Transcript Tiered Aquatic Life Use Model

Tiered
Aquatic Life
Use Model
Christy Pickens, Physical Research Scientist
Water Quality Control Division
Colorado Dept. of Public Health and Environment
30 July 2003
Purpose of Model
• The tiered aquatic life use framework
is a conceptual model predicting the
response of aquatic communities to
increasing human disturbance.
• The conceptual model is a draft
framework for using biological
assessment information to refine
designated aquatic life uses.
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Purpose of Model
EPA developed the TALU model for a
nationally consistent approach.
• Scientifically defensible benchmarks
• Common framework for communication and
evaluation- public, stakeholders, across political
boundaries
• Protection for excellent quality waters
• Achievable goals for incremental restoration
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Purpose of Model
National ALUS Workgroup
• Biological Condition Gradient (BCG) focus
of workgroup in 2001.
• Human Disturbance Gradient (HDG) focus
of workgroup in 2002.
• Workgroup recommendations going forward
to EPA this spring with the conceptual
models, implementation options, case
examples.
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TALU Model Basics
Bioassessments help states develop
expectations for acceptable biological
conditions.
This is accomplished through the technical
process of developing aquatic life goals,
aquatic life uses (ALUs).
Biological assessments allow various levels
of ALUs.
Using several types, or tiers, of ALUs allows
states and tribes to allocate limited
resources to waterbodies in proportion to
their need for protection.
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ALUS Integrity
ALUS is determined by assessing:
• Response variable (biological
condition) to determine
impairments and full support
• Stressors (physical and chemical
conditions) to determine
impairment
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TALU Conceptual Model
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TALU Model Basics
The tiered system of use designations
provides for different levels of
protection and reflects the choices
implicit in reconciling the “ideal”
(represented by least impacted
reference conditions) with the “reality”,
the ongoing effects of two centuries of
intensive human use of the state’s land
and water resources.
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TALU Model Basics
Key Points to Emphasize:
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Framework is conceptual
Number of tiers to be determined by State
“Best Fit” approach recommended
The framework may be quantitatively
defined by many possible methods
• BCG is a quality gradient, not a
classification
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TALU Model Basics
• Human Disturbance Gradient
(HDG)
• Biological Condition Gradient
(BCG)
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TALU Model Basics
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TALU Model Basics
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TALU Model Basics
Human Disturbance
Gradient
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TALU Model Basics
HDG Layout
Six tiers (A-F)
Six major stressor classes
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Habitat Structure
Flow Regime
Water Quality
Toxics and Bioengineered Chemicals
Energy Sources
Biotic Interactions
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TALU Model Basics
HDG Layout
Six major disturbance classes
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•
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Landscape Character
Riparian Condition
Barriers
Channel Morphology (map scale)
Atmospheric Deposition
Biotic Interactions
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TALU Model Basics
HDG Rationale
• Essential for determining reference sites and minimal
disturbance
• Necessary for metric and index development and
evaluation
• Often represents half the variability in biological
response scores
• Easier to assess than large suite of stressors
• Assists in diagnosing stressors
• Source of most manageable stressors
• Critical for stream protection, BMPs and restoration
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TALU Model Basics
1.
2.
3.
4.
5.
6.
Draft Model Tiers – 6 levels
Natural structure and function of biotic community
maintained
Minimal changes in structure and function
Evident changes in structure and minimal changes
in function
Moderate changes in structure and minimal
changes in function
Major changes in structure and moderate changes
in function
Severe changes in structure and function
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TALU Conceptual Model
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TALU Conceptual Model
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HDG Concepts
Human disturbance gradient does not
necessarily imply degradation.
Human disturbance gradient
addresses two basic questions:
What is the departure from expected condition
as a result from human activities?
What is the impact of this departure from
expected condition on the biotic community?
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TALU Model Basics
Biological Condition
Gradient
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TALU Model Basics
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TALU Model Basics
Biological Condition Gradient (BCG)
BCG is a quality gradient, with the upper end of the
scale reflecting “natural conditions” corresponding
with the CWA integrity objective.
BCG is not a model to be used for classification of
natural systems, such as ecoregions. BCG would
only be applied once they have been appropriately
classified.
BCG provides consistency among states using
different approaches.
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TALU Model Basics
Biological Condition Gradient
(BCG)
The first tier of the model characterizes the
natural expectations for a waterbody
unimpacted or minimally impacted by
human activities.
The subsequent tiers show the response of
the biological community to increasing
human disturbance.
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TALU Model Basics
BCG Layout
10 Major Attributes
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Taxonomic composition and tolerance
– Attributes I-V
– Regionally Endemic through Tolerant
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Non-Native taxa
– Attribute VI
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Organism condition
– Attribute VII
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Ecosystem function
– Attribute VI
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Physical-biotic interactions
– Attributes IX-X
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BCG Attributes
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BCG Attributes
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BCG Attributes
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BCG Attributes
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BCG Attributes
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BCG Attributes
1
Native or natural condition
2
Biological
Condition
Natural
Minimal loss of species;
some density changes may
occur
Some
replacement of
sensitive-rare
species; functions
fully maintained
3
4
Some sensitive species
maintained but notable
replacement by more
tolerant taxa; altered
distributions; functions
largely maintained
Tolerant species show
increasing dominance;
sensitive species are rare;
functions altered
Severe alteration of
structure and
function
5
Degraded
Low
Stressor Gradient
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High
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BCG Attributes EX
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ALUS Tiers Provide Consistency
a
Natural
1 b 2 c
3 d
4 e
5 f
6
Degraded
Susan P. Davies, MDEP
TALU Model
Thinking ahead…
How can we transition from
describing what we see to
establishing thresholds?
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Designated Aquatic Life Uses in Vermont
natural/
minimally
altered
Class A1: Excellent - Biota within the
range of the natural condition
1
Threshold criterion A1
3
4
highly
altered
5
6
Low
Biocondition Gradient Tiers
Biological
Condition
2
Class B1: Very Good - Minor changes to
structure and function; tolerant/intolerant
forms within the range of reference
condition.
Threshold criterion B1
Class B2/3: Good - Moderate changes in
the relative proportions of tolerant,
intolerant, taxonomic and functional
components.
Threshold criterion B2/3
Non-Support: Fair-Very Poor
Not meeting CWA 101a uses for protection &
propagation of aquatic life
Human Disturbance
High