A N, P, C, and water flows metabolism study in a peri-urban territory in France: The case-study of the Saclay plateau

Facing environmental issues, such as excess of nitrogen in the biosphere, water eutrophication, carbon emission in the atmosphere or hydrological impacts, peri-urban areas are not receiving as much attention as urban areas. In this research, we focus on a French peri-urban area in the Parisian region, the Saclay plateau. Following the territorial ecology approach, we consider this territory as a system organizing agricultural, food and waste flows, and we have analyzed the metabolism of this territory through its N, C, P and water flows. The results show first that the metabolism of the Saclay plateau is largely open, i.e. the main flows are input and output flows, and internal flows are small or nonexistent. This is particularly the case for nitrogen and phosphorus flows. The same findings hold for carbon flows although primary production and respiration play the major role in the carbon metabolism. Besides the uncertainty of the available data, water flows also reveal a clear uncoupling between compartments of the system. The analysis of these material flow budgets reveals the high potential for reconnections of the different flows, mainly due to the presence of large areas of agricultural land and a large population. Implementation of biowaste recovery, recovery of human excreta at source, as well as rain recovery systems, could help to realize this potential provided that environmental and sanitary risks can be effectively managed. Developing a foresight approach based on scenarios of territorial metabolism can assist in the building process of a territorial project in periurban areas.