Geospatial Regression Equation for European Nutrient losses

GREEN is a statistical model used to assess the impact of agricultural fertilizers and other sources of nutrients on the environment. The GREEN model estimates the mass discharge of total nitrogen (N) and total phosphorus (P) through the stream network down to marine coastal areas, the concentration of N and P, and the relative contribution of diffuse and point sources to the total mass discharge/concentration. 

GREEN is a simplified conceptual model, which distinguishes between two different pathways in nutrient transfer from sources to catchment outlet (Grizzetti et al., 2006, 2005a, 2005b). Diffuse sources (DS), which include applied synthetic and manure fertilisers, atmospheric deposition and emissions with wastewater from scattered dwellings (i.e. homesteads that are disconnected from sewerage systems), first undergo degradation in the soil via various processes including crop uptake, atmospheric losses and soil storage, before reaching the stream network. Point sources (PS), which include discharges from sewers, waste water treatment plants, industries and paved areas are directly emitted to the stream network. Once in the stream network, nutrients are partially retained in the streams due to algae growth, atmospheric losses etc. The calculation is performed on a catchment of interest, which is subdivided into a number of sub-basins (n) based on a topographic discretisation. A routing structure is then elaborated and serves to establish an emitting-receiving sub-basins relationship, i.e. an up-stream nutrient load is considered as an additional point source to the receiving down-stream sub-basin. With this representation, the emissions of N and P from upstream are transferred downstream taking into account the mass fraction lost in the basin and in the stream network.

Model inputs are:

• Annual climate data (precipitation)
• Annual input of fertilizer application (manure, mineral fertilizers), atmospheric nitrogen deposition and biological fixation, extent of agricultural and non-agricultural area.
• Discharges of N and P from industrial installations, untreated and treated wastewater. The latter are usually estimated from population density and connectivity to waste water collecting and treating systems, or available datasets of wastewater discharge points (Vigiak et al. 2018; 2020; 2023). Geomorphological information is needed in order to build the hydrographic model used in the calculation. The model consists of a set of interconnected sub-basins each containing a segment of the stream network.