IPILPS Workshop

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IAEA CRP on 18O (MIBA) and Planning for Tumbarumba

• IPILPS Workshop
• ANSTO 18-22 April 2005

2
Overview of talk

• Data acquisition - How did we get to where we are
  today?
• The MIBA network
• IAEA and other planning meetings
• ANSTOs contribution
• Why Tumbarumba?
• Sampling
• a priori estimates and our working hypothesis

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The MIBA network

• Moisture Isotopes in the Biosphere and Atmosphere
  
• Initiated at a meeting in Vienna, May 2004
• Building on GNIP ( GNIR) in collaboration with
  WMO
• Primary aim - to facilitate acquisition of data
  on stable isotopes in biospheric and atmospheric
  water.

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Moisture Isotopes in the Biosphere and Atmosphere
(MIBA) IAEA
Idealized distribution- 100 sites 90
continental, 10 oceanic (water vapor)
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Moisture Isotopes in the Biosphere and Atmosphere
(MIBA)
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The MIBA network

• Objectives
• 1 Regional scale hydrological budgets
• 2 The partitioning of annual carbon fluxes
• 3 The development of new global change
  indicators
• 4 Ecosystem functioning
• 5 Interpretations of 13C and 18O analyses in
  organic matter
• 6 The validation of general circulation models
  and
• 7 Past global responses to climate change.

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The IAEA CRP

• Title Isotope methods for the study of water and
  carbon cycle dynamics in the atmosphere and
  biosphere
• 1st RCM this May in Vienna

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The MIBA network

• IAEA Membership
• P. Aggarwal, Head, Isotope Hydrology Section IAEA
• D, Yakir (Israel Chair), G. Farquhar
  (Australia), L. Flanagan (Canada), F. Longstaffe
  (Canada), R. Siegwolf (Switzerland), G. Hoffman
  (France), H. Meijer (the Netherlands), H.
  Griffiths (UK), J. Berry (USA). P. Tans (USA), P.
  Ciais (France), N. Buchmann (Switzerland), L.
  Sternberg (USA), T. Dawson (USA), G. Lin (China),
  W. Stichler (Germany), J. White (USA), and J.
  Santruek (Czech Republic), Brent Helliker (USA),
  A. Henderson-Sellers (Australia).

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The IAEA CRP- the Australian contribution

• Routinely measure SI in Canberra vapour.
• Compare fortnightly 18O in grasses, trees,
  soil-water, rain and vapour near Canberra.
• Monitor 18O less frequently in grasses, trees,
  soil-water, rain and vapour at sites in the MDB
  use these data to evaluate climate models and for
  model intercomparisons.
• Measure SI and chemistry in monthly rain-water
  samples across the continent.
• Characterisation of 18O in ground-water in
  relation to soil properties.
• Refine MDB water balance models using the data
  above.

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ANSTOs contribution to the CRP

• IPILPS
• Water isotopologues
• 1H216O 1H218O and 1H2H16O
• Comparison of LSS
• By output, and against real data
• Real field data required at appropriate time
  scales
• Not much exists.

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Initial site selection

• Ozflux sites in Murray Darling Basin (MDB)

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Tumbarumba- Oz-flux tower

• CSIRO Division of Atmospheric Research, Dr. R.
  Leuning Dr. H. Cleugh

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Tumbarumba

• Bago Forest. 35ºS, 148ºE
• 1200 m
• Cool-temperate zone, MDB
• Dominant vegetation Eucalyptus delegatensis
  (Alpine Ash) with E. dalrympleana (Mountain Gum)

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Tumbarumba
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Tumbarumba

• Routine measurements comprise temperature,
  humidity (bulk concentration of water vapour),
  wind (speed and direction), net radiation (both
  shortwave and longwave components), surface
  pressure, soil moisture and temp as well as the
  fluxes of (bulk) water vapour and heat.

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Tumbarumba - other major collaborators

• University of Wollongong, Prof D. Griffith
• portable FTIR MS
• ANU, Prof G. Farquhar Dr C. Keitel Dr H.
  Stuart-Williams
• leader of the IAEA CRP and of a research team
  interested in C and O isotope fractionation
  applications in plant physiology. Stable isotope
  analysis.
• CSIRO Forestry, Dr H. Keith
• primary interested in forest productivity
• CSIRO Land Water, Dr A. Herczeg Dr F. Leany
  Dr J. Deighton
• GNIP. Stable isotope analysis

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What has ANSTO sampled?

• Precipitation, dew, surface soil, deeper soil,
  tree stem, leaves and vapour at various heights
  above the ground, sampling most types hourly
  during daylight and less frequently at night over
  5 days in early March 05.
• We will infer from our results
• surface water vapour fractionation (from
  soil-surface water values, using the Craig
  Gordon model)
• equilibrium transpired vapour and root zone water
  fractionation (from stem water)
• non-equilibrium transpired vapour (from total
  flux and leaf water)

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Sample preparation and analysis

• All samples were sealed and frozen or chilled in
  the field ASAP after collection.
• Vegetation samples will be vacuum distilled at
  ANSTO to collect unfractionated water ( 2hrs per
  sample).
• Plant distillates, precipitation, dew and vapour
  condensates are being analysed for SWIs at ANU.
• A pyrolysis method is used. 2H lt1 o/oo and 18O
  lt0.3 o/oo precision.

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Sample preparation and analysis

• Soil waters are being analysed by CSIRO Land
  Water in Adelaide following azeotropic
  distillation using kerosene to prevent
  fractionation. With CO2 equilibration the
  precision is lt0.05 o/oo for 18O
• Total soil moisture has been measured at ANSTO by
  drying to constant weight. This will be followed
  by particle size analysis for soil
  characterisation.

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Sampling - Precipitation

• Event-based precipitation was collected at ground
  level, using collection devices that ANSTO built
  according to an IAEA (2003) design
• Dew was collected several mornings from a plastic
  sheet laid on the ground

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a priori sample estimates- Precipitation

• Should lie on the GMWL
• d2H 8 x d18O 10 o/oo
• but will vary due to local conditions,
  particularly
• distance from the source altitude
• Estimates for Tumbarumba at 1300 m altitude using
  an on-line calculator range from
• -4.8 to -7.2o/oo (d18O) and -25 to -50o/oo (d2H)
  with averages of -6.5 and -39o/oo

• http//www.waterisotopes.org/

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Sampling - Vapour

• Lagged sample tubes were installed on the tower
  to nine heights (separate matched sets for our
  vapour UoWs FTIR)
• Filtered to prevent contaminants and blockage

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Sampling - Vapour

• Vapour tubes were attached to ANSTO cold traps
  amended from Helliker et al (2002) design.
• Samples were collected hourly during daylight.
• Lower frequency at night due to lower vapour
  pressures

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Sampling - Vapour

• Last minute amendment based on advice from ANU.
• Installed a ground level sampler with a lid
  collecting input air at 10 m
• Lid removed between FTIR cycles to avoid humidity
  and temperature effects and replaced to allow
  signal to re-establish

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a priori sample estimates- vapour

• Atmospheric vapour will be depleted with respect
  to precipitation depending upon the temperature
  (and hence altitude).

Majoube et al 1971

• Soil vapour will be depleted along LEL compared
  to the soil water but will become more enriched
  and approach LMWL as time passes after rain (?
  Equilibrium?).

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a priori sample estimates- soil vapour

• How will soil vapour change over time following
  rain?
• Percent H2O in surface soil will decline due to
  surface evaporation until it reaches a steady
  state due to replacement from deeper water by
  capillary action
• Vapour from surface soil will initially be
  primarily affected by phase change (equilibrium
  fractionation). It will then enrich due to
  kinetic fractionation as the proportion of heavy
  isotopes remaining in the surface water becomes
  larger. In addition, as the surface gets drier,
  diffusive fractionation will also come into play
  as vapour is formed and migrates from lower down
  the soil profile.
• Help from the audience on understanding this
  process more clearly would be appreciated

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Sampling - soil water

• Surface scoops (? 5cm incl litter) were collected
  at the same time as, and adjacent to, leaf and
  stems samples. At hourly intervals during
  daylight.
• Cores taken 4 times per day to a depth of 1m.
  Samples were split for depth profile and then
  measured for moisture content or sent for SWI
  analysis.

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a priori sample estimates

• Soil water
• Surface water will reflect any recent rainfall.
  It will become more enriched over time due to
  evaporation. It should lie on the LEL.
• Deeper samples will reflect heavy or longer
  rainfall and will be biased towards the depleted
  end of the LMWL range at the intercept with the
  LEL and will not be enriched. It is assumed this
  will be well mixed, not change dramatically with
  incident rainfall (eg Neal Rosier 1990), and be
  equivalent to local seeps and xylem water
  (initial estimates -6o/oo d18O and -40o/oo d2H).

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Sampling - xylem

• Bark (phloem) must be removed to avoid
  contamination with enriched leaf water and
  photosynthates.
• The exposed end is cut off
• by gt2cm to minimise the
• potential for exchange with
• atmospheric vapour.
• The sample is cut into 1 cm sections to enhance
  the ease of vacuum distillation. The stem is cut
  directly into a 12mL Exetainer

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a priori sample estimates- xylem

• Should be unfractionated with respect to the root
  zone (deeper) soil water (estimates -6o/oo d18O
  and -40o/oo d2H).
• The height of the sample should not matter.
  Hence, samples from the under story are OK.
• At equilibrium, should equal transpired water
  vapour (but this may only occur for a few hours
  each day).

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Sampling - Leaf water

• Leaf water
• Leaves in sunlight were preferred.
• An estimate of the hours of sunlight exposure is
  made.
• Samples were quickly placed into Exetainers
• Main vein was removed.
• Air temperature and cloud cover estimates were
  also made.

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a priori sample estimates- leaf water

• Will vary considerably diurnally due to stomatal
  opening (light, time and water potential
  dependent) and local climatic conditions
  including temperature, humidity, wind speed and
  incident radiation.
• Pre-dawn, should be equivalent to xylem ( -6o/oo
  d18O and -40o/oo d2H.
• Morning, should start to enrich to a maximum
  around noon in the order of 15-20o/oo (D18O),
  60-80 (D2H).
• Afternoon, should plateau but then start to
  return to xylem values as stomata close.
• Evening, relax back to xylem signature.

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a priori sample estimates

• Transpired water
• At equilibrium, it is assumed that transpirate
  will be equivalent to xylem/source water.
• Due to the lag induced by the enrichment of the
  leaves in the morning and the relaxation of that
  enrichment in the afternoon, transpirate will be
  more depleted in the morning and more enriched in
  the afternoon (eg Harwood et al 1998). The degree
  of difference will depend on the overall water
  flux rates.

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Diurnal variation of (a) the 18O of transpired
water vapour for leaves on day 1 (?) and day 2 (
?,?,?) indicating the vapour pressure deficit
(VPD) status and general trend over the day
(solid line). (b) Evaporative site enrichment
(de) for different leaves. Solid lines calculated
using H2 18O of transpired vapour. Dashed lines
represent the trendline fitted to the same data
points assuming isotopic steady state (ISS) held
throughout the day.
Harwood et al 1998 Plant, Cell Environment 21
(3) 269-283)
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a priori inferred estimates

• Vapour from soil water
• Should be depleted with respect to surface soil
  water according to Craig Gordon (1965) model
  (in the order of -10 to -12o/oo (D18O), -40 to
  -50o/oo (D2H)).
• Should lie on the LEL.
• After rainfall it should become less depleted as
  the surface soil water becomes more enriched and
  it should approach the LMWL.

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What is the data to be used for?

• A
• Evaluation of LSS output
• B
• Describing a three-point mixing model of
  dual-isotope fractionation in vapour from the
  atmosphere, soil evaporation and plant
  transpiration at hourly intervals in daylight
  hours and less frequently overnight.

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GMWL
rainwater
Surface water
Root zone water stem water transpired water
Surface evaporate
LEL
Local vapour