EVAPOTRANSPIRATION FROM A LAKESHORE TYPHA MARSH ON LAKE-ONTARIO

Evapotranspiration (E(t)) was measured over a Typha marsh bordering La ke Ontario, and open water evaporation was estimated from a pond (E(o) (POND)) within the marsh system, and from Lake Ontario (E(o)(LAKE)). E vapotranspiration from the marsh averaged 4.8 mm day-1, whereas open w ater evaporation from the pond was estimated to be 4.9 mm day-1, and f rom Lake Ontario between 0.4 and 1.3 mm day-1. The ratio of E(t)/E(o)( POND) = 0.97 (r2 = 0.96) indicates that E(t) was very close to the pot ential rate, as defined by open water evaporation. The ratio E(t)/E(o) (LAKE) ranged between 3.7 and 12.5. This wide range reflects uncertain ty in the net radiation over the lake. Nevertheless, evaporation from Lake Ontario was low, owing to the very large heat storage, which was 76-92% of net radiation. The average Bowen ratio measured at the marsh was 0.17, and canopy and aerodynamic resistance were 74 s m-1 and 31 s m-1, respectively. Aerodynamic resistance over open water was estima ted to have an average value of 201 s m-1. Although there were differe nt resistance networks over the Typha and the pond surfaces, the end r esult is that similar values of latent heat flux were produced.