Transcript Shenandoah National Park

Shenandoah National Park:
Critical Load/Target Load Case Study
Photo credit: University of
Virginia
WESTAR November 2005
Tamara Blett- National Park Service
Shenandoah National Park:
Critical Load/Target Load Case Study
Focus on:
1.Use of ecosystem and deposition data in
critical loads development for aquatic
ecosystems
2. Selection of critical loads and target loads
from modeling outputs
3. Why land health goals are needed before
each critical load or target load is developed
No such thing as a
“generic” critical
load for a park or
wilderness area….
A CL is the loading
at which
SOMETHING
happens in an
ecosystem.
Defining which
SOMETHING is
relevant to the FLM
area is a critical
part of CL
development …
Forest
dieback
Chronic
acidification
Episodic
acidification
Changes in
soil
productivity
Aquatic plant
species
shifts from
fertilization
Load (kg/ ha /yr)
Shenandoah National Park:
Critical Load/Target Load Case Study
Critical load:
The quantitative estimate of an exposure to
one or more pollutants below which
significant harmful effects on specified
sensitive elements of the environment do
not occur according to present
knowledge.”
WESTAR FRAMEWORK WORKGROUP QUESTION:
What are the AQRVs that should be addressed and what are
the criteria for addressing them?
3 types of critical loads development efforts:
1. N & S acidification effects to aquatic
ecosystems (via water chemistry
thresholds)
Simulation
modeling
2. N & S acidification effects on forest
ecosystems (via soil chemistry
thresholds)
3. N fertilization effects on aquatic and
terrestrial plant and animal species (via
species shifts)
Field data
and
experiments
Which AQRVs to use in CL development?
• FLMs have the
responsibility to identify our
AQRVs and develop
strategies to protect them
• FLMs will protect most
sensitive resources from
unacceptable change
• FLMs will base critical loads
on best available science
and revise and update as
appropriate
Shenandoah National Park:
Use of Ecosystem and Deposition Data in CL Development
Current Deposition
Loadings:
• Shenandoah
National Park has
long experienced
high deposition
loadings.
• Sulfur deposition
(rather than N) is
the primary cause of
acidification of park
soils and waters.
Photo credit: University of
Virginia
Stream chemistry sampling tells us which aquatic plants and
animals can grow, survive, reproduce… and which cannot
Park streams are highly impacted by deposition:
•Pre-1900, all Shenandoah streams had
ANC>50 ueq/l (levels that sustain
healthy aquatic biota)
•In a 1992 survey, about half of the
most sensitive streams had ANC<0,
with lethal effects on brook trout
probable
•The rest had ANC between 0-20, with
sub-lethal or lethal effects possible.
•Modeling suggests that most sensitive
streams in the park have lost up to 4
fish species
WESTAR FRAMEWORK WORKGROUP QUESTION:
Are there simple endpoints (like visibility thresholds)
that can be used to assess effects?
FLM selects desired endpoints and effects
Aquatic ecosystems
Desired goals: healthy biota (invertebrates, fish,
aquatic plants, etc.)
Measurement endpoints: ANC, pH, base cations, Al
– ANC of 50-100 ueq/l considered acid-sensitive
but capable of supporting healthy biota
– ANC < 50 ueq/l sensitive to acidification;
potential effects to biota
– ANC < 20 ueq/l: episodically acidic, sub-lethal or
lethal effects on biota
– ANC < 0 ueq/l: chronically acidic, lethal effects
on many biota
Acidified*
Extremely Acid Sensitive*
Acid Sensitive*
7.0
Healthy!
6.5
small decrease
in species
richness*
loss of acid
sensitive
species*
Daily stream pH
6.0
5.5
Loss of
additional fish /
invertebrates*
5.0
metals soluble
free ionic form
4.5
Toxic!
4.0
-40.0
-30.0
-20.0
-10.0
0.0
10.0
20.0
30.0
40.0
50.0
60.0
70.0
Daily stream ANC (ueq/L)
Less soil buffering capacity
More soil buffering capacity
*Baker et al. 1990
Deposition accumulates in soils
over time:
•Soils soak up pollutants like a
sponge over time
•Excess sulfur accumulates in
soils, acidic conditions develop,
which then strip beneficial
nutrients from the soils and
weaken plants
•Acidic compounds “use up” the
buffering ability of soils and
surface waters.
Development of Critical load or
Target load
Critical load:
“The quantitative estimate of an exposure
to one or more pollutants below which
significant harmful effects on specified
sensitive elements of the environment do
not occur according to present
knowledge.” (Nilsson and Grennfelt 1988)
Significant harmful effects from deposition have been documented in
Shenandoah streams BUT they are above the critical load… and we
don’t know the loading at which they first began……
Now the more relevant question is: what loading is
desired to achieve to meet ecosystem goals?
Target load:
The level of exposure to one or more pollutants
that results in an acceptable level of resource
protection; may be based on political, economic, or
temporal considerations.
Surface Water Effects Thresholds Used to Develop Critical & Target Loads
Chronic
acidification
Episodic
acidification
<0 ueq/L
<20 ueq/L
Healthy aquatic >50ueq/L
biota
Changes in soil &
water chemistry
Load (kg/ ha /yr)
Critical loads are defined for specific indicators and effects.
Water quality data
used in modeling CL/TL
14 streams in Shenandoah have
sufficient water chemistry
data for calibrating the
MAGIC* model.
Streams were routinely sampled for
12 yrs as part of the SHEN
Watershed Study and the
Virginia Trout Stream
Sensitivity Study.
Of the 14 streams, only 5 were on
very sensitive (siliciclastic)
bedrock; the remainder were
relatively insensitive.
*Modeling for Acidification of Groundwater In Catchments
Deposition
reduction
Deposition (kg/ha/yr)
Current
Re-evaluate; adjust
•Set interim target
•Establish glide path
Interim Target
•Re-evaluate periodically
Natural
Time
Developing Interim Target Loads
• FLM sets management goal: “restore healthy
ecosystems (ANC=50) to Shenandoah NP”
• Scientists may/may not be able to determine the
actual CL (the deposition loading at which
Shenandoah ecosystems became unhealthy in the
past)
• Target loads to achieve ANC of 50 in 50 years ranges
from 0-4 kgS/ha/yr (depending on individual stream).
• Models (MAGIC and others) used to determine how
deposition reductions could improve stream
chemistry conditions
• Deposition in Shenandoah is now ~10 kg S/ha/yr.
• States (w/FLM involvement) develop Interim Target
Loads to set improvement goals over time (similar to
a glide path for visibility improvement).
Current vs. 40% Reduction
60
% of brook trout streams
Not acidic
(Suitable for brook trout)
50
Chronically Acidic
(Unsuitable for brook trout)
40
30
20
10
0
Current (1991)
Future (2041)
Shenandoah researchers project that streams will continue to acidify in the
future due to S and N deposition, even with projected reductions in SO2
emissions.
So…. May need longer time frames for recovery
when developing target loads
AND
May need to consider more stringent emissions
reductions if ecosystem goals are to be met to
protect parks for “future generations”
Eastern US sites are worse off… there is still time
to avoid major ecosystem damage in the west if
deposition levels are reduced.
Conclusions
1.Need good ecosystem data as model inputs
to develop critical loads/target loads
modeling estimates
2. Critical loads may be difficult to
determine where already exceeded
(unless we know when they were first
exceeded and what the deposition was in
that time and place)
3. Target loads can be established via
modeling for areas where CL have been
exceeded
4. Defining ecosystem health and recovery
goals is crucial before using modeled
critical load or target load outputs.