Ecohydrology_Lecture4_F11

Ecohydrology_Lecture4_F11 - Arid Ecohydrology Ecohydrology...

Info icon This preview shows pages 1–12. Sign up to view the full content.

View Full Document Right Arrow Icon
Arid Ecohydrology Ecohydrology Fall 2011
Image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Ecosystem RUE All terrestrial ecosystems use MAP to create NPP, and are therefore, at some level, water dependent Differential sensitivity to variance in MAP NPP:MAP defines rain use efficiency Sensitivity effectively measures the strength of water limitation vis-à- vis nutrient or evolutionary constraints Huxman et al. (2004) - Nature
Image of page 2
Convergent RUEmax? RUEmax generally occurs at low water availability There is a convergence of RUEmax across all biomes RUEmax is close to RUEmean for arid sites RUEmax is really low compared to RUEmean for humid sites
Image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Two Predictions 1 – NPP will be affected a lot if PPT is driven below the historic minimum 2 – Removal of other resource limitations will allow RUE to approach RUEmax
Image of page 4
Ergo Water limitation imposes a common constraint on NPP across biomes Ecosystems have the same RUEmax despite large differences in ppt, physiology, phytogenetic origin and climate history Altering resource limitation underscores the relevance of biogeochemistry on NPP (i.e., compared with species)
Image of page 5

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Inhibited Deep Drainage Over Millenia In dry areas (<500 mm) there is a nearly ubiquitous pore-water Cl- peak at 5-15 m below grade Mass balance of Cl yields 10,000-15,000 years of accumulation (without major downward flux event) Consistent with ~ 1 mm/yr deep drainage Seyfried et al. (2005) - Ecology
Image of page 6
But… Upward water potential gradient Water is moving out of the soil Ergo, no downward movement Seyfried et al. (2005) - Ecology
Image of page 7

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Strong Climatic Control Cl inventory suggests 7,000-8,000 years of accumulation at a site with 360 mm MAP Inventory is 1,000 years at 400 mm MAP at nearby site
Image of page 8
Ecohydrologic Mechanism Walvoord et al. (2002) propose a conceptual model to reconcile these attributes Low water potentials at the base of the root zone were established at the end of the Pleistocene (dramatically increased dryness) Potentials (< -1 MPa) were maintained continuously during the Holocene Any deep wetting event would reset the chloride concentrations Slow upward movement of water above ca. 20 m Drainage below 20 m of
Image of page 9

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Vegetation is Essential Plants are required to impose and maintain the low potentials Two key attributes: Deep roots (2-3 m) of sufficient density to capture all downward percolating water Able to maintain low water potentials at depth continuously The demand for continuous maintenance has enormous implications for contemporary vegetation management Clearing vegetation can result in huge fluxes of Cl (and nitrate!) to the deep groundwater
Image of page 10
Deep Roots Root density decreases exponentially with depth, though slower in arid biomes Max rooting depths ~ 5 m, almost all co-dominant shrubs ~ 1.8 m Root depths increased with MAP and soil coarseness Maintaining root potentials demands cavitation avoidance Geometry of xylem Soil hydraulic conductance goes to 0
Image of page 11

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Image of page 12
This is the end of the preview. Sign up to access the rest of the document.

{[ snackBarMessage ]}

What students are saying

  • Left Quote Icon

    As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

    Student Picture

    Kiran Temple University Fox School of Business ‘17, Course Hero Intern

  • Left Quote Icon

    I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

    Student Picture

    Dana University of Pennsylvania ‘17, Course Hero Intern

  • Left Quote Icon

    The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

    Student Picture

    Jill Tulane University ‘16, Course Hero Intern