1. Climate Change and Aquatic Ecosystems N. LeRoy Poff Department of Biology Colorado State University USEPA Workshop February 19, 2008

2. Objectives Connecting global climate change to local- scale 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

3. Broader Context: Global Change Climate change Land Use Nonnative Species

4. http://www.pewclimate.org/global-warming-in-depth/all_reports/aquatic_ecosystems

5.  Air Temp  Precipitation  CO 2  Water Temp  Runoff regime - magnitude - frequency - duration - timing (  Vegetation & ET) Physico-chemical Responses - water chemistry - habitat quality - habitat stability Biological/Ecological Responses - structural - functional Sensitive bioindicators? GCMs Hydrologic Models Ecological Response Models Conceptual Model

6. Ecosystem Energy/Material Flow & Cycling Productivity, Food web structure Community Species tolerances and interactions Species diversity, Species composition, Sensitive/native spp. Population Demographic rates (birth, death, etc.) Abundance, Age Structure Individual Vital Rates ( growth, reproduction) Body size, Fitness Biological / Ecological Responses

7.  Air Temp  Precipitation  Runoff regime - magnitude - frequency - duration - timing  Water Temp Physico-chemical Responses - water chemistry - habitat quality - habitat stability (  Vegetation & ET)  CO 2 Ecosystem Productivity, Food web structure Community Species diversity, Species composition, Sensitive/native spp. Population Abundance, Age Structure Individual Body size, Fitness Sensitive bioindicators that reflect mechanistic responses to temperature and runoff? Other Stressors!

8. How do temperature and runoff currently influence the structure and function of aquatic ecosystems? Streams & Rivers Lakes

9.  Temperature –Stratification and dissolved oxygen –Metabolism and decomposition rates –Ecosystem productivity –Nuisance algal species –Thermal habitat and fish species Climatic controls on LAKE structure and function …  Runoff –Lake levels –DOC and water transparency

10. Stratification: DO and Temp Warmer, more O 2 Cooler, less O 2 Summer conditions Warmer air temperatures reduce volume of hypolimnion Productive lakes have less DO in hypolimnion Falling lake levels reduce extent of littoral zone

11. Lake thermal types reflect seasonal mixing and vary with latitude and altitude (Wetzel, 1983, Limnology (2nd ed).)

12. (Magnuson et al., 2000, Science 289:1743-1746) Evidence for Lake Warming - Reduced Ice Cover since 1846

13. (Hostetler and Small, 1999, Journal of the American Water Resources Association 35: 1625-1637) August control August 2 x CO 2 Summer (June-August) 2 x CO 2 minus control 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. Some projections about lake warming

14. (Mohseni et al., 2003, Climatic Change 59:389-409) Coolwater -15% Warmwater +36% Coldwater -36% Warming and shifts in fish habitat

15. Range shifts: Invasive species Modeling invasive species spread in terms of current thermal niches Rainbow smelt (Drake and Lodge 2006 Fisheries 31(1):9-16) Eurasian ruffe

16. Eutrophication can increase even without added nutrients, if flushing rates are reduced. And warmer waters favors noxious blue-green algae.

17. 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

18. 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.

19. 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?

20. (Friedman et al., 2005, Biological Invasions 7: 747-751 ) Biological Invasions (2005) 7: 747 – 751 Invasive riparian species Eurasian Saltcedar Russian Olive

21. (Loo et al., 2007, Ecological Applications, 17:181-189 ) Occurrence in 1995 and 2007 New Zealand Mud Snail

22. 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)

23. 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

24. Streams differ in natural flow regimes

25. Hydrogeography of natural flow regimes in U.S. Poff & Ward (1989, 1990), Poff (1996). Reflect differences in climate, geology, vegetation, topography, position in stream network

26. Flow regime and riparian species … Cottonwoods –Establishment Flows: Flood … Magnitude, Timing, Duration, Rate-of-change –Survival flows: baseflow

27. (Mahoney and Rood, 1998, Wetlands) Rate of Decline (i.e., 2.5 cm/d) River Stage Recruitment Box Concept Populus (seed release) Time of Year MAYJUNJUL Timing of seed release Inundation of floodplain Rate of flow recession

28. (Stewart et al., 2005, J. Climatology18:1136-1155.) 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 Evidence for changing runoff - earlier snowmelt in montane West

29. Flow and fish assemblages (Poff and Allan, 1995, Ecology ) Hydrologically variable High flood frequency Variable daily flows Hydrologically stable Stable baseflow Predictable daily flows Functional traits rather than species names

30. Flow and food webs (after Wootton et al. 1996) Winter floods in northern California streams reduces success of predator-invulnerable insect grazer and lengthens food chain algae vulnerable grazers invulnerable grazers Predators (small steelhead)

31. Timing of flood disturbance relative to fry emergence in introduced rainbow trout rainbow dictates establishment success Native Range Low Invasion Success Moderate Invasion Success Flood timing and invasion emergence (Fausch et al., 2001, Ecol. Appl.)

32. 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”? Variable perennial streams more intermittent? Snowmelt streams altered timing, drier in late season

33. 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?

34. Other confounding factors?! Air Temp Precipitation Runoff regime - magnitude - frequency - duration - timing Water Temp Physico-chemical Responses - water chemistry - habitat quality - habitat stability (  Vegetation & ET) CO 2 Ecosystem Productivity, Food web structure Community Species diversity, Species composition, Sensitive/native spp. Population Abundance, Age Structure Individual Body size, Fitness Sensitive bioindicators that reflect mechanistic responses to temperature and runoff? Other Stressors! Dams, water abstraction, land use, etc. variably modify thermal and runoff. Systems are already stressed. Climate change will exacerbate or interact with these. Are there “unique” responses to climate change?

35. Global Change Nonnative Species Land Use Climate change

36. 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 (Sala et al.,2000, Science 287:1770-1774) For all Earth’s biomes

37. 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.)

38. http://cfpub.epa.gov/caddis/index.cfm Causal drivers, mechanistic responses

39. Aquatic insects Variety of morphological, life history, tolerance traits “mechanistically” to environmental drivers?

40. Rheophily (3) Desiccation tolerance (2) Armoring (3) Habit (5) Shape (2) Size at maturity (3) Feeding mode (5) Thermal preference (3) Generations/year (3) Development (3) Emergence synchronization (2) Adult life span (3) Adult female dispersal (2) Adult flying strength (2) Adult exiting ability (2) Occurrence in drift (3) Maximum crawling rate (3) Swimming ability (3) Attachment (2) Traits for North American lotic insects (19 traits; 54 states, or ‘modalities’) (Poff et al., 2006, JNABS 25:730-755)

41. Key Environmental Drivers - Habitat structure & dynamics - Temperature - Food resources Species responses - What traits should vary “mechanistically”? Habitat stability Food resources Thermal regime mobility trophic habit size, voltinism thermal preference (Poff et al., JNABS, 2006)) Trait responses along environmental gradients

42. Thank you