It was known during the 18th century that air contains at least two gases, one of which supports combustion and life, and the other of which does not. Nitrogen was discovered by Daniel Rutherford in 1772, who called it noxious air. The element seemed so inert that Lavoisier named it azote, meaning "without life".

The Atmosphere  78% N 2  21% O 2  ~0.0396% CO 2

The Paradox that is Nitrogen N is the most abundant gas in the atmosphere, yet N is the most commonly limiting plant nutrient on the planet! N is the most abundant gas in the atmosphere, yet human N additions are a concern due to: acid rain eutrophication of water and watersheds – US EPA Drinking Water criterion for NO 3 -N tropospheric ozone nitrogen aerosols. N additions to most forests will increase growth (as can climate warming and rising atmospheric CO 2 concentrations!). For most terrestrial plant communities only inorganic N is available (e.g., NH 4 + and NO 3 - ). And while there are thousands of soil organisms that can convert organic-N to NH 4 +, most are sensitive creatures (e.g., pH, moisture) and very few can nitrify NH 4 + to NO 3 - (the favored form for most crops). The majority of the N deposited on forested watersheds is retained in the watershed, even in N saturated forests.

The Nitrogen Paradox The Nitrogen Paradox Cliffs Notes Version Although there are huge pools of N in the atmosphere as a gas, in soil as organic matter, and in rocks, nearly all of that is unavailable and most biological systems remain N deficient (except in highly polluted areas). Therefore, the introduction of even small amounts of reactive N (i.e., Nr) have a disproportionately large impact on ecosystem function and ecosystem services to society.

Valclav Smil, Nature 1999 July 1909 Haber-Bosch Discovery Haber-Bosch Process and Reactive Nitrogen H.H. Janzen 2004 The discovery of the process to fix atmospheric nitrogen (N 2 ) into ammonia (NH 4 + ) by Haber, which was then industrialized by Bosch (an engineer for BASF in Germany), sparked an agricultural revolution that can take credit for the existence of approximately 2 of every 5 humans on the planet today.

EPA-SAB August …and gave us the means to produce ≈43% of reactive nitrogen (Nr) in the US today.

N2 N Fixation to C-NH 2 N Deposition as NH 4 + and NO 3 - atmosphere terrestrial Organic Matter (C-NH 2 ) NH 4 + NO 3 - NO 2 - Denitrification as NO  N 2 O  N 2 Leaching Loss NH 3 Volatilization

Bear Brook Watershed in Maine

West Bear Brook Treated East Bear Brook Reference

West Bear Treatments Initiated Nov, eq ha -1 yr -1 (NH 4 ) 2 SO 4 = 25.2 and 28.8 kg ha -1 yr -1 N and S Added in 6 bi-mo. applications

Atmospheric Inputs (e.g., N, S, CO 2 ) Stream Exports The Watershed Black Box

Inside the Box Tree foliar chemistry Tree foliar chemistry Tree physiology Tree physiology Understory vegetation Understory vegetation Litterfall and decomposition Litterfall and decomposition Roots Roots Soil chemistry Soil chemistry Soil microbiology Soil microbiology Nitrogen mineralization, nitrification Nitrogen mineralization, nitrification Soil solutions Soil solutions Trace gas flux Trace gas flux Groundwater Groundwater Stream chemistry Stream chemistry Stream sediments Stream sediments Hydrology Hydrology Ecosystem mass balance Ecosystem mass balance …etc. …etc

Fernandez et al. 2012

Navratil et al East Bear Stream NO 3 West Bear Stream NO 3 Runoff from East Bear:

B IOGEOCHEMICAL C ONTROLS ON A LTERED N ITROGEN C YCLING IN THE T HIRD D ECADE OF W HOLE -W ATERSHED S IMULATED N D EPOSITION

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