1. Ecosystem Responses to
Nitrogen Deposition
in the
Western United States
Jill Baron
U.S. Geological Survey
Colorado State University
Fort Collins CO

2. Against Prevailing Winds
Conversion to
NO3 and NH4
Against Prevailing Winds
NOx
NH3
Fertilizers

5. NITRATE
TRENDS IN WET
PRECIPITATION
CONCENTRATION
(LYNCH et al. 1996)
AMMONIUM
SULFATE

6. Change is in concentration
Nilles and Conley 2001

7. Nilles, M.A. and B.E. Conley 2001,
Wat. Air Soil Pollut. 130:

8. Trends of NH4-N Concentration in Precipitation
1.00
1.40
1.80
2.20
2.60
3.00
(log) ueq/l
1984
1985
1986
1987
1988
1989
1990
1991
1992
1993
1994
1995
1996
1997
1998
Loch Vale (p=0.003)
Niwot Saddle (p=0.001)
Sunlight Peak (p=0.89)
Brooklyn Lake (p=0.04)
Snowy Range (p=0.02) + o -
Trends of NO3-N Concentration in Precipitation
(log) ueq/l
1.00
1.40
1.80
2.20
2.60
3.00
1984
1985
1986
1987
1988
1989
1990
1991
1992
1993
1994
1995
1996
1997
1998
Loch Vale (p=0.68)
Niwot Saddle (p=0.01)
Sunlight Peak (p=0.16)
Brooklyn Lake (p=0.21)
Snowy Range (p=0.97) + o

9. - Trends of H Concentration in Precipitation +
0.5 1
1.5 2
2.5
1984
1985
1986
1987
1988
1989
1990
1991
1992
1993
1994
1995
1996
1997
1998
(log) ueq/l
Loch Vale (p=0.0005)
Niwot Saddle (p=0.03)
Sunlight Peak (p=0.0009)
Brooklyn Lake (p=0.20)
Snowy Range (p<0.001) + o
Trends of SO4 Concentration in Precipitation 1
1.5 2
2.5 3
1984
1985
1986
1987
1988
1989
1990
1991
1992
1993
1994
1995
1996
1997
1998
Loch Vale (p<0.0001)
Niwot Saddle (p=0.47)
Sunlight Peak (p<0.0001)
Brooklyn Lake (p=0.01)
Snowy Range (p=0.002) o -
(log) ueq/l

12. Multiscale Air Quality Model (CMAQ)(36 km resolution)
(b)
NHx-N
NOy-N
(c)
Simulated annual N
deposition for 1996 using
Models-3/Community
Multiscale Air Quality Model
(CMAQ)(36 km resolution)
(from Fenn et al. 2003)
Total N

13. Housing density 2000
WELD
MORGAN
ADAMS
JEFFERSON
DENVER

14. NOx
Elect.+Ind
NOx
Highway
NOx
Off Road
NH3
Livestock
NOx
Agriculture
NH3
Crops

15. EFFECTS OF NITROGEN DEPOSITION?
WHAT ARE THE ECOSYSTEM
EFFECTS OF NITROGEN DEPOSITION?

16. Pathways and Effects of Excess Nitrogen Deposition
Fertilization
Loss of Soil
Base Cations
N Saturation
Changes in
Plant Communities
Loss of Lake ANC
(acidification)
Changes in
Aquatic Species
Lake
Eutrophication

17. Figure 1

18. Coastal Sage Scrub Communities of Southern California
Nitrogen Deposition linked to:
Decrease in symbiotic soil fungi
(mycorrhizae) that enable native
shrubs to get nutrients
-Endangerment of native butterflies
and up to 200 sensitive plant species
Increase in non-native annual
grasses
-Increase in fire frequency
(work by Edith Allen and colleagues,
UC Riverside)

19. San Bernardino Mountains, California
-Up to 90 kg N/ha/yr at some sites
-Ozone and N interact:
a) cancel each other out for aboveground processes,
b) combine to dramatically reduce root biomass and
growth
c) increased risk of severe fire
d) nitrate in some streams exceed drinking water
standards
Fenn, Bytnerowicz,
et al., USDA
Forest Service

20. Weedy, nitrogen-loving pollution indicators
Alectoria sarmentosa
Loss of sensitive
lichen species in
Columbia River Gorge,
Willamette Valley,
San Bernardinos.
Replacement species
show high tissue N
Xanthoria polycaropa
Weedy, nitrogen-loving
pollution indicators
Lobaria oregana
Described in Fenn et
al. 2003
Physcia adscendens
Pollution sensitive species

22. Mineralization Rate vs. Organic Horizon %N
Sites with
measurable
nitrification
The results from this study show a similar relationship between mineralization rate, not nitrification rate and organic horizon soil %N. Soils with less than 1.3 %N had low mineralization rates and soils with %N greater than 1.3 had higher mineralization rates.
Point out: west vs. east side sites.
Colorado Front Range
Baron et al. 2000
Rueth & Baron 2001
New England, USA
McNulty et al. 1991

23. increased microbial N cycling
N deposition:
increased soil %N,
lowered C:N ratios,
increased microbial N cycling
Fertilization studies in low and high N dep’n stands
suggest a trajectory for future change
Between kg N ha-1
initiates biogeochemical changes
Within the 2nd year of fertilization we observed
significant changes at Loch Vale
What can we say about the amount of N required to initiate biogeochemical changes and the rate at which these changes occur?
Within the study we have a gradient of N inputs:
FC - reference point
FF from fert
LVC from atmospheric deposition
LVF from atmospheric and fert inputs
If we take Fraser control as our reference point - somewhere been 100 and 160 kg N ha-1 initiates bgc changes - because 100 did cause significant changes in Fraser however, Loch Vale was significantly different than Fraser.
Within the 2nd year of fertilization we observed significant changes at Loch Vale.
Suggesting that high-elevation Englemann spruce forest will respond rapidly to relatively low N additions.
Soil waters in fertilized plots show high NO3, NH4,
also high levels of Ca, Mg, K.
Leaching of cations is a step toward acidification.

24. Pathways and Effects of Excess Nitrogen Deposition
Fertilization
Loss of Soil
Base Cations
N Saturation
Changes in
Plant Communities
Loss of Lake ANC
(acidification)
Changes in
Aquatic Species
Lake
Eutrophication

26. Indian Peaks Wilderness
Rocky Mtn Nat Park
EVW NO3
Continental Divide
Means: East 10.5 (5.0) West (4.3)
p = 0.02
Front Range – NO3
Indian Peaks Wilderness

27. Annual dynamics,
but no long-term
trends are evident
for alkalinity (ANC)
Nitrate dynamics
are biannual, but
do not show
long-term trends

28. Asterionella formosa
Fragilaria crotonensis

29. Sky Pond
Lake Louise

30. Chl-a
Productivity

31. Analyzing Taxonomic Data…

32. Phytoplankton Results
(PRC)
Green Algae
Chrysophytes

33. WLS NO3 Mean = 1.66 Std dev = 3.59 Range = 0 - 43.05
Western – NO3 – 5 categories
Mean = Std dev = 3.59 Range =

34. Seattle Salt Lake City San Francisco Denver Los Angeles$
Denver
Salt Lake City
Los Angeles
San Francisco
Seattle
WLS NO3 hotspots
Western – NO3 – 4 categories

35. N&P lim 17% 22% (N&P 61%) Nutrient limitation predicted by
DIN:TP ratio
Western – nutrient limitation – 2 categories

36. Eutrophication Acidification
Low NO3
N limitation (17%)
In-lake ANC production from algal NO3 assimilation
High NO3
P limitation
In-lake ANC production from denitrification (less efficient)
Increased N and acid deposition
+ P
Eutrophication, not acidification

37. Summary for Aquatic Ecosystems
-High N deposition => high [NO3] lakes
-Primary productivity in high N lakes
not limited by N
-Substantial species change with N deposition
-Increased N deposition => acidification?

38. Pathways and Effects of Excess Nitrogen Deposition
Fertilization
Loss of Soil
Base Cations
N Saturation
Changes in
Plant Communities
Loss of Lake ANC
(acidification)
Changes in
Aquatic Species
Lake
Eutrophication

39. Comparing sites east and west of the continental divide we found that the eastern sites had characteristics indicating that these forests have been altered by greater N deposition inputs.
Our fertilization experiment supported this conclusion. At low in deposition sites N pools increased without initiating changes in N cycling while at the higher deposition sites N pools where less responsive while N cycling and leaching losses increased dramatically.
These forests are capable of responding to relatively low increases in N inputs.