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 vegetation 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 ecosystems, and (b) how feedbacks from biotic processes impact the water 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 (ecosystem boundaries) ¾ Because of wide elevation and precipitation gradients ¾ Potential for catastrophic change is high (Buffington and Herbel, 1965; Eagleson, 1982; IGPCC, 1996) Drought 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 surface runoff and erosion? • How will climate variability and change influence woody cover dynamics? • Research confined to the realm of either ecology or hydrology 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 groundwater? • 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?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 biomass (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 soil moisture; 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% Vadose zone nitrate and chloride profiles Mojave Desert Los Alamos Mesa for warm deserts 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