New approaches to modeling denitrification

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Within the past few decades, humans have dramatically altered the earth’s nitrogen (N) cycle. Introduction of reactive nitrogen (N) into the biosphere by humans now exceeds the rate of biological N2-fixation in native terrestrial ecosystems (Galloway et al. 2004). This increased reactive N is due primarily to N fertilizer production and fossil fuel combustion used to support the food and energy demands of a rapidly expanding human population. The negative human and environment health effects of this increased N are many (Galloway et al. 2008; Howarth et al. 2005; UNEP and WHRC 2007). Denitrification is the main process that permanently removes fixed N from the environment. Denitrification, the microbial production of N2 from nitrate and nitrite, is a facultative anaerobic process (‘‘classical denitrification’’); therefore, partially to fully saturated soils and aquatic sediments, and low oxygen waters are ideal sites for denitrification. We now know that denitrification occurs in almost all terrestrial, freshwater, coastal and (some) oceanic ecosystems, as well as human engineered systems (Seitzinger et al. 2006). Despite the large number of denitrification studies there are still only a few locations with measurements adequate to quantify denitrification rates, or to understand factors controlling denitrification, at the ecosystem scale. This also has severely limited development and incorporation of denitrification into models which are necessary to scale-up measurements to local ecosystem, regional or global scales. A Denitrification Research Coordination Network (Denitrification RCN) was established in 2005, with the overall goal to develop a coordinated network of denitrification scientists from a wide array of disciplines, from molecular biology to ecosystem science, and from soil science to oceanography. The efforts of the Denitrification RCN are intended to advance quantification of denitrification rates, development of process-based relationships between rates of denitrification and controlling factors, and production of spatially explicit, process-based models that can be used to scale-up site specific measurements to ecosystem, regional and global scales. Specific objectives include facilitating the sharing of recent methodological advances in denitrification measurement and models, stimulating additional methodological P. M. Groffman (&) Cary Institute of Ecosystem Studies, Box AB, Millbrook, NY 12545, USA e-mail: groffmanp@ecostudies.org