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".

NITROGEN

The Atmosphere

78% N2

21% O2

~0.0396% CO2

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 NO3-N

• tropospheric ozone• nitrogen aerosols.

• N additions to most forests will increase growth (as can climate warming and rising atmospheric CO2 concentrations!).

• For most terrestrial plant communities only inorganic N is available (e.g., NH4+ and NO3

-). And while there are thousands of soil organisms that can convert organic-N to NH4

+, most are sensitive creatures (e.g., pH, moisture) and very few can nitrify NH4

+ to NO3- (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 ParadoxCliffs 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 (N2) into ammonia (NH4

+) 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-11-013 August 2011 www.epa.gov/sab

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

N2

N Fixationto

C-NH2

N Depositionas

NH4+ and NO3

-

atm

osph

ere

terr

estr

ial

Organic Matter(C-NH2)

NH4+ NO3

-

NO2-

Denitrificationas

NO N2O N2

Leaching Loss

NH3

Vola

tiliza

tion

Bear Brook Watershed in Maine

West Bear BrookTreated

East Bear BrookReference

• West Bear Treatments Initiated Nov, 1989• 1800 eq ha-1 yr-1 (NH4)2SO4

= 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, CO2)

StreamExports

The WatershedBlack Box

Inside the Box

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

1

23

45

678

Fernandez et al. 2012

http://www.cleanair-coolplanet.org/information/pdf/winterindicators_09.pdf

Navratil et al. 2010

East Bear Stream NO3 West Bear Stream NO3

Runoff from East Bear: 2003-2006

1988-1989

1996-2006

BIOGEOCHEMICAL CONTROLS ON ALTERED NITROGEN CYCLING IN THE THIRD DECADE OF WHOLE-WATERSHED SIMULATED N

DEPOSITION

Questions?