Clean Air Status and
Trends Network
(CASTNET)
2003
Program and
Technical Summary
May 2005
A
-------
CASTNET 2003 Program and Technical Summary
Table of Contents
About CASTNET 2
CASTNET Operations 3
Cooperative Long-Term Environmental Monitoring at CASTNET Sites 3
CASTNET Monitoring Sites 4
Atmospheric Species Measured by CASTNET 5
Total Deposition 6
Ozone Monitoring 7
CASTNET Monitoring in Sensitive Ecosystems
Coastal Environments 8
Great Smoky Mountains National Park and the Southern Appalachians 9
Documentation for the network including past annual reports and the CASTNET Quality
Assurance Project Plan can be found at the CASTNET on-line library:
www.epa.gov/castnet/library.html
The CASTNET database is available to the public via EPA's
CASTNET data web page:
www.epa.gov/castnet/data.html
Prepared by MACTEC Engineering and Consulting, Inc. for:
U.S. Environmental Protection Agency
Office of Air and Radiation
Clean Air Markets Division
Washington, DC
-------
EPA's Clean Air Status and Trends Network
Pisgah National Forest, NC (PNF126)
Air pollution has far-reaching effects. It negatively
impacts human health, agricultural crops, natural
ecosystems, national monuments, buildings, and
other man-made products. Emissions of sulfur,
nitrogen, and other substances react in the
atmosphere with particles, water droplets, oxygen,
and oxidants to form acidic compounds. These
compounds are often transported long distances and
then deposited to the environment by precipitation,
clouds, and other meteorological events. Dry
deposition, a component of total deposition, involves
complex atmospheric processes such as settling,
impaction, and absorption whereby, in the absence
of precipitation, airborne particles and gases reach
the earth's surface. Dry deposition makes up 10 to
70 percent of total deposition depending on location
and climate.
In 1990, Congress passed the Clean Air Act
Amendments (CAAA), which mandated ambient
monitoring to provide information and to track trends
in pollutant concentrations and the dry deposition
component of total atmospheric deposition. The
information and trends data collected through
ambient monitoring are used to determine the
effectiveness of sulfur dioxide (SO^ and nitrogen
oxides (NOX) emission reductions promulgated by
the CAAA. To meet this monitoring need, the U.S.
Environmental Protection Agency (EPA) established
the Clean Air Status and Trends Network
(CASTNET) in 1991, incorporating sites from the
National Dry Deposition Network (NDDN), which
began operation in 1987. Since 1991, many sites
have been added, and there are now more than 85
sites across the United States. The National Park
Service (NPS) joined with EPA in 1994 as a principal
sponsor and currently sponsors 30 CASTNET sites.
CASTNET Principal Sponsors
United States Environmental Protection Agency
National Park Service
CASTNET Partners
In addition to EPA and NPS, other partners support the operation of CASTNET sites. These partners include:
Alabama-Coushatta Tribe Long Term Ecological Research Program (LTER)
Canadian Air and Precipitation Monitoring
Network (CAPMON)
Interagency Monitoring of Protected
Visual Environments (IMPROVE)
Cherokee Nation St. Johns River Water Management District
Kansas State University State University of New York
National Atmospheric Deposition Program (NADP) U.S. Department of Agriculture Forest Service
-------
CASTNET Operations
The original network design was based on the
assumption that dry deposition, or flux, could be
estimated as the linear product of measured
pollutant concentration and modeled deposition
velocity.
Weekly integrated averages of atmospheric
concentrations are obtained through laboratory
analysis of the 3-stage filter packs installed weekly
at each CASTNET site. The influence of
meteorological conditions, vegetation, and chemistry
is simulated by the deposition velocity, which is
calculated using the Multi-Layer Model. To support
the estimation of deposition velocity, all CASTNET
sites include equipment to measure a
comprehensive suite of meteorological parameters.
All field equipment is subject to semiannual
inspections and multipoint calibrations using
standards traceable to the National Institute of
Standards and Technology (NIST). Results of field
calibrations are used to assess sensor accuracy and
validate field data.
CASTNET operations include a comprehensive
quality assurance (QA) program that was designed
to ensure that all reported data are of known and
documented quality. QA is emphasized in order for
CASTNET data to meet CASTNET objectives and
be reproducible and comparable with other
monitoring networks and laboratories.
Cooperative Long-Term Environmental Monitoring at CASTNET Sites
Many CASTNET site locations serve multiple monitoring efforts, some of which belong to long-term networks
designed to monitor environmental factors not covered by the CASTNET design. The following table summarizes
10 such networks whose activities include a wide range of measurements. The number of sites listed for each
network represents the number of sites located within 10 kilometers of a CASTNET site.
Network
Year
Began
Sites Collocated
with CASTNET
Sponsoring Agency
Types of Measurements
Atmospheric Integrated Research 1992
Monitoring Network (AIRMoN)
Canadian Air and Precipitation 1978
Monitoring (CAPMoN)
Climate Reference Network (CRN) 2004
Interagency Monitoring of Protected 1985
Visual Environments (IMPROVE)
Long-Term Ecological Research 1980
Network (LTER)
Mercury Deposition Network (MDN) 1995
National Dioxin Air Monitoring Network 1997
(NDAMN)
National Trends Network (NTN) 1978
Surface Radiation Budget Network 1993
(SURFRAD)
UV-B Monitoring and Research 1992
Program
5 active
17 planned
35
12
58
National Atmospheric Deposition Program (NADP)
Wet deposition - event-based sampling
http://nadp.sws.uiuc.edu
Environment Canada
Dry and wet components of total deposition
http://www.msc.ec.gc.ca/capmon
National Oceanic and Atmospheric Administration (NOAA)
Homogenous measurements of temperature/ precipitation
http://www.ncdc.noaa.gov/oa/climate/uscrn
Multi-agency collaboration
Visibility in Class I areas
http://vista.cira.colostate.edu/improve
National Science Foundation
Ecological processes
http://www.lternet.edu
National Atmospheric Deposition Program (NADP)
Wet deposition/ methyl mercury
http://nadp.sws.uiuc.edu
Environmental Protection Agency (EPA)
Dioxinsand PCBs
National Atmospheric Deposition Program (NADP)
Wet deposition component of total deposition
http://nadp.sws.uiuc.edu
National Oceanic and Atmospheric Administration (NOAA)
U.S. radiation budget
http://www.srrb.noaa.gov/surfrad
U.S. Department of Agriculture
Ultraviolet-B radiation
http://nadp.nrel.colostate.edu
-------
State
AL
AK
AZ
AR
CA
CO
CT
FL
GA
HI
IL
IN
KS
KY
ME
MD
Ml
MN
MS
MT
NV
NH
NJ
NY
NC
ND
OH
OK
ON
PA
SD
TN
TX
UT
VT
VI
VA
WA
WV
Wl
WY
Site ID
SND152
DEN417
POF425
CHA467
GRC474
PET427
CAD150
CON186
DEV412
JOT403
LAV410
PIN414
SEK402
YOS404
GTH161
MEV405
ROM206
ROM406
ABT147
EVE419
IRL141
SUM156
GAS153
HVT424
ALH157
BVL130
STK138
SAL133
VIN140
KNZ184
CDZ171
CKT136
MAC426
MCK131
ACA416
ASH135
HOW132
BEL116
BWR139
ANA115
HOX148
UVL124
VOY413
CVL151
GLR468
GRB411
WST109
WSP144
CAT 175
CTH110
HWF187
BFT142
CND125
COW137
PNF126
THR422
DCP114
LYK123
OXF122
QAK172
CHE185
EGB181
ARE128
KEF112
LRL117
MKG113
PSU106
WNC429
ESP127
GRS420
SPD111
BBE401
CAN407
LYE145
VII423
PED108
SHN418
VPI120
MOR409
NCS415
OLY421
CDR119
PAR107
PRK134
CNT169
PND165
YEL408
Station
Sand Mountain
Denali National Park
Poker Flats Research Range
Chiricahua National Monument
Grand Canyon National Park
Petrified Forest National Park
Caddo Valley
Converse Station
Death Valley National Monument
Joshua Tree National Monument
Lassen Volcanic National Park
Pinnacles National Monument
Sequoia National Park
Yosemite National Park
Gothic
Mesa Verde National Park
Rocky Mountain National Park
Rocky Mountain National Park
Abington
Everglades National Park
Indian River Lagoon
Sumatra
Georgia Station
Hawaii Volcanoes National Park
Alhambra
Bondville
Stockton
Salamonie Reservoir
Vincennes
Konza Prairie
Cadiz
Crockett
Mammoth Cave National Park
Mackville
Acadia National Park
Ashland
Howland
Beltsville
Blackwater National Wildlife Refuge
Ann Arbor
Hoxeyville
Unionville
Voyageurs National Park
Coffeeville
Glacier National Park
Great Basin National Park
Woodstock
Washington's Crossing
Claryville
Connecticut Hill
Huntington Wildlife Forest
Beaufort
Candor
Coweeta
Pisgah National Forest
Theodore Roosevelt National Park
Deer Creek State Park
Lykens
Oxford
Quaker City
Cherokee Nation
Egbert, Ontario, Canada
Arendtsville
Kane Experimental Forest
Laurel Hill State Park
M.K Goddard State Park
Pennsylvania State University
Wind Cave National Park
Edgar Evins State Park
Great Smoky Mountains National Park
Speedwell
Big Bend National Park
Canyonlands National Park
Lye Brook
Virgin Islands National Park
Prince Edward
Shenandoah National Park
Virginia Poly Tech
Mount Rainier National Park
North Cascades National Park
Olympic National Park
Cedar Creek State Park
Parsons
Perkinstown
Centennial
Pinedale
Yellowstone National Park
CASTNET Monitoring Sites
As of December 2003, 87 CASTNET monitoring sites
were operational (Figure 1). Most CASTNET sites are
located in rural, regionally representative locations away
from pollution emission sources and heavily populated
areas. The map shows reasonable geographic coverage
in most regions of the United States. Less coverage is
provided in the central United States from South Dakota
to Texas. The addition of new sites in the central United
States will enhance the ability of the network to
determine patterns and trends in air pollutant
concentrations and deposition rates and will help assess
the effectiveness of emission control regulations.
CASTNET's primary goal is to monitor trends in
regional-scale air quality and dry deposition. For the
time period 1990 through 2003, 34 CASTNET sites
were selected as reference sites (shown in red on
Figure 1) based on the completeness of their 14-year
data record and on criteria similar to those used by the
U.S. Environmental Protection Agency in its National Air
Quality and Emission Trends Report (2000). As the
network ages and the period of interest changes,
additional sites will meet these requirements and will be
added as reference sites.
Figure 1. CASTNET Sites as of December 2003
Sites
Not Displayed:
Alaska - 2 sites
Hawaii -1 site
U.S. Virgin Islands - 1 site
-------
Atmospheric Species Measured by CASTNET
Figure 2. Mean Annual SO2
Concentrations (ug/m3)
(1991-1993)
D18
D 14
D 10
D 6
D 2
(2001-2003)
The table below details the atmospheric species routinely
measured at CASTNET sites. Following laboratory analysis
of a filter pack, atmospheric concentrations for each of the
analytes, except ozone, are calculated by dividing the mass
on each filter by the total flow volume through the filter pack
during the sampling period. Ozone concentrations are
measured hourly by a separate instrument.
The maps to the left (Figure 2) display annual mean SO2
concentrations in ug/m3 for 1991 through 1993 (top) and
2001 through 2003 (bottom). The dramatic reduction of SO2
between the two periods indicates the success of the
Phase I and II SO2 emission reductions mandated by the
Clean Air Act Amendments of 1990. Only CASTNET sites
with valid measurements during both 3-year periods are
included on the maps. For CASTNET sites along the Ohio
River Valley, SO2 concentrations decreased by an average
of approximately 60 percent.
Particulate sulfate concentrations also decreased between
the two time periods while atmospheric concentrations of
nitrogen species and ozone showed no significant change.
For maps of concentrations of other analytes, please see the
CASTNET 2003 Annual Report.
Species
Chemical
Symbol
State
Description
Sulfur Compounds
Sulfur dioxide
Sulfate
S02
so24
gas
particle
Emitted through the combustion of coal and oil that contain sulfur; reacts to form various
acidic compounds including sulfuric acid (H2SO4), a significant contributor to acid rain.
Typically exists in the atmosphere as ammonium sulfate (NH4)2SO4, major component of fine
particle matter (PM2.5).
Nitrogen Compounds
Nitric acid
Nitrate
Ammonium
HNO3
NO;
NH*4
gas
particle
particle
Created by emissions of nitrogen oxides (NOX) produced during combustion; a significant
contributor to acid rain.
Created by emissions of nitrogen oxides (NOX) produced during combustion; typically exists
as ammonium nitrate (NH4)NO3, a major component of PM25.
Formed when ammonia (NH3) reacts with sulfate and nitrate particles in the atmosphere.
Other Ions and Cations
Potassium
Sodium
Magnesium
Calcium
Chloride
K+
Na+
Mg2+
Ca2+
cr
particle
particle
particle
particle
particle
These particles occur naturally in the atmosphere through weathering and soil erosion and
from urban and industrial sources. Cation particles counteract the acidity of the sulfur and
nitrogen anion particles through their ability to neutralize the anions.
Surface Level Ozone
Ozone
03
gas
Formed through complex chemical reactions among precursor emissions of volatile organic
compounds (VOC) and nitrogen oxides (NOX) in the presence of sunlight.
-------
Total Deposition
Total deposition at CASTNET sites is estimated by
combining dry deposition fluxes modeled using the
Multi-Layer Model (see page 3) with wet deposition
estimated from National Atmospheric Deposition
Program/National Trends Network (NADP/NTN)
sites. Dry deposition accounts for about 10 to
70 percent, depending on location and climate, of
total deposition for both sulfur and nitrogen. Median
values are approximately 40 percent for sulfur
deposition and 30 percent for nitrogen deposition.
Figure 3 illustrates the magnitude of total sulfur
deposition during 2003, shown by the diameter of
the circles and the relative contributions from dry
and wet deposition. Relatively high rates of sulfur
deposition were observed in the states along and
downwind of the Ohio River Valley. Lower rates of
sulfur deposition were observed along the
peripheries of the network, i.e., in the northernmost
states, the Great Plains, Florida, and throughout the
western states.
Figure 4 depicts the magnitude of total nitrogen
deposition rates during 2003. In the states along the
Ohio River Valley, contributions to total nitrogen
deposition from dry and wet deposition were more
evenly distributed than the respective contributions
to total sulfur deposition for the same area. Lower
nitrogen fluxes were observed in the northernmost
states, Florida, and throughout the West.
Figure 5 shows that total sulfur deposition at the
reference sites (Figure 1) has declined significantly
over the last 14 years. The sharp decline in 1995
closely parallels the decline in sulfur dioxide
emissions that resulted from the electric generating
utilities' compliance with Phase I of the Acid Rain
Program. The trend line for total nitrogen deposition
shows no significant change over the time period.
However, there has been an increase in rates over
the last two years. Increases in sulfur and nitrogen
are associated, in part, with increased precipitation
in the Eastern United States particularly in 2003.
Figure 3. Total Sulfur Deposition for 2003 (kg/ha/yr)
D Dry Deposition
D Wet Deposition
Figure 4. Total Nitrogen Deposition for 2003 (kg/ha/yr)
D Dry Deposition
D Wet Deposition
Figure 5. Timeline of Total Deposition (kg/ha/yr)
16
-------
Ozone Monitoring
Although not a regulatory network, CASTNET ozone
(O3) monitoring provides information on geographic
patterns in regional ozone and on how
concentrations in rural areas compare to the national
standard for the pollutant. The 8-hour ozone
standard is 0.080 ppm and is assessed by
calculating an 8-hour "design value," which is
determined by taking the fourth highest daily value
measured at a site for each year of a 3-year period
and finding the average. In practice, sites with
design values greater than or equal to 85 ppb are
considered to be in violation of the standard.
CASTNET ozone data are not explicitly used in the
determination of attainment, and, therefore, design
values are not calculated for CASTNET sites.
However, fourth highest daily maximum 8-hour
concentrations are calculated according to EPA
protocol for specific years for the purpose of
examining non-urban ozone levels.
Figure 6. Fourth Highest Daily Maximum 8-Hour
Ozone Concentrations (ppb) for 2003
Eastern Sites
(2003)
Figure 6 shows the fourth highest daily maximum
8-hour concentrations for CASTNET sites in the
eastern United States for 2003. To demonstrate
where nonattainment regions exist and relate the
depicted CASTNET concentrations to these areas,
EPA attainment designations for counties in the
eastern United States are also shown on the map.
The maps are based on designations released
in 2004.
CASTNET sites with fourth highest daily maximum
8-hour concentrations for 2003 that are greater than
or equal to 85 ppb are shown in blue. Sites with
concentrations lower than 85 ppb are shown in
black. Of the 42 sites considered, five eastern sites
observed a fourth highest daily maximum 8-hour
value greater than or equal to 85 ppb. For 2003, the
mean of the fourth highest daily maximum 8-hour
concentrations for the 42 sites is 77 ppb.
Figure 7. Timeline of Fourth Highest Daily Maximum
8-hour Ozone Concentrations (ppb)
100
.1 90 H
'ro
I
° 80 H
70
OT-CNco-a-iocor^oo
O5O5O5O5O5O5O5O5O5O5OOOO
O5O5O5O5O5O5O5O5O5O5OOOO
CNCNCNCN
] Nonattainment Areas (full county)
] Nonattainment Areas (partial county)
1 Unclassified Areas
Figure 7 depicts trends in fourth highest daily
maximum 8-hour O3 concentrations aggregated over
all eastern reference sites (Figure 1) for 1990-
2003. The diagram shows that the 2003 value was
the lowest in CASTNET history. No overall trend is
evident in the time series. The lower value in 2003
was produced in part by cool, cloudy, wet weather
during the ozone season.
-------
CASTNET Monitoring in Sensitive Ecosystems:
Coastal Environments
CASTNET includes five sites along the eastern
coast of the United States that provide valuable
information about the coastal and estuarine
environment (Figure 8). Two of these sites are in
national parks: Acadia National Park, ME (ACA416)
and Everglades National Park, FL (EVE419). The
other three sites are located in estuaries that are
part of EPA's National Estuary Program: Maryland
Coastal Bays, MD (BWR139); Albemarle-Pamlico
Sounds, NC (BFT142); and Indian River Lagoon, FL
(IRL141). The National Estuary Program was
established by Congress in 1987 to improve the
quality of important estuaries.
Figure 8. Costal CASTNET Sites
Acadia
(ACA416)
Maryland Coastal Bays
(BWR139)
Albemarle-Pamlico Sounds
(BFT142)
Indian River Lagoon
(IRL141)
Everglades
(EVE419)
analyses suggest that approximately 13 percent of
total external nitrogen loading into the Sebastian
Inlet region of the Indian River Lagoon results from
atmospheric deposition processes. Estimates of the
dry deposition of nitrogen are being used in similar
estuarine research efforts as interest increases
regarding the role of atmospheric deposition in the
nutrient enrichment and eutrophication of sensitive
water bodies.
Figure 9 shows 3-year annual averages (2001-2003)
of the wet and dry components of total nitrogen
deposition for the five coastal CASTNET sites
(Figure 7). Also included for comparison is the total
nitrogen deposition profile for the same time period
for the 34 CASTNET reference sites (Figure 1).
Figure 9. Components of Annual Mean Total
Nitrogen Deposition (kg/ha/yr) 2001-2003
10 -,
9 -
8 -
7 -
i e-
!5
& 4
3
2 -
1 -
D NH4+Wet Deposition (as N)
D NO3" Wet Deposition (as N)
D NH4+ Dry Deposition (as N)
D NO3" Dry Deposition (as N)
D HNO3 Dry Deposition (as N)
Acadia Maryland Albemarle- Indian Everglades Mean of
National Coastal Pamlico River National CASTNET
Park Bays Sounds Lagoon Park Reference
(ACA416, ME) (BWR139, MD) (BFT142, NC) (IRL141, FL) (EVE419, FL) Sites
The site at IRL141, FL is sponsored by Florida's
St. Johns River Water Management District to help
quantify the contribution of atmospheric deposition
to the total nutrient load to the estuary. Using the dry
deposition estimates from the CASTNET site with
wet deposition data from an adjacent National
Atmospheric Deposition Program / National Trends
Network (NADP/NTN) style collector, preliminary
Nitrogen deposition levels are highest at the coastal
sites in North Carolina and Maryland with total
deposition for BWR139, MD greater than the mean
of the reference sites. Sites in Maine and Florida
have lower deposition rates. The Florida sites show
dry deposition of nitrogen as contributing the lowest
percentage of the total deposition with an average of
17 percent. The splits for the other sites are similar
to the split for the reference sites.
-------
CASTNET Monitoring in Sensitive Ecosystems:
Great Smoky Mountains National Park and the Southern Appalachians
High elevation ecosystems are often sensitive to
deposition because they lack the ability to neutralize
and/or assimilate atmospheric inputs. Several
CASTNET sites span the Southern Appalachian
Mountains (Figure 10) including, from north to south,
Shenandoah National Park, VA (SHN418); Virginia
Polytechnic Institute, VA (VPI120); Pisgah National
Forest, NC (PNF126); Great Smoky Mountains
National Park, TN (GRS420); and Coweeta
Hydrologic Laboratory, NC (COW137).
Figure 10. Southern Appalachian CASTNET Sites
Shenandoah
(SHN418)7 O
iGreat Smoky Mountains
(GRS420)
' Virgin ia Tech v
(VPI120)
,
Pisgah National Forest1
(PNF126)
Coweeta Hydrologic Lab
(COW137)
These sites experience relatively high rates of total
atmospheric deposition. Figures 11 and 12 show
annual mean contributions to total sulfur and
nitrogen deposition rates, respectively, for the 3-year
period 2001 - 2003. Annual total sulfur deposition
was more than 9 kg/ha/yr at all of the Appalachian
sites except COW137, NC, which experienced a rate
of 6 kg/ha/yr. Annual total nitrogen deposition
ranged from 5 kg/ha/yr at COW137, NC to more
than 8 kg/ha/yr at GRS420, TN.
Figure 11. Components of Annual Mean Total
Sulfur Deposition (kg/ha/yr) 2001-2003
14 -,
12 -
10 -
0 p
+3 O ~
'(/I
O
Q. r*
0) D
Q
4 -
-
n
n
n
n
S04
SO4
S02
• Wet Dep
" Dry Dep
Dry Depo
ositior
osition
sition
(asS)
(asS)
asS)
Shenandoah Virginia Pisgah Great Smoky Coweeta
National Polytechnic National Mountains Hydrologic
Park Institute Forest National Park Laboratory
(SHN418, VA) (VPI120, VA) (PNF126, NC) (GRS420, TN) (COW137, NC)
Figure 12. Components of Annual Mean Total
Nitrogen Deposition (kg/ha/yr) 2001-2003
12 -
10 -
8 -
c
•e
8 6 -
Q.
Q
4 -
2
n NH4+ Wet Deposition (as N)
D NO3" Wet Deposition
D NH4+ Dry Deposition
D NO3" Dry Deposition
as N)
asN)
asN)
D HNO3 Dry Deposition (as N)
^^^^~
^^~
Shenandoah Virginia Pisgah Great Smoky Coweeta
National Polytechnic National Mountains Hydrologic
Park Institute Forest National Park Laboratory
(SHN418, VA) (VPI120, VA) (PNF126, NC) (GRS420, TN) (COW137, NC)
Clingmans Dome, TN (CLD303)
In addition to wet and dry deposition, higher
elevation sites in the Appalachians may experience
significant cloud water deposition. Clingmans
Dome, TN (CLD303), at an elevation of 2014 meters
-------
in Great Smoky Mountains National Park, is the only
CASTNET site at which cloud water deposition is
measured. The site is sponsored by the National
Park Service and the Tennessee Valley Authority in
cooperation with EPA's Region IV. Figure 13 shows
the large amount of sulfur and nitrogen deposition
that is contributed by clouds bringing total
deposition estimates up to 17 kg/ha and 12 kg/ha,
respectively, for June through September 2003.
Because the CASTNET cloud monitor at CLD303,
TN only operates during the summer season, the
park also measures throughfall, which incorporates
wet, dry, and cloud water deposition on a year-round
basis. Throughfall measurements conducted at the
CLD303, TN site during 2003 were approximately
24 kg/ha/yr for sulfur and 17 kg/ha/yr for nitrogen.
Figure 13. Total Deposition (kg/ha) at CLD303, TN
for June - September 2003
• Cloud Deposition
DWet Deposition
D Dry Deposition
Sulfur
Nitrogen
Atmospheric deposition at Great Smoky Mountains
National Park is one of many stressors affecting the
park's ecosystems. Research shows that both
chronic and episodic acidification adversely affect
streams, soils, and sensitive plants including spruce
fir forests. Due to high rates of atmospheric nitrogen
deposition, high elevation ecosystems are
experiencing advanced stages of nitrogen
saturation. This condition limits the availability of
nutrients (mainly calcium) to plants and causes the
release of toxic aluminum that can harm vegetation
and stream biota.
Figure 14. Timeline of Total Deposition (kg/ha/yr)
with Precipitation (cm) at GRS420, TN
12 -,
10 -
8 -
0
1 6-
Q.
* 4
2 -
0 -
CH Total Sulfur Deposition
EH Total Nitrogen Deposition
-•- Precipitation
.— —
— |
—
-
^
O) O i-
-------
U.S. Environmental Protection Agency
Office of Air and Radiation
Clean Air Markets Division
Washington, D.C.
------- |