Landscape and regional scale studies of nitrogen gas fluxes

Abstract

Nitrogen (N) gas fluxes have great relevance to soil fertility, water quality and air quality. Analysis of these fluxes presents several conceptual and practical scaling challenges because they are mediated by microorganisms at the scale of microns and seconds but have relevance at relatively large spatial (meters to kilometers and larger) and temporal (years, decades) scales. In this chapter, we evaluate three scaling issues that arose as part of an analysis of the effects of N deposition on gaseous N loss from temperate forest ecosystems in the northeastern U.S. How does this chapter fit into the context of this book and the topic of "scaling and uncertainty analysis in ecology?" It occurs to us that there are three main groups of scientists grappling with scaling issues: (1) those with an inherent conceptual interest in scaling, (2) those interested in micro-scale processes (e.g., N gas fluxes) that are relevant at large scales and (3) those interested in solving large scale problems (e.g., nitrate delivery to coastal waters) that are regulated by micro-scale processes. We fall solidly in the second group, researchers who have been struggling to measure N gas fluxes at micro-scales being asked to evaluate the importance of our results to large-scale problems such as the fate of atmospheric N deposition or nitrate delivery to coastal waters (these knotty problems are defined below). Given that N gas fluxes are miserable to measure at micro-scales (lousy methods, absurd variability over small spatial and temporal scales), we, and most other micro-scale researchers, are uncomfortable scaling our miserable data to larger scales. That is, if you take a bad number measured at a small scale and extrapolate it to a very large scale, do you end up with a "very bad number" or a "big bad number" or what? So, be warned gentle reader, that landscape and regional scale studies of N gas fluxes are "not for the squeamish." But, given the difficulty of our challenge, we are pleased to contribute to a book that includes representatives from all three scaling motivation groups. In our view, exchange of ideas and challenges among these groups is the key to making progress in this critically important area of environmental science. Our case study addresses three distinct scaling challenges: (1) how to account for landscape scale variability in regional studies ? an experimental design issue, (2) how to account for the episodic nature of gas flux ? a temporal scaling issue, and (3) how to validate landscape and regional scale flux estimates ? an uncertainty and validation issue. The experimental design issues that we address are also discussed in the chapters by Wu and Li (Chapters 1 and 2), Bradford and Reynolds (Chapter 6), and Peters et al. (Chapter 7). Li and Wu (Chapter 3) provide a relevant discussion of uncertainty and error analysis that is relevant to our third challenge. © 2006 Springer.