HR: 1340h
AN: B33D-1579    [Abstracts]
TI: Vegetation Cover Decreases Evaporative Water Loss in a Wetland Ecosystem
AU: * Wang, X
EM: xin@bio.miami.edu
AF: Department of Biology, University of Miami, 1301 Memorial Dr., Coral Gables, FL 33146, United States
AU: Sternberg, L O
EM: leo@bio.miami.edu
AF: Department of Biology, University of Miami, 1301 Memorial Dr., Coral Gables, FL 33146, United States
AU: Miralles-Wilhelm, F R
EM: miralles@fiu.edu
AF: Department of Civil and Environmental Engineering, Florida International University, 10555 West Flagler Street, Suite EC-2330, Miami, FL 33174, United States
AB: Analysis of oxygen and hydrogen isotope ratios of water is a useful tool for quantitative measurements of water evaporation. Water molecules with the lighter isotopes, H₂¹⁶O, evaporate faster than H₂¹⁸O and DH¹⁶O, leaving the residual water enriched in D and ¹⁸O. Therefore, the greater the evaporation, the higher the δ¹⁸O and δD values in the remaining water body. Here we used stable isotope analyses to study evaporative processes in the a wetland water conservation area (WCA-1, South Florida Water Management District) where the primary purpose is to conserve regional water resources. Evaporation is one of the major paths of water loss in WCA-1. We collected water from 50 sampling stations located in the 145,920 acres of WCA-1 area for the months of August, September, and November 2006 and January 2007. Water samples were analyzed for oxygen and hydrogen isotope ratios. The results confirm that the water in this area is enriched by evaporation since a plot of water δD versus δ¹⁸O lies off the meteoric water line. However, the enrichment of ¹⁸O and D within WCA-1 is not homogeneous, with differences in δ¹⁸O values between stations of up to 2‰. We GIS mapped the δ¹⁸O values of water for the entire area and found the isotopic enrichment pattern is consistent through time. This result suggests that water at different locations in WCA-1 has different evaporation rates. Possible factors that contribute to this evaporation pattern are: distance to the peripheral canal discharge station, water depth, and vegetation coverage. To find out which is (are) the determining factor(s) affecting water evaporation of the area, we mapped δ¹⁸O values of water with elevation and vegetation type of WCA-1 and calculated average elevation and percentage of vegetation coverage of a 100m² area around each sampling station. A multiple linear regression between δ¹⁸O values of water and average distance from the discharge gates, elevation, and percentage coverage indicate that the observed evaporation pattern is not caused by water depth. Distance from the discharge gates and percentage vegetation coverage are both significantly correlated with δ¹⁸O values of water. The effect of distance is related to the water turnover rate, i.e. the further the location is to a discharge station the greater the time the water at that location has been exposed to evaporation. In contrast, the higher the vegetation coverage the lower the loss of water through evaporation. In the future, we will determine if the effect of vegetation coverage in diminishing water loss by evaporation is annulled by the loss through transpiration.
DE: 0497 Wetlands (1890)
DE: 1813 Eco-hydrology
DE: 1880 Water management (6334)
DE: 4870 Stable isotopes (0454, 1041)
SC: Biogeosciences [B]
MN: 2007 Fall Meeting