Evapotranspiration in a Subtropical wetland savanna using low-cost
Lysimeter, Eddy Covariance and Modeling approaches
Abstract
Evapotranspiration (ET) constitutes the largest loss of water from
subtropical grassland and wetland ecosystems, yet estimates have high
uncertainty at the landscape scale as there is little information on
plant water use. A major reason for this is the complexity and expense
of field-based ET quantification methods such as agricultural lysimeters
and eddy covariance systems. This study developed two different low-cost
lysimeters – weighing-type and water level based, to measure ET under
controlled conditions for single species as well as mixed grassland and
wetland communities. Lysimeters were placed in an open sided shadehouse
with a transparent roof to exclude rainfall. ET values were then
compared with (i) Actual ET measurements from an eddy covariance tower
onsite, (ii) vapor transport-based ET models - FAO Penman-Monteith,
Modified Turc and Abtew Simple Radiation models, and (iii) ET data from
the Florida Automated Weather Network. Both weighing-type and water
level lysimeters showed seasonal patterns and annual magnitudes similar
to the other ET methods. Annual ET measurements from weighing lysimeters
(881-1278 mm for four plant species, n=5 per species) and water level
lysimeters (1085 mm, n = 30) were similar to model estimates
(1000-1200mm). Actual ET from eddy covariance was 722 mm for ten months
(missing data for February and March), similar to lysimeter measurements
for the dominant grass Paspalum notatum (885mm for 10 months).
Low-cost lysimeters can easily inform regional ET models/remote sensing
data lacking field validation and thus are potentially useful for water
resources and ecosystem management in data-poor regions of the world.