Large bottomless lysimeters were investigated for their suitability as a tool in the study of water balances of treeless and tree-covered areas on a raised mire. The lysimeters, large enough to contain a mature tree, were developed to measure the liquid discharge from the peat monolith they enclosed. By determining the other, less elusive components of the water balance, this approach enables evapotranspiration rates to be estimated and comparisons between treeless and tree-covered areas to be made.
The principal features of the design and operation of the lysimeters are described. Discharge measured with the lysimeters was analysed for short-term periods as well as for a hydrological year, and was compared with expected amounts of discharge obtained from a simpliยฎed water balance (D exp P 7 1 . 1 E t for the winter, and D exp P 7 0 . 8 E t for the summer). Results indicated that D was reliable for short intervals (10 days on average) with moderate amounts of rainfall. Under more extreme weather conditions, leakage underneath the lysimeter walls could occur, resulting from the strong slope-dependent water exchange across the lysimeter. Suggestions are made for improvements to the design of the lysimeter system.