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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 • • • • • 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