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CUAHSICUAHSI FallFall 20042004 VisionVision PaperPaper CyberseminarCyberseminar SeriesSeries www.cuahsi.orgwww.cuahsi.org

BrentBrent NewmanNewman Coming to you from Los Alamos, NM October 21st, 2004 To begin at 3:05 ET

EcohydrologyEcohydrology ofof AridArid andand SemiSemi--AridArid EnviroEnvironmentsnments WelcomeWelcome toto thethe 33rd SemesterSemester ofof CUAHSICUAHSI EducationEducation andand OutreachOutreach DistinguishedDistinguished LecturesLectures

Problems? Host:Host: JonJon DuncanDuncan Send a chat to Host CUAHSICUAHSI CommunicationsCommunications DirectorDirector Feedback? Please send an email to [email protected]

The Presentation can be downloaded From www.cuahsi.org FallFall ScheduleSchedule

•• Remote Sensing Witold Krajewski, U Iowa October 26th •• Bridging Scales and Processes… Dave Dewalle, Penn State October 29th •• Watersheds and Urbanization Bill Johnson, University of Utah November 2nd

Go to CUAHSI website for complete calendar, links to papers, presentations, and discussion forums TheThe EcohydrologyEcohydrology ofof AridArid andand SemiaridSemiarid Environments:Environments: AA ScientificScientific VisionVision Authors & Workshop Participants: • Brent Newman, Los Alamos National Laboratory • Steve Archer, University of Arizona • Dave Breshears, University of Arizona • Cliff Dahm, University of New Mexico • Chris Duffy, Penn St. • Nate McDowell, Los Alamos National Laboratory • Fred Phillips, New Mexico Tech • Bridget Scanlon, Bureau Economic Geol., Univ. of Texas • Enrique Vivoni, New Mexico Tech • Brad Wilcox, Texas A&M

Acknowledgments: Gary Langhorst, Los Alamos Nat. Laboratory PresentationPresentation OutlineOutline 1. Why and what is arid and semiarid ecohydrology? 2. Case Studies • Regional scale tree mortality • Invasion of non-native along riparian corridors 3. Six scientific themes 4. Strategy 5. Expected Impact WhatWhat isis Ecohydrology?Ecohydrology?

• Ecohydrology seeks to elucidate (a) how hydrological processes influence the distribution, structure, function, and dynamics of , and (b) how feedbacks from biotic processes impact the cycle.

(see Bonell, 2002; Hunt and Wilcox, 2003; Kundzewicz, 2002; Newman et al., 2003; Nuttle, 2002; Porporato and Rodriguez-Iturbe, 2002; Rodriguez-Iturbe, 2000) WhyWhy anan EcohydrologicalEcohydrological Perspective?Perspective?

• All eight of the NRC’s (2001a) Environmental Grand Challenges require an ecohydrological component (and often a major one) • The NRC (2001b) has defined integrative research in the “Critical Zone” as a research priority.

¾ “The critical zone is the heterogeneous, near-surface environment in which complex interactions between rock, soil, water, air, and living organisms regulate the natural habitat and determine the availability of life sustaining resources”. WhyWhy shouldshould wewe carecare aboutabout aridarid andand semiaridsemiarid environments?environments?

• ~ 1/3 of the Earth’s land surface is arid or semiarid

¾ This fraction is projected to rise & increasingly impact human society, biogeochemical functioning, and land surface-atmosphere interactions (Bonan, 2002; Schlesinger et al., 1990). • These regions contain some of the fastest growing urban and exurban centers in the world (Brown et al., 2005). ¾ Chronic and acute natural resource management problems • Many sensitive ecotones ( boundaries) ¾ Because of wide elevation and gradients ¾ Potential for catastrophic change is high (Buffington and Herbel, 1965; Eagleson, 1982; IGPCC, 1996) Effects on Lake Powell

Estimated Population Increases in six western states

June, 2000

Source: Greg Garfin/SAHRA May, 2002

Source: J. Dohrenwend CaseCase StudyStudy 1:1: RegionalRegional--ScaleScale DroughtDrought--InducedInduced MortalityMortality ofof TreesTrees Oct., 2004, Los Alamos, NM • Changes in woody plant abundance has a wide range of ecological, hydrological, and societal implications. • Current drought (1999-?) has caused large-scale Source: B. Newman & G. Langhorst mortality in piñon-juniper Sept., 2003, San Francisco Peaks, AZ woodlands. • Piñon mortality has exceeded more than 98% at some locations in New Mexico (Breshears, unpublished data). Source: J. Betancourt & N. Cobb CaseCase StudyStudy 1:1: RegionalRegional--ScaleScale DroughtDrought-- InducedInduced MortalityMortality ofof TreesTrees

Bandelier National Monument, NM • 1950’s drought shifted the ponderosa pine/PJ ecotone by more Dead ponderosa than 2 km in <5 pines & live PJ years because of tree mortality • Shift resulted in a loss of herbaceous cover & persistently high runoff and erosion rates (Allen and Breshears, 1998) Tree Mortality: Questions & Scientific Challenges

• What is the critical level of plant available water that triggers tree mortality? • Will current changes in woody plant abundance trigger changes in recharge, or and erosion? • How will climate variability and change influence woody cover dynamics? • Research confined to the realm of either ecology or cannot adequately address these questions. ¾ Highlights the importance of an ecohydrological approach. CaseCase StudyStudy 2:2: InvasionInvasion ofof NonnativeNonnative VegetationVegetation AlongAlong RiparianRiparian CorridorsCorridors • Arid and semiarid riparian Riparian Salt Cedar corridors represent a distinct ecotone. ¾ Water budgets of basins are strongly influenced by riparian vegetation (Dahm et al., 2002). Salt Cedar ¾ Character of these ecotones is Source: C. Dahm impacted by non-native vegetation. ¾ Non-native plants of importance in SW arid and semiarid riparian zones include Russian olive (Elaeagnus angustifolia) and salt cedar (Tamarix spp.) Source: C. Hart CaseCase StudyStudy 2:2: InvasionInvasion ofof NonnativeNonnative VegetationVegetation AlongAlong RiparianRiparian CorridorsCorridors

• Salt cedar has colonized about Salt Cedar along the Pecos River a million hectares in the western U.S. (Brock, 1994).

• Russian olive is widely distributed throughout 17 western states, reaching densities exceeding 1000 trees Source: C. Hart ha -1 (Katz and Shafroth, Salt Cedar along the Rio Grande 2003). • Prevalence of riparian plant communities dominated by non-native plants is increasing

throughout the western US. Source: C. Dahm Tree Mortality: Questions & Scientific Challenges

• How does water use by non-natives compare to that of the natives they displace? • Do non-native plants alter ET or E/T partitioning, thus influencing streamflow and ? • How do non-native dominated riparian communities affect fundamental ecosystem processes such as primary production and nutrient cycling? • Does establishment of non-native plants alter disturbance regimes (e.g., pest outbreak and fire) in ways that feed back to local hydrology? ThemeTheme 1:1: IsIs ItIt ImportantImportant toto PartitionPartition EvaporationEvaporation andand ?Transpiration? • Arid and semiarid ecosystems are water limited ( ET > typically 95% of the water budget) (Wilcox et al., 2003). Above canopy eddy covariance station • Most studies lump interception, soil evaporation (E), and transpiration (T) into a single term (ET). ¾ Obscures differences between biologically available water (T), and biologically unavailable water (E).

• Although expedient, does lumping of E & T limit our understanding of how ecosystems and physical processes regulate the hydrological cycle? Source: C. Dahm Partitioning of E & T: Questions & Scientific Challenges • Will the ratio of E to T increase dramatically in response to extensive tree mortality or vegetation management?

¾ Will E/T change because of a reduction in (hence lower T), or because of a change in the near- ground energy distribution (hence higher E)? ¾ To what extent are E and T compensating; how do they vary temporally and spatially in a patchy arid and semiarid landscapes?

• Lack of experiments and modeling prevents robust generalizations or predictions about E and T, and how their relative importance varies among sites, through time, or in response to land management. ThemeTheme 2:2: WhatWhat isis thethe ValueValue ofof StudyingStudying WaterWater andand NutrientNutrient Interactions?Interactions? Water has typically been regarded as ‘the’ limiting resource in arid and semiarid ecosystems. Is this really true? • Hooper and Johnson (1999) tested the relative importance of water and nutrient (N) limitation in arid-subhumid locations. ¾ Found no strong evidence of a shift from water- to nutrient- limitation across a wide arid to subhumid gradient. ¾ Their results (& others) suggest a strong N control and perhaps even a co-dominant one • Nutrients and water are inextricably linked. Nutrient availability can limit vegetation responses to precipitation

and ; and soil moisture drives N2-fixation microbial mineralization of soil organic matter. NitrateNitrate InventoriesInventories inin AridArid andand SemiaridSemiarid VadoseVadose ZonesZones • In many arid/semiarid locations, thick vadose zones have acted as a sink for nitrate for many thousands of years.

• Potentially increases N inventories by 14 to 71% nitrate and chloride profiles Mojave Los Alamos Mesa for warm and Nitrate-N (mg L-1) Nitrate-N (mg L -1) shrublands worldwide 0 1000 2000 3000 4000 0 20406080100 0 and 3 to 16% globally Cl 5 NO3--N

(Walvoord et al., 2003). 10

• Also a potential water h (m) 15

quality threat if nitrate is Dept 20 Cl NO3--N flushed into groundwater 25 MD1 LAM1 as a result of climate or 30 0 1000 2000 3000 4000 0 2000 4000 6000 land use change. -1 Chloride (mg L-1) Chloride (mg L )

Source: Walvoord et al., 2003 Water & Nutrient Interactions: Questions & Scientific Challenges • Atmospheric N deposition in Northern Hemisphere ecosystems receive on average more than four times that of pre-industrial levels (Holland et al., 1999). ¾ How will N-limited arid and semiarid ecosystems respond to this change? • Why do large vadose zone nitrate inventories develop in ecosystems with strong nitrogen imitations? ¾ Are there hydrological processes that limit more efficient utilization of nitrogen in the soil zone?

• To what extent has our focus on water rather than, or in isolation from nutrients constrained our understanding and management of arid and semiarid ecosystems? ThemeTheme 3:3: HowHow dodo PlantsPlants AffectAffect Streamflow?Streamflow?

• Vegetation plays a critical Juniper in Texas uplands role in determining temporal and spatial variations in soil moisture and runoff within hillslopes and channel networks. •The tight coupling between vegetation and water lead to the reasonable assumption that water supply in arid and semiarid zones may be augmented through vegetation management. Source: B. Wilcox VegetationVegetation controlcontrol toto increaseincrease streamflowstreamflow isis aa majormajor economiceconomic andand naturalnatural resourceresource issueissue • ~40 M dollars has been ¾ E and T are huge! allocated in Texas for shrub It may not matter what kind of plants you have. control to increase streamflow. ¾ Runoff is episodic & largely • Congress is considering funding Hortonian, so you might salt cedar control at a level of increase peak flow, but what about baseflow? $20M/year with the goal being of increasing water availability. • However, there is considerable uncertainly as to the magnitude and feasibility of increasing water yield through vegetation management, especially on a large scale Source: C. Hart (Wilcox, 2002). ThemeTheme 4:4: HowHow dodo PlantsPlants AffectAffect GroundwaterGroundwater Recharge?Recharge?

• Differences in recharge beneath nonvegetated and vegetated lysimeters in the Western US illustrate that plants can substantially influence (Gee et al., 1994).

• Large-scale conversion of eucalyptus woodlands to agriculture and pasture in Australia, resulted in an increase in recharge rates by two orders of magnitude (Allison et al., 1990). ThemeTheme 4:4: HowHow dodo PlantsPlants AffectAffect GroundwaterGroundwater Recharge?Recharge?

• Pleistocene-Holocene shift from Chloride profile from mesic to xeric vegetation Los Alamos, NM changed SW interfluvial areas ¾ Chloride inventory from recharging to discharging represents a vadose (Scanlon et al., 2003; Walvoord et al., zone residence time 2002; Seyfried et al., 2005). of about 10,000 years.

Mesita del Buey • Using chloride mass balance, 0.0 Phillips, (1994) showed there 5.0 10.0 has been little to no recharge ) m

h ( 15.0 pt

over much of the regional SW e D since the Pleistocene. 20.0 25.0

30.0 0 1000 2000 3000 4000 5000

Pore Water Chloride (mg/L)

Source: B. Newman Plants and Recharge: Scientific Challenges

• Vegetation types and characteristics may be way of identifying recharge areas in arid and semiarid environments where little to no recharge occurs over much of the landscape (Walvoord and Phillips, 2004). ¾ Yield better estimates of basin-scale recharge ¾ Identify optimal areas for vegetation management • Need to integrate climatic variables, vegetation characteristics, and hydrologic information (e.g., chloride profiles & matric potentials). ¾ Will enable identification of critical climate forcing required to produce episodic recharge for a given vegetation state. ThemeTheme 5:5: HowHow dodo Climate,Climate, Water,Water, andand LandscapeLandscape ComponentsComponents Interact?Interact? • Environmental change will • A way around this stimulate feedbacks that problem is to build and will cause characteristics of use models to simulate drainage basins (e.g., past events during which major responses have vegetation type and been documented. distribution, soils, water tables, drainage networks) Creosote bush 1915 invasion, to evolve. Sevilleta Nat. Wildlife Refuge, • Currently, our ability to NM simulate such complex 1989 feedback responses is unproven.

Source: E. Vivoni Climate,Climate, Water,Water, andand LandscapeLandscape Interactions:Interactions: AA PaleoPaleo PerspectivePerspective • Arid/semiarid drainage basins are well-suited for understanding feedbacks Midden and responses ¾ They contain unusually long and complete records of past environmental change. • Tree rings, packrat middens, speleothems, aquifers, thick vadose zones, & lacustrine sediments can all be used to build integrated records of basin-scale feedbacks and response. Source: F. Phillips • Paleoenvironmental studies can be synthesized to construct a comprehensive accounting of the hydrological, vegetational, climatic, and geomorphic history of the basin. • A basin model can then be Paleoreconstruction of Malpais driven using climate records. precipitation record from tree rings

• Modeled basin responses can 550 then be compared to the An n u al D a t a 3 0 - y r R unn in g M e a n paleorecord. 500 1 50- y r R u n n in g M e a n m m (

450 n o

• The model can be iteratively i t a it

ip 400

refined to reflect actual c e r P l

processes and outcomes a u 350 n n A

¾ Improve forecasting 300

250 ¾ Mechanistic insights on 10 00 110 0 12 00 1 3 0 0 14 00 15 00 160 0 1 700 1 8 0 0 1 9 0 0 2 00 0 feedbacks & responses Ye ar (C E )

Source: F. Phillips ThemeTheme 5:5: HowHow dodo Climate,Climate, Water,Water, andand LandscapeLandscape ComponentsComponents Interact?Interact?

• In addition to the paleo approach a modern perspective is also needed. • Reductions in rainfall and an increase in temperature occurred in SW Australia in the mid-20th century.

• were first interpreted as being caused by a reorganization of atmospheric circulation & an enhanced greenhouse effect. • Later, Pitman et al. (2004) argued that major changes in vegetation explain the observed shifts through feedback to the atmosphere. • A collective “new way of looking” is necessary, whereby the science of change takes a more integrated approach to land surface-atmosphere interactions. Theme 6: How Does Vegetation Respond to Hydrological Change?

• Vegetation spatial patterns exhibit self-organization and are optimality related to climate and to landscape characteristics (Caylor et al., 2004; Fernandez-Illesca and Rodríguez-Iturbe, 2004; and Van Wijk and Rodríguez-Iturbe, 2002). • Seasonality of precipitation has dramatic impacts on vegetation life forms, diversity, sensitivity to invasion, and of arid and semiarid ecosystems (Chesson et al., 2004; Fernandez-Illescas & Rodriguez-Iturbe, 2004; Huxman et al., 2004; Weltzin, 2003b). Vegetation Response to Hydrological Change: Scientific Challenges

• Predicting vegetation response to changes in the hydrologic regime requires models based on first principles of plant carbon-water balance (Landsberg and Waring, 1997; Running and Coughlan, 1988; Williams et al. 1996). • However, data to support modeling is sparse and models do not yet capture important vegetation-water dynamics. • Need for nested-scale field experiments coupled with remote sensing to test models & improve forecasts of vegetation response to change. ¾ In the hydrological observatory framework, experiments should explicitly address modeling needs from the experimental design phase through data collection. StrategyStrategy forfor AchievingAchieving anan Arid/SemiaridArid/Semiarid EcohydrologyEcohydrology VisionVision • High-level strategy is to develop a framework wherein ecologists and hydrologists proactively collaborate on complex environmental problems and challenges. ¾ Promote synergistic growth and development of new perspectives - May reveal novel and more powerful approaches to environmental problem solving.

¾ Marrying of the two disciplines has not yet been done on any significant scale; thus, the full benefit of integrated interdisciplinary research is unrealized. StrategyStrategy forfor AchievingAchieving anan Arid/SemiaridArid/Semiarid EcohydrologyEcohydrology VisionVision WeWe believe:believe:

¾ At least one of the CUAHSI HOs should have an explicit focus on Ecohydrology. ¾ An arid or semiarid observatory would be an excellent place to do this. - Because of the high sensitivity of ecohydrological processes to environmental change. ¾ An arid or semiarid observatory provides an infrastructure where ecologists and hydrologists could work together from the experimental design phase through interpretation and modeling. ¾ Enable training of a new generation of scientists with essential cross-disciplinary experience. ExpectedExpected ImpactsImpacts • The ability of scientists to forecast environmental change scenarios will affect the choices societies make and how they adapt and function in a future of great and potentially rapid change (Clark et al., 2001). – A major component of our vision is to provide a rigorous scientific basis for environmental management. • Successful implementation of our vision will have broad social and economic impacts. – Addresses serious issues related to water supply and quality, ecosystem health and diversity, and the goal of becoming better stewards of sensitive arid and semiarid environments.