Transcript Climate Change and Aquatic Ecosystems

Climate Change and
Aquatic Ecosystems
N. LeRoy Poff
Department of Biology
Colorado State University
USEPA Workshop
February 19, 2008
Objectives
• Connecting global climate change to localscale ecological responses
– Conceptual model
– Causal linkages and mechanistic responses?
• Ecosystems, climate, and sensitivity
– Structure and Function
– Present and Future
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Major responses
Regional vulnerabilities to climate change
Confounding environmental drivers
Critical knowledge gaps for bioindicators
Give overview - stimulate discussion
Broader Context: Global Change
• Climate change
• Land Use
• Nonnative Species
http://www.pewclimate.org/global-warming-in-depth/all_reports/aquatic_ecosystems
Conceptual Model
CO2
 Air Temp
 Precipitation
( Vegetation & ET)
 Water Temp
 Runoff regime
GCMs
Hydrologic
Models
- magnitude
- frequency
- duration
- timing
Biological/Ecological
Responses
- structural
- functional
Physico-chemical
Responses
- water chemistry
- habitat quality
- habitat stability
Sensitive bioindicators?
Ecological
Response
Models
Biological / Ecological Responses
Ecosystem
Energy/Material Flow
& Cycling
Community
Population
Species tolerances
and interactions
Demographic rates
(birth, death, etc.)
Individual
Vital Rates
(growth, reproduction)
Productivity,
Food web structure
Species diversity,
Species composition,
Sensitive/native spp.
Abundance,
Age Structure
Body size,
Fitness
CO2
 Air Temp
 Precipitation
( Vegetation & ET)
 Water Temp
 Runoff regime
- magnitude
- frequency
- duration
- timing
Other
Stressors!
Ecosystem
Productivity,
Food web structure
Community
Species diversity,
Species composition,
Sensitive/native spp.
Population
Abundance,
Age Structure
Individual
Body size,
Fitness
Physico-chemical
Responses
- water chemistry
- habitat quality
- habitat stability
Sensitive bioindicators that reflect mechanistic
responses to temperature and runoff?
How do temperature and runoff
currently influence the structure
and function of aquatic
ecosystems?
Lakes
Streams & Rivers
Climatic controls on LAKE
structure and function …
 Temperature
– Stratification and dissolved oxygen
– Metabolism and decomposition rates
– Ecosystem productivity
– Nuisance algal species
– Thermal habitat and fish species
 Runoff
– Lake levels
– DOC and water transparency
Stratification: DO and Temp
Summer conditions
Warmer, more O2
Cooler, less O2
• Warmer air temperatures reduce volume of hypolimnion
• Productive lakes have less DO in hypolimnion
• Falling lake levels reduce extent of littoral zone
Lake thermal types reflect seasonal
mixing and vary with latitude and altitude
(Wetzel, 1983, Limnology (2nd ed).)
Evidence for Lake Warming - Reduced Ice
Cover since 1846
(Magnuson et al., 2000, Science 289:1743-1746)
Some projections about lake warming
10-year average lake temperatures (°C) simulated using the Canadian Climate
Center Atmosphere Ocean General Ciruculation Model (CGCM1) as input data.
Warming reflects increased air temperatures and reduced ice cover.
August
control
August
2 x CO2
Summer (June-August)
2 x CO2 minus control
(Hostetler and Small, 1999, Journal of the American Water Resources Association 35:
1625-1637)
Warming and shifts in fish habitat
Warmwater +36%
Coolwater
-15%
Coldwater
-36%
(Mohseni et al., 2003, Climatic Change 59:389-409)
Range shifts: Invasive species
Modeling invasive species spread in terms of current thermal niches
Rainbow smelt
Eurasian ruffe
(Drake and Lodge 2006 Fisheries 31(1):9-16)
Eutrophication can increase even without added
nutrients, if flushing rates are reduced. And warmer
waters favors noxious blue-green algae.
Climatic controls on STREAM
structure and function …
 Temperature
– Dissolved oxygen
– Metabolism and decomposition rates
– Ecosystem productivity
– Thermal habitat and invert and fish species
 Runoff
– Disturbance regimes
– Baseflow conditions
Temperature and loss of
coldwater habitat for trout
Present day potential
distribution based on 22°
isopleth of mean July air
temperature.
Future potential
distribution based on 3°
warming, showing a 49.8%
loss of potential habitat.
Keleher and Rahel, 1996, Transactions of the American Fisheries Society 125:1-13.
Species migration to maintain thermal
preferences or tolerances
– higher latitudes or altitudes
• Alpine systems lost
– requires connectivity
• Great Plains (East-West)
Many species of fishes in
Great Plains streams near
thermal maximum and
cannot move northward.
Where is their “refuge”
during a period of regional
warming?
Invasive riparian species
Russian Olive
Eurasian Saltcedar
Biological Invasions (2005) 7: 747–751
(Friedman et al., 2005, Biological Invasions 7: 747-751 )
New Zealand Mud Snail
Occurrence in 1995 and 2007
(Loo et al., 2007, Ecological Applications, 17:181-189 )
Streamflow
• Varies over time
– Day to day, week to week,
year to year
– Inter-annual variation of
wet and dry years
• Varies along a river’s
length
• Varies with climate
and geology
• Flow is viewed as a
‘master variable”
(Poff et al., 1997, Bioscience 47:769-784)
Streams differ in natural flow regimes
Magnitude of discharge
– Amount of water moving past a
point, per unit time
Frequency of events
– How often a flow of specified
magnitude occurs
Duration
– The time period of a specified
flow
Timing
– Regularity and seasonal
predictability of events
Rate of change
– How quickly flow increases and
decreases
Streams differ in natural flow regimes
Hydrogeography of
natural flow regimes in U.S.
Reflect differences in climate, geology, vegetation,
topography, position in stream network
Poff & Ward (1989, 1990), Poff (1996).
Flow regime and riparian species … Cottonwoods
– Establishment Flows:
• Flood … Magnitude, Timing, Duration, Rate-of-change
– Survival flows: baseflow
Recruitment Box Concept
River Stage
• Timing of seed release
• Inundation of floodplain
• Rate of flow recession
Rate of Decline
(i.e., 2.5 cm/d)
Populus
(seed release)
MAY
JUN
JUL
Time of Year
(Mahoney and Rood, 1998, Wetlands)
Evidence for changing runoff - earlier
snowmelt in montane West
Spring pulse and center of
mass of annual flow (CT)
over the period 1948-2002
show earlier onset (10-30
days) throughout western
North America
Partly but not completely
explained by PDO
(Stewart et al., 2005, J. Climatology18:1136-1155.)
Flow and fish assemblages
Functional traits
rather than
species names
Hydrologically stable
• Stable baseflow
• Predictable daily flows
Hydrologically variable
• High flood frequency
• Variable daily flows
(Poff and Allan, 1995, Ecology)
algae
Flow and food webs
Winter floods in northern California streams
reduces success of predator-invulnerable
insect grazer and lengthens food chain
vulnerable
grazers
invulnerable
grazers
Predators
(small steelhead)
(after Wootton et al. 1996)
emergence
Flood timing and invasion
Timing of flood disturbance relative to
fry emergence in introduced rainbow
trout rainbow dictates establishment
success
Native
Range
Moderate
Invasion
Success
Low
Invasion
Success
(Fausch et al., 2001, Ecol. Appl.)
Changing flow regimes?
• Expect more variable and severe precipitation
– More frequent flooding
– Longer dry spells
Ecological responses will reflect how regime changes relative to
current “template.”
Groundwater
streams
“buffered”?
Snowmelt
streams altered
timing, drier in
late season
Variable perennial
streams more
intermittent?
Regional Vulnerabilities ?
• Runoff patterns
– Snowmelt in West
• Altered timing of peak and ecological impacts
• Lower late-season baseflow and reduced water
quality / less habitat
• Change environmental template and cause native
species loss and exotic species spread
– Small non-groundwater streams in East
become intermittent?
Other confounding factors?!
CO2
Precipitation
Air Temp
( Vegetation & ET)
Dams, water abstraction,
land use, etc. variably
modify thermal and
runoff.
Systems are already
stressed.
Climate change will
exacerbate or interact
with these.
Runoff regime
Water Temp
- magnitude
- frequency
- duration
- timing
Other
Stressors!
Are there “unique”
responses to climate
change?
Ecosystem
Community
Population
Individual
Productivity,
Food web structure
Species diversity,
Species composition,
Sensitive/native spp.
Abundance,
Age Structure
Physico-chemical
Responses
- water chemistry
- habitat quality
- habitat stability
Body size,
Fitness
Sensitive bioindicators that reflect mechanistic responses to
temperature and runoff?
Global Change
• Nonnative Species
• Land Use
• Climate change
What’s more “important” for future biodiversity: climate
change, land use, or nonnative species?
- Land use change may overwhelm climate change signal.
- Will certainly interact strongly with it.
- Expect regional differences
For all Earth’s biomes
(Sala et al.,2000, Science 287:1770-1774)
Identifying biological indicators of climate
change in aquatic ecosystems-criteria
• Ecosystem specific?
• Appropriate spatial distribution and rapid
temporal response
• Sensitivity to drivers (process-based,
mechanistic)
– Taxonomic and functional
• Interactions with other drivers of global change
(e.g., land use change, eutrophication, etc.)
Causal drivers, mechanistic responses
http://cfpub.epa.gov/caddis/index.cfm
Aquatic insects
Variety of morphological, life history, tolerance traits
“mechanistically” to environmental drivers?
Traits for North American lotic insects
(19 traits; 54 states, or ‘modalities’)
Generations/year (3)
Development (3)
Emergence
synchronization (2)
Adult life span (3)
Adult female dispersal (2)
Adult flying strength (2)
Adult exiting ability (2)
Rheophily (3)
Desiccation tolerance (2)
Armoring (3)
Habit (5)
Shape (2)
Size at maturity (3)
Feeding mode (5)
Thermal preference (3)
Occurrence in drift (3)
Maximum crawling rate (3)
Swimming ability (3)
Attachment (2)
(Poff et al., 2006, JNABS 25:730-755)
Food resources
Key Environmental Drivers
- Habitat structure
& dynamics
- Temperature
- Food resources
Species responses
- What traits should vary
“mechanistically”?
Trait responses along
environmental gradients
trophic thermal
habit preference
size,
voltinism
mobility
Habitat stability
(Poff et al., JNABS, 2006))
Thank you