POTENTIAL WATER-BALANCE RESPONSE TO CLIMATIC WARMING - THE CASE OF A COASTAL WETLAND ECOSYSTEM OF THE JAMES BAY LOWLAND

The present study investigates the potential impacts of climate warmin g on the water balance and vegetation patterns in a coastal wetland ec osystem on James Bay, Canada. The study illustrates some of the linkag es within this system and how they might respond to a change in mean s ummer temperature. These linkages are outlined in a simple conceptual model with hydrology, salinity, topography, and vegetation distributio n components. The model includes two feedbacks: a vegetation/evaporati on feedback, and a hydrologic, runoff/storage feedback. A mathematical model is developed to examine changes in evaporation and water balanc e under a range of temperature change scenarios. Although the model is relatively insensitive to the internal feedbacks, model runs for temp erature-change scenarios of +2 to +8 degrees C above present summertim e normal showed evaporation increased by 18 to 64%, respectively, whic h resulted in decreases in wetland water table of 40 to 129% below the normal summer drawdown. These changes in basin storage significantly affect the distribution of woody species in the wetland. The basin are a inhabited by woody species increased from the present 25% to 32% for a +2 degrees C temperature change and to 51% for a +8 degrees C chang e. Increased stomatal resistance of the wetland vegetation, which migh t result from increased CO, concentrations, partially offsets the evap oration enhancement from warmer summer temperatures.