June-July 2003
Rio Frio, Portugal
Cork oak plantation (montado) in Portugal, during summer 2003

The main objective of IOP2 was to test the concurrent deployment and use of the various integrated techniques to study water fluxes in the different segments of the Soil-Plant-Atmosphere System including those that were developed elsewhere in the WATERUSE project, and to compare the results with those for the olive system used in the previous year (IOP1).

IOP2 took place from June 23rd to July 14th, 2003 in a cork oak (montado) test site near the village of Rio Frio, between Palmela and Montijo (38°38'N, 8°51'W; 30 m a.s.l.), low Tagus valley, about 50 km E of Lisbon, Portugal. The age of the trees was 80 years and they were planted in rows with 10 x 11 m distance. The tree density was 76 trees per ha in 2001 with some reduction in early 2003. The average canopy height was 10 m (see WP6). The understorey was patchy and varied between dry grass and shrubs (e.g. Cistus spp), the latter reached in average up to 0.4 m. Fetch conditions in the main wind direction (NW) were very good, with some variation in tree density further upwind, and terrain was almost level.

In addition to measurements over the short period of the IOP, longer-term measurements, especially of meteorological conditions and fluxes, soil moisture and sap flow were made to determine seasonal trends. Intensive monitoring of water content at significant points by classical methods, was done by Partner 1, during two annual drying cycles (Spring-Summer). Sap-flow studies were initiated by Partners 1 and 5 in March; these remained installed until Autumn. Additionally, Partners 6 and 8 made measurements at Rio Frio in May. The sound tomography device was used to investigate the internal stem structure of cork oaks, which were pre-selected for sap flow measurements by the team from Brno. These pre-selected trees were analysed for the internal stem structure by means of the sound tomography. Already on site, the trees not suitable for sap flow analysis due to internal structural defects were identified and discarded from the list of pre-selected candidates. That meant the sound tomography allowed Partner 5 to pick healthy and structural intact stems for the later sap flow measurements. Another approach was used by Partner 1 who obtained long term measurements of sap flow with the Granier technique for almost 2 years and, considering their previous experience on this stand, preferred to sample trees randomly to give the best measure of stand transpiration.

The sap-flow studies ranged from Granier-type sensors, to a method inspired by the heat balance equation and to the more complex heat field deformation technique developed by Partner 5 (see WP2), the later with the aim of following a possible new water stress related variable. In fact, variables based on characteristics of sap flow index, especially its night/day ratio, and long-term sap flow dynamics in different xylem layers of tree stems have been found as possible stress indicators and potential tool for water resource management.

Measurements of soil physical, hydrological and geo-pedological properties were used (Partner 1 and new tools from WP1, WP3, Partners 6 and 8) to study the capability of the different techniques used by Partner 6 in monitoring water uptake by the root zone at different spatial resolutions. Partner 6 also studied infiltration properties of the soil. A very extensive survey of soil electromagnetical properties has been performed by Partner 8 in a line (see WP3), using the Ground Penetrating Radar technique. It showed interesting features of the soil structure, especially related to the vertical profile, and spatial (horizontal) variability, which was very useful in the interpretation of other soil measurements, especially geo-electrical and time-domain reflectometry. Several trenches more then 1 m deep have been dug out. An opportunity to see nearby profiles of more then 5 m enabled us to observe directly how deep these roots could exploit the water.

Plant canopy structure over much of the micrometeorological footprint was investigated by combination of destructive and non-destructive techniques by Partners 4, 5 and 7 and later by Partner 1 using both Sunscan canopy analysers (Partner 4) and a LiCor LAI-2000 canopy analyser (Partner 7). These surveys were based on the collecting radiation transmittance values under the tree canopy on a regular grids (e.g. 2 m ´ 2 m), in order to study the spatial variability of tree architectural parameters in the area contributing to turbulent fluxes measured by the eddy covariance systems. Some further measurements on the density and distribution of the under storey vegetation were made by Partner 4; these included detailed measurements of Cistus ground cover, which involved destructive methods, and two Cistus surveys, one using a sunscan and the other estimating cover by eye.

General validation of evapotranspiration (ET) loss to the atmosphere and partitioning between transpiration and soil evaporation were gathered through analytical micrometeorological measurements, based on the eddy covariance technique and the measurements of the energy balance components. Micrometeorological measurements, during IOP2, have been provided by Partner 7 (sensors from Partner 1, used at seasonal scale, were installed in their tower, during 2 weeks), together with his subcontractor MetInform and the team of the MCR-Lab of the University of Basel. These included: downward and upward fluxes of short and long-wave radiation above and below the canopy, air temperature and humidity, atmospheric pressure, soil temperature at different depths and heat flux, precipitation. A 21 m tall tower has been erected in the plantation, and instrumented with 3-dimensional sonic anemometers at 9 heights. The overall availability of 5 Open-Path LiCor LI-7500 IR Gas Analyzers allowed the measurement of latent heat flux at multiple heights, and that helped very much in understanding how ET was composed from soil evaporation and canopy transpiration, a key-information to validate the alternative measurement techniques which are studied by the WATERUSE project. For some days, turbulent fluxes have been measured at several locations below the crown canopy, to assess spatial variability of forest floor ET. Radiation budget has been measured in all its components (short- and long-wave, down- and up-welling radiative fluxes) at the tower top. Energy flux into the soil and temperature was measured at several locations, both in the shade and in the open, down to 0.5 m, along with soil water content and general thermal properties of the medium. The campaign was a success and very interesting data have been collected, especially useful in assessing the partitioning of plant transpiration and soil evaporation.

Partner 4 established a range of micrometeorological sensors within the experiment, and in addition mounted a series of stationary infrared temperature sensors on the meteorological tower to follow temperature dynamics of trees, shrubs, grass and soil, in both sun and shade. Boundary layer conductances in oak and Cistus canopies were estimated using artificial heated leaves and soil heat flux was estimated under oak canopy and in open grass areas. Radiation, air temperature and wind speed was measured at 1 m above ground. Two hand-held infra-red cameras were used to take infra-red images at ground level, from a raised platform and from a 20 m tower. Unfortunately, Landsat 7 was not functioning during July, so no satellite data was acquired during the field campaign, however, late in the project NASA eventually provided partially corrected Landsat data for a period close to the IOP period which are being used for comparative studies and will be included in the combined publication comparing estimates of evapotranspiration rates at different scales, which is in preparation. All partners exchanged meteorological and other data needed for writing the output publications.

Operations center at Rio Frio

Participants of IOP 2 stayed at KIP

Some calm moments between field tasks