project 4: evolution, structure and function of hydrologic subsystems in hillslopes
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Project 4: Evolution, structure and function of hydrologic subsystems in hillslopes. Paul Brooks, Jon Chorover, Ciaran Harman, Travis Huxman, Jeff McDonnell, Craig Rasmussen, Siva Sivapalan, Peter Troch. Why hillslopes…? [From a simplistic hydrologic point of view]. - PowerPoint PPT PresentationTRANSCRIPT
Project 4: Evolution, structure and function of hydrologic subsystems in hillslopes
Paul Brooks, Jon Chorover, Ciaran Harman, Travis Huxman, Jeff
McDonnell, Craig Rasmussen, Siva Sivapalan, Peter Troch
Why hillslopes…? [From a simplistic hydrologic point of view]
• Almost all of the precipitation reaching a catchment has passed over or through a hillslope before evaporating, recharging, or running off (Kirkby, 1988)
• The hydrologic response of a catchment is driven by precipitation and solar radiation (the climate), but controlled by the geological, topographic, hydraulic, pedologic and ecological properties of the landscape (hillslope, riparian zone, channel).
• Is it possible to de-convolute the integrated output signals present in stream flow in such a way that we determine, upon removing climatic variations, how catchments respond to forcing?
Why hillslopes…?
• Linking physical flow processes/paths to landscape characteristics (e.g., through similarity analysis), we can make significant advances in the search for a unifying theory of catchment hydrology (Kirchner, 2003) by emphasizing where water goes when it rains (McDonnell, 2003).
• Doing this across a range of climate settings (from humid to semi-arid landscapes) will result in a fundamental understanding of the different dominant controls on hydrologic response and water residence time distributions.
Research questions
• What are the key interactions between the soil, ecology, geomorphology and biogeochemistry that create hydrologic storages and flow-paths and partition incoming water into them?
• What role do these storages and flow-paths have in maintaining the regimes of soil, ecology, geomorphology and biogeochemistry, particularly with respect to the temporal variability imposed by the climate?
• Can an organizing principle be identified that could drive the evolution of the hydrologic system in a hillslope?
Example: Baseflow mean residence time
2
2cos sinc
S S S Sf kpD i a k i fNwt x x x
10,000 synthetic hillslopes
( )( ) ( ) 0
cS cQ cD S N t w x
t x x x
where: c is concentration of inert tracerD is dispersion coefficient is recharge concentration
Size d
oesn
’t mat
ter!
Example: Baseflow mean residence time
Pe tan2 2
ca LLi
pD
1
2 2 cosK
fL L
k pD i
Dynamics in heterogeneous hillslopes: multiple timescales control flow
High slope / low intensity Low slope / high intensity
• Heterogeneous aquifer– Fast pathways respond to peaks in intensity– Slow pathways create power-law recession
10log 1K
HeterogeneousHeterogeneous
Ciaran Harman
© Oregon State University
HillslopeHydrologyChallenges
Kurt R
oth, University H
eidelberg, Germ
any
0.01 m 1 m
Markus W
eiler, UB
C
100 m
10,000 m
Jim Kirchner, UC Berkeley
Markus Weiler, UBCWeiler and McDonnell, WRR in review
Community ConsensusNetwork behavior at all scales
Jeff McDonnell
© Oregon State University
HillslopeHydrologyChallengesHillslope networks
Our theory does not include them or adequately deal with them
These are calibrated-away in our modelsWe ignore them at our peril if we want to
do something more than water flowOur measurement technologies are not able
to describe themNetwork structures are the evolutionary
outcome of integrated climatic, geomorphological, ecological, pedological feedbacksThis could promote exciting research
programs between hydro-eco-biogeochemical-pedology
Jeff McDonnell
Biogeochemical, soil, vegetation processes affecting hillslope
hydrologic subsystems
Hillslope hydrology(catena shape,
topographic fine structure,
pore structure,flow paths, K(Ψ)
distribution) Spatial distribution of plants and
microbes(Veg. structure, C fixation,
infusion of roots & C, plant litter decay)
Patterns of biogeo-weathering
(aq. geochem. conditions, Ω distribution, aggregation, pore complexity,
biophysical microenvironments,)
Evolution of subsurface connectivity
(macropores, preferential flow,
gas/solute transport, bulk density changes )
Jon Chorover
Biogeochemical Hot Spots and Hot Moments
•Hot spots leave a “signature” in water chemistry •They also may leave a signature on the landscape •These signatures should be consistent with (or can be used to infer) hydrological flowpaths
Paul Brooks
Soil-Landscape RelationshipsSoil-Landscape Relationships
• (Strong) link between soil properties and landscape position needs to be better understood to aid hydrologic controls on hillslope flow and transport processes
Craig Rasmussen
Current Challenges in Ecohydrology
Biologically induced feedbacks
Time-depth distribution of soil water (time)
Hydraulic redistribution (space and time)
Buffering & Community Organization (dealing with variability)
Acclimation, Adaptation and Assembly
The Stoichiometry of Water
Water budget partitioning
Dry-rewetting cycle
Climatology of Size Appropriate Triggers of Biology
Are all dry years alike for all organisms (populations, communities)? Travis Huxman
Growing Season PPT
50 100 150 200 250 300 350 400
Rai
n-u
se E
ffici
ency
(G
EP
/ P
PT
)
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
WoodlandShrublandGrassland
Impact of precipitation on photoautotrophs
Greater access to deep water keeps photosynthetic processes high when precipitation is low in woody plant systems
Grassland
Shrubland
Woodland
Travis Huxman
Proposed work
• Organize a series of workshops (1 each year, so 4 in total)• Workshops are run by core group of people with different
background (hydrology, biogeochemistry, soil sciences, ecology)• Each year, a workshop is held at different a research site
– Year 1: Valles Caldera or Catalinas– Year 2: H.J. Andrews– Year 3: Panola– Year 4: Synthesis at B2-Earth Sciences
• Local scientists from different disciplines are invited to present unsolved puzzles in their data (to provoke discussion and possible collaboration)
• Number of participants: ~30 (+ grad students)• Output: 2-pager that is distributed to larger hydrologic community• Follow-up: special session at AGU meeting• Synthesis paper submitted to WRR• Budget: $40,000/year
Synergistic efforts
• B2 Earth Sciences’ institutional experiment: artificial hillslopes in controlled (mass exchange and climate) environment to study interaction between hydrology, biogeochemistry, pedology and ecology
• Design of artificial hillslopes is the ultimate synthesis activity (different disciplines need to agree on common design)
• B2 Institute will host SLICE-2 (Slope Intercomparison Experiment) workshop convened by Jeff and Peter
• Main focus will be on hydrologic design, but with significant input from other disciplines
• Similar discussion sessions will be held to arrive at final design
Discussion
• Topics of workshops?– Subsurface networks: evolution, structure, function?– Organizing principle: EEMT?
• Deliverables?