David Stone, IPILPS Workshop ANSTO April 2005 Diurnal Cycle Observations of Stable Water Isotopes in the Biosphere

IPILPS: isotopes at the land surface Scientific Hypothesis Observation and analysis of the diurnal fluxes of H 2 18 O and HDO between the soil, plants and atmosphere can accurately determine the partitioning of precipitation into transpiration, evaporation and total runoff. Method Three ecosystems were selected as study areas Tropical forest, such as the Amazon Basin, Sth America Cool, humid temperate forest, such as Central Europe, or Nth America Warm, dry temperate forest, such as SE Australia Exploit stable water isotopes H 2 18 O and HDO to investigate the hypothesis. Observations would be required at Tumbarumba Field data expected to be available for the Amazon, Europe and America

IPILPS Stable Isotope data needs ã Data expected to be available include ãprecipitation ãatmospheric vapour ãplant (stem and leaf) water ãsoilwater ãgroundwater ( not expected to vary significantly) ãriverwater ãThe data will be used within IPILPS to evaluate isotope enabled LSS output:

Overview of presentation Expected ranges of values ãthe precipitation input at the three ecosystems ãvapour<stem<leaf order of enrichment Data sets examined ãAmazon; Manaus, Santarem and Trinidad  Central Europe; Munich, other German sites  North America; temperate and semi-arid  others

THE WATER CYCLE Variation in del 18 O ( ‰ ) Leafwater 3 to10 ‰

GMWL LEL Local vapour Root zone water = stem water = transpired water Surface water Surface evaporate rainwater 9-10 ‰ Expected isotope ratios for SE Australia (Tumbarumba) 9-10 ‰ Leaves

Mean rainfall 10 ‰ depletion

Precipitation Input Signal; 3 sites

Munich Vapour and Precipitation Vapour and precipitation lie along a single MWL data source: W. Stichler, unpublished

Munich; vapour/precipitation equilibrium Regression; r 2 = 0.7 Delta 18 O(p-v) = 8.5 ‰ Regression; r 2 = 0.7 Delta 18 O(p-v) = 8.5 ‰ data source: W. Stichler, unpublished

IPILPS data requirements and sources Water isotopologues  del H 2 18 O and 1 H 2 H 16 O (‰) both desired Comparison of LSS  By output, and against real data Real field data required at appropriate time scales, monthly, daily, hourly Prefer data at diurnal timescale BASIN database; (Ehleringer), Americas CarboEuroflux; (various), Europe

Data collection methods Towers fitted with tubing for cryogenic vapour trapping, water kept frozen Soil and Leaf samples sealed in exetainers; distilled cryogenically before analysis del D and del O-18 performed by IR-MS

Tropical Rainforest data; Manaus, Amazon LBA BASIN sites Manaus Santarem Trinidad

10 ‰ enrichment data source: Matsui et al,1983, Acta Amazonica, 13,

10.4 ‰ average enrichment am pm Data source: LBAdatabase (Ometto); submitted for publication Canopy Leaves enriched Understory Leaves less enriched Enrichment increases during day 11 ‰ 9 ‰

11 ‰ Data source: LBA (Ometto); unpublished Dry season vapour, leaf and stem water more enriched 7 ‰ 11 ‰

‰ 6 ‰ Data source: LBA (Ometto); unpublished Inter-annual differences possible? Much less leaf enrichment than in previous year 11 ‰

‰ 8 ‰ Data source: LBA (Ometto); unpublished 8 ‰

‰ 5 ‰ Data source: LBA (Ometto); unpublished 10 ‰ 9 ‰ Much less leaf enrichment than in previous year Dry season vapour, leaf and stem water more enriched

Data source: LBA (Ometto); unpublished Vapour less enriched mid-morning, but more enriched in afternoon 5 ‰ difference in canopy 12 ‰ 8 ‰

Data source: LBA (Ometto); unpublished Vapour more enriched midday, but less enriched in afternoon 5-10 ‰ difference in canopy 12 ‰ 8 ‰ small difference between vapour and stems!!

Amazon Forest Vapour daytime variation, June 2000 Data source: LBA (Ometto); unpublished Vapour more enriched midday, but less enriched in afternoon Vapour less enriched mid-morning, but more enriched in afternoon

Data source: Leo Sternberg, IAEA 2004 Amazon Forest Vapour Keeling Plot analysis, June 1995

Data source: Leo Sternberg, IAEA 2004 Amazon Forest Vapour Keeling Plot analysis, May - Dec 1995

Average precip, calc

Conclusions Amazon  Leaf enrichment increases during day  Canopy Leaves enriched, understory much less so  Stem water enriches slightly in dry season  Dry season vapour, leaf & stem water more enriched  Vapour<Stem<Leaf enrichment close to optimum  Keeling plot analysis, 18 O, indicates transpiration predominant flux of return vapour to atmosphere

Cool Temperate; Munich, Germany CarboEuroFlux sites Jena and Dresden

data source: W. Stichler, unpublished

Munich Vapour and Precipitation data source: W. Stichler, unpublished

Leaf water depletes overnight Samples taken in evening 19:00-23:00 Stem and soilwater: little variation

Leaf water depletes summer to winter Stem and soilwater show little variation

Leaf water depletes summer to winter Stem and soilwater show little variation

Cool Temperate; Ottawa and Oregon BASIN sites Oregon sites Ottawa Oklahoma Arizona

data source: Flanagan, L.B. and Varney, G.T. 1995, Oecologia 101: ‰ enrichment

Average precip, calc Leafwater enriched during daytime 10 ‰ enrichment

Average precip, calc

Shallow soilwater deeper soilwater

Average precip, calc 13 ‰ enrichment

Conclusions Europe  Leaf enrichment decreases during evening (6-11pm)  Stem, roots, soil and litter show small variations, but little systematic seasonal change  Vapour<Stem<Leaf enrichment less than optimum Humid North America  Soilwater data have a large variation  Forest stem<leaf enrichment at optimum  Grassland stem<leaf enrichment at optimum  Forest and Grassland vapour<stem enrichment less than optimum ( Summer data only available)

Warm Temperate - semi arid regions; Israel, Arizona

Average precip

Depletion during daytime

LEL GMWL

Conclusions Semi-arid Israel and North America  Israel: vapour<stem<leaf enrichment at optimum  Arizona: vapour became depleted during the day  Keeling plot analysis, using both 2 H and 18 O indicates transpiration predominant flux of return vapour to atmosphere