Return to List of Research Summaries
TITLE:
Water Source Determination and Controls on Water Utilization in Cottonwood/Willow And Mesquite Forests on the San Pedro River
INVESTIGATORS:
Keirith Snyder and Dave Williams (UA)
OBJECTIVES
The objective of this work is to identify water sources and patterns of water utilization and seasonal stress in riparian tree species. Emphasis will be place on understanding mechanisms that may limit the distribution of these species. The role of root and xylem cavitation, and the ability to use monsoonal precipitation will be investigated.
APPROACH
Water sources will be determined with stable isotopic analysis of the water found in xylem tissue, and compared to the isotopic signature of ground, rain, soil and stream water. Diurnal courses of stomatal conductance and photosynthesis will be assessed to determine patterns of water stress. Predawn and midday water potentials will be measured with a pressure chamber to further identify patterns of seasonal water stress. Soil moisture will be monitored to determine the availability of water in soil layers. Soil temperature will be measured because it is an important environmental control on root function, and may influence the vulnerability of roots to cavitation events.
DATA COLLECTION (Variable, Units, Method, Location, Frequency):
1. Variable: oxygen isotopic composition. Units: parts per mill. Method: vacuum extraction and mass spectrometry. Location: Escapule, Lewis Springs, and Boquillas. 5-10 trees of each species at all threes sites. Frequency: Four times Spring, Drought, monsoon, post monsoon.
2. Variable: stomatal conductance. Units: mmol/m2/s. Method: porometry. Location: 4 tree clumps. Frequency: over a 48 period (daytime only) assessed at 2 hr intervals on each synoptic period.
3. Variable: leaf water potential. Units: MPa. Method: pressure chamber. Location: 10 trees at every site. Frequency: predawn and midday during each synoptic.
4. Variable: soil temperature. Units: Celsius. Method: thermocouples. Locations: One place at every site, under riparian tree canopy on east side. Frequency: continuously during synoptic at 5, 10, 25, 50 cm depth.
DATA REQUIRED FROM OTHER INVESTIGATORS:
1. Russ: soil temperatures in mesquite area and soil moisture (WCR probes).
2. Martha and Russ: any curves or measurements developed to assess soil water potential or matrix potential (if these happen).
Return to List of
Research Summaries
homepage