The choice of system boundaries for effective long-term management of phosphorus

Material flow analysis (MFA) is a well-established tool for supporting decisions on nutrient management. This paper shows the importance of the system boundary chosen when an MFA system is established. To reach this goal, data of existing regional and global phosphorous studies was investigated in view of phosphorous-flows (P-flows) and stocks within and outside the systems observed. Then, internal flows and stocks to be managed are juxtaposed with upstream flows and stocks beyond the system boundaries. The results show that narrow system boundaries yield useful findings to improve regional P management on the short term. If, however, regional and global P-availability is to be secured for longer time periods, system boundaries must include the use and losses of P in the so-called 'Hinterland', defined as the total amount of P used and lost abroad for the production of all goods imported into a country. In some cases, these Hinterland flows appear to be dominant, jeopardizing measures to manage P in a cost effective, resource conserving, and environmentally sound regional way. Hence, the choice of system boundaries is crucial for MFA research. In particular, the huge losses of P in the global agriculture, as well as the magnitude of mining wastes must be considered for effective decisions regarding P management. Taking the Hinterland into account by linking global and regional P flows and stocks is mandatory if priorities for P management are defined.