The largest stressors to terrestrial ecosystems and biodiversity worldwide have been shown to be land use change, climate change, and atmospheric deposition of nitrogen (N) and sulfur (S). Land use change can directly destroy habitat for wild organisms, or indirectly impair remaining habitat through fragmentation and other effects. Climate change can cause an increase or decrease in plant growth, alterations in species distributions, and changes in biogeochemical cycling and runoff patterns.
Nitrogen deposition is an especially complex stressor as it can have a variety of positive and negative effects. It can cause increased plant growth, decreased plant biodiversity, soil acidification, increased invasive species, increased damages from pests and frost, and increased N leaching to water bodies.
Nitrogen deposition and climate change can also have interacting effects: N deposition can release systems from nutrient limitations that can lead to plant growth, potentially enhancing their responsiveness to changes in climate. Alternatively, elevated concentrations of carbon dioxide (CO2) can increase nutrient limitation, increasing the effect of a given amount of N deposition. How these two stressors interact needs to be more fully understood and can help decision makers prioritize remediation and adaptation efforts.
Summary of the Research
EPA conducted research to better understand how N deposition and climate change can interactively affect ecosystems. Broadly speaking, these efforts fall into two categories:
- Advancing fine-scale models to improve characterization of how atmospheric deposition and climate change interactively affect soil processes and plant biodiversity, and
- Advancing large-scale Earth-Systems-Models (ESMs) to improve characterization of how landscape-level processes (e.g. hydrology, carbon sequestration, and nutrient limitation) are affected by N deposition and climate change.
Merging model improvements at both of these scales will provide a flexible modeling framework to examine how these two major stressors may influence the environment now and in the future.