients for plants, but it is not clear how these elements are transported around the world. Arthur Beusen developed mathematical models to decribe the global biochemical cycles of these nutrients and make projections. This research was done as part of the Integrated Model to Assess the Global Environment (IMAGE), and a result of close collaboration between PBL Netherlands Environmental Assessment Agency and the University of Utrecht.
One of the models developed was a lumped global model to calculate global annual river export of dissolved silicon to the ocean. Results show that the main factors determining river export of dissolved sillicon include precipitation, soil bulk density, the occurrence of volcanic rock and relief. The importance of soil bulk density confirms the role of biological processes in the global silicon cycle.
Another model analysed the uncertainty s of ammonia volatilisation. In large parts of the world, the animal nitrogen excretion rate is the largest determinant in the total emission of agricultural ammonia. However, in countries with industrial production systems, contributions from animal housing and storage systems are more important.
Furthermore, the models showd that denitrification has not kept pace with the increase in anthropogenic nitrogen sources (fertilizers and manure) and that riparian zones could be an important global source of nitrous oxide.
Finally, the thesis reveals that, over the past century, the increasing nutrient delivery by anthropogenic sources (expanding and intensifying agriculture, and sewage) and decreasing contributions from natural sources (deforestation) have led to increasing nitrogen and phosphorus export. The contribution of allochtonous organic matter from floodplain and wetland vegetation to nitrogen and phosphorus delivery to surface water is likely to be important, from a global perspective, but also very uncertain, and this source is among the main candidate subjects for future research.