The supply of water to the Nueces River Delta near Corpus Christi, Texas, and its estuarine marshes is limited by low tidal ranges in the Gulf of Mexico and by channelization of the Nueces River which restricts freshwater inflow. Micrometeorological measurements were made at the upper end (high marsh) of the delta to determine how daily and seasonal changes in the surface energy balance were affected by availability of water. The marsh consists of shallow ponds interconnected by narrow channels, and elevated areas containing emergent vegetation. During the spring and fall when ponds were flooded, latent and sensible heat flux averaged 67% and 30%, respectively, of net radiation. In the summer when ponds dried, energy partitioning was reversed with sensible heat flux accounting for 65% of net radiation and latent heat accounting for 27%. When ponds were flooded, heat storage in the water column was the major component of storage heat flux. When ponds dried, storage heat flux was controlled by sediment water content, largely through its effect on thermal diffusivity. The ratio of actual to equilibrium evaporation averaged 0.7 in the spring and fall, and 0.3 in the summer, indicating that the marsh behaved more like a dryland ecosystem than a wetland. ¿ 2000 American Geophysical Union