Hi! I am doing research on analysing land use change impact on ecosystem services. One of the ecosystem services models that I am using for the analysis is the NDR model. However, after running the NDR model for many times, my nitrogen surface export values were negative. I even changed my watershed shapefile into subbasin and subwatersheds, but the values were still negative. What could these values imply? Is Nitrogen being retained?
I hope you could guide and enlighten me with regards to this.