Mapping Stable Nitrogen Isotopes Using Hyperspectral Imagery

Abstract

As nitrogen deposition increases globally, ecosystem changes will occur. It is important to understand the growth response of different ecosystems and where nitrogen retention will occur. Stable isotopes of foliar nitrogen can provide insight into how this process is occurring in the soil. Previous studies have found links between foliar nitrogen and optical properties.This study focuses on the Southern Piedmont Forests. A study at the Duke Forest's Blackwood Division in Chapel Hill, North Carolina, allowed for foliar sampling across various soil types, elevations, and species. Concurrent hyperspectral imagery was taken, allowing for the relationship between environmental drivers, optical properties, and nitrogen content to be identified. These relationships will be used to map nitrogen content at the canopy level. Foliar sampling was performed in species identified as major contributors to the canopy. Major canopy contributors were oak, hickory, poplar, sweetgum, and pine. Foliar samples were analyzed for chlorophyll, macronutrients, carbon, nitrogen, and stable isotope N15. The relationship of these characteristics, as well as elevation, soil type, species, and optical properties, were input to predict the spectral signature associated with the N15 content.Ancillary data on elevation, soil type, and species, coupled with hyperspectral imagery, will use the relationships to predict canopy level nitrogen at the image scale.