Effects of Rising Nitrogen Deposition
on Forest Carbon Sequestration
and N losses in the Delaware River Basin
Yude Pan, John Hom, Richard Birdsey, Kevin McCullough
USDA Forest Service, Newtown Square, PA 19073, USA
Delaware River Basin
Collaborative
Environmental
Monitoring and
Research Initiative
(CEMRI)
A Pilot Program of the
National Environmental
Monitoring Initiative
(NEMI)
USDA Forest Service
USGS
National Park Service
Delaware River Basin 1991 MRLC LULC
1%5% 2%
9%
Water
1%
25%
Developed
Open
Forest
Agriculture
Grasses
57%
Wetland
Scientific issues
 How does the increased atmospheric N
deposition interact with other stressors to affect
forest carbon sequestration in the Delaware
River Basin?
 What is the potential capacity of the forests
retaining the atmospheric N deposition and how
much of nitrate is lost annually from forests to
surface water in the Delaware River Basin?
Diagram of PnET Model
Carbon/Nitrogen
4
3
Water
2
1
17
11
12
Foliar
Canopy
Wood 7 Plant
8
5
C/N
C/N
9
Bud
6
C/N
Wood
Fine 24
19
Root
13
10
Dead
Wood
22
23
Soil
14
NH4
NO3
20
Snow
16
25
21
Soil
Water
18
15
1. Gross photosynthesis
2. Foliar respiration
3. Transfer to mobile C
4. Growth and maintain resp.
5. Allocation to buds
6. Allocation to fine roots
7. Allocation to wood
8. Foliar production
9. Wood production
10. Soil production
11. Precipitation
12. Interception
13. Snow-rain partition
14. Snowmelt
15. Fast flow
16. Water uptake
17. Transpiration
18. Drainage
19. Wood litter
20 Root litter
21. Foliar litter
22. Wood decay
23. Mineralization
24. N uptake
25. To soil solution
Model concepts
 Process-based, mechanistic models.
 Simulate carbon, nitrogen and water cycles, pools and
fluxes based on mass-balance.
 We can more successfully predict the variables in
terrestrial ecosystems if we model the basic processes
controlling them.
 Methodology differs from classic statistical based
empirical relationships.
 Feedbacks and constraints on fluxes and pools affect the
ecosystem as a whole.
Diagram of PnET Model
Carbon/Nitrogen
4
3
Water
2
1
17
11
12
Foliar
Canopy
Wood 7 Plant
8
5
C/N
C/N
9
Bud
6
C/N
Wood
Fine 24
19
Root
13
10
Dead
Wood
22
23
Soil
14
NH4
NO3
20
Snow
16
25
21
Soil
Water
18
15
1. Gross photosynthesis
2. Foliar respiration
3. Transfer to mobile C
4. Growth and maintain resp.
5. Allocation to buds
6. Allocation to fine roots
7. Allocation to wood
8. Foliar production
9. Wood production
10. Soil production
11. Precipitation
12. Interception
13. Snow-rain partition
14. Snowmelt
15. Fast flow
16. Water uptake
17. Transpiration
18. Drainage
19. Wood litter
20 Root litter
21. Foliar litter
22. Wood decay
23. Mineralization
24. N uptake
25. To soil solution
Model Experiments under Different Atmospheric Chemistry Scenarios (version 3)
Model Run /input
Run1, control
Run 2, scenario
Run 3, scenario
Run 4, scenario
Run 5, scenario
Run 6, scenario
Run 7, scenario
Run 8, scenario
Run 9, scenario
Run 10, scenario
Run 11, scenario
N deposition
No N input (0.0 g/m2)
Ramped up to N deposition level of 2000
No N input (0.0 g/m2)
Ramped up to N deposition level of 2000
Ramped up to N deposition level of 2000
Doubled N input by 2000
Doubled N input by 2000
Ramped to N deposition level of 2000, then
continue to increase linearly
Ramped up to N deposition level of 2000,
then level off
Ramped up to N deposition level of 2000,
then level off
Ramped to N deposition level of 2000, then
continue to increase linearly
CO2
Ozone
Running
years
200 yrs up to 2000
200 yrs up to 2000
200 yrs up to 2000
200 yrs up to 2000
200 yrs up to 2000
200 yrs up to 2000
200 yrs up to 2000
300 yrs up to 2100
Fixed, 280 ppmv
Fixed, 280 ppmv
Ramped (280-366 ppmv)
Ramped (280-366 ppmv)
Ramped (280-366 ppmv)
Fixed, 280 ppmv
Ramped (280-366 ppmv)
Ramped up to 600 ppmv
No
No
No
No
Yes
No
Yes
Yes
Interaction
No
No
No
No
Yes
No
Yes
Yes
Ramped up to 366 ppmv in
2000, then fixed
Fixed, 280 ppmv
Yes
Yes
300 yrs up to 2100
No
No
250 yrs up to 2050
Fixed, 280 ppmv
No
No
250 yrs up to 2050
Wet+dry
Scenarios of Atmospheric Chemistry
Elevated CO2 (ppmv)
Year
Year
Scenarios of Atmopsheric N Deposition
N deposition (Kg/ha)
24
20
1xN
2xN
1 x N increase
1 x N regulation
16
12
8
4
0
1900
1925
1950
1975
Year
2000
2025
2050
Annual NPP (g/m2)
Annual NPP under Different Scenarios
(Delaware River Basin )
+22%
+12% +47% +25%
Annual NPP under N deposition scenarios
Annual NPP (g/m2/yr)
(Delaware River Basin)
1200
1000
800
600
400
Control
1X N
2xN
1 x N regulation
200
0
+22%
+25%
+24%
Biomass (Mg /ha)
Forest Biomass under Different Scenarios
+11%
+18% +38% +4%
Forest biomass under N deposition scenarios
BIomass (Mg/ha)
300
250
200
150
100
Control
1x N
2xN
1 x N regulation
50
0
+11%
+4%
+10%
Soil organic matter (Mg/ha)
Soil Organic Matter under Different Scenarios
+22%
+5% +28%
+34%
Soil mass under N deposition scenarios
180
Soil mass (Mg/ha)
160
140
120
100
80
60
Control
1x N
2xN
1 x N regulation
40
20
0
+22%
+34%
+39%
Soil N leaching under N deposition scenarios
N leaching loss (kg/ha)
10
8
Retention rates:
75%
6
4
2
0
85%
79%
Control
1xN
2xN
1 x N regulation
Table 2a. The predictions of the forest N exports to streams and N
retention rates in the Delaware River Basin.
Current N Scenario (Mean N deposition = 11.5 kg N ha-1 yr-1 )
Tree
Forest area Total N loss
Min
Max
Mean
Groups
(km2)
(Mg N)
(kg N ha-1 yr-1)
STdev N retention
(%)
N. Hardwood
Oak-hickory
Pine
Oak-pine
Region
0.350
0.486
2.654
1.406
0.990
3,455
11,919
1,242
1,075
17,695
649.56
175.43
314.50
316.20
3037.91
0.813
0.508
0.665
0.569
0.508
4.478
4.066
12.340
10.770
12.340
1.879
1.474
2.530
2.938
1.716
84
87
75
74
85
Doubled N Scenario (Mean N deposition = 23.1 kg N ha-1 yr-1)
Tree
Forest areas Total N loss
Min
Max
Mean
Groups
(km2)
(Mg N)
(kg N ha-1 yr-1)
STdev N retention
(%)
N. Hardwood
Oak-hickory
Pine
Oak-pine
Region
3.239
3.526
3.193
3.038
3.810
3,455
11,919
1,242
1,075
17,695
2292.10
5589.62
1316.06
844.32
10043.13
1.702
0.990
3.965
2.407
0.990
20.310
21.280
22.500
25.190
25.190
6.632
4.689
10.587
7.846
5.675
71
80
47
65
75
Table 2b. The predictions of the forest N exports to streams and N
retention rates in the Delaware River Basin.
Current N Scenario (Mean N deposition = 11.5 kg N ha-1 yr-1 )
Tree
Forest area Total N loss
Min
Max
Mean
Groups
(km2)
(Mg N)
(kg N ha-1 yr-1)
STdev N retention
(%)
N. Hardwood
Oak-hickory
Pine
Oak-pine
Region
0.350
0.486
2.654
1.406
0.990
3,455
11,919
1,242
1,075
17,695
649.56
175.43
314.50
316.20
3037.91
0.813
0.508
0.665
0.569
0.508
4.478
4.066
12.340
10.770
12.340
1.879
1.474
2.530
2.938
1.716
84
87
75
74
85
N regulation Scenario (Mean N deposition = 11.5 kg N ha-1 yr-1)
Tree
Forest areas Total N loss
Min
Max
Mean
2
-1
Groups
(km )
(Mg N)
(kg N ha yr-1)
STdev N retention
(%)
N. Hardwood
Oak-hickory
Pine
Oak-pine
Region
1.423
1.337
2.145
1.597
1.737
3,455
11,919
1,242
1,075
17,695
893.08
2223.31
655.51
433.27
4205.67
0.803
0.507
1.768
1.003
0.507
10.200
10.880
12.310
12.880
12.880
2.584
1.865
5.273
4.026
2.376
78
84
48
65
79
Selected FIA sites
(mature) for
validation (n=98)
Modeled veg biomass (Mg/ha)
400
300
200
N. Pine
S. Pine
Oak-pine
Oak-hickory
Ash-elm
N. Hardwood
100
n=318
0
0
100
200
300
FIA derived biomass (Mg/ha)
400
Modeled veg biomass (Mg/ha)
400
n=318
300
200
N. Pine
S. Pine
Oak-pine
Oak-hickory
Ash-elm
N. Hardwood
100
0
0
100
200
300
FIA derived biomass (Mg/ha)
400
Modeled N losses (kg N ha-1 yr-1)
6
n=180
5
4
3
2
1
0
0
1
2
3
4
5
USGS observed N losses (kg N ha-1 yr-1)
6
Atmospheric Inputs and Stream N Exports in the Delaware
River Basin
Watershed
Mean
stream
output
(kgN
/ha/yr)
N
N
Deposition Retention
(kgN
/ha/yr)
(%)
1
Delaware Bay
1.83
12.65
86
2
Delaware Bay
2.96
12.65
77
3
PnET-CN (mean)
1.71
11.53
85
4
PnET-CN (range)
5
PnET-CN (adjusted mean)
1
1.47-2.93 10.04-11.68
2.12
11.56
74-87
81
Estimates based on measured data (Stacey and others 2000).
Estimates by the SPARROW model (Alexander and others 2000).
3
Estimate for forested lands by the PnET-CN model.
4
Ranges of the values predicted by PnET-CN for forests.
5
Estimate based on the PnET-CN result after adjusting to urban lands.
2
Conclusions:
 The modeling results suggest that chronic N increases in
the past 70 years has increased forest productivity by
22%, forest biomass of 11% and soil organic matter of
22%. Overall, the interactive effects of rising N
deposition and CO2 caused remarkable C gains in
forest living biomass (38%) and soil mass (28%). The
forest regrowth in the region only counted for about
62% of the carbon sequestrated in the forest
ecosystems.
 Forests in the Basin seem close to N saturation status
under current N deposition level. 2X N deposition
resulted in similar increases in annual NPP, and lower
forest biomass with respect to 1X N.
 The current N leaching loss from the forested land of the
DRB is 1.7 Kg/ha, and N retention rate is 85%.
 With 2X N deposition scenario, the N retention rate will
drop to 75% and the total N export to stream water
would nonlinearly increase by 330%.
 Extending the current 1X N regulation for another 50
years, leveling off N deposition at the current level would
lower retention to 79% from 85%, and the total N export
would increase by 38%, suggesting there will eventually
be N saturation at current deposition levels.
Future Work:
 Explore the effects of zone and calcium depletion on forest
productivity.
 Improve the modeling predictions at the basin level by
incorporating information of forest fragmentation and
land-use types.
 Refine the modeling work with the MODIS vegetation
classes and the new parameterization.
 Explore the effects of climatic variations and interactions
with other global change factors.
 Project the forest conditions under the 2100 scenario with
multiple stressors.
Thank You !