EVAPOTRANSPIRATION FROM A LAKESHORE TYPHA MARSH ON LAKE-ONTARIO

Evapotranspiration (E(t)) was measured over a Typha marsh bordering Lake Ontario, and open water evaporation was estimated from a pond (E(o)(POND)) within the marsh system, and from Lake Ontario (E(o)(LAKE)). Evapotranspiration from the marsh averaged 4.8 mm day-1, whereas open water evaporation from the pond was estimated to be 4.9 mm day-1, and from 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 potential 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 uncertainty 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 estimated to have an average value of 201 s m-1. Although there were different resistance networks over the Typha and the pond surfaces, the end result is that similar values of latent heat flux were produced.