Print PageOne of the grand challenges of the 21st Century is to understand biogeochemical cycles in the biosphere, and in particular, to understand how to manage nitrogen (N) in the environment to maximize agricultural productivity while minimizing negative environmental effects. Developing a clear understanding of climate and human-induced changes in environmental N cycling in tightly coupled atmospheric, terrestrial, and aquatic systems, including how these changes feed back into the climate system, is critical to addressing this challenge. The overall objective of this study is to create a regional modeling framework by integrating a network of state-of-the-art process-based models that are currently in existence and that are undergoing continuous development. Coined as “BioEarth”, this EaSM aims to improve understanding of the interactions among C, N, and H2O at the regional scale in the context of global change to inform decision makers’ strategies regarding natural and agricultural resource management. As a first step towards building BioEarth, this research examines how atmospheric deposition of nitrogen (ADN) changes in response to global change, how ADN affects C and N cycling in the terrestrial biosphere, and how this linkage feeds back to the atmosphere.
Results/Conclusions
Simulated ADN data from the Community Multi-scale Air Quality (CMAQ) model are used as an external input to the Regional Hydro-Ecologic Simulation System (RHESSys). RHESSys is a process-based watershed-scale hydrologic model that incorporates biogeochemical cycling, while CMAQ is a comprehensive chemical transport model that explicitly accounts for wet and dry deposition of a suite of N gas and aerosol species. The HJ Andrews Long-Term Ecological Research (LTER) site in central Oregon is used for model application and evaluation because of the readily available observations of ADN and stream chemistry concentrations. The influence of climate change on temperate forests in the Pacific Northwest (PNW) is explored using CMAQ-simulated changes in N. RHESSys output of net primary productivity (NPP), nitrification, and streamflow nitrates are analyzed under standard climate scenarios. Results show reactive nitrogen’s impact on forest growth, as well as the terrestrial biosphere’s capacity to sequester carbon in a changing climate. While NPP increases with warmer temperatures, the terrestrial biomass continues to be regulated by carbon, rather than nitrogen. However, selection of watersheds closer to urbanized areas in the PNW may provide different results.
