SiSPAT-Isotope modelBetter estimates of E and T

Jessie CablePostdoc - IARC

Very green landscapes that are fluxing water to the atmosphere

http://www.marietta.edu/~biol/biomes/

images/wetlands/sphagnum_6449a_A80.jpg

Transpiration

EvaporationTranspiration = Plants control the water vapor flux

Evaporation = mosses are an evaporating surface (BUT, they are NOT bare ground)

- Combination of vascular and non-vascular plants- Different water flux dynamics necessitate distinguishing between them

(E and T vs. ET)

BIRCH-WILLOW SHRUB ECOSYSTEM

5/25/09 6/8/09 6/22/09 7/6/09 7/20/09 8/3/09

TRA

NSP

IRA

TIO

N

0

1

2

3

4

5 Black SpruceCranberryLabrador TeaBlueberry

BLACK SPRUCE ECOSYSTEM

TRA

NSP

IRA

TIO

N

0

1

2

3

4

5

6Dwarf BirchBlueberryWillowBow WillowLabrador Tea

BLACK SPRUCE ECOSYSTEM WITHOUT DEGRADING PERMAFROST

TRA

NSP

IRA

TIO

N

0

1

2

3

4

5

6Dwarf BirchBlack SpruceCranberryLabrador TeaWillowBlueberry

BLACK SPRUCE ECOSYSTEM WITH DEGRADING PERMAFROST

6/1/09 6/15/09 6/29/09 7/13/09 7/27/09 8/10/09

TRA

NSP

IRA

TIO

N

0

1

2

3

4

5

Need better assessment of E and T

Need more accurate representation of E and T in atmosphere, hydrological, or

vegetation growth models

Tape et al. 2006

CREW-NASA

ET

Rainfall recycling and watershed/soil water balance

Changes in landscape / vegetation distributions impact magnitude and

partitioning of ET

• Little data exist to validate the partitioning of E and T in SVAT (Soil Vegetation Atmosphere Transfer) models

• Concentration measurements of stable isotopes of water in soil, plants, and vapor can aid in partitioning / quantifying E and T– E and T differentially impact

concentration of isotopes in soil or vapor

• soil stable isotope concentrations useful for – determining plant rooting profiles

(for validation of root extraction submodels in SVAT)

– better quantification of water transfer within soils (vapor diffusion coefficients and hydraulic properties)

1H, 2H16O, 18OH2O

SiSPAT-Isotope modelBraud et al., Journal of Hydrology 309 (2005) 277-300, 301-320

• Modification of the pre-existing 1D SiSPAT model (Simple Soil Plant Atmosphere Transfer model) to include transport of stable isotope species to better estimate E and T

• Coupled heat, water, and isotope transport equations solved for temperature and matric potential and isotope profiles

• forced by air temp, humidity, wind speed, incoming solar and long wave radiation, rainfall

• bare ground, saturated soils, steady state conditions (equilibrium between vapor and liquid phases for isotopes)

• Currently focused on estimating kinetic fractionation coefficient

Issues with adding isotope transport

• Correctly accounting for fractionation associated with molecular diffusion

• turbulent vs molecular diffusion affecting resistance to isotope vapor flux

• Need a plant component and proper treatment of plant physiology

• Kinetic fractionation factor for drying soils and non-saturated conditions

1H, 2H16O, 18O

Data-model integration issues• The solution of the isotope

species transport equation requires high resolution of the vertical profile near the surface (particularly to capture the vapor return)

• Problem: require fine time steps that field sampling can not yet provide

D (0/00)

-180 -170 -160 -150 -140 -130 -120 -110D

epth

(cm

)

0-55-10

10-2020-3030-4040-5050-6060-7070-80

80-100post-rainpre-rain

Spec

ies

betula

ledum

rubus

spruce

blueberry

post rainpre rain