WATER-BALANCE OF A TROPICAL WOODLAND ECOSYSTEM, NORTHERN AUSTRALIA - A COMBINATION OF MICRO-METEOROLOGICAL, SOIL PHYSICAL AND GROUNDWATER CHEMICAL APPROACHES

A combination of micro-meteorological, soil physical and groundwater c hemical methods enabled the water balance of a tropical eucalypt savan na ecosystem in Northern Australia to be estimated. Heat pulse and edd y correlation were used to determine overstory and total evapotranspir ation, respectively. Measurements of soil water content, matric suctio n and water table variations were used to determine changes in soil mo isture storage throughout the year. Groundwater dating with chlorofluo rocarbons was used to estimate net groundwater recharge rates, and str eam gauging was used to determine surface runoff. The wet season rainf all of 1585 mm is distributed as: evapotranspiration 810 mm, surface r unoff (and shallow subsurface flow) into the river 410 mm, groundwater recharge 200 mm and increase in soil store 165 mm. Of the groundwater recharge, 160 mm enters the stream as baseflow in the wet season, 20 mm enters as baseflow in the dry season, and the balance (20 mm) is di stributed to and used by minor vegetation types within the catchment o r discharges to the sea. In the dry season, an evapotranspiration of 3 00 mm comprises 135 mm rainfall and 165 mm from the soil store. Becaus e of the inherent errors of the different techniques, the water balanc e surplus (estimated at 20 mm) cannot be clearly distinguished from ze ro. It may also be as much as 140 mm. To our knowledge, this is the fi rst time that such diverse methods have been combined to estimate all components of a catchment's water balance. (C) 1998 Elsevier Science B .V. All rights reserved.