Post on 15-Jan-2016
description
Robert Howarth Cornell UniversityIthaca, NY USA
Ocean Hypoxia and its Impacts on Ecosystems UNDP Side Event at GESAMP #39
New York City, USA
18 April 2012
Nutrient Pollution of Coastal Waters: Trends, Drivers, and Potential Solutions
(Rockstrom et al. 2009)
Global status of earth’s 10 life-sustaining biophysical systems
nitrogen
Nitrogen (and not phosphorus) is the primary culprit for coastal eutrophication and hypoxia
(although controlling both is best policy)
+ nitrogen
+ phosphorus
+ nitrogen & phosphorus
No nutrients added
Oviatt et al. 1996
Seine and Scheldt Basins and Belgian coast of North Sea
North Sea
English Channel
0
200
400
600
800
1970 1980 1990 2000 2010
ann
ual
mea
n d
isch
arg
e, m
3/s
0
500
1000
1500
2000
2500
3000
1970 1980 1990 2000 2010
TN
flu
x, k
gN
/km
²/yr
0
50
100
150
200
250
300
1975 1980 1985 1990 1995 2000 2005 2010
TP fl
ux, k
gP/k
m²/y
r
Seine River basinFreshwater discharge
TN load TP load
0
10
20
30
1970 1980 1990 2000 2010
ma
x C
hla
, mg
/m3 Chlorophyll in
North Sea on Belgian coast
0
500
1000
1500
2000
2500
3000
1970 1980 1990 2000 2010
TN
flu
x, k
gN
/km
²/yr
Seine River N load
0
1000
2000
3000
4000
1970 1980 1990 2000 2010
TN
flu
x, k
gN
/km
²/yr
Scheldt River N load
0
50
100
150
200
1900 1920 1940 1960 1980 2000
Ter
agra
ms
of
nit
rog
en
Natural N fixation on the continents
Total humaninputs
Fertilizer
N fixation in agro-ecosystems
Fossil fuel burning
Global trends in nitrogen use per year
(modified from Howarth et al. 2005)
Regional scale perspective important for nutrients.
Changes are driven by global energy and agricultural policies.
But with exception of N2O, nutrient cycles are altered at local to regional scales, not global scales, and effects are manifested at these local to regional scales.
New York Times (4/30/08)
Townsend & Howarth 2010
0 500 1000 1500 2000
1
2
3
4
5
6
7
8
9
Series1
Republic of Korea
North Sea watersheds
Northeastern U.S.
Yellow River basin
Mississippi River basin
Baltic Sea watersheds
St. Lawrence River basin
Southwestern Europe
Labrador and Hudson’s Bay
Natural background flux
Flux of nitrogen from the landscape to coastal oceans in rivers for contrasting regions of the world in the temperate zone (kg per km2 of watershed
area per year; from Howarth et al. 2005).
Kg N km-2 year-1
NorthAtlanticOcean
International SCOPE N Project(Howarth et al. 1996)
NANI(net anthropogenic N inputs)
(Howarth et al. 2012)
~ 150 watersheds on two continents
~ 25% of NANI exported to coastal oceans on average from 150 watersheds in Europe and the US
Swaney et al. 2012
Chinese watersheds
(Hong et al. 2011)
NOy deposition Fertilizer Ag N fixation Net food & feed
NANI
Hong et al., 2012
Region
Nutrient fertilizer
consumption (kg N/capita,
2009)
NOx Emission
(kg N/capita,
2000)
N fixation and net flux of N in food
and feeds
Sum of Reactive Nitrogen
(kg N per
capita)
Consumption relative to
safe operating boundary
Africa 2.5 0.9 ? 3.4 0.7
South America 12.2 1.2 ? 13.4 2.6
Southeast Asia 12.7 0.7 ? 13.4 2.6
India 13.0 0.5 ? 13.5 2.6
North America 35.9 9.6 ? 45.5 8.9
Europe 18.4 3.1 ? 21.5 4.2
East Asia 24.3 1.2 ? 25.4 5.0
Australia 30.8 7.9 ? 38.8 7.6
Other 10.5 0.6 ? 11.0 2.2
Global 15.4 1.5 4.6 21.5 4.2
Per capita NANI by region (partial analysis)
UNEP Sustainable Resource Use Panel (2011 draft)
Technical solutions for nitrogen pollution:
• Agricultural fields: reduce fertilizer amount and timing; change cropping systems; plant winter cover crops; control drainage seasonally
• CAFOs: treat wastes as society does for human waste
• Vehicle exhaust: tighten emission standards; encourage hybrid vehicles and electric vehicles
• Power plants: tighten emission standards; encourage renewable electricity (solar, wind)
• Sewage treatment: require denitrification treatment
Howarth et al. (2005) Millennium Ecosystem Assessment
But also think about policy solutions, particularly regarding diet and biofuels….
FieldLevel
Leached to water
Harvested in crops
3.6
10.5
0.2 (4.2)(1.2)
1.3
5.9
(3.1)
AnimalConsumption
Leached to water?Denitrified?
NH3
1.9
Denitrified?Building up in soil?NH3
Landfilled?Leached? Landfilled?
Denitrified?
(0.8)
1.4
Wastewater&
Denitrified
Human Consumption
0.9
Exported from U.S.
2.1
18.5
(Howarth et al. 2002)
Farm nitrogen balance for US (~1995; Tg per year for entire US)
If everyone in the US ate this:
Instead of this:
The country would use only 1/3rd as much fertilizer, and would have much less nitrogen pollution!
0.02.04.06.08.0
10.012.014.016.018.020.0
1960
1970
1980
1990
2000
2010
2020
2030
fert
iliz
er u
se, T
gN y
r -1
increasing grain exports,standard US dietconstant grain exports,standard US dietconstant grain exports,Swedish dietconstant grain exports,Mediterranean diet
(Howarth et al. 2002)
Howarth et al. 2009
Global Production of Liquid Biofuels:
0
200
400
600
800
1000
1200
1975 1979 1983 1987 1991 1995 1999 2003 2007
Year
Pe
ta J
ou
les
Ethanol
Biodiesel Equiv.
15 billion liters
Biofuels
2009: National goal to reduce nitrogen pollution down Mississippi River by 45% to limit size of dead zone.
Several models indicate national ethanol policy will make this difficult or impossible, and instead nitrogen pollution likely to increase…. 30% to 40% or more (Donner and Kucarik 2008; Simpson et al. 2008, 2009; EPA 2009; Costello et al. 2010)
2.0
1.0
0
Predicted Nitrogen Load from Mississippi River basin to meet US Ethanol TargetsM
illio
n to
ns n
itrog
en p
er y
ear
No biofuels
EtOh fro
m corn
plus cellu
losic
(corn st
over)
EtOh fr
om corn
plus cellu
losic
(switc
hgrass
)
Cellulosic
EtO
h only
(switc
hgrass)
2015 targets
2022 targets
(Costello et al. 2010)
National target to reduce area of Dead Zone
CONCLUSIONS:
Nitrogen is the primary culprit.
Nitrogen pollution is growing globally, with agriculture as the primary driver.
Technical solutions exist, and can help, often at little cost.
But policy considerations of diet (meat!) and energy (liquid biofuels!) are critical.
Thanks for invitation to participate!
Coastal Hypoxia Research Program
Agriculture, Energy & Environment Program at
Cornell University
Thanks for many collaborators, especially:
• Dennis Swaney• Bongghi Hong• Roxanne Marino• Christine Costello• Gilles Billen• Josette Garnier• Christoph Humborg• Alan Townsend