CC-26: Mapping Loading Rates and Sources of Reactive Nitrogen across the United States suggests Regional Interactions with Climate Change
Daniel J.
a,b
Sobota ,
sobota.dan@epa.gov
compton.jana@epa.gov
Shweta
a,d
Singh ,
and Douglas J.
e
Norton
norton.douglas@epa.gov
singh.shweta@epa.gov
Ecology Division, US Environmental Protection Agency, Corvallis, OR: bOak Ridge Institute for Science and Education; cNational Health and Environmental Effects Research Laboratory; dNational Research Council
eOffice of Water, US Environmental Protection Agency, Washington, DC
Colin Bishop
kg N ha-1 yr-1
0-1
1-3
3-5
5 - 10
10 - 30
30 - 50
50 - 100
100 - 130
0 250 500
1,000 km
Products & Energy
Colin Bishop
O
Energy &
products
Harmful Algal Blooms & Hypoxia
Human-created N is critical for our modern society
and economy. However, its overabundance in the
environment harms human health, alters ecosystem
function, and contributes to climate change.
Air pollution
Largest human-created reactive N sources
8-digit USGS Hydrologic Units
The Nitrogen Cascade
Stratospheric
effects
Particulate
N 2O
Matter
effects
Greenhouse
effects
N2 O
Air
Ozone
effects
Project mid-century shifts in riverine N
export due to climate change.
NHx
Biological
N fixation
NOy
NH3
Land
Forests &
Grasslands
effects
Agroecosystem
effects
Animal
Crop
NHx
NOy
Plant
N2O
(terrestrial)
Soil
Soil
Human
consumption
Coastal
effects
Surface water
effects
Groundwater
effects
20
15
10
5
0
w
Ne
atu
n
hu
ral
a
e
r
-c
ted
n
a
m
Percent
-13.6 to -5.0
-5.0 to -2.5
-2.5 to 0
0 to 2.5
2.5 to 5.0
5.0 to 11.1
Riverine N export data
100
10
1
0
5
10
15
20
Mean Annual Temperature (oC)
100
10
1
ln(annual riverine export of watershed N inputs) =
1.83+0.0018*Mean Annual Temperature - 0.11*Mean Annual Precipitation
n=71; p<0.0001; r2=0.66
0
500 1000 1500 2000
Mean Annual Precipitation (mm yr-1)
Changes in annual temperature and precipitation regimes may
reduce or increase riverine N export depending on region.
www.whoi.edu
NOx
Identify important reactive N sources
across conterminous US watersheds.
Projected changes in riverine N export, 2040 -2059
8-digit USGS Hydrologic Units
25
Human activities currently put 7.5 times more new reactive N into
the US annually than do natural processes alone.
Objectives
Agricultural
production
30
w
e
N
Water pollution
Projected changes in climate for the 21st century may
dampen or exacerbate human health and ecosystem
effects of overabundant, human-created N.
Understanding the interactions between reactive N
and climate change is critical.
Energy consumption
National reactive N inputs
Annual riverine export of
watershed N inputs (%)
Technology now allows us to create N fertilizers,
increasing food production. Currently, 50% of N in
the human body is synthetic N fertilizer. N also is an
important component of many industrial products.
New human-created reactive N inputs
8-digit USGS Hydrologic Units
Reactive N input (Tg N yr -1)
Enhanced crop production
Reactive nitrogen (N) is essential to life, making up
compounds such as proteins and nucleic acids.
Estimate reactive N inputs across the
conterminous United States (US).
Shifts in riverine N exports due to climate change
Reactive nitrogen inputs and sources, circa 2000
Reactive nitrogen is a wicked problem
N2O
(aquatic)
Water
Ocean
effects
Galloway JN, Aber JD, Erisman JW, et al. 2003. The nitrogen cascade. Biosci
53:341-356.
National reactive N sources
Reactive N input (Tg N yr -1)
aWestern
Jana E.
a,c
Compton ,
Atmospheric deposition
Legumes
Manure
Synthetic fertilizer
Sewage
12
Methods
Source data for reactive N inputs
Reactive N source
Spatial resolution
Time scale
Synthetic fertilizer
County
1997-2001
8
Legumes
County
1997, 2001
6
Atmospheric deposition
36 km grid
2002
4
Industrial products
National
2002 - 2009
Manure
County
1997
Sewage
County
2000
Trade export
National
2002
10
2
0
Spatial data were reformatted to 8-digit USGS Hydrologic Unit Codes
(HUC8s) using the Zonal Statistics Tool in ArcMap 10.0 (ESRI Inc.,
Redlands, CA).
For data references, see:
Sobota DJ, Compton JE, Harrison JA. 2013. Reactive nitrogen in US lands and waterways:
How certain are we about sources and fluxes? Fron Ecol Environ 11:82-90.
-2
-4
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e
z
li um siti duc anu wa xp
i
t
er Leg epo pro M Se de e
f
d rial
tic
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T
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sp Ind
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At
Synthetic fertilizer is clearly the largest national reactive N source.
However, atmospheric deposition is important in the East and
Southwest, while legumes are important in the West.
Changes in riverine N exports due to climate change
We compiled data from 71 watersheds in the US that described riverine
export of annual watershed N inputs (fractional N export):
Boyer, EW, Goodale CL, Jaworski NA, Howarth RW. 2002. Anthropogenic nitrogen sources
and relationships to riverine nitrogen export in the northeastern USA. Biogeochem
57/58: 137-169
Schafer SC, Alber M. 2007. Temperature controls a latitudinal gradient in the proportion of
watershed nitrogen exported to coastal ecosystems. Biogeochem 85:333-346.
Schafer SC, Hollibaugh JT, Alber M. 2009. Watershed nitrogen input and riverine export on
the west coast of the US. Biogeochem 93:219-233.
Sobota DJ, Harrison JA, Dahlgren RA. 2009. Influences of climate, hydrology, and land use
on input and export of nitrogen in California watersheds. Biogeochem 94:43-62.
Mean annual temperature and precipitation were used to predict
fractional N export (see equation in climate change panel).
Acknowledgements: Funding was provided by Oak Ridge Institute for Science and Education, the National Research Council, and the US Environmental Protection Agency.
Ensemble average data (4.5 km grids) for mean annual
temperature and precipitation changes for 2040 – 2059
were downloaded from the National Center for
Atmospheric Research (https://gisclimatechange.ucar.edu).
Ensemble temperature and precipitation data were scaled
to HUC8s using ArcMap 10.0.
Coefficients for the fractional N export~precipitation and
temperature regression equation presented in the climate
change panel were applied to HUC8 climate change data.